The Journal of Neuroscience, June 1995, f5(6): 4678-4686 Negative Feedback Neuroendocrine Control of the Inflammatory Response in Rats Paul G. Green,’ Frederick J.-P. Miao,” Wilfrid J3nig,5 and Jon D. Levinei~2~3~4 Departments of ‘Oral Surgery, 2Medicine, and 3Anatomy and 4Division of Neurobiology, University of California, San Francisco, California 94143 and 5Physiologisches Institut, Christian-Albrechts-Universitat, 24098 Kiel, Germany We describe that an ongoing inflammatory response at one The inflammatory responseis a physiological processthat pro- site (produced by complete Freund’s adjuvant injection in tects the organismagainst infection and repairs tissue after trau- the hindpaw) produces a negative feedback inhibition on matic injury. The mechanismswhich initiate the inflammatory plasma extravasation, produced by perfusion of the inflam- responseare well documented,and involve both humoral (Wil- matory mediator, bradykinin (160 rim), at a second site (the liams et al., 1988) and cellular (Keshav et al., 1990; Roos and knee joint). This negative feedback process is abolished in Dolman, 1990; Haskill et al., 1992) componentsof the immune rats that have been neonatally treated with capsaicin to de- system, neuroendocrinemechanisms (Garcia-Leme et al., 1992; plete most of their unmyelinated primary afferent fibers, Sternberg et al., 1992), as well as sensory (Kowalski and Kali- which suggests that this negative feedback process is me- ner, 1988; Mantyh et al., 1989; Barnes, 1991) and autonomic diated by activation of primary afferent fibers. Electrical components(Levine et al., 1987; Khalil and Helme, 1989; Kidd stimulation of the hindpaw at intensities that excite C-fibers et al., 1992) of the peripheral nervous system (PNS). While in- also inhibited bradykinin-induced plasma extravasation. flammation is normally a tissueprotective and/or reparative pro- Stimulation at intensities that only excite A-fibers had no cess, and beneficial to the organism (Basbaum and Levine, effect on bradykinin-induced plasma extravasation. Platelet 1991), the inflammatory processitself, especially if prolonged, activating factor-induced plasma extravasation, which is can lead to tissue injury, as in the presenceof chronic inflam- not dependent on the innervation of the joint, was not in- matory disease,such as rheumatoid arthritis. Thus, one would hibited by stimulation of C-fibers from the hindpaw. expect that there exists a mechanism(s)for the appropriate ter- Acute surgical interruption of the lumbar sympathetic mination of the inflammatory response,and that deficienciesin outflow to the hind limb (the paravertebral ganglia between such mechanismsmight contribute to production of inflamma- L, and L4) did not attenuate the depression of bradykinin- tory disease(Calogero et al., 1992; Zelazowski et al., 1992). induced plasma extravasation produced by C-fiber stimu- While removal or cessationof the stimulus that has initiated lation. This indicates that the depression is not mediated an inflammatory responsemay be sufficient to terminate inflam- by activity in the sympathetic outflow. Transection of the mation, there is also evidence that there are physiological mech- spinal cord, hypophysectomy, inhibition of corticosterone anismswhich produce negative feedback control of the inflam- synthesis, and adrenalectomy (but not adrenal medullec- matory response.For example, the inflammatory responsere- tomy) all prevented the inhibition of BK-induced plasma ex- sults, in part, from the opening of interendothelial gaps, which travasation by electrical simulation, indicating that the neg- quickly close again, even though the permeability-inducing ative feedback inhibition on plasma extravasation is de- agentscontinue to be present(Casley-Smith and Window, 1976). pendent on an intact neuraxis and an intact hypothalamic- Another mechanismthat may act to inhibit or terminate the in- pituitary-adrenocortical axis. flammatory responseis activation of the hypothalamic-pitui- In summary, our data demonstrate a negative feedback tary-adrenocortical (HPA) axis. Of interest, inflammation is inhibition of an inflammatory process, which is elicited by known to cause local releaseof a number of substances,such stimulation of C-fiber afferents. It is mediated by ascending as cytokines, that can act in the central nervous system to acti- pathways in the spinal cord, and probably the hypothalam- vate the HPA axis (Payne and Krueger, 1992; Dunn, 1993). Ac- ic-pituitary-adrenocortical axis. tivation of the HPA axis, in turn leads to the release of sub- [Key words: primary afferent nociceptor, sympathetic stances,such as corticosterone,which act to suppressthe inflam- nervous system, hypothalamic-pituitary-adrenal axis, ad- matory response(Sternberg