Subfornical organ stimulation excites paraventricular neurons projecting to dorsal medulla

Electrical stimulation in the subfornical organ (SFO) of pentobarbital-anesthetized Sprague-Dawley rats was noted to influence the excitability of paraventricular nucleus (PVN) neurons antidromically identified as projecting to the dorsomedial medulla. Extracellular recordings indicated that 60% (n = 34) of these caudally projecting PVN neurons increased activity in response to single shock stimuli delivered to the SFO. Short-latency [30.0 +/- 2.7 (SE) ms] and long-latency (162.5 +/- 32.5 ms) responses were observed. The remaining neurons were either unaffected (38%) or inhibited (2%) by SFO stimulation. These data suggest functional connectivity between the SFO and the dorsomedial medulla. It is proposed that such a pathway may mediate pressor responses observed to follow electrical stimulation in the SFO.