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Chapter 2: and the : Neuroscience and Neurobehavior

The of Alcohol

The brain is a major target for the actions of Neuropathologic Changes alcohol, and heavy alcohol consumption has long been associated with . Studies The brain contains as many as 1 trillion nerve clearly indicate that alcohol is neurotoxic, with cells, or . They come in a variety of direct effects on nerve cells. Chronic alcohol shapes and sizes, some looking like old oak trees abusers are at additional risk for brain and others like weather balloons. Many of these from related causes, such as poor nutrition, cells project into other brain areas where they , and head trauma. regulate the activity of those areas, thereby affecting thoughts, consciousness, decisions, The potential cost to society of alcohol-induced mood, and attention. For every nerve in the brain damage is enormous. Approximately brain that is actively engaged in such things as 14 million Americans—about 7.4 percent of the thoughts, emotions, and movements, there are adult population—meet the diagnostic criteria for 10 other cells, called , that provide important alcohol or (Grant et al. 1994). support to nerve cells. Both of these cell types On any given day, more than 700,000 people in are damaged by chronic . Loss of a the receive alcoholism treatment in critical few due to alcohol-induced brain damage either inpatient or outpatient settings (National may have subtle but important effects on Institute on Alcohol Abuse and Alcoholism decision-making processes, mood, and behavior. [NIAAA] 1997). Approximately 9 percent of alcohol-dependent individuals have clinically There appears to be a continuum of brain damage diagnosable brain disorders (Eckardt and Martin in long-term alcoholics, progressing from mod- 1986). Indeed, alcoholic is the second- erate deficits in the majority of long-term alcohol leading cause of adult dementia in the United abusers to the severe of Wernicke- States, accounting for 10 percent of cases (Eckardt (Butterworth 1995; Pfeffer- and Martin 1986). It is exceeded only by baum et al. 1996). This syndrome includes Alzheimer’s disease. Many studies report that Wernicke’s and Korsakoff’s 50 to 75 percent of detoxified long-term alcohol- psychosis, also called Korsakoff’s amnestic dependent individuals show some degree of syndrome. Wernicke’s encephalopathy is cognitive impairment (Eckardt and Martin 1986), associated with deficiency resulting suggesting that brain dysfunction may persist from . Prompt treatment with even after the individual has stopped drinking. massive doses of thiamine may improve symptoms of this disorder, which include Individual susceptibility to alcohol-induced brain confusion, (disordered gait), and visual damage is highly variable and is related to many abnormalities. Patients have characteristic factors, such as gender, genetics, environment, brain that may be detected by magnetic and sociodemographics (Dufour 1993). Suscepti- resonance imaging (MRI). Korsakoff’s psychosis bility to is similarly variable; is characterized by anterograde , where some people become dependent at much lower the individual is unable to retain new information levels of consumption than others do. Therefore, (Eckardt et al. 1981). For example, the patient it is difficult to specify the levels of alcohol views as total strangers people who were encoun- consumption that are likely to to alcohol- tered moments before. The dysfunction induced brain damage. There is a serious need correlates with the presence of lesions in the for further research in this area. , a brain structure involved in the routing of sensory information in the brain

134 The Neurotoxicity of Alcohol

Figure 1: Reduced brain mass in alcoholics

Axial magnetic resonance images from a healthy 57-year-old man (left) and a 57-year-old man with a history of heavy alcohol consumption (right). Images are courtesy of Dr. Adolf Pfefferbaum.

(Victor et al. 1989). Although these two condi- observations are supported by imaging analyses. tions usually occur in sequence, they may exist For example, studies using MRI and computed independently; not all patients with Wernicke’s tomography (CT) show enlargement of the encephalopathy progress to Korsakoff’s psychosis, cerebral ventricles (cavities within the brain and Korsakoff’s psychosis may occur without a that are filled with ) and preceding episode of Wernicke’s encephalopathy. sulci (furrows on the surface of the cerebrum) in most alcoholics. Enlargement of these Extremely heavy alcohol consumption for a structures reflects a shrinkage of brain mass prolonged period is generally required to produce (figure 1), consistent with postmortem studies the most severe organic brain disease. One study that show reduced brain weight in alcoholics. In that compared Wernicke-Korsakoff patients with severe alcoholics, the reductions in weight of the alcoholics who did not have serious neuro- cerebral hemispheres and the (a brain psychological deficits found that both age of structure predominantly involved in and onset and duration of heavy drinking correlated movement; see figure 2) are significant compared with the development of Korsakoff’s psychosis with nondrinkers and moderate drinkers (Harper (Jacobson 1990). Those with Wernicke-Korsakoff and Kril 1993). The reduced brain mass is syndrome began consuming approximately probably due to a combination of actual loss 12 drinks a day at age 25 and drank at that of nerve cells and reduction in cell size. With level for 27 years. sustained for 1 to 5 months, the defect begins to disappear. This recovery probably Morphological Changes involves increases in neuronal cell size, number and size of the supporting glial cells, and arbori- Postmortem studies of brain tissue in both zation (branching) of nerve endings (Franke et al. humans and animals suggest that chronic heavy 1997). However, neurons that die are lost forever. alcohol use changes brain structure. These

