Changes in body temperature produced by cholinomimetic substances injected into the cerebral ventricles of unanaesthetized cats.

1. The effects on body temperature of a number of substances injected into a lateral cerebral ventricle were examined in the unanaesthetized cat.2. Nicotine (50 and 100 mug) caused a fall in body temperature ranging from 0.95-2.1 degrees C associated with skin vasodilatation, tachypnoea and panting. These responses were prevented by the intraventricular injection of hexamethonium or mecamylamine, but not of atropine or phentolamine.3. Carbachol (5 mug) caused a rise in temperature associated with skin vasoconstriction, piloerection and severe shivering. These effects were prevented by the intraventricular injection of atropine, but not of hexamethonium or mecamylamine.4. An acetylcholine/eserine mixture (10 mug of each) had no reproducible effect on body temperature. Because of the variability in the response, interaction studies with antagonist drugs were not performed.5. Hexamethonium (100 mug) or mecamylamine (100 mug) caused a prolonged rise in temperature, together with skin vasoconstriction, piloerection and intense shivering. Atropine (200 mug) was without effect on body temperature.6. Noradrenaline (100 mug) caused a fall in temperature with skin vasodilatation. The fall was converted to a rise with skin vasoconstriction, piloerection and vigorous shivering following an intraventricular injection of phentolamine (100 mug).7. These observations suggest the existence of cholinergic heat loss and heat gain mechanisms in the hypothalamic thermoregulatory pathways of the cat and the interaction studies with hexamethonium, mecamylamine and atropine, support the involvement of ;nicotinic' and ;muscarinic' receptors within the cholinergic thermoregulatory system.