What Do Animals Really Feel?

WellBeing International WBI Studies Repository

1982

The Problem of Pain: What Do Animals Really Feel?

Dana H. Murphy

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Part of the Animal Studies Commons, Comparative Psychology Commons, and the Other Animal Sciences Commons

Recommended Citation Murphy, D.H. (1982). The problem of pain: What do animals really feel? International Journal for the Study of Animal Problems, 3(4), 275-282.

This material is brought to you for free and open access by WellBeing International. It has been accepted for inclusion by an authorized administrator of the WBI Studies Repository. For more information, please contact [email protected]. The fundamental signs that indicate Separating the Dogs from the Coyotes obscured by a smokescreen of insistence that a predator may be responsible for upon the necessity of accumulating more recent deaths include: Focus and more objective data to complete a • Recent predator problems in the During the 3-year period from 1975 to highly detailed picture of the neural cir area 1977, J.M. Schaefer, R.D. Andrews, and J.J. cuitry of the various animal species. • Eccentric behavior of sheep Dinsmore investigated the realities be In his introduction to an American • Signs of struggle hind the claims of southern Iowa produc The Problem of Pain: What Do Veterinary Medical Association-sponsor • External wounds. ers about losses of sheep to coyotes and Animals Really Feel? ed symposium, "Pain Perception in Ani dogs. Among other things, the study (pub For example, predator attacks on pastur mals" in April of this year, R.L. Kitchell lished in j Wild/ Manage 45(4):883-893, ed sheep will often induce the sheep to (University of California, Davis) summa 1981) attempted to compare the relative return ·to the nighttime bedding area, rized the essential elements of this posi tion. He asserted that we would proba validity of data from several reporting whether it is located in the pasture or in The Limits of Language methods- a one-time questionnaire, a corral. Sheep that have been subjected bly not have any rei iable methods for monthly postcard surveys, and records to several attacks may also show reluc Much of the contention and confu "objectively" demonstrating that pain of domestic-animal claims- as opposed tance to leave an enclosure, even during sion that seem inevitably to arise when as we know it- occurs in animals for to the findings from necropsies perform normal feeding times. ever the subject of pain in animals comes many years, until all of the nerve path ed by the authors. There are some recognizable indi up appear to stem principally from prob ways and central nervous system (CNS) , Forty-one percent of the question cators that a coyote, rather than a dog, lems with the word "pain" itself. When interconnections related to pain have naire respondents reported that they had has been responsible for a particular used to describe responses in humans, been teased out in humans, as well as in had one or more sheep killed by preda sheep killing. One point that is stressed "pain" can mean any subset of an in the wide range of phylogenetically diverse tors in 197 5 ( average, 7.6 sheep). Of this repeatedly in the pamphlet is the broad credibly broad spectrum of sensations species that are used in laboratories. Un group, 63 percent attributed all preda range of behavior patterns among coy and emotions, ranging from the instanta til that time, he cautioned, we should be tion losses to coyotes, while 25 percent otes, such that they must always be con neous, galvanizing effect of a dentist careful to speak only about presumed reported that dogs were responsible; on sidered, and dealt with, on an individual drill hitting the nerve in a molar, to more "noxious stimuli" in animals, and that ly 12 percent attributed predation losses basis. Some coyotes may kill sheep on a airy notions such as the "pain" of rejec we ought to be wary about making any to a mix of both coyotes and dogs. regular basis, while others may live out tion or "painfully" embarrassing situa direct inferences that what we common However, other survey methodolo their whole lives and never touch one tions. Humans even use concepts as ab ly think of as pain occurs as a direct re gies provide a somewhat different view. sheep. Dogs, however, seem to enjoy at struse as the German term, weltschmerz, sult of applying these sorts of stimuli. Both the field necropsies of respondents' tacking sheep as an end in itself, rather or "world pain," which denotes a vague But on the other hand, Kitchell also sheep and the domestic-animal claims than actually seeking a required food ly defined kind of sentimental depression stated categorically that "pain is a sub records revealed that dogs killed more source. Often, many sheep will be injured or despair. jective phenomenon, which is unique to sheep per reported incident and more by the typical scatter-shot attack of a dog. Few people today would attempt to each of us." So a troublesome question sheep per rancher than did coyotes. Fur This pattern may explain the finding in the reiterate the position of the seventeenth arises when the standard scientific ap ther, a seasonal pattern was observed authors' survey study, that dogs were re century philospher Descartes, who held proach to the study of pain is used with with coyotes (80 percent of the coyote ported by ranchers to have killed more that animals, since they lacked the god out consideration of other ways of attack incidents occurred between May 1 and sheep per incident than did coyotes. like element of soul, were simply unrea ing the problem: Why bother to continue October 1 ), while dog predations seemed How to tell dog tracks from those soning machines. Nevertheless, there is collecting ever-more sophisticated data, to occur at random times throughout of a coyote, how to differentiate hair a pervasive reluctance among the great obtained by doggedly subjecting experi the year. and feces, feeding patterns, and kinds of majority of the scientific community, mental animals to years of onslaughts of In 94 percent of all sheep mortali wounds inflicted are also covered. Then many of whom use live animals on a daily "noxious stimuli," in order to learn every ties that were autopsied by one of the the authors list some of the newer ways basis for research and toxicology stud thing possible about nervous pathways, authors, the author's determination of of protecting sheep from all predators, ies- to make any firm or concrete state neurotransmitters, and the I ike, if the cause of death agreed with that of the such as confinement, guard dogs, and ments about the nature of the pain experi whole phenomenon of pain can never real sheep producers. Nonetheless, the three aversive devices. ence in animals. Their position seems to ly be subjected to rigorous study at all? authors thought it wise to draft a "how One interesting aspect of the whole be partly based on the assumption that Must it not