Inputs from the nucleus of the solitary tract to subfornical organ neurons projecting to the paraventricular nucleus in the rat.

Extracellular single-unit activity was recorded from 26 subfornical organ (SFO) neurons antidromically identified as projecting to the hypothalamic paraventricular nucleus (PVN) in urethane-anesthetized male rats. Of these identified SFO neurons, 10 displayed an inhibitory response and 2 exhibited an excitatory response in neuronal excitability following electrical stimulation of the nucleus of the solitary tract (NTS), while the remaining neurons were unresponsive. Eight out of 10 SFO neurons that demonstrated the inhibitory response to NTS stimulation also displayed a reduction in ongoing activity in response to activation of peripheral baroreceptors, achieved by rising arterial blood pressure with an intravenous administration of the alpha-agonist metaraminol, whereas the remaining responsive neurons to NTS stimulation were ineffective. These results show that a part of SFO neurons projecting to the PVN may receive inhibitory inputs from the peripheral baroreceptors through NTS neurons.