Responses of cells in the XXXX supraoptic nucleus in vivo to stimulation of afferent pathways are different at different times of the light/dark cycle.

@entity35 @entity398
To determine whether the daily rhythms of spike activity in the supraoptic nucleus (SON) were accompanied by changes in the behaviour of its inputs, we used conventional extracellular single cell recordings from cells in the SON of anaesthetized @entity35 while stimulating the contralateral optic nerve and the ipsilateral suprachiasmatic nucleus (SCN). Neurones in the SON region were identified by antidromic activation and classified as @entity398 or vasopressin cells, on the basis of their spontaneous firing patterns. Approximately 27% of both @entity398 (29/108) and vasopressin (39/147) neurones were excited by stimulation of the optic nerve, and the majority of responses had a long latency (>20 ms). Very few @entity398 (3/108) and vasopressin cells (2/147) were inhibited by stimulation of the optic nerve. The pattern of the responses (excitatory, inhibitory or nonresponsive) of @entity398 and vasopressin cells to stimulation of the optic nerve was significantly related to the time of day (chi-square test; P = 0.012, @entity398 cells; P = 0.006, vasopressin cells). The proportion of @entity398 cells excited by stimulation of the optic nerve was highest at ZT 4-8 and lowest at ZT 20-24. For vasopressin cells, it was highest at ZT 12-16 and lowest at ZT 20-24. The proportion of excitatory, inhibitory and complex responses seen in @entity398 and vasopressin cells following stimulation of the SCN also changed and was significantly different at different times of day ( @entity398 cells: highest proportion of excitatory responses at ZT 12-16, P = 0.029; chi-square test; vasopressin cells: highest proportion of excitatory responses at ZT 0-4, P = 0.005; chi-square test). Thus, inputs to @entity398 and vasopressin neurones from the optic nerve and some outputs from the SCN changed during the light/dark cycle. Such changes may contribute to the generation of 24-h rhythms in activity of @entity398 and vasopressin neurones and release of the peptides.