always remain a purely sub to" pamphlet for ranchers, Recognizing coyote problem that emerges from these pain in humans must be considered a jective experience, whose qualities and and Reducing Sheep Predator Losses (avail two publications is that it is a lot easier priori as a far more elaborate nexus of intensity cannot be communicated pre able from the Iowa Cooperative Extension to get compensation for sheep lost to coy mechanisms and subsequent reactions, cisely by humans, let alone by nonspeak ing animals? Service, Ames, lA 50011). This document otes than for those killed by uncontrol especially in terms of emotional and in provides a detailed manual for piecing led dogs. In the latter case, the rancher tellectual consequences, than could ever On closer inspection, in light of together the several clues that can be used must prove, with substantiation by a wit be considered possible in animals. In what we know now about pain in animals, to discriminate between deaths due to ness, that a specific dog was the culprit. most formal scientific presentations, this sort of conceptual paradox becomes coyotes and those attributable to dogs. This, it would seem, is no easy task. though, this assumption usually remains much less of a problem. We already have

/NT I STUD ANIM PROB 3(4) 1982 /NT I STUD ANIM PROB 3(4) 1982 275 a highly detailed picture of the mecha The Basic Physiology of Pain Sensations such as heat must reach an impulse transmission that some inter nisms of pain reception and conduction Nociceptors intensity sufficient to produce possible species differences appear. The lateral in the peripheral nervous system and a damage to tissue before impulses will spinothalamic (or neospinothalamic) somewhat more sketchy, but neverthe For all species, pain can be consid begin to pass along nociceptor axons. tract, which carries impulses to the less substantial, body of knowledge ered as an adaptive response that func The structure of the nerve fibers has thalamus of the brain, is highly develop about the interpretation of incoming tions to promote the avoidance of injury been correlated with the type of pain ed in primates, but only rudimentary in pain signals in the CNS. In addition, we and potentially dangerous situations, as perceived. The A-delta fibers, which are some species like the cat (J. Vierck, jAm have comparative data on how species well as to protect damaged parts after coated with thin myelin sheaths (and are Vet Med Assoc 168:150-513, 1976). This of varying levels of complexity perceive an injury has occurred. Sharp pain tells therefore better conductors of impulses), tract seems to be most important for and respond to noxious stimuli. And we an animal that it has entered into a dan are associated with rapid conduction of fast conduction of data related to locali have learned that there is no species in gerous situation. Dull, chronic pain in impulses and sharp pain. The activation zation, orientation, and quick reactions which pain perception, and the subse dicates a need for rest and self-protection of unmyelinated, or C fibers (which are to potentially damaging stimuli. In con quent response, is a simple process. For (Report of the Panel of Enquiry into Shoot slower conductors) tends to be associat trast, the spinoreticulothalamic (paleo example, it has recently been discovered ing and Angling, RSPCA, U.K., 1980). On ed with aching, long-lasting pain. spinothalamic) tract is more likely to that a great number of species- even ly the intractable pain of diseases asso When cells near the nociceptors are carry information related to activation those quite phylogenetically remote from ciated primarily with old age (such as damaged, they release many kinds of of arousal and emotional systems, since humans- secrete a class of biochemi cancer) appears to have little adaptive biochemicals. Among these is a specific this tract terminates in the brain areas cals that are used to make sophisticated value. But under natural conditions, few protein (peptide), bradykinin, which serves (the limbic system and hypothalamus) that and minute adjustments in selecting which animals (including primitive man) would as the chemical transmitter that causes participate in the mediation of emotions pain signals are transmitted to the CNS, survive long enough to experience this the pain receptor to discharge. When in and expression. and at what level of intensity. Attacking kind of pain. jected into humans, bradykinin causes In rats, K.L. Casey (University of Mi the problem from a different perspec Pain is first perceived in the body instantaneous and extreme sensations of chigan) reports that areas of the cord tive, behaviorists have designed elegant via specialized receptors of the peripheral pain, even in the presence of concurrent containing both the neospinothalamic experiments, using avoidance mecha nervous system, termed nociceptors. Lo anesthesia. Extrapolating from these data, and paleospinothalamic tracts can be nisms, that can test an animal's thres cated in the skin, these appear to differ we can say that a test for the presence of severed, and the animals will still re hold to various kinds of pain stimuli and very little from similar receptors also bradykinin might constitute one type of spond to painful stimuli, since in this spe furnish answers to questions about is found in skin, which detect other sensa reliable proof that a given species posses cies pain conduction pathways that pass sues such as memory of pain, and the tions such as low-intensity heat and pres ses the basic rudiments of biochemical directly to the brain are located in the amount of "anxiety" an animal feels sure. Although similar structures have pain transmission. peripheral nerves, as well as in the cord. when placed in an environment where a been found in other vertebrates includ A second peptide, substance P, has painful stimulus was previously applied. ing fish, their anatomical similarity to also been implicated in the transmission The several pain conduction tracts With all this accretion of knowledge other receptors has so far made it im of nerve signals indicative of pain. It of the cord terminate in various areas of the brain, such as the reticular forma from older work as well as from more re possible to tell if they are responsible serves as the neurotransmitter between tion, a fundamental relay center which cently developed techniques, we can be for sensing and transmitting "noxious the afferent pain-sensing nerve and the controls respiration, heart activity, and reasonably certain that animals, when stimuli." L.E. Krueger (University of Cali spinal cord. The presence of this biochem blood pressure and which may be in exposed to noxious stimuli, do indeed fornia, Davis) is utilizing the electron mi ical could therefore possibly serve as a second indicator of pain-sensing mecha volved in the conscious perception of sense something that contains many of croscope to elucidate the specific struc nisms in a species. pain (T.A. Yoxall, 