CONTROL OF SYMPATHETIC OUTFLOWS BY THE HYPOTHALAMIC PARAVENTRICULAR NUCLEUS

1. The functional role of the paraventricular nucleus (PVN) has been e xamined by studying its connections with cardiovascular neurons in the medulla and spinal cord and its influence on activity in several symp athetic nerves. 2. Chemical stimulation of neurons within the PVN can elicit presser responses and can excite reticulo-spinal vasomotor neur ons in the rostral ventrolateral medulla (RVLM). 3. The PVN-RVLM excit ation is blocked by kynurenic acid applied iontophoretically in the vi cinity of RVLM-spinal neurons, suggesting this is a glutamate-dependen t pathway. 4. Electrical stimulation of PVN neurons evoked action pote ntials in RVLM neurons after 27ms with a small variability. 5. Anterog rade and retrograde labelling of PVN and RVLM neurons revealed PVN ter minals closely associated with RVLM-spinal neurons and showed that the PVN is connected to the spinal cord via three pathways. 6. Chemical a ctivation of PVN neurons can produce a pattern of activation of cardio vascular neurons similar to that occurring in defence against plasma v olume expansion. 7. It is concluded that the PVN connections with the RVLM and spinal cord are important to a role in defending against life -threatening disturbances.