Cardiovascular effects of carbachol and other cholinomimetics administered into the cerebral ventricles of conscious cats.

1. The cholinomimetic substances acetylcholine, nicotine, tetramethylammonium chloride and carbachol were infused intracerebroventricularly (i.c.v.) into conscious, normotensive cats and their effects on behaviour, blood pressure and heart rate recorded. 2. Intracerebroventricular acetylcholine, nicotine and tetramethylammonium chloride each produced small, mainly stimulant, effects on the cardiovascular system which were not accompanied by any marked behavioural effects. 3. Intracerebroventricular carbachol at a dose of 30 microgram produced marked and persistent cardiovascular stimulant effects accompanied by a striking rage/fear reaction. When the dose of carbachol was reduced to 7.5 microgram the behavioural effects were no longer seen but marked cardiovascular stimulant effects remained. 4. The cardiovascular stimulant effects of i.c.v. carbachol were apparently mediated via the peripheral sympathetic system since they were abolished by peripheral adrenergic neurone blockade. 5. The blood pressure and heart rate increases produced by i.c.v. carbachol were blocked by prior i.c.v. treatment with atropine, hexamethonium, guanethidine, bethanidine or propranolol. 6. The data are consistent with an interaction between central cholinergic and catecholaminergic neural pathways involved in central regulation of blood pressure and further suggest the involvement of beta-adrenoreceptors in the responses to centrally-administered cholinomimetics.