1978). Also involved is the elements that humans would list as ture and function of the various types of the limbic system, which is concerned components of consequences of pain. nociceptors. Kreuger also uses microelec with factors such as memory, attention, These include physical discomfort, neg trodes, in conjunction with horseradish Impulse Transmission Through and emotion: One component of the limb ative affect, and the formulation of avoid peroxidase and lectin transport techni the Cord ic system is the thalamus. Finally, through ance strategies. While it may present a ques, to study the stimulus threshold of The impulses that originate at the connections from the thalamus to the real challenge to learn how to translate single nociceptor fibers, the conduction nociceptors located in the skin travel to higher centers of the brain, or cortex, the "language" (internal and external pathways of individual fibers after stim the spinal cord, via the dorsal roots. The pain can influence thought and decision signals) that each individual species uses ulation, and the average conduction axons of these nerves may extend direct making processes. as part of its own particular way of per speeds of the different fiber types. Among ly to the brain or they may make various Here, again, we see some differences ceiving and responding to painful stimu other findings, he has discovered that kinds of interconnections with other spi among species. For example, nerves of li, especially when a given species is re each spot on a nociceptor axon has a dif nal cord cells, and the intensity of the the spinothalamic tract end in different mote from humans, it can be, and is being ferent level of excitability-excitable pain signal may be modified in the pro areas within the thalamus, depending done. Further, these efforts can be of im zones are intermixed with unexcitable cess. Pain signals then proceed on to the upon the type of animal. In primates, the mediate use for drafting workable guide areas in a highly complex pattern. brain, through one of several ascending tract terminates in the ventral postero lines on the kinds and levels of pain Physiologically, the nociceptors dif tracts of the cord. lateral (VPL) nucleus of the thalamus, laboratory animals ought to be allowed fer from other receptors in that they It is at this point in the anatomy of whereas in carnivores it ends in a thin to endure. have a higher threshold for stimulation. /NT 1 STUD ANIM PROB 3[4) 1982 277 276 /NT 1 STUD ANIM PROB 3[4) 1982 a highly detailed picture of the mecha The Basic Physiology of Pain Sensations such as heat must reach an impulse transmission that some inter nisms of pain reception and conduction Nociceptors intensity sufficient to produce possible species differences appear. The lateral in the peripheral nervous system and a damage to tissue before impulses will spinothalamic (or neospinothalamic) somewhat more sketchy, but neverthe For all species, pain can be consid begin to pass along nociceptor axons. tract, which carries impulses to the less substantial, body of knowledge ered as an adaptive response that func The structure of the nerve fibers has thalamus of the brain, is highly develop about the interpretation of incoming tions to promote the avoidance of injury been correlated with the type of pain ed in primates, but only rudimentary in pain signals in the CNS. In addition, we and potentially dangerous situations, as perceived. The A-delta fibers, which are some species like the cat (J. Vierck, jAm have comparative data on how species well as to protect damaged parts after coated with thin myelin sheaths (and are Vet Med Assoc 168:150-513, 1976). This of varying levels of complexity perceive an injury has occurred. Sharp pain tells therefore better conductors of impulses), tract seems to be most important for and respond to noxious stimuli. And we an animal that it has entered into a dan are associated with rapid conduction of fast conduction of data related to locali have learned that there is no species in gerous situation. Dull, chronic pain in impulses and sharp pain. The activation zation, orientation, and quick reactions which pain perception, and the subse dicates a need for rest and self-protection of unmyelinated, or C fibers (which are to potentially damaging stimuli. In con quent response, is a simple process. For (Report of the Panel of Enquiry into Shoot slower conductors) tends to be associat trast, the spinoreticulothalamic (paleo example, it has recently been discovered ing and Angling, RSPCA, U.K., 1980). On ed with aching, long-lasting pain. spinothalamic) tract is more likely to that a great number of species- even ly the intractable pain of diseases asso When cells near the nociceptors are carry information related to activation those quite phylogenetically remote from ciated primarily with old age (such as damaged, they release many kinds of of arousal and emotional systems, since humans- secrete a class of biochemi cancer) appears to have little adaptive biochemicals. Among these is a specific this tract terminates in the brain areas cals that are used to make sophisticated value. But under natural conditions, few protein (peptide), bradykinin, which serves (the limbic system and hypothalamus) that and minute adjustments in selecting which animals (including primitive man) would as the chemical transmitter that causes participate in the mediation of emotions pain signals are transmitted to the CNS, survive long enough to experience this the pain receptor to discharge. When in and expression. and at what level of intensity. Attacking kind of pain. jected into humans, bradykinin causes In rats, K.L. Casey (University of Mi the problem from a different perspec Pain is first perceived in the body instantaneous and extreme sensations of chigan) reports that areas of the cord tive, behaviorists have designed elegant via specialized receptors of the peripheral pain, even in the presence of concurrent containing both the neospinothalamic experiments, using avoidance mecha nervous system, termed nociceptors. Lo anesthesia. Extrapolating from these data, and paleospinothalamic tracts can be nisms, that can test an animal's thres cated in the skin, these appear to differ we can say that a test for the presence of severed, and the animals will still re hold to various kinds of pain stimuli and very little from similar receptors also bradykinin might constitute one type of spond to painful stimuli, since in this spe furnish answers to questions about is found in skin, which detect other sensa reliable proof that a given species posses cies pain conduction pathways that pass sues such as memory of pain, and the tions such as low-intensity heat and pres ses the basic rudiments of biochemical directly to the brain are located in the amount of "anxiety" an animal feels sure. Although similar structures have pain transmission. peripheral nerves, as well as in the cord. when placed in an environment where a been found in other vertebrates