CIRCADIAN-RHYTHM OF NEURONAL-ACTIVITY IN SUPRACHIASMATIC NUCLEUS SLICES FROM THE VASOPRESSIN-DEFICIENT BRATTLEBORO RAT

In vitro extracellular recordings were made from tissue slices of supr achiasmatic nucleus from homozygous Brattleboro rats which are deficie nt in vasopressin. A high proportion (56%) of neurons were excited by application of exogenous vasopressin, indicating that the V-1 receptor s expressed by these neurons were functional. Basal activity of these vasopressin-sensitive neurons showed a marked circadian variation (hig her during the subjective light phase) while vasopressin-insensitive n eurons showed no significant variation, suggesting the presence of the V-1 receptor identifies a population of highly circadian neurons. Sup rachiasmatic neurons from both homozygous rats and their heterozygous (vasopressin-containing) litter males displayed a circadian rhythm of spontaneous (basal) activity, with firing rates declining during the s ubjective dark phase, indicating that the endogenous pacemaker driving the circadian rhythm was not dependent upon the presence of vasopress in. However, the peak of spontaneous activity displayed during the sub jective light phase was significantly lower in the vasopressin-deficie nt animals. These data show that the presence of endogenous vasopressi n within the suprachiasmatic nucleus is not necessary for the generati on of the circadian pattern of activity. However, vasopressin does fun ction to amplify the rhythm by its excitatory effect during the light phase. Copyright (C) 1996 IBRO.