Brain Research, 526 (1990) 351-354 Elsevier

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Depletion of brain a-MSH alters prostaglandin and interleukin fever in rats S.M. Martin 1, T.J. Malkinson 2, W.L. Veale 2 and Q.J. Pittman 2 1Biology Department, Mount Saint Vincent University Halifax, N.S. (Canada) and 2Neuroscience Research Group, Faculty of Medicine, University of Calgary, Calgary, Alta. (Canada) (Accepted 29 May 1990)

Key words: a-Melanocyte stimulating hormone; Rat; Prostaglandin; Interleukin; Fever

Alpha-melanocyte stimulating hormone (a-MSH), a putative endogenous antipyretic agent, is synthesized largely within neurons in the arcuate nucleus. To test the hypothesis that destruction of this area would increase the febrile response, male Wistar rats, treated as neonates with intraperitoneal injections of monosodium glutamate (MSG) or saline, were given intracerebroventricular (i.c.v.) injections of prostaglandin E 1 (20 ng; 200 ng) or purified interleukin-1 (20 U) and body temperature was monitored. The fevers displayed by the MSG-treated animals were significantly greater (P < 0.05) than those of the controls for the lower dose of PGE 1 at 10-30 min and for IL-1 at 3-6 h after the injections. MSG-treated rats showed significant reduction (P < 0.01) in a-MSH content of the medial basal hypothalamus and lateral septum when compared to saline controls. Body temperature response of non-febrile animals to high ambient temperature was not affected by the MSG treatment. These data support the hypothesis that a-MSH is an endogenous antipyretic in the rat. A body of evidence exists to support the hypothesis that the neurotransmitter, alpha-melanocyte stimulating hormone (a-MSH), acts as an endogenous antipyretic agent. This peptide, when injected centrally 8 or peripheraUy 13 in rabbits, inhibits an interleukin-1 (IL-1) fever. Additionally, a - M S H has been shown to reduce fever in squirrel monkeys 23 and guinea pigs 11, but to have no effect in cats ~8. The primary site in the brain for the antipyretic a-MSH appears to be the septum, an area that receives axonal projections from a - M S H producing cell bodies in the arcuate nucleus of the hypothalamus 7. Increased levels of a - M S H are present in the septum of rabbits during fever 3'1°'21 and microinjection of a-MSH into the septum of rabbits reduces fever 4'9. In addition, the antipyretic effect of a - M S H can be blocked by pretreatment with a - M S H antisera given i.c.v. 22. The antipyretic effect of a-MSH have been well established in rabbits; the present investigations were undertaken to assess whether a-MSH also may induce antipyresis in the rat. We hypothesized that lesioning of the a - M S H cell bodies in the arcuate nucleus with the excitatory amino acid, monosodium glutamate (MSG) 16' 24, would reduce the level of a-MSH in the brain 1,6A5 and alter the fever response. Wistar neonates were given randomly intraperitoneal (i.p.) injections of monosodium glutamate (4 mg/kg body weight) or an equal volume of 0.9% saline on days 2, 4,

6, 8, 10 after birth. At maturity, male rats, weighing 235-321 g were anesthetized with sodium pentobarbital (65 mg/kg), given i.p.; 20-gauge stainless steel guide tubes were implanted stereotaxically 17 above the lateral cerebral ventricles and a precalibrated transmitter (VMFM disc; Minimitter Inc., Sun River, OR) was placed into the peritoneal cavity. After recovery from surgery, each animal was placed in its own cage without restraint in a temperature controlled chamber and conditioned to the experimental environment. On the days of the experiments, manually delivered i.c.v, injections of PGE1 (20 ng/10/~l; 200 ng/10/~1; Sigma Chemical Co., St. Louis, MO) or purified interleukin-1 (p|L1, 20U/10 /~1; Cistron Technology, Pinebrook, N J) were administered by gravity over I min using a 25 gauge needle lowered through the guide cannula and connected by polyethylene tubing to a Hamilton microliter syringe. Body temperatures of the animals were monitored continuously and recorded on-line (Dataquest III, Data Sciences Inc., Minneapolis, MN) at 5-min intervals using a Zenith AT computer for 2 h before and for 4 h or 10 h following the injections. The ability of these same animals to respond to a thermoregulatory challenge was tested. Body temperature was monitored for 2 h at an ambient temperature of 23 °C after which the animals were exposed in a temperature controlled room, for a further 6 h to a warm (31°C) ambient temperature.

Correspondence: Q.J. Pittman, Neuroscience Research Group, Faculty of Medicine, University of Calgary, 3330 Hospital Drive N.W., Calgary, Alta. T2N 4N1, Canada. 0006-8993/90/$03.50 (~) 1990 Elsevier Science Publishers B.V. (Biomedical Division)

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Fig. 1. Mean changes in intraperitoneal body temperature following i.c.v, injection of 200 ng of prostaglandin E~ at time 0 in rats treated as neonates with MSG or saline. Vertical bars represent + S.E.M. n = 14 observations from 7 animals in each group.

Fig. 3. Mean change in intraperitoneal body temperature following i.c.v, injection of 20 units of purified interleukin-1 at time O. Vertical bars represent + S.E.M. n = 14 observations from 7 rats in each group.

At the completion of the experiments, the rats were anesthetized deeply with sodium pentobarbital and killed by decapitation. The lateral septum (area between the lateral ventricles, bordered dorsally by the corpus collosum and ventrally by the ventral septal area), the medial basal hypothalamus (bordered anteriorly by the optic chiasm, dorsally by the level of the anterior commissure, caudally by the mamilliary bodies and laterally by the supraoptic nuclei) and the vermis of the cerebellum were quickly dissected. Tissues were weighed, homogenized over ice in 0.1 NHCL/0.5% BSA, centrifuged at 4 °C and the supernatent lyophylized. The lyophylized samples were assayed in triplicate for a-MSH as previously described 25 using a specific RIA for a-MSH having a sensitivity of 5-10 pg/tube, a-MSH content was corrected

for the weight of individual brain areas. Data were analyzed using one-way analysis of variance corrected for repeated measures, followed by the Scheffe post hoc test and by the Student's t-test. Rats given i.c.v. PGE 1 (200 ng) showed the typical rapid onset fever which peaked at 20 min (Fig. 1). The baseline temperatures were identical and peak fevers were similar (MSG 2.09 + 0.21 °C vs saline 1.71 + 0.12 °C; F1,26 = 2.54; P > 0.10) after which there was a rapid defeverscence. As it is possible that the fevers produced by this dose of PGE were too great to reveal subtle differences in antipyresis, further experiments were carried out with lower quantities of PGE. When 20 ng PGE were given i.c.v. (Fig. 2), the fever displayed by the MSG-treated animals rose faster and within 20 min

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Depletion of brain alpha-MSH alters prostaglandin and interleukin fever in rats.

Alpha-melanocyte stimulating hormone (alpha-MSH), a putative endogenous antipyretic agent, is synthesized largely within neurons in the arcuate nucleu...
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