135 Chapter 2: Alcohol and the Brain: Neuroscience and Neurobehavior

Figure 2: Anatomy of the brain

Cerebrum Cortex Largest portion of the brain, Outer layer of gray matter covering the including the cerebral surface of the cerebrum and the cerebellum hemispheres ( and basel ganglia); involved in controlling consciousness and Neocortex voluntary processes Outermost portion of the cerebral cortex that contains the most Corpus callosum structurally complex brain tissue A bundle of fibers connecting the brain’s hemispheres Diencephalon Hippocampus • Septal area–related to the Part of the , which limbic system, which is is involved in emotional aspects involved in emotional of survival behavior; also plays aspects of survival behavior a role in memory • Thalamus–a communication center that relays information to the A group of structures lying deep cerebral cortex in the brain involved in • –important in movement and cognition Cerebellum maintaining the body’s Involved in maintenance internal environment, or of posture, balance, and homeostasis, through the coordination receipt of sensory and chemical input Source: Mattson et al. 1994.

Data from tissue and quantitative morphometry developed in humans; among its functions, it is (structural) studies demonstrate selective neuronal the center for intellectual capacity.) Alcoholics loss, reduced arborization, and reduction of with severe brain disorders, such as Wernicke- synaptic complexity in specific brain regions of Korsakoff syndrome, show more significant alcoholics. The frontal lobes (of the cerebrum)— reduction in white matter and more extensive whose functions encompass the initiation of brain degeneration than do alcoholics with less motor activity and the integration of behavior, severe disorders. intellect, and emotion—appear to be particularly sensitive to alcohol-induced changes (Jernigan et Investigators have found a 22-percent reduction al. 1991). They show the greatest decrease in in the number of neurons in the superior frontal mass and account for much of the associated cortex and motor cortex of alcoholics compared ventricular enlargement. Both gray matter, which with nonalcoholic controls, but no significant is composed largely of neurons, and white matter, differences in other areas of the cortex (Harper which is composed of myelinated nerve fibers, et al. 1987). Recent studies of alcoholics have appear to be decreased. (The myelin sheath reported a relationship between around nerve fibers facilitates the conduction of shrinkage and a history of alcohol withdrawal nerve impulses.) There appears to be a selective , while frontal lobe shrinkage occurs in loss of white matter, particularly in the frontal alcoholics regardless of their history lobes, but it is uncertain how the observed (Sullivan et al. 1996). A decrease in the amount cellular lesions relate to this loss. One of N-acetylaspartate in the frontal lobe, a measure these changes are more evident is the greater of viability, is another indication of fron- proportion of white matter to cortical gray matter tal lobe degeneration in alcoholics (Jagannathan in the frontal regions. (Cortical refers to the et al. 1996). The findings of severe damage to cerebral cortex, a thin layer of gray matter on the the frontal cortex in alcoholics are consistent with surface of the cerebrum. It is most extensively clinical and neuroradiological findings, which