includ A second peptide, substance P, has painful stimulus was previously applied. ing fish, their anatomical similarity to also been implicated in the transmission The several pain conduction tracts With all this accretion of knowledge other receptors has so far made it im of nerve signals indicative of pain. It of the cord terminate in various areas of the brain, such as the reticular forma from older work as well as from more re possible to tell if they are responsible serves as the neurotransmitter between tion, a fundamental relay center which cently developed techniques, we can be for sensing and transmitting "noxious the afferent pain-sensing nerve and the controls respiration, heart activity, and reasonably certain that animals, when stimuli." L.E. Krueger (University of Cali spinal cord. The presence of this biochem blood pressure and which may be in exposed to noxious stimuli, do indeed fornia, Davis) is utilizing the electron mi ical could therefore possibly serve as a second indicator of pain-sensing mecha volved in the conscious perception of sense something that contains many of croscope to elucidate the specific struc nisms in a species. pain (T.A. Yoxall, 1978). Also involved is the elements that humans would list as ture and function of the various types of the limbic system, which is concerned components of consequences of pain. nociceptors. Kreuger also uses microelec with factors such as memory, attention, These include physical discomfort, neg trodes, in conjunction with horseradish Impulse Transmission Through and emotion: One component of the limb ative affect, and the formulation of avoid peroxidase and lectin transport techni the Cord ic system is the thalamus. Finally, through ance strategies. While it may present a ques, to study the stimulus threshold of The impulses that originate at the connections from the thalamus to the real challenge to learn how to translate single nociceptor fibers, the conduction nociceptors located in the skin travel to higher centers of the brain, or cortex, the "language" (internal and external pathways of individual fibers after stim the spinal cord, via the dorsal roots. The pain can influence thought and decision signals) that each individual species uses ulation, and the average conduction axons of these nerves may extend direct making processes. as part of its own particular way of per speeds of the different fiber types. Among ly to the brain or they may make various Here, again, we see some differences ceiving and responding to painful stimu other findings, he has discovered that kinds of interconnections with other spi among species. For example, nerves of li, especially when a given species is re each spot on a nociceptor axon has a dif nal cord cells, and the intensity of the the spinothalamic tract end in different mote from humans, it can be, and is being ferent level of excitability-excitable pain signal may be modified in the pro areas within the thalamus, depending done. Further, these efforts can be of im zones are intermixed with unexcitable cess. Pain signals then proceed on to the upon the type of animal. In primates, the mediate use for drafting workable guide areas in a highly complex pattern. brain, through one of several ascending tract terminates in the ventral postero lines on the kinds and levels of pain Physiologically, the nociceptors dif tracts of the cord. lateral (VPL) nucleus of the thalamus, laboratory animals ought to be allowed fer from other receptors in that they It is at this point in the anatomy of whereas in carnivores it ends in a thin to endure. have a higher threshold for stimulation. /NT 1 STUD ANIM PROB 3[4) 1982 277 276 /NT 1 STUD ANIM PROB 3[4) 1982 area that forms a kind of shell around nerve synapses, but far less about the of endorphin, the 5-peptide enkephalin. pleasurable. He also suggests, therefore, this nucleus. In rats, terminations of spi roles and functions of individual nerves From these findings, it is tempting to postu that this sort of self-stimulation apparatus nothalamic nerves are also found pre and the inter-relationships among the late that the enkephalin receptors, as might provide us with a tool for obtaining dominantly in the YPL nucleus, but in an various CNS components that are involv well as those for other opiates, may be clear-cut evidence of when an animal is area that is located more toward the front ed in nociception. Nor are we any more located on the nerve endings that con experiencing pain. of the animal's head. certain that, having obtained these data tain substance P, and that these opiates W.O. Willis (University of Texas we will be any closer to making succinc~ therefore function by blocking the release Anxiety and Suffering Medical Branch, Galveston) reports that lists of the differences between the of substance P (Report of the Panel of En Another class of receptors, which the area of the thalamus that is activat meaning of the word "pain" to a human, quiry into Shooting and Angling, RSPCA, selectively bind the anxiety-reducing ed seems to be correlated, to some de as compared with what animals may sense, U.K., 1980). The sophisticated mecha drugs, the benzodiazepines (Valium is gree, with the nature and intensity of the feel, and think. nism of pain mediation by naturally oc behavioral response that ensues after perhaps the best known of these) has A Few Other Wrinkles curring opiates is not unique to the high the application of a painful stimulus. been localized within the brains of many Endogenous Analgesics and er vertebrates: endorphins have been iso However, it is not possible at this time to animals. The existence of such sites sug Psychological Effects lated in species as phylogenetically dis make sweeping generalizations about tinct from humans as the earthworm (J. gests that animals may be producing a natural biochemical to counter the af how different animal species feel in the One of the most important scientific Alumets eta/., Nature 279:805-806, 1979). presence of noxious stimuli, or of how discoveries of the last decade was the fect of anxiety, just as the endorphins they are likely to react in terms of be recognition that the perception of pain L.R. Watkins and D.J. Mayer (Science work to counter pain impulses (Sci News havioral responses, solely on the basis of was not a one-way street, running in a 216:1185-1192, 1982) recently studied 117:164, 1980). fine differences in neurophysiology, since simple pathway from nociceptor to cord the pain-moderating role of another kind Binding sites for benzodiazepines we simply do not know the real signifi to CNS centers. In fact, pain perception of endogenous system, a system that does have been found in brain tissue of mam cance of many of these differences. Per is a two-way street, because the descend not seem to be activated by endorphin, mals, rodents, reptiles, and bony fishes haps most important, we have not yet ing spinal never tracts that connect the since its effects are not reversed by the (Brain Res 