Interaction between descending paraventricular neurons and vagal motor neurons.

The hypothalamic paraventricular nucleus is known to send projections to the dorsal medullary area where it appears to innervate the nucleus tractus solitarius and the dorsal motor nucleus of the vagus. Experiments were carried out in urethane anesthetized rats to identify single vagal motor neurons identified by antidromic invasion and to determine their response to stimulation of the paraventricular nucleus (PVN) of the hypothalamus. From the ipsilateral vagus, 26 single units were antidromically activated. Of these, the majority were unresponsive to PVN stimulation; however, 3 of these neurons demonstrated orthodromic excitation following paraventricular stimulation. These studies provide electrophysiological evidence in support of an interaction between descending paraventricular neurons and vagal motor neurons, but indicate that the majority of such vagal neurons are not influenced directly by the PVN.