The role of the solitary and paramedian reticular nuclei in mediating cardiovascular reflex responses from carotid baro‐ and chemoreceptors

Abstract

SUMMARY1. With dye-filled micro-electrodes single neurones in the medulla of anaesthetized paralysed cats were identified which: (a) fired rhythmically in synchrony with or were modulated by the cardiac cycle, and which ceased firing with occlusion of the ipsilateral common carotid artery (carotid sinus baroreceptor neurones); (b) were excited by stimulation of carotid body chemoreceptors by close intra-arterial injection of lobeline into the thyroid artery (carotid body chemoreceptor neurones).2. Twelve carotid baroreceptor neurones were identified, in thirty-three cats, nine of which were localized in the intermediate area of the nucleus of the solitary tract (NTS) within 1 mm ahead of or behind the obex; three units were located either in the parahypoglossal area or the dorsal portion of the paramedian reticular nucleus (PRN).3. Of the twenty-one carotid chemoreceptor neurones which were identified, thirteen were localized in the NTS, three in the parahypoglossal area and four in the dorsal PRN. 4. Bilateral lesions of the paramedian reticular area of medulla destroying the PRN, abolished or reversed the depressor response to electrical stimulation of myelinated fibres of the carotid sinus nerve (CSN), attenuated the depressor response to carotid sinus stretch and augmented the pressor response to chemoreceptor stimulation by lobeline. Such lesions did not significantly alter the reflex heart rate responses.5. Small lesions of the NTS within an area 1 mm rostral to the obex abolished all reflex blood pressure and heart rate responses to electrical stimulation of the CSN or natural stimulation of carotid baro-or chemoreceptors.

Carotid Body Ablation Abrogates Hypertension and Autonomic Alterations Induced by Intermittent Hypoxia in Rats

“…It is well known that hypoxic chemoreflex activation evokes baroreflex inhibition attributed to central nervous system modulation at the level of the nucleus of the solitary tract. 42,43 The hypertension induced by CIH is associated with reduced BRS efficiency in adult animals exposed to CIH for 1 to 3 months, 9,[11][12][13][14]40,41,44 but other studies performed in juvenile rats have shown that juvenile rats exposed to CIH for 15 days showed an increased cardiac baroreflex gain associated with a rightward shift on the operating point to higher pressures, as related to control rats. 38 Zoccal et al 38 proposed that the sympathetic-mediated hypertension is not secondary to a reduction in cardiac baroreflex gain, but to an enhanced respiratory-sympathetic coupling.…”

Brain Stem Terminations of the Trigeminal and Upper Spinal Ganglia Innervation of the Cerebrovascular System: WGA-HRP Transganglionic Study

“…Different reports have shown that the nTs receives inputs from baroreceptor (Crill and Reis, 1968; Miura and Reis, 1972;Berger, 1979;Kalia and Welles, 1980;Sawchenco and Swanson, 1981), re spiratory (von Euller et a!., 1973), gustatory (Blom-visualization of nerve terminations throughout the brain stem. Pretreatment with capsaicin reduced the density of labeled neurons and terminals within the trigeminal gan glion and the brain stem, respectively, following WGA HRP application over the middle cerebral artery.…”

Increased Peripheral Chemoreceptors Sensitivity and Exercise Ventilation in Heart Transplant Recipients

“…Arterial baroreceptor sensitivity is impaired because of chronic cyclosporine uptake. 29 The close proximity of baroreceptor and chemoreceptor neurons in the solitary and paramedian reticular nuclei in the medulla could explain the interactions between these reflexes 30,32 ; however, such an interference between baroreceptors and central chemoreceptors has not been described. Thus, although the surgical procedure improves cardiac function, which may favor normalization of central chemoreceptor sensitivity, it also alters inhibitory loops and necessitates drug treatments, which may suppress baroreflex restraint on peripheral chemoreflex control.…”