ANALYSIS OF THE EFFECTS ON BODY TEMPERATURE OF INTRACEREBROVENTRICULAR INJECTION IN ANAESTHETIZED DOGS OF GAMMA‐AMINOBUTYRIC ACID

Abstract

The cerebral ventricles of dogs under intravenous pentobarbitone sodium anaesthesia, were perfused with artificial cerebro‐spinal fluid (CSF) at a rate of 0.4–0.5 ml/min from the ventricular to the aqueductal cannulae. The effluent was collected from the aqueductal cannula in 20 min samples. The animals' temperatures were recorded from the rectum. γ‐Aminobutyric acid (GABA) 0.1–5 mg when injected into the ventricles produced variable temperature effects. Doses of 0.1 and 0.5 mg always produced hyperthermia and 1 and 5 mg doses sometimes produced hyperthermia and sometimes hypothermia. Intraventricular perfusion with 2‐bromolysergic acid diethylamide (BOL) and hyoscine did not block hyperthermia. Tests on the rat isolated stomach strip or the guinea‐pig isolated superfused ileum for the possible release, respectively, of 5‐hydroxytryptamine or acetylcholine by GABA were negative. When tested for the presence of prostaglandin E(PGE)‐like substances on the isolated rat stomach strip, both the control effluent and the GABA effluent showed activity, the latter being much more potent. There was a temporal correlation between this effect and hyperthermia. Intraventricularly administered sodium salicylate converted the GABA‐induced hyperthermia to hypothermia and blocked the release of PGE‐like substances. Hypothermia induced by GABA alone or in the presence of sodium salicylate was associated with the release of noradrenaline into the effluent. Intraventricular administration of GABA in reserpinized dogs produced hyperthermia and not hypothermia. Similar results were obtained with phentolamine perfusion in normal dogs. Perfusion with calcium‐free solution blocked both the noradrenaline‐releasing and hypothermic actions of GABA. It is concluded that hyperthermia associated with intraventricular injections of GABA is due to the release of PGE‐like substance and hypothermia is due to the release of noradrenaline. 1974 British Pharmacological Society