The influence of food deprivation, exposure to cold and immobilization on monoamine oxidase activity in some hypothalamic nuclei of the rat brain.

The activity of deaminating monoamine-O-oxidoreduc tase E.C. 1.4.3.4. (MAO) has been found in almost all tissues of vertebrates which have been studied (4, 7). This activity seems to occur exclusively in the outer membrane of the mitochondria and as a result of this localization, MA0 deaminate extravesicular catecholamines in the intracellular compartment. Appropriate aldehydes, further oxidated to acids and ammonia, are products of this recation. These metabolities are physiologically inactive and therefore can not stimulate any monoamine receptors (19). In the rat brain both the "A" form of MA0 activity specific to noradrenaline and serotonin, and sensitive to inhibition by clorgiline and its analogues (22), as well a s the other deprenyl-sensitive "B" form of MAO; specific to benzylamine and phenylethylamine were detected (22, 23). It should be mentioned, that the tryptamine we used is the substrate for both forms of MAO. In the hypothalamus of rats relatively high activity of the enzyme was found (17). This activity depends on age, strain, hormones, and especial on the level of estrogens which were found to be greatly involved in the regulation of hypothalamic MA0 activity (5). Since there were changes in catecholamine concentrations in particular hypothalamic nuclei of rats exposed to different kinds of stress (5, 6, 8, 9, 14, 15). as well