The diurnal variations of M A 0 activities (type A and type B) in the individual hypothalamic nuclei, in addition to some areas of the rat brain, were studied under two different lighting schedules, D-L condition and D-D condition.Type A M A 0 activities in some nuclei increased significantly in the light period in D-L condition and the change in N. suprachiasmaticus (SCN) and N. supraopticus (SON) was also maintained in D-D condition. Type B MA0 activities in some nuclei showed preferably the opposite phase to that of type A M A 0 activity. These diurnal changes of each M A 0 type activity may reflect the biological actions of monoamines in relation to a circadian rhythm of the neuroendocrinological system in the brain to some extent.
The diurnal rhythmicity of glutamic acid decarboxylase (GAD) activity in the nucleus level of the rat brain was examined by the radiochemical micromethod in a light-dark condition. GAD activity showed a biphasic variation in globus pallidus and substantia nigra (zona reticulata and compacta), but a monophasic variation, i.e. high in the dark, in colliculus superior (stratum griseum superficiale and stratum opticum). As for hypothalamus GAD activity of some nuclei (N. arcuatus, N. periventricularis, N. preopticus, etc.) it indicated a monophasic variation, while that of some nuclei (N. suprachiasmaticus, N. ventromedialis, A. lateralis, etc.) it showed no significant variations despite their proved functional activity with rhythmicity.
The inhibiting effect of monoamine oxidase (MAO) activities towards 5‐hydroxytryptamine, dopamine and β‐phenylethylamine by an acute and chronic administration of clorgyline was investigated in five locations of the rat brain. Inhibiting the percentage distributed unevenly in each hypothalamic nucleus and in the circumventricular areas, except the median eminence, the percentages were significantly low as compared with the hypothalamic lateral nucleus. A significant percentage of inhibition for type B MAO towards β‐phenylethylamine was noticed in the chronically administered group. In conclusion, the MAO‐inhibiting effect of clorgyline administered intraperitoneally was unevenly distributed in the discrete brain nuclei and the regional difference depended upon the dose and the duration of the clorgyline administration.
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