136 The Neurotoxicity of Alcohol suggest that the frontal lobe may be more the brain, including the regulation of mood susceptible than other cortical regions to alcohol- states, thinking patterns, appetite, , and induced brain damage. The large neurons that even behavior, such as alcohol drinking. The are lost in this frontal region (the pyramidal serotonergic system appears to be disrupted in neurons) are also recognized as being more alcoholics, particularly in severe alcoholics (Baker vulnerable in Alzheimer’s disease and as part et al. 1996; Halliday et al. 1995). Recent studies of the normal aging process. of alcoholics have found a reduction of up to 50 percent in the number of serotonergic neurons Recent studies have found that in addition to from both these raphe nuclei compared with the global shrinkage of brain regions, neurons in nonalcoholic controls. Further, chemical studies certain structures called nuclei are selectively lost have shown abnormally low levels of serotonergic with chronic alcohol abuse. Nuclei are clusters metabolites in the cerebrospinal fluid of alcoholics of neurons that have broad-ranging functions in with Wernicke-Korsakoff syndrome. brain activity; they are distinguishable by cell type or by clear demarcation from the surrounding Specific types of brain cells appear to be dis- tissue. Perhaps the most extensively studied rupted. Recent studies have indicated that certain nuclei are the nuclei in the basal neurons containing the peptide may forebrain. Neurons within these nuclei are be sensitive to chronic alcohol-induced neuro- involved with the production and release of in both humans and animals (Harding et , a associated with al. 1996; Madeira et al. 1997). Vasopressin is a many important physiologic functions. Both that is involved in the regulation of human and animal studies suggest that this both physiologic processes and neurobehavioral region is particularly susceptible to damage in function. Damage to neurons containing alcoholic subjects. Researchers have reported that vasopressin and other peptides could disrupt a Korsakoff’s psychosis causes both neuronal loss variety of hormone functions as well as the daily and shrinkage in this area, with one study rhythms that are important for healthy living. reporting a significant loss of neurons (Arendt Further studies are needed to determine whether 1993). Neurons in the cholinergic nuclei are also additional specific cell groups within the brain are lost in Alzheimer’s disease. particularly susceptible to damage. Neuronal loss in small but functionally significant brain areas Other brain nuclei that appear to be particularly could result in global changes in attention, mood, sensitive are the locus ceruleus and the raphe and personality that are difficult to quantify but nuclei. These nuclei are small but important have a great impact on brain function and overall because their neuronal processes project through- behavior. out the brain and modulate global aspects of brain activity. For example, lesions in the locus Recent animal studies have found that long-term ceruleus, which contains many of the noradren- is not necessary for brain ergic neurons (those that secrete the neuro- damage to occur. As little as a few days of transmitter ) in the brain, may intoxication can lead to neuronal loss in several impair attention and information processing and specific areas of the cerebral cortex (Collins et al. may affect learning and memory. Several studies 1996). These findings are consistent with recent have reported significant noradrenergic cell loss in studies in human alcoholics that report damage to the locus ceruleus (Arango et al. 1996; Arendt et one of these cortical areas (Ibanez et al. 1995) and al. 1995; Lu et al. 1997), but not all studies have significant shrinkage of the hippocampus, an area found this loss (Harper and Kril 1993). The involved in learning and memory (Harding et al. median and dorsal raphe nuclei together provide 1997). Chronic alcohol treatment of animals has the primary source of serotonergic axons in the shown that hippocampal damage is correlated cerebral cortex. These neurons secrete , with deficits in spatial learning and memory a neurotransmitter that affects multiple actions in (Franke et al. 1997). These studies indicate that

