It has been revealed by the open field tests that Wistar male rats with a high motor activity exhibit elevated emotional reactivity and sensitivity to small doses of L-DOPA. This rat group was examined for acetylcholine (AC) metabolism according to choline acetyltransferase (CAT) and acetyl cholinesterase (ACE) activity in fractions of light (C) and heavy (D) synaptosomes of the hypothalamus and nucleus of the solitary tract (NST) in health and after three-fold administration of L-DOPA. In health, the D fraction of the NST demonstrated "non-classic" high activity of both enzymes. In view of this fact it may be assumed that terminals of the fibers of craniocerebral nerves IX and X are localized in that fraction. In the NST, L-DOPA produces a decrease of CAT and ACE activity and of protein content in the D fraction, which corresponds with inhibition of the function of the parasympathetic (AC-ergic) system in response to activation of the peripheral adrenergic system. In the C fraction of the NST, the analogous but opposiely directed changes are observable, which may be related to compensation of the peripheral effect produced by L-DOPA. In turn, the C and D fractions of hypothalamic synaptosomes manifest noticeable activation of ACE, with CAT activity and protein content being unchanged. In contrast to the NST, this phenomenon is not connected with the changes in the rate of AC synthesis. Therefore, the status of the AC system of hypothalamic synaptosomes does not correlate with its possible appearance on the NST and is thus not related to participation of the hypothalamus in regulation of vegetative functions.(ABSTRACT TRUNCATED AT 250 WORDS)