et al., 1989; Sweep et al., 1991; renal medulla, adrenal cortex, neurogenic inflammation, Calogero et al., 1992). Additional evidence for a contribution of bradykinin, hypophysectomy, capsaicin, sympathectomy, the HPA axis to the negative feedback control of inflammation spinal transection, adrenalectomy] comesfrom studiesinvolving pharmacological,anatomical, and genetic lesions of the HPA axis. For example, there is an in- Received Nov. 9, 1994; revised Jan. 23, 1995; accepted Jan. 24, 1995. creasedsusceptibility to arthritis in Lewis rats that have a ge- This work was supported by NIH Grant AR32634 and by the Arthritis Foun- netically determined corticotropin-releasing factor (CRF) defi- dation (Northern California Chaoterl. ciency and hyporesponsivenessto administeredCRF (Sternberg Correspondence should be addressed to Jon D. Levine, M.D., Ph.D., De- et al., 1989), in adrenalectomized(Harbuz et al., 1993) or hy- partment of Medicine, S-1334/Box 0452A, UCSF, San Francisco, CA 94143. 0452A. pophysectomized (Neidhart and Fluckiger, 1992) rats, and in Copyright 0 1995 Society for Neuroscience 0270.6474/95/154678-09$05.00/O chickens with impaired HPA-axis function (Brezinschek et al., The Journal of Neuroscience, June 1995, 15(6) 4679 1990). A decreased susceptibility to inflammatory disease is, in filaments dissected from the nerve, using sharpened jeweler’s forceps. The filaments were placed on a silver-wire electrode for recording, and fact, seen in CRF-hyperresponsive Fischer rats (Sternberg et al., the reference electrode was attached to nearby tissue. Stimulating elec- 1990; Calogero et al., 1992; Zelazowski et al., 1992). In humans trodes were placed transversely across the paw (see above) approxi- with rheumatoid arthritis, there is an altered HPA axis circadian mately 6 cm distal to the recording electrode. The stimulus intensities rhythm and an abnormality of the HPA axis response to inflam- applied to the paw, which were found to reliably excite either A-fibers matory stimuli (Neeck et al., 1990; Chikanza et al., 1992); how- or A- and C-fibers, were 2.5 and 25 mA. The inset in Figure 1 dem- onstrates that a 2.5 mA stimulus intensity is below the threshold for ever, it is unclear whether this is the consequence of rheumatoid exciting C-fibers, but above the threshold for exciting A-fibers, and that arthritis or a causative factor in the generation of rheumatoid the 25 mA stimulus intensity also activate C-fibers. arthritis. Some rats received non-noxious (A-fiber strength) or noxious (C-fiber In this report, we describe the results of experiments which strength) electrical stimulation to the hindpaw during the assessment of show that ongoing inflammation at one site, the hindpaw, pro- BK-induced plasma extravasation: 25 min after the initiation of BK perfusion in the knee joint, rats received non-noxious (2.5 mA, 0.25 duces a negative feedback inhibition of bradykinin (BK)-in- msec duration pulses, 3 Hz) or noxious electrical stimulation (25 mA, duced plasma extravasation (a component of inflammation) at 0.25 msec duration pulses, 3 Hz) via the two stimulating electrodes, another site, the knee joint. Our data demonstrate that this neg- which continued for the duration of the experiment, except in one group ative feedback inhibition is mediated by afferent C-fibers and is where the stimulation was stopped to determine the time course for recovery from inhibition. In one group of rats, transcutaneous electrical dependent on spinal ascending pathways as well as an intact stimulation was applied to one forepaw. HPA axis. Materials and Methods Surgical and pharmacological manipulations Animals Acute surgical interruption of the lumbar sympathetic chain. The sym- pathetic chain was isolated bilaterally and loosely tied with two 2-O silk The experiments were performed on 300-400 gm male Sprague-Daw- threads, one at the level of L,~? and the other at L?.?. The incision ley rats (purchased from Bantin and Kingman, Fremont CA, except for wounds were closed and sutured, and the animal prepared for knee joint hypophysectomized rats and their normal controls, which were pur- perfusion. Acute sympathectomy was performed during knee joint per- chased from Charles River. Hollister. CA). The rats were housed in a fusion by applying tension to the silk threads to interrupt the sympa- temperature and humidity controlled environment, and were maintained thetic chain. Perfusion of BK through the knee joint and electrical stim- on a 12 hr light/dark cycle (lights on at 06:OO). Food and water were ulation continued uninterrupted following acute surgical interruption of available ad libitum. Care and handling of animals was performed in the lumbar sympathetic chain. accordance with The American Physiological Society guidelines.