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

Abstract

Orthostatic hypotension is most common in elderly people, and its prevalence increases with age. Attenuation of the vestibulo-sympathetic reflex (VSR) is commonly associated with orthostatic hypotension. In this study, we investigated the role of glutamate on the vestibulo-solitary projection of the VSR pathway to clarify the pathophysiology of orthostatic hypotension. Blood pressure and expression of both pERK and c-Fos protein were evaluated in the nucleus tractus solitarius (NTS) after microinjection of glutamate into the medial vestibular nucleus (MVN) in conscious rats with sodium nitroprusside (SNP)-induced hypotension that received baroreceptor unloading via sinoaortic denervation (SAD). SNP-induced hypotension increased the expression of both pERK and c-Fos protein in the NTS, which was abolished by pretreatment with glutamate receptor antagonists (MK801 or CNQX) in the MVN. Microinjection of glutamate receptor agonists (NMDA or AMPA) into the MVN increased the expression of both pERK and c-Fos protein in the NTS without causing changes in blood pressure. These results indicate that both NMDA and AMPA receptors play a significant role in the vestibulo-solitary projection of the VSR pathway for maintaining blood pressure, and that glutamatergic transmission in this projection might play a key role in the pathophysiology of orthostatic hypotension.

Functional Connections of the Vestibulo-spino-adrenal Axis in the Control of Blood Pressure Via the Vestibulosympathetic Reflex in Conscious Rats

“…SNP-induced hypotension also increased blood levels of epinephrine; however, pretreatment with microinjection of glutamate receptor antagonists, MK-801 and CNQX, into the MVN abolished this increased epinephrine secretion. Moreover, blood pressure was increased following microinjection of glutamate receptor agonists into the MVN, which was different from our previous study [ 38 ]. The difference is likely related to the dose of glutamate receptor agonists which was injected into the MVN.…”

Role of peripheral vestibular receptors in the control of blood pressure following hypotension

“…The signaling pathway from the vestibular nuclei to the STN was also pharmacologically investigated by Li et al [ 46 ]. It was found that pretreatment with glutamate receptor antagonists (MK801 or CNQX) in the MVN abolished the increase in expression of both c-Fos and pERK proteins in the STN following hypotension.…”