ABSTRACT
The participation of GABAergic mechanisms in the regulation of circadian rhythmicity by the suprachiasmatic nuclei (SCN) has been suggested from different lines of evidence. Little is known, however, whether GABA synthesis, release, uptake or content within the SCN may show a circadian pattern. The present results show that the activity of the GABAergic system within the SCN region of the rat exhibits circadian rhythmicity, which is manifested by correlative changes of the GABA content and the glutamic acid decarboxylase activity under the light/dark cycle, and by changes in the GABA content in animals kept under constant darkness.
Subject(s)
Circadian Rhythm/physiology , Suprachiasmatic Nucleus/physiology , gamma-Aminobutyric Acid/physiology , Animals , Biomarkers/analysis , Darkness , Glutamate Decarboxylase/analysis , Nerve Tissue Proteins/analysis , Neurons/enzymology , Rats , Rats, WistarABSTRACT
GABA accumulation was studied in the substantia nigra after treatment with L-glutamic acid-gamma-hydrazide (GAH) in rats 3 h following hemisection at the posterior hypothalamic level. GAH-induced GABA accumulation was significantly reduced on the hemisectioned side (P < 0.05, Wilcoxon's test). Two or three weeks after hemisection, glutamic acid decarboxylase activity was reduced in the substantia nigra of the hemisectioned side by 80%, showing that the descending GABA pathway to the substantia nigra had been transected. It is concluded that GAH-induced GABA accumulation might be nerve impulse-dependent.