137 Chapter 2: Alcohol and the Brain: Neuroscience and Neurobehavior

cortical and hippocampal damage can occur in Alcoholics who do not suffer from Wernicke- animals with both chronic and short-term Korsakoff syndrome still show greater loss of alcohol exposure. This suggests that, in humans, neuropsychological performance than peer relatively short durations of alcohol abuse are nonalcoholics do on tests of learning, memory, likely to cause some form of damage. abstracting, problem solving, visuospatial and perceptual motor functioning, and information Exciting new studies have begun to address the processing (Parsons 1993). Alcoholics are less effects of gender on alcohol-induced brain accurate and take considerably longer to complete damage. Interestingly, alcoholic women appear tasks. Many of the deficits appear to recover to to have an increased sensitivity for brain damage age-appropriate levels of performance after 4 to compared with alcoholic men (Hommer et al. 5 years of abstinence (Parsons 1993). However, 1996). This difference appears to be true for liver even though global may return and heart damage as well. Although more men to near normal levels with extended abstinence, than women are diagnosed as alcoholic, the not all cognitive functions return. Some number of alcoholic women is increasing. abstinent alcoholics appear to have permanent Therefore, the increased susceptibility of women cognitive impairments, particularly in memory to alcoholic brain damage is an area that needs and visual-spatial-motor skills (Di Sclafani et al. further investigation. 1995). Other studies support a loss of logical memory and paired-association learning tasks in Functional Changes alcoholics that may be long lasting (Eckardt et al. 1996). Chronic alcohol abuse clearly to changes in brain function, with the degree of dysfunction Recent studies have emphasized the role of the dependent upon the duration and amount of prefrontal cortex in executive cognitive function alcohol consumed. Many brain functions related (ECF) (Hoaken et al. 1998). This is the ability to the frontal cortex appear to be affected. Pre- to use higher mental processes such as attention, frontal (the most anterior part of the cortex) planning, organization, sequencing, abstract damage typically is associated with changes in reasoning, and the use of external and internal personality and cognitive abnormalities. Although feedback to adaptively shape future behavior these types of changes in brain function are more (Foster et al. 1994). ECF processes are dysfunc- difficult to assess than physical changes, they tional in alcoholics and in persons with other are consistent with the morphological changes showing prefrontal damage (Boller et al. found in the frontal cortex of alcoholics. 1995). Changes in ECF and prefrontal cortical characteristics are associated with decreased Both clinical and experimental studies support regulation of human social behavior, including a role for frontal cortical involvement in neuro- disinhibition syndrome, which is characterized by psychological deficits in alcoholics, particularly , socially inappropriate behavior, and those with Korsakoff’s psychosis (Oscar-Berman aggression (Giancola and Zeichner 1995a). and Hutner 1993). These deficits include Disruption of ECF has also been implicated dysfunction in emotional control, problem- in the underlying aggression associated with solving ability, and attention. Electrophysiologic (Giancola and Zeichner 1995b). studies using electroencephalograms and event- related potentials have suggested that alcoholics Mechanisms of Action have difficulty differentiating relevant and irrelevant, easy and difficult, and familiar and Researchers have only recently begun to elucidate unfamiliar stimuli (Porjesz and Begleiter 1993). the mechanisms involved in the neurotoxic effects These deficits appear to be consistent for alco- of alcohol on the brain. As research techniques holics and may be related to frontal cortical have become more sophisticated and data from function. experimental and clinical studies have accumu- lated, however, investigators have had a more

138 The Neurotoxicity of Alcohol substantial basis for speculation as to the nature The administration of an antagonist to NMDA of these mechanisms. receptors, such as MK-801 (), elimi- nates both (Khanna et al. 1992; NMDA Receptor Supersensitivity Szabo et al. 1994) and withdrawal seizures (Grant et al. 1990), as well as blocks NMDA-stimulated One promising avenue of research involves the neuronal (Chandler et al. 1993a). In interaction between glutamate, an animal studies using thiamine-deficient rats as a that is the major excitatory neurotransmitter model for Wernicke’s encephalopathy, extra- in the brain, and a specific , cellular concentrations of glutamate in the brain the N-methyl-D-aspartate (NMDA) receptor. increased several fold during seizures (Langlais Glutamate and the NMDA receptors are and Zhang 1993). Administration of the NMDA extensively discussed in other sections of this MK-801 reduced the neuro- chapter. The NMDA receptor is inhibited by biological symptoms and the severity of neural alcohol at a greater level of sensitivity than is any lesioning in these animals (Langlais and Mair other known glutamate receptor. The acute 1990). These studies and others provide evidence alcohol-induced inhibition leads to adaptive that NMDA receptor supersensitivity may con- changes in the NMDA receptor that make it tribute to alcohol tolerance, dependence, and supersensitive to glutamate during chronic neurotoxicity and to the hyperexcitability and alcohol exposure. seizures associated with alcohol withdrawal. However, further research is needed in this area. Excessive stimulation of NMDA receptors by glutamate can kill neurons, and chronic alcohol Hyperexcitability of the central exposure increases sensitivity of neurons to is a key component of alcohol withdrawal. NMDA-stimulated killing (Chandler et al. 1993a; A supersensitive glutamate-NMDA response Crews and Chandler 1993; Iorio et al. 1993). appears to be involved, although a reduction in is a term applied to the direct lethal gamma-aminobutyric acid-mediated inhibition damage to neurons in extreme cases of excessive also may contribute to this hyperexcitability glutamate receptor activity, usually accompanied (Crews et al. 1996). (Gamma-aminobutyric acid by an excessive accumulation of intracellular is a neurotransmitter that inhibits the activity of ions. This neurotoxic property of the nerve cells.) One of the earliest findings suggest- receptors appears to play a key role in neuro- ing glutamate involvement was the increased degenerative diseases in general, as well as in binding of radioactively labeled glutamate , brain trauma, and other types of brain ([3H]glutamate) in the hippocampus of alcoholics damage (Crews et al. 1996). The extreme neuro- (Michaelis et al. 1990). Although it is not clear degeneration associated with Wernicke’s which subtype of glutamate receptor is involved, encephalopathy also appears to involve increases this finding is consistent with increased glutamate in glutamate-NMDA excitotoxicity. Several receptor and sensitivity. studies using cultured neuronal cells have indicated that a few days of chronic alcohol The mechanisms of NMDA receptor supersen- treatment lead to supersensitive NMDA receptor- sitivity are not fully understood, but it is clear stimulated calcium flux (an increase in the that chronic alcohol administration can induce intracellular concentration of calcium ions) this supersensitivity. This supersensitivity could (Ahern et al. 1994; Iorio et al. 1992), as well occur through a number of mechanisms, in- as NMDA receptor-stimulated excitotoxicity cluding an increase in the density of NMDA (Chandler et al. 1993b; Crews and Chandler receptors, changes in the NMDA receptor 1993; Crews et al. 1993; Iorio et al. 1993) subunit composition, or chemical changes in the and NMDA receptor-stimulated nitric NMDA receptor that could change its sensitivity. formation (Chandler et al. 1997). All of these Some, but not all, studies have found increases in reactions lead to severe neuronal damage. NMDA receptor density. These results, although

