Control of sympathetic outflows by the hypothalamic paraventricular nucleus.

1. The functional role of the paraventricular nucleus (PVN) has been examined by studying its connections with cardiovascular neurons in the medulla and spinal cord and its influence on activity in several sympathetic nerves. 2. Chemical stimulation of neurons within the PVN can elicit pressor responses and can excite reticulo-spinal vasomotor neurons in the rostral ventrolateral medulla (RVLM). 3. The PVN-RVLM excitation is blocked by kynurenic acid applied iontophoretically in the vicinity of RVLM-spinal neurons, suggesting this is a glutamate-dependent pathway. 4. Electrical stimulation of PVN neurons evoked action potentials in RVLM neurons after 27 ms with a small variability. 5. Anterograde and retrograde labelling of PVN and RVLM neurons revealed PVN terminals closely associated with RVLM-spinal neurons and showed that the PVN is connected to the spinal cord via three pathways. 6. Chemical activation of PVN neurons can produce a pattern of activation of cardiovascular neurons similar to that occurring in defence against plasma volume 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.