141:342-346, 1978), but not in discovered what degree of overlap in various CNS centers to levels in the opiate antagonist naloxone. Activity of cartilaginous fishes or invertebrates. How function and response may exist among spinal cord can modulate input from the this second system has been localized to ever, since we do not yet know the whole the different anatomical areas of the afferent fiber. These nerves appear to a specific region of the body. In rats, story relative to the pharmacology and cord and brain that are used to convey work by releasing neurotransmitters com electric shock to the front paw induced benzodiazepine binding, it may well be perceptions of pain in the various spe ing in from the periphery (L.R. Watkins endorphin-mediated analgesia, which was that invertebrates are also producing cies. Although traveling on a different and D.J. Mayer, Science 216:1185-1192, reversed by naloxone, but in the hind biochemicals that are analogous in struc tract, to a different location in the brain, 1982). E.A. Carstens (University of Cali paw, naloxone had no effect on painkill ture and function to the yet-unidentified an impulse may be conveying similar in fornia, Davis) has hypothesized that this ing activity. However, the precise phar anti-anxiety agent secreted by vertebrates. formation and may elicit a similar set of kind of endogenous analgesia might work macological basis for this type of anal Goodman and Gilman, in the stan responses. to provide a critical edge in the selective gesia remains unknown. dard reference work The Pharmacological The relationship between what we survival of an individual by permitting In addition, analgesia can be pro Basis of Therapeutics (1975) assert that: know about the ascending pathways of an animal that has been severely hurt to duced by a whole range of other mecha The effects of the benzodiazepines pain versus what we do not yet know continue to function and to fight, if that is nisms. Direct electrical stimulation to in the relief of anxiety can readily might be compared to the study of the necessary, in spite of severe pain. the brain can activate both opiate- and be demonstrated in experimental ani geography of some newly discovered Several classes of pain-mediating nonopiate-mediated analgesic pathways. mals. In conflict punishment proced area. We have the basic maps of the re chemicals have been isolated. These in Acupuncture and the analgesia induced ures, benzodiazepines greatly re gion drawn up in pretty elaborate detail, clude the endorphins, serotonin, and 5- by long-duration shock to all four paws duce the suppressive effects of pun and we know something about the vari hydroxytryptam in e. Of these, we know of the rat seem, at least in part, effects ishment. However, anxiety in the rat ous peoples who live in the region, but most about the endorphins. Chemically, of hormones, since surgical removal of the and man can hardly be equated (em not so much about how the individuals endorphins are peptide molecules that pituitary or adrenal glands reduces or phasis added). in each culture function, and very little are structurally similar to morphine. Like abo! ishes the effect. at all about how the various cultures in morphine, they bind to appropriate recep Interestingly, pain reduction caused In light of the research demonstrating teract. Similarly, the work of tracing the tor sites in the brain stem and cord to by these mechanisms doesn't seem to be the close analogy of the physiological pathways of nociception in animals ap block the transmisssion of pain impulses. coupled with any sense of euphoria, as is roles played by bradykinin, substance P, pears to be making steady progress. We Also, their effect is countered by the the rule with morphine administration. and the endorphins in a broad spectrum know a lot more than we did 10 years same agents that antagonize the action E.A. Carstens (University of California, of invertebrates, this last sentence seems a ago about the fundamental similarity in of artificial opiates, for example, the drug Davis) has found that when an animal is rather premature and cavalier conclu structure and function of these path naloxone. A close association has been allowed to self-apply electrical stimula sion. It seems far more likely that just as ways among the higher vertebrates, and noted between nerve endings that contain tion to induce analgesia, it will only do the detection of certain neurotransmit of the identity of the biochemicals used the pain impulse neurotransmittter, sub so when a noxious stimulus is present, ters furnishes evidence for a similar pat in transmission of pain signals across stance P, and those that contain one type implying that the stimulus is not in itself tern of sensation and response to pain in

278 /NT I STUD ANIM PROB 3(4) 1982 /NT I STUD ANIM PROB 3(4] 1982 279 area that forms a kind of shell around nerve synapses, but far less about the of endorphin, the 5-peptide enkephalin. pleasurable. He also suggests, therefore, this nucleus. In rats, terminations of spi roles and functions of individual nerves From these findings, it is tempting to postu that this sort of self-stimulation apparatus nothalamic nerves are also found pre and the inter-relationships among the late that the enkephalin receptors, as might provide us with a tool for obtaining dominantly in the YPL nucleus, but in an various CNS components that are involv well as those for other opiates, may be clear-cut evidence of when an animal is area that is located more toward the front ed in nociception. Nor are we any more located on the nerve endings that con experiencing pain. of the animal's head. certain that, having obtained these data tain substance P, and that these opiates W.O. Willis (University of Texas we will be any closer to making succinc~ therefore function by blocking the release Anxiety and Suffering Medical Branch, Galveston) reports that lists of the differences between the of substance P (Report of the Panel of En Another class of receptors, which the area of the thalamus that is activat meaning of the word "pain" to a human, quiry into Shooting and Angling, RSPCA, selectively bind the anxiety-reducing ed seems to be correlated, to some de as compared with what animals may sense, U.K., 1980). The sophisticated mecha drugs, the benzodiazepines (Valium is gree, with the nature and intensity of the feel, and think. nism of pain mediation by naturally oc behavioral response that ensues after perhaps the best known of these) has A Few Other Wrinkles curring opiates is not unique to the high the application of a painful stimulus. been localized within the brains of many Endogenous Analgesics and er vertebrates: endorphins have been iso However, it is not possible at this time to animals. The existence of such sites sug Psychological Effects lated in species as phylogenetically dis make sweeping generalizations about tinct from humans as the earthworm (J. gests that animals may be producing a natural biochemical to counter the