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

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.

Regulation of metabotropic glutamate subtype 7 and 8 receptors in nucleus tractus solitarius in cardiac nociception in rats / 吉林大学学报(医学版)

Objective To explore the role of metabotropic glutamate receptors (mGluRs)group Ⅲ and its subtypes mGluR7 and mGluR8 in nucleus tractus solitarius(NTS)in cardiac-somatic motor reflex (CMR),and to clarify the modulation role of mGluR Ⅲ and its subtypes in NTS in cardiac nociceptoion.Methods 40 SD rats were randomly divided into L-AP4 group,microinjection of mGluRs Ⅲ agonist L-AP4 0.1,1.0,10.0 or 20.0 nmol in NTS;AMN082 group,microinjection of mGluR7 agonist AMN082 1,2 or 4 nmol;DCPG group,microinjection of mGluR8 agonist DCPG 4, 6 or 8 nmol;MSOP group, microinjection of mGluR Ⅲ antagonist MSOP 20 or 100 nmol,20 nmol MSOP+410 nmol L-AP,20 nmol MSOP+2 nmol AMN082,20 nmol MSOP+6 nmol DCPG. The changes of CMR of the rats in various groups were observed.Results Compared with control,the CMR in L-AP4 and AMN082 groups was decreased (P0.05);the CMR in MSOP group after injection of 100 nmol MSOP was increased (P0.05).Conclusion The group Ⅲ mGluRs in the NTS play an inhibitory role in cardiac nociception, and mGluR7 has anti-nociceptive effects while mGluR8 has pro-nociceptive effects.

Role of glutamate receptor subtypes in cardiac nociception in nucleus tractus solitarius in rats / 吉林大学学报(医学版)

Objective To study the role of glutamate receptor subtypes in nucleus tractus solitarius(NTS)in cardiac-somatic motor reflex (CMR)induced by intrapericardial administration of capsaicin,and to clarify the modulation mechanism of NTS to cardiac nociceptoion.Methods 60 SD rats were randomly divided into ibotenic (IBO)group, glutamate group, MK-801 group, MCGP group, MK-801 + MCPG group and DNQX group. The NTS microinjected with 130 mmol·L-1 IBO 100 nL,100,200,500 mmol·L-1 L-glutamate 100 nL,NMDA receptor antagonist 40 and 60 mmol · L-1 MK-801 100 nL, metabotropic glutamate receptors antagonist 25 and 50 mmol·L-1 MCPG 100 nL,25 mmol· L-1 MCPG 50 nL plus 40 mmol· L-1 MK-801 50 nL,non-NMDA receptor antagonist 20 and 50 mmol·L-1 DNQX 100 nL,respectively.The changes of CMR of the rats in various groups were observed.Results Compared with control group,the CMR of the rats in IBO group was decreased (P0.05).Conclusion NTS play an facilictory role in cardiac nociception,and the NMDA receptors and mGluRs receptors mediate this facilitory modulation.

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

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.

Intragastric gavage with denatonium benzoate acutely induces neuronal activation in the solitary tract nucleus via the vagal afferent pathway

Natural toxic substances have a bitter taste and their ingestion sends signals to the brain leading to aversive oral sensations. In the present study, we investigated chronological changes in c-Fos immunoreactivity in the nucleus