Supraoptic nucleus afferents from the main olfactory bulb--II. Intracellularly recorded responses to lateral olfactory tract stimulation in rat brain slices.

To establish the functional nature of the anatomically demonstrated main olfactory bulb inputs to the supraoptic nucleus, electrophysiological responses of intracellularly recorded supraoptic neurons to lateral olfactory tract stimulation were recorded in horizontal slices of basal forebrain and hypothalamus. A total of 71 synaptically influenced neurons were studied in slices from adult rats of both sexes. Of these, 60 cells (84%) were monosynaptically activated by olfactory tract stimulation; seven cells (10%) were activated via polysynaptic pathways; and four cells (6%) were characterized by long latency inhibitory responses. Lucifer Yellow was injected into 64 cells and subsequent immunocytochemical identification of 44 of these neurons showed that both oxytocin and vasopressin cells, in approximately equal numbers, were excited by olfactory stimulation. Polysynaptically mediated excitation, however, was only associated with oxytocin cells (six of the six identified cells). These results corroborate anatomical tract tracing data showing main olfactory bulb efferents to both supraotic neurons and to neurons of the perinuclear zone. Also supported are earlier speculations of olfactory participation in release of oxytocin and vasopressin during various physiological states.