Sleep induced by drugs injected into the inferior horn of the lateral cerebral ventricle in dogs.

1 In unanaesthetized dogs, cholinomimetic drugs and their antagonists were injected into the inferior horn of the left lateral cerebral ventricle. Injection volumes of 5 mul were used to limit spread of the drugs beyond the inferior horn. The effects on EEG and behaviour were recorded and compared with the effects of the same doses given into the body of the right lateral ventricle a little behind the foramen on Monro. 2 injections of cholinomimetic drugs into the inferior horn (acetylcholine 1-2 mug, physostigmine 1.0 mug, pilocarpine 100 mug and nicotine 10 mug) induced sleep during the following hour. The same doses injected into the body of the lateral ventricle did not produce sleep. 3 Cholinolytic drugs (atropine 10-20 mug, hyoscine 0.4-1.6 mug (+/-)-tubocuraine 10-20 ng and hexamethonium 40 mug) injected into the inferior horn also produced sleep, but the same doses injected into the body of the lateral ventricle were without effect. The EEG recorded after tubocurarine showed high voltage slow waves during sleep and desynchronized activation during rapid eye movement sleep. 4 Noradrenaline (10 mug) injected into the inferior horn produced sleep whereas the same dose given into the body of lateral ventricle did not produce sleep. The results with 5-hydroxytryptamine were equivocal. 5 It is suggested that the site for induction of sleep lies in structures lining the inferior horn of the lateral cerebral ventricle and that the cholinomimetic drugs probably act by a depolarizing block and the acetlycholine antagonists by a competitive block.