af how different animal species feel in the One of the most important scientific Alumets eta/., Nature 279:805-806, 1979). presence of noxious stimuli, or of how discoveries of the last decade was the fect of anxiety, just as the endorphins they are likely to react in terms of be recognition that the perception of pain L.R. Watkins and D.J. Mayer (Science work to counter pain impulses (Sci News havioral responses, solely on the basis of was not a one-way street, running in a 216:1185-1192, 1982) recently studied 117:164, 1980). fine differences in neurophysiology, since simple pathway from nociceptor to cord the pain-moderating role of another kind Binding sites for benzodiazepines we simply do not know the real signifi to CNS centers. In fact, pain perception of endogenous system, a system that does have been found in brain tissue of mam cance of many of these differences. Per is a two-way street, because the descend not seem to be activated by endorphin, mals, rodents, reptiles, and bony fishes haps most important, we have not yet ing spinal never tracts that connect the since its effects are not reversed by the (Brain Res 141:342-346, 1978), but not in discovered what degree of overlap in various CNS centers to levels in the opiate antagonist naloxone. Activity of cartilaginous fishes or invertebrates. How function and response may exist among spinal cord can modulate input from the this second system has been localized to ever, since we do not yet know the whole the different anatomical areas of the afferent fiber. These nerves appear to a specific region of the body. In rats, story relative to the pharmacology and cord and brain that are used to convey work by releasing neurotransmitters com electric shock to the front paw induced benzodiazepine binding, it may well be perceptions of pain in the various spe ing in from the periphery (L.R. Watkins endorphin-mediated analgesia, which was that invertebrates are also producing cies. Although traveling on a different and D.J. Mayer, Science 216:1185-1192, reversed by naloxone, but in the hind biochemicals that are analogous in struc tract, to a different location in the brain, 1982). E.A. Carstens (University of Cali paw, naloxone had no effect on painkill ture and function to the yet-unidentified an impulse may be conveying similar in fornia, Davis) has hypothesized that this ing activity. However, the precise phar anti-anxiety agent secreted by vertebrates. formation and may elicit a similar set of kind of endogenous analgesia might work macological basis for this type of anal Goodman and Gilman, in the stan responses. to provide a critical edge in the selective gesia remains unknown. dard reference work The Pharmacological The relationship between what we survival of an individual by permitting In addition, analgesia can be pro Basis of Therapeutics (1975) assert that: know about the ascending pathways of an animal that has been severely hurt to duced by a whole range of other mecha The effects of the benzodiazepines pain versus what we do not yet know continue to function and to fight, if that is nisms. Direct electrical stimulation to in the relief of anxiety can readily might be compared to the study of the necessary, in spite of severe pain. the brain can activate both opiate- and be demonstrated in experimental ani geography of some newly discovered Several classes of pain-mediating nonopiate-mediated analgesic pathways. mals. In conflict punishment proced area. We have the basic maps of the re chemicals have been isolated. These in Acupuncture and the analgesia induced ures, benzodiazepines greatly re gion drawn up in pretty elaborate detail, clude the endorphins, serotonin, and 5- by long-duration shock to all four paws duce the suppressive effects of pun and we know something about the vari hydroxytryptam in e. Of these, we know of the rat seem, at least in part, effects ishment. However, anxiety in the rat ous peoples who live in the region, but most about the endorphins. Chemically, of hormones, since surgical removal of the and man can hardly be equated (em not so much about how the individuals endorphins are peptide molecules that pituitary or adrenal glands reduces or phasis added). in each culture function, and very little are structurally similar to morphine. Like abo! ishes the effect. at all about how the various cultures in morphine, they bind to appropriate recep Interestingly, pain reduction caused In light of the research demonstrating teract. Similarly, the work of tracing the tor sites in the brain stem and cord to by these mechanisms doesn't seem to be the close analogy of the physiological pathways of nociception in animals ap block the transmisssion of pain impulses. coupled with any sense of euphoria, as is roles played by bradykinin, substance P, pears to be making steady progress. We Also, their effect is countered by the the rule with morphine administration. and the endorphins in a broad spectrum know a lot more than we did 10 years same agents that antagonize the action E.A. Carstens (University of California, of invertebrates, this last sentence seems a ago about the fundamental similarity in of artificial opiates, for example, the drug Davis) has found that when an animal is rather premature and cavalier conclu structure and function of these path naloxone. A close association has been allowed to self-apply electrical stimula sion. It seems far more likely that just as ways among the higher vertebrates, and noted between nerve endings that contain tion to induce analgesia, it will only do the detection of certain neurotransmit of the identity of the biochemicals used the pain impulse neurotransmittter, sub so when a noxious stimulus is present, ters furnishes evidence for a similar pat in transmission of pain signals across stance P, and those that contain one type implying that the stimulus is not in itself tern of sensation and response to pain in

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humans and animals, so the discovery of discussion) that the old subjective-objec scribe the part of animal experimen from "no pain or only minimal and benzodiazepine-binding sites in other spe tive dichotomy, as employed by scientists tation objected to by many people, momentary pain" (category 1) to "ex cies provides a possible indication that such as Dr. Kitchell, emerges as empty and therefore considered in the na periments on unanesthetized animals (or something akin to the human emotion of sophistry. J.C. Liebeskind (University of tion's regulations and standards, are: only local anesthesia) where the animal anxiety is experienced by most vertebrate California, Los Angeles) commented: "I pain and discomfort is curarized or paralyzed" (category 6). animals. see no difference in the appreciation of pain or distress Examples of typical procedures that are Corroborating evidence for an anxi pain between man and animals. In both suffering and injury likely to produce each degree of pain ety state in animals is provided by new cases, we