FOS PRODUCTION IN RETROGRADELY LABELED NEURONS OF THE LAMINA TERMINALIS FOLLOWING INTRAVENOUS-INFUSION OF EITHER HYPERTONIC SALINE OR ANGIOTENSIN-II

The lamina terminalis consists of neurons which are activated by both osmotic and angiotensinergic stimuli and which project axons to many s ites including regions of the hypothalamus responsible for vasopressin production. Combination of retrograde neuronal tracing procedures wit h the identification of Fos protein following discrete stimuli shows p opulations of neurons, projecting to the supraoptic nuclei, which are preferentially activated by intravenous infusion of either hypertonic saline or angiotensin II. Following infusion of hypertonic saline, the greatest percentage of neurons both labelled with cholera toxin-gold and having elevated levels of Fos protein occurred in that part of the lamina terminalis called the organum vasculosum lamina terminalis. Co nversely, angiotensin infusion resulted in greatest numbers of Fos and cholera toxin-gold-labelled neurons in the subfornical organ with few er double-labelled cells represented in the other components of the la mina terminalis, the median preoptic nucleus and the organum vasculosu m lamina terminalis. While these data do not support more than a gener al separation of the functions examined among neurons of the lamina te rminalis, they do highlight a discrete group of osmoresponsive neurons in the dorsal cap of the organum vasculosum lamina terminalis. These cells, by virtue of their response to infusions of hypertonic saline a nd their axonal connections to regions of the hypothalamus responsible for vasopressin production, are likely candidates for cerebral osmore ceptors.