Baroreceptor-sensitive neurons in the rat paratrigeminal nucleus

The paratrigeminal nucleus (Pa5) is a small collection of medullary neurons localized in the dorsal lateral spinal trigeminal tract. Electrophysiological and anatomical studies showed functional Pa5 efferent connections to the rostroventrolateral reticular nucleus (RVL) and the nucleus of the solitary tract (NTS), both well-studied components of the baroreflex arch. Similarly to the NTS, the main site for termination of cardiovascular peripheral afferents, the Pa5 receives primary sensory inputs of glossopharyngeal and vagus nerves, which suggests that the Pa5 may play a role in the baroreceptor reflex modulation. Simultaneous recording from multiple single neurons in 10 freely behaving rats showed that 37% of recorded Pa5 neurons altered firing rates (35% increased and 2% decreased) during the peak arterial blood pressure response to i.v. phenylephrine. Forty two percent of the 84 identified Pa5 baroreceptor-excited neurons showed high correlation to cardiac cycle denoting the synchronous phasicity to fast changes of blood pressure. Autocorrelation analysis revealed that 48 pressure-sensitive and 55 nonpressure-sensitive neurons have periodical activities which were not directly linked to cardiac cycle. We suggest that the Pa5, a yet unknown component of the baroreflex pathway, may relay baroreceptor information to the NTS and by passing other components of the baroreceptor reflex arch, directly to sympathetic premotor neurons in the RVL.