must rely on inferential data. discomfort are given for each category. Experiments work on "anti-Valiums," drugs that block Humans use language, while animals use He observed that "these words and phrases in categories 1 to 3 require only notifica the action of benzodiazepines (Science behavior." are subjective," so that "some have pro tion of a regional committee (comprised 216:604-605, 1982). One such agent, beta C.J. Vierck (University of Florida) posed that more specific descriptions be of scientists, lab technicians, and lay carboline, induces wakefulness in rats stressed the fact that a knowledge of the used in the Animal Welfare Act by the people), whereas those in categories 4 to but, unlike amphetamine, does not in specific pattern of the pain response in a NIH." However, Loew also recognizes 6 require the Committee's formal ap crease motor activity. Beta-carboline is particular individual is as important for the validity of the counterargument that, proval (M. Ross, Austr Psych 13:375-378, also being tested in animals to deter animals as it is for humans. He asserted since no set of regulations could ever be 1978). mine whether it has anxiety-producing that reactions such as fear and depression, written so as to anticipate every possible Although superficially divergent, effects, by observing the animals' behav as consequences of pain, were continuous permutation in experimental design, broad these two approaches are similar in that ior, specifically, their preference between along evolutionary lines. Quibbling about er terminology may hold the key to suc they both aim at circumventing the prob a dark and lighted chamber (under stan whether or not the sensations and responses cessful minimization of pain. In the end, lem of attempting to guess about the ex dard conditions, the light tends to frighten of animals to harmful stimuli were suffi though, Loew recommends that self-reg act relationship between pain as sensed them). ciently analagous to human perception ulation, i.e., the thoughtful use of ani by animals and what is felt, under simi Finally, when addressing the prob to permit us to convey the noble title of mals by scientists themselves, is the es lar circumstances, by humans, and the lem of pain, the whole issue of the role "pain" upon them was only a matter of sential element in protecting these experi consequential use of vague or abstract of the higher CNS centers in mediating semantic triviality. As another investiga mental subjects from unnecessary pain. language in codes and regulations. In pain signals must be considered, especi tor put it, there is no "a priori reason to But he also mentions, in passing, that a the Swedish code, the correspondence ally since there are innumerable anecdo suppose that, in evolution, the percep more specific set of guidelines for inves between human and animal pain is sim tal reports of bizarre responses to trau tion of pain appears as a wholly new sen tigators of experimental pain in animals ply taken for granted; in the instance of matic injury, in both animals and humans. sory phenomenon in man" (D. Pratt, Alter has been drafted by the Committee for the Pain guidelines, the investigators are Soldiers in the Yom Kippur War, for ex natives to Pain in Experiments on Ani Research and Ethical Issues of the Inter advised to use themselves as their first ample, when interviewed about their in mals, New York, Argus Archives, 1980). national Association for the Study of Pain experimental subjects, in order to get a itial reactions to severe injuries, describ (published in the journal, Pain 9:141-143, precise fix on the degree of pain that is ed them as painless and only mentioned Practical Consequences: 1980). involved. other simultaneously occurring stimuli, The Formulation of Codes and These guidelines emphasize peer In the U.K., the dramatic increase in I ike loud noises. Regulations review of procedures, careful observa the use of experimental animals after T. Wolfle (NIH), at the same sym But What Does It All Mean? tions of the animals' behavior as com World War II compelled a re-thinking on posium on pain in New Orleans, noted pared with behavior under suspected questions about their welfare, by scien Even if we were to consider only the that, given the gravity of society's con pain or stress, and measurement of para tists as well as the general public. One data presented in this brief overview, it cern about suffering in laboratory ani meters like electroencephalogram, eat result of this self-examination was the would seem that we have already garner mals, "we cannot wait until all the data ing and drinking, rank order in society, formulation of the now-famous "three ed enough "objective" data to formulate on acute pain in animals are in"- even and body weight. The Committee also R's," in 1959, by Russell and Burch (The plausible hypotheses concerning the un if these data could answer all of our sci advocates the ultimate method for mak Principles of Humane Experimental Tech broken phylogenetic continuity of mecha entific and ethical questions about pain ing a good guess about what an animal nique, London, Methuen): replacement, nisms for perception and response to nox to begin addressing the issue of how might be feeling during an experimental refinement, and reduction. ious stimuli among animal species. Ver best to regulate the allowable extent procedure: trying the painful stimulus However, this approach, although tebrates show homology in terms of ner and intensity of that suffering. out on yourself before subjecting th.e an highly useful both as a conceptual vous structure and function, and most of However, efforts aimed at formulat imals to the procedures. model and as a means of countering ex the biochemicals identified as playing ing workable guidelines on animal pain A somewhat different approach is tremist reactions (both for and against an essential role in pain impulse transmis have foundered, in nearly every instance, represented by the Swedish codes of vivisection), had I ittle real effect on the sion and modulation have been found in on the problem of defining "pain"; even practice on experiments in animals. day-to-day practice in laboratories. species as rudimentary as earthworms. more difficulty arises with more nebulous Here, the regulations attempt to provide So, in the early 1960's pub! ic pres Further, on the basis of these and similar words like "suffering." workable guidelines for scientists by sure induced the government to estab kinds of findings, several participants at In an article published in Lab Animal dividing procedures into six categories, lish a departmental committee to inves the Symposium on Pain Perception in Ani (10:36-38, 1981) F.M. Loew noted that according to the degree of pain that is tigate the question of pain in lab animals. mals in New Orleans admitted (in private The words and phrases used to de likely to result. The categories range The Littlewood Committee decided that

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280 INTI STUD ANIM PROB 3(4) 1982 /NT I STUD ANIM PROB 3(4) 1982 281 the most workable way of defining pain dicators of some type of adverse state. It was to consider it as three separate men matters I ittle whether we choose to de tal states, with three correspondingly dif nominate this adverse state as "pain," or Comments ferent sets of symptoms (quoted from J. decide to call it something else and re H. Seamer, Vet Rec 110: 341-344, 1982): serve the word "pain" for usages that 1. Discomfort- such as may be char contain more subjective elements and acterized by negative signs such as are thus only describable in language, poor condition, torpor, and diminish thereby limiting its use to the human The Future of Research into ed appetite. realm of experience. 2. Stress- a condition of tension or Extrapolating further from this con Relationships Between People anxiety predictable or readily explica clusion, we can say that "pain," as a re ble from environmental causes, wheth sponse, should perhaps best be consider and Their Animal Companions er distinct from or including physi ed on a species-by-species basis. For ex cal causes. ample, vocalization as a reaction to nox 3. Pain- recognizable by more posi ious stimuli is probably of importance tive signs such as struggling, scream only to relatively socialized species, Boris M. Levinson, Ph.D. ing or squealing, convulsions, severe either to warn others in the group or to palpitation. get assistance from them. In addition to In sharp contrast to prevalent public attitudes of 20 years ago, the field of animal Although this "Littlewood formula" has the adoption of some approach that in human rel~tionships is now respected as a legitimate area of scientific investigation. not been formally incorporated into law, tegrates the best features of the Little H_ow_ev_er, 1t has not yet evolved into a full-fledged discipline: a specific term for this many of its components have been put wood formula, the Swedish code, and the d1s_c1pl1ne, a body of theory, and a methodology of its own must still be developed. into use, via administrative mechanisms, Pain guidelines, it might be a good idea Th1s methodology should make use of both the intuitive and scientific approaches in by the Home Office. in setting up policy on animal experi order to encompass the full richness of animal-human interaction. Four main areas of Conclusion mentation to admit that there are some investigation would be fruitful at this point: {1) the role of animals in various human In one sense, the issue of pain in very real differences among species, in cu~tures and ethnic groups over the centuries; {2) the effect of association with animals can be considered as an isolated terms of their internal (neural and bio an1mals on human personality development; {3) human-animal communication· and element of the more general question of chemical) and external (behavioral) indi {4) ~he t~erapeutic use of animals in formal psychotherapy, institutional setting; and animal consciousness, a topic that is cators of pain. What we may need, then, res1dent1al arrangements for handicapped and aged populations. currently undergoing a relatively radical is a multiplicity of handbooks on animal . An ambivalent relationship has existed between humans and animals since an revision.]. Levy, a University of Chicago pain, for each of the several species that Cient days, b~t we may now be ready to translate into reality the myth of the Golden neurophysiologist, has decided- on the are commonly used in laboratories, that Age when an1mals and humans lived at peace with each other. basis of neurological studies that dem would set forth general guidelines on care, onstrate the continuity between the along with the specific signs of pain that ought to be carefully monitored for that components that make up animal and It was only 20 years ago, at a meet academic world has granted recognition human brains- that "we have no reason species and what is known about the idio ing of the American Psychological Asso to our field by awarding doctorates in to suppose that there are any unique syncrasies of administering anesthesia to ciation, that I first presented a paper on the discipline of animal-human relation properties of the human organ of the animals. the "Dog as a Co-therapist" (Levinson, ships. However, in spite of these promis thought." He also reiterates the com As Peter Medawar has stated (in 1961). The reception was lukewarm. While ing beginnings and accomplishments, it mon insight that much of our medical re Hope of Progress, Methuen, 1967, p. 72) some accepted the ideas, others met them seems to me that this field has not be search on animals assumes a continuity I think that the use of experimental with ridicule, even inquiring as to whether come a true discipline as yet. of consciousness from one species to an animals on the present scale is a the dog shared my fees. I became known Perhaps there are advantages to this other (Psych Today 16:36-44, 1982). temporary episode in biological as the co-therapist. dog's rather ambiguous status, since our at Surely, then, it would seem that we and medical history .... In the mean Obviously, much water has flowed tempts to define our field help us tore can say with some degree of certainty time, we must grapple with the para under the bridge since then. The prob main spontaneous and flexible in both that the evidence furnished, to date, by dox that nothing but research on lems raised in my original paper and in methodology and subject matter. How, the traditional measures of the classical animals will provide us with knowl subsequent articles have come to be tak for example, do we account in our re scientific approach has only served to edge that will make it possible for en seriously by society at large. Even the search for such factors as the intimate, substantiate the theory that animals not us, one day, to dispense with the use of them altogether. only feel an immediate reaction to pain Boris M. Levinson is Professor Emeritus of Psychology at Yeshiva University. He resides at 86-35 Queens that is similar to our own, but also en Until that day arrives, it is imperative Blvd. 7K, Elmhurst, NY 11373. This article was presented as an invited address at the First International Con dure many of the longer-term ram ifica that we formulate workable guidelines ference on the Human/Companion Animal Bond at the University of Pennsylvania, Philadelphia, PA on Oc tions of pain. Their "feelings" are com for using animals with more compas tober 6, 1981, In respon_se to receipt of the Delta Society Achievement Award for Contributions to the Study municated by their reactions, which con sion-and intelligence-than we are at of the Human/Companwn An1mal Bond. He is also Director of Human/Companion Animal Therapy at Blue berry Treatment Centers, Inc., Brooklyn, NY. stitute reasonably reliable, objective in- present. Dana H. Murphy /NT I STUD ANIM PROB 3(4) 1982 282 /NT I STUD ANIM PROB 3(4) 1982 283