PARAVENTRICULAR NUCLEUS NEURONS PROJECTING TO THE SPINAL-CORD RECEIVEEXCITATORY INPUT FROM THE SUBFORNICAL ORGAN

The present study utilized electrophysiological techniques to determin e the effects of subfornical organ (SFO) stimulation on the activity o f neurons in the paraventricular nucleus (PVN) projecting to the spina l cord. Single-unit recordings were obtained from 79 PVN neurons antid romically identified as projecting to the intermediolateral cell colum n (IML). Antidromically evoked action potentials showed a mean latency of 94.6 +/- 5.3 ms and a mean threshold for activation of 1.58 +/- 0. 11 mA. Electrical stimulation of SFO (100 mu A-1.5 mA, 0.1 ms) resulte d in excitatory responses in 18 of the 27 neurons tested (67%). Perist imulus histogram analysis of such effects demonstrated a duration of < 50 ms in 14 of the 18 cells so influenced (78%), whereas the remaining 4 cells (22%) showed excitatory responses with a longer duration. Sys temic administration of the nonpeptidergic angiotensin II (ANG) type 1 (AT(1)) receptor antagonist losartan (3 mg/kg) blocked the long-durat ion excitatory responses in 100% (3 of 3) of the cells tested but was without effect on the short-duration excitations (0 of 5). Twenty-two identified PVN neurons were also tested for their responses to systemi c ANG (20-500 ng), which had no observable effect on the activity of a ny of these cells. These data demonstrate that neurons in SFO provide excitatory input to PVN cells that project to the IML. One of the neur otransmitters responsible for communication in this pathway is ANG.