139 Chapter 2: Alcohol and the Brain: Neuroscience and Neurobehavior

inconclusive, suggest that this may be one of the overproduction of free radicals, the result is oxida- mechanisms underlying chronic alcohol-induced tive stress. This imbalance between increased NMDA receptor supersensitivity (Chandler et al. production of free radicals and decreased avail- 1997; Crews et al. 1996; Rudolph et al. 1997). ability of antioxidants can result in . Free radicals also may attack in cell A second mechanism for inducing NMDA membranes, causing peroxidation. This receptor supersensitivity could involve changes in is a reaction between radicals and the subunit composition of the receptor. The components of the that results NMDA receptor is thought to be made up of five in membrane injury and eventual cell death. subunits, and changes in the type of subunit could change NMDA receptor supersensitivity. Studies examining the effects of both acute Studies have reported that the number of subunits and chronic alcohol administration on cellular expressed during chronic alcohol exposure is oxidation in the rat brain have focused primarily altered (Follesa and Ticku 1995, 1996). on alcohol’s effects on the activity of antioxidants, such as alpha-tocopherol, ascorbate, , Other studies, however, found alcohol-induced catalase, and dismutase (Ledig et al. NMDA receptor supersensitivity without subunit 1981; Montoliu et al. 1994; Nordmann 1987; changes (Chandler et al. 1997), suggesting that Rouach et al. 1987), or on potential sources of other mechanisms, such as phosphorylation, oxidative radicals. One of these sources is nitric might be involved. This is a chemical reaction oxide, which has been implicated in neuronal that is involved in regulation of receptor activity. toxicity resulting from the formation of highly that phosphorylate (add phosphate to) oxidative metabolites (Crews and Chandler amino acid residues within the NMDA receptor, 1993). Another source of oxidative radicals is including tyrosine kinases such as Fyn tyrosine cytochrome P450 2E1, an that kinase, may affect NMDA receptor sensitivity metabolizes alcohol and is a potent generator of during alcohol treatment (Miyakawa et al. 1997). these radicals (Montoliu et al. 1994, 1995). These mechanisms could occur as a continuum, Increases in cytochrome P450 2E1 and other with phosphorylation causing initial supersen- oxidases induced in rats by chronic alcohol sitivity, and more prolonged and excessive alcohol administration have been related to increased consumption causing additional supersensitivity lipid peroxidation and the formation of reactive through changes in subunits and slight increases oxygen radicals in the brain (Montoliu et al. in NMDA receptor density. Because of the 1994). However, levels of antioxidant enzymes, consistent finding that NMDA supersensitivity such as catalase and , appear during chronic alcohol treatment leads to to increase as a compensatory mechanism increased NMDA receptor-stimulated neuronal (Montoliu et al. 1994). excitotoxicity, all of these mechanisms are being further investigated. The brain is particularly susceptible to lipid peroxidation because it consumes a large amount of oxygen and is rich in polyunsaturated fatty acids, which are particularly prone to injury from Another possible mechanism for alcohol-induced oxygen radicals. Experiments with cells of rat brain damage involves oxidative stress of neurons. have shown that a single dose of alcohol As a by-product of alcohol , free results in both increases in lipid hydroperoxide radicals may be formed. These are highly reactive levels and decreases in glutathione levels (Nord- molecular fragments that are capable of inflicting mann et al. 1990, 1992; Uysal et al. 1986, 1989). serious damage on cells if they are not quickly It is not clear whether or how this increased neutralized. Normally, free radicals are rapidly oxidation is associated with increased brain inactivated by antioxidants, which are protective damage. Most studies have focused on whole- that inhibit oxidation. However, if brain homogenates, rather than on cells of specific these defenses are impaired, or if there is an brain regions. However, a recent study of

140 The Neurotoxicity of Alcohol alcohol-induced depression of glutathione and possibility that growth factors may be used to glutamine synthetase levels, two indices of treat alcohol-induced brain damage as well as increased oxidative formation, used cells other neurodegenerative conditions. Studies of from specific brain regions. Researchers found the actions of growth factors and of their role changes only in cells from the striatum (a center in alcohol-induced brain damage represent an involved in the programming of movement), but exciting new area of discovery that could provide not in cells from the cerebral cortex or cerebellum new approaches to treatment of neurodegener- (structures involved in balance and motor ation. coordination) (Bondy and Guo 1995). In Closing Oxidative stress has been implicated in the effects of aging and in a variety of neurodegenerative Alcoholism is a progressive disease that starts disorders, such as Alzheimer’s disease, - with experimentation and progresses to addiction, sonism, and stroke. Much more research on usually over the course of several years. Addiction alcohol-induced is needed to involves the loss of control over the ability to provide a more complete of how abstain from the and an excessive preoccupa- oxidation damages neurons and how other brain tion with obtaining and using the drug. Discov- cells respond to increased oxidative stress. eries continue to unravel structure-function Alcohol-induced neurodegeneration may be aspects of the brain and suggest that some of the related to an induction of oxidative enzymes; behavioral problems of alcoholism may be related alcohol research provides an opportunity to to alcohol-induced damage to specific brain areas. clearly address this aspect of neurodegeneration, While earlier studies focused on alcohol-induced which could impact a broad range of diseases. changes in cognition, more recent studies are focusing on the frontal cortex, which is partic- ularly sensitive to alcohol-induced damage, Growth Factors and on the role of this brain region in behavior. Growth factors are specific elements of Experimental subjects with poor prefrontal the brain that stimulate growth and extensions functioning appear unable to inhibit impulsive of neurons and that are essential to neurons behavior (Lau and Pihl 1996), particularly for their survival and maintenance of normal violence (Lau et al. 1995). Results of neuro- function. Growth factors also are known to imaging studies also indicate that reduction of increase the activity of neuronal antioxidant and metabolic functions in the frontal lobes is excitotoxic protective mechanisms. The growth associated with violence (Raine et al. 1994). factors include, among others, nerve growth factor (NGF), brain-derived neurotrophic factor Taken together, these studies suggest that some of (bDNF), neurotrophin 3 (NT-3), and basic the greatest sociopathic problems of alcoholism, fibroblast growth factor (bFGF). such as violence and loss of control over the drug, may be directly related to the neurotoxic effects Researchers have found that alcohol alters brain of alcohol on prefrontal cortical function. This levels of growth factors in rats (Arendt et al. is a particularly exciting hypothesis, because it 1995; Baek et al. 1996; MacLennan et al. 1995; suggests that it may be possible to detect Nakano et al. 1996). Recent studies have found individuals at risk for addiction through studies that chronic alcohol administration reduces the of their brain function and to determine whether level of bDNF but does not change the levels recovery of normal function is associated with the of NGF, NT-3, or bFGF (Baek et al. 1996; ability to sustain abstinence. Identification of MacLennan et al. 1995). Receptors for the these individuals would allow focused efforts at growth factors remain intact after chronic alcohol prevention and education, with the aim of abuse (Arendt et al. 1995; MacLennan et al. preventing addiction and its accompanying 1995). This finding presents the promising sociopathic behaviors.

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