Barosensitive neurons in the rat tractus solitarius and paratrigeminal nucleus: a new model for medullary, cardiovascular reflex regulation

Abstract

The nucleus of the solitary tract (NTS), a termination site for primary afferent fibers from baroreceptors and other peripheral cardiovascular receptors, contains blood pressure-sensitive neurons, some of which have rhythmic activity locked to the cardiac cycle, making them key components of the central pathway for cardiovascular regulation. The paratrigeminal nucleus (Pa5), a small collection of medullary neurons in the dorsal lateral spinal trigeminal tract, like the NTS, receives primary somatosensory inputs of glossopharyngeal, vagal, and other nerves. Recent studies show that the Pa5 has efferent connections to the rostroventrolateral reticular nucleus (RVL), NTS, and ambiguous nucleus, suggesting that its structure may play a role in the baroreceptor reflex modulation. In the present study, simultaneous recording from multiple single neurons in freely behaving rats challenged with i.v. phenylephrine administration, showed that 83% of NTS units and 72% of Pa5 units were baroreceptor sensitive. Whereas most of the baroreceptor-sensitive NTS and Pa5 neurons (86 and 61%, respectively) increased firing rate during the ascending phase of the pressor response, about 16% of Pa5 and NTS baroreceptor-sensitive neurons had a decreased firing rate. On one hand, the decrease in firing rate occurred during the ascending phase of the pressor response, indicating sensitivity to rapid changes in arterial pressure. On the other hand, the increases in neuron activity in the Pa5 or NTS occurred during the entire pressor response to phenylephrine. Cross-correlational analysis showed that 71% of Pa5 and 93% of NTS baroreceptor-activated neurons possessed phasic discharge patterns locked to the cardiac cycle. These findings suggest that the Pa5, like the NTS, acts as a terminal for primary afferents in the medullary-baroreflex or cardiorespiratory-reflex pathways.

Somatotopy in the Medullary Dorsal Horn As a Basis for Orofacial Reflex Behavior

“…Examples include the IX–X and lingual nerves (Figure 1 ), the superior laryngeal nerve and receptive areas surrounding the fauces ( 13 , 16 , 19 – 26 ), and the sensory inputs from the muscles of mastication ( 27 , 28 ) and molar teeth ( 26 , 29 ). These studies on projections from primary afferent fibers and other studies ( 30 – 32 ) suggest Pa5 may have a role in ingestion. Others, however, showed that cardiorespiratory activity influences Pa5 ( 30 , 33 ).…”

“…These studies on projections from primary afferent fibers and other studies ( 30 – 32 ) suggest Pa5 may have a role in ingestion. Others, however, showed that cardiorespiratory activity influences Pa5 ( 30 , 33 ). Whether Pa5 is a separable entity or a dissociated component of another nucleus is unknown, but its translucent appearance resembles that of the substantia gelatinosa of the MDH (laminae I and II) as well as the gelatinous nucleus tractus solitarii.…”

The Role of the Paratrigeminal Nucleus in Vagal Afferent Evoked Respiratory Reflexes: A Neuroanatomical and Functional Study in Guinea Pigs

“…Whether these differential responses relate to the nodose and jugular afferent circuits described herein is not known, but conceivably possible. Furthermore, studies from other laboratories have already demonstrated vagal afferent inputs from some baroreceptor afferents terminate in the Pa5 playing a role in cardiovascular control (Junior et al, 2004 ) and it is intriguing to speculate that these may also be of jugular ganglia origin.…”

Repetitive Diving in Trained Rats Still Increases Fos Production in Brainstem Neurons after Bilateral Sectioning of the Anterior Ethmoidal Nerve

“…The ventral paratrigeminal nucleus receives somatosensory afferents from trigeminal nerves innervating the nose, cornea, and anterior facial skin (Shigenaga et al, 1986 ; Panneton, 1991 ; Hollandsworth et al, 2009 ). In contrast, the dorsal paratrigeminal nucleus receives trigeminal, glossopharyngeal and vagal inputs (Shigenaga et al, 1986 ; Panneton, 1991 ; Saxon and Hopkins, 2006 ) and is involved in baroreceptor reflexes and cardiovascular regulation (De Sousa Buck et al, 2001 ; Yu and Lindsey, 2003 ; Junior et al, 2004 ). Neurons within the ventral MDH and paratrigeminal nucleus show an increase in the number of Fos-positive neurons, and thus are activated, both during repetitive trained diving in conscious animals (present study; McCulloch, 2005 ; Panneton et al, 2012a ) and nasal stimulation in anesthetized animals (Dutschmann and Herbert, 1997 ; McCulloch and Panneton, 1997 ; Rybka and McCulloch, 2006 ).…”