Bradykinin microinjection in the paratrigeminal nucleus triggers neuronal discharge in the rat rostroventrolateral reticular nucleus

Abstract

A small collection of neurons in the dorsal lateral medulla, the paratrigeminal nucleus (Pa5), projects directly to the rostroventrolateral reticular nucleus (RVL). Bradykinin (BK) microinjections in the Pa5 produce marked pressor responses. Also, the Pa5 is believed to be a component of the neuronal substrates of the somatosensory response and the baroreflex arc. Considering the developing interest in the functional physiology of the Pa5, the present study was designed to characterize RVL neuronal activity in response to BK microinjections in the Pa5 as well as to phenylephrine-induced blood pressure increases in freely behaving rats. Of the 46 discriminated RVL neurons, 82% responded with a 180% mean increase in firing rate after BK application to the paratrigeminal nucleus, before the onset of the blood pressure increase. Thirty (79%) of the RVL BK-excited neurons were baroreceptor-inhibited units that responded with a 30% decrease in firing rate in response to a phenylephrine-produced increase of blood pressure. Twenty-seven (71%) units of the latter population displayed cardiac-cycle-locked rhythmic activity. The findings demonstrate a BK-stimulated functional connection between the Pa5 and RVL that may represent the neural pathway in the BK-mediated pressor response. This pathway may be relevant to baroreflex mechanisms since it relates to cardiovascular pressure-sensitive neurons.

Somatostatin in the rat rostral ventrolateral medulla: Origins and mechanism of action

“…Enkephalin, calbindin, and neuronal nitric oxide synthetase (nNOS) have been detected in Pa5 neurons that project to the dorsal motor nucleus of the vagus (Armstrong and Hopkins, ); these groups may also overlap with the PPS‐containing population described here. Pa5 microinjection of bradykinin evokes pressor effects (Lindsey et al, ) via direct activation of barosensitive RVLM neurons (Caous et al, ). Many (60–80%) Pa5 neurons are themselves barosensitive, increasing their firing rate in response to phenylephrine administration (Balan et al, ; Sousa and Lindsey, ), while bilateral Pa5 ablation reduces cardiac barosensitivity (Sousa and Lindsey, ).…”

Ultrastructural transneuronal degeneration study of axonal elements within the paratrigeminal nucleus in sinoaortic deafferented rats

“…Degenerated cellular components identified herein represent barosensitive neurons recorded in the Pa5 in earlier studies (9) . This functional pathway between the Pa5 and RVL was evidenced through cardiocyclelocked neurons recorded in the RVL that respond to bradykinin microinjections in the Pa5 (6,12) . Our findings hypothesize that the medial extent of the Pa5 containing degenerated axoplasmatic cellular components after sinoaortic denervation, may be the same one that receives afferent projections of the rostroventrolateral medulla as shown in previous retrograde neurotracing studies, in which a distributive characteristic of the Pa5 was based on the topographical organization of neuroanatomical primarily afferent connections (2,5,31) , although this relevant information should be confirmed by neurotracing and electron microscope conjugated experiments.…”

“…The Pa5, a dorsal lateral medullary structure within the spinal trigeminal complex, has been studied with emphasis to morphological (4,5) and functional aspects. The latest participates in cardiovascular (6)(7)(8) , respiratory (9,10) and thermoregulatory reflex mechanisms (11) .…”

Expression and Distribution of Kinin B2 Receptor in Medulla and Spinal Cord Tissues of Rats Treated with Capsaicin

“…Stimulation of arterial B 2 kinin receptor causes resistance to vessel vasodilatation and hypotension (Sharma et al, 2006). On the other hand, stimulation of central kinin receptors leads to blood pressure increases (Lindsey et al, 1997), mediated by central sympathetic mechanisms (Caous et al, 2004). Thus, among other impor-tant functions, such as blood pressure regulation, kinins are characterized as mediators of pain and inflammatory responses, both in the central and in the peripheral nervous systems (Leeb-Lundberg et al); they are also important mediators in the cascade of the febrile response (Pessini et al, 2006).…”