Activation within dorsal medullary nuclei following stimulation in the hypothalamic paraventricular nucleus in rats.

The influence of the hypothalamic paraventricular nucleus (PVN) on neurones in the dorsal medulla has been examined in 71 urethane/sagatal-anaesthetised rats. Of 536 neurones localised and tested for responses to electrical stimulation of both the vagus and/or the PVN, 378 were synaptically or antidromically activated following vagal stimulation 72 of which were synaptically activated by stimulation within PVN. The majority of those were located at the border between NTS and dorsal motor nucleus of the vagus in caudal NTS. None showed cardiac or ventilatory rhythm. Neurones showing such rhythms were not affected from PVN. Of 89 neurones in dorsal motor nucleus of the vagus, ten were synaptically activated and two synaptically depressed from PVN. PVN activated neurones in NTS tested for responses to stimulation of arterial baroreceptors and carotid body chemoreceptors were either unaffected or inhibited, but gastric inflation excited them. The results suggest a powerful PVN influence on the dorsal medulla, which is largely confined to the ventral and caudal NTS. There is little evidence for an effect on neurones with a cardiovascular function, but the abdominal vagal influence suggests a link with feeding.