RELEASE OF ENDOGENOUS ACETYLCHOLINE IN THE HYPOTHALAMUS OF CONSCIOUS RATS

The release of endogenous acetylcholine was investigated by the push-pull technique. The posterior hypothalamus of conscious rats was superfused through a push-pull cannula with artificial cerebrospinal fluid (ACSF) which contained 1-mu-mol/l neostigmine. Acetylcholine was determined in the superfusate by high pressure liquid chromatography and electrochemical detection. Hypothalamic superfusion with potassium-rich (100 mmol/l) ACSF led to a pronounced increase in the release rate of acetylcholine. Tetrodotoxin (1-mu-mol/l) almost abolished the basal release of the neurotransmitter. Superfusion of the hypothalamus with atropine (10 or 50-mu-mol/l) led to a concentration-dependent increase, whereas superfusion with oxotremorine (50-mu-mol/l) inhibited the release rate of acetylcholine. It is concluded that acetylcholine released into the superfusate of the hypothalamus originates from cholinergic neurons. Furthermore, the release of acetylcholine seems to be modulated by muscarinic acetylcholine receptors, probably located on cholinergic neurons of the hypothalamus.