The diurnal variations of glutamic acid decarboxylase activity in some discrete nuclei of rat brain

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.