Thermoregulatory changes induced by intrahypothalamic injections of cholinomimetic substances in the pigeon

Abstract

Thermoregulatory responses to intrahypothalamic injections of cholinomimetic drugs (acetylcholine, ACh and carbamylcholine, CCh) and their inhibitors (atropine, Atr and tubocurarine, Tbc) were recorded from six unanaesthetized pigeons exposed to cold (6°C). The substances were administered into hypothalamus in a constant volume of 1 μl. Acetylcholme + physostigmine (Phy) in a dose range 5–20 μg + 5 μg inhibited shivering and evoked slight hypothermia which was not potentiated by larger doses. Also, CCh (0.25–1.5 μg) produced cessation of shivering and led to a marked fall in body temperature and oxygen consumption. The effects of CCh proved to be dose-dependent. Atropine, given 30 min prior to CCh prevented hypothermia while Tbc was ineffective. The results suggest that a muscarinic central cholinergic pathway may be involved in temperature regulation of thepigeon. Before definite conclusions are drawn, the effect of different ambient temperatures as well as dependence upon injection sites in the hypothalamus should further be tested.