EFFECTS OF ANESTHETICS AND SEPTAL-LESIONS AND STIMULATION ON ACETYLCHOLINE-H-3 FORMATION IN RAT HIPPOCAMPUS

The rate of 3H-acetylcholine (ACh) formation from i.v. injected 3H-choline was studied in the rat hippocampus after various treatments which alter the activity of cholinergic septal-hippocampal neurons. Administration of pentobarbital and placement of acute septal lesion reduced the formation of 3H-ACh but did not change 3H-choline content. Chloral hydrate administration reduced the formation of 3H-ACh and increased 3H-choline content. The chloral hydrate induced increase in 3H-choline occurred in animals with chronic septal lesions. Electrical stimulation of the septum increased both 3H-ACh and 3H-choline. Chronic septal lesion reduced both radioactive and endogenous ACh but did not affect radioactive or endogenous choline. There are probably multiple pools of choline in the brain. The precursor pool for ACh synthesis is apparently difficult to measure. The parameter that best correlated with cholinergic activity was the level of 3H-ACh. Possible mechanisms for this finding are discussed.