Effect of Vestibulosympathetic Reflex and Baroreflex on Expression of pERK in the Nucleus Tractus Solitarius following Acute Hypotension in Conscious Rats

Abstract

Control of blood pressure is maintained by the interaction between the arterial baroreflex and vestibulosympathetic reflex during postural changes. In this study, the contributions of vestibular receptors and baroreceptors to the maintenance of blood pressure following acute hypotension were compared in terms of phosphorylated extracellular regulated protein kinase (pERK) expression in the nucleus tractus solitaries (NTS). Expression of pERK in the NTS was measured in conscious rats that had undergone bilateral labyrinthectomy (BL) and/or sinoaortic denervation (SAD) 5, 10, 20, and 40 min following acute hypotension induced by sodium nitroprusside (SNP) infusion. Expression of pERK increased significantly in the NTS in the control group following SNP infusion, and the expression peaked at 10 min after SNP infusion. The number of pERK positive neurons increased following SNP infusion in BL, SAD, and BL+SAD groups, although the increase was smaller than in control group. The BL group showed a relatively higher reduction in pERK expression than the SAD group, and the pERK expression in the NTS was localized to the caudal portion of the nuclei in the BL and SAD groups. These results suggest that the vestibular receptors may play a key role in maintaining blood pressure following acute hypotension; thus, the vestibular system may contribute to compensate for orthostatic hypotension.

Effect of Glutamate on the Vestibulo-Solitary Projection after Sodium Nitroprusside-Induced Hypotension in Conscious Rats

“…SNP-induced hypotension increased the expression of pERK and c-Fos protein in the NTS, which likely resulted from excitation of peripheral vestibular receptors by SNP-induced hypotension; this result is consistent with those of our previous studies [ 9 , 22 ]. pERK and c-Fos protein expression in the NTS following hypotension results from afferent vestibular receptor signals only, not from baroreceptors.…”

“…In our previous study, expression of pERK in the NTS peaked at 10 min after SNP-induced hypotension [ 22 ], so pERK expression was measured 10 min after SNP infusion or microinjection of glutamate receptor agonist into the MVN. The NTS showed a few pERK-immunoreactive neurons under resting conditions in SAD rats, but SNP-induced hypotension significantly increased the number of pERK-positive NTS neurons to 83.8±9.2.…”

“…This could be because c-Fos protein is expressed in the nucleus only, but pERK is expressed in various cellular and subcellular compartments including the nucleus, cytoplasm, axons, and dendrites [ 17 ]. On the basis of previous studies in our laboratory, expression of pERK and c-Fos protein peaked at 10 and 90 min, respectively, after hypotension [ 9 , 22 ]. Thus, expression of pERK and c-Fos protein was measured at 10 and 90 min, respectively, after SNP infusion in this study.…”

Dual control of the vestibulosympathetic reflex following hypotension in rats

“…Several studies have reported changes in sympathetic nervous activity and blood pressure following postural changes [ 8 31 32 33 ]. Doba and Reis [ 34 ] observed that when the head was elevated, a significant decrease in blood pressure occurred following the removal of the bilateral peripheral vestibular receptors in cats.…”

“…Baroreceptors, vestibular receptors, muscular receptors, and mechanical receptors of the skin are involved in the reflex control of blood pressure [ 44 45 ]. Afferent signals from the baroreceptors and the vestibular receptors are integrated into the solitary tract nucleus and the RVLM [ 5 16 33 46 ]. The baroreceptor reflex responds to both increases and decreases in blood pressure, however the VSR is more sensitive to decreases in blood pressure [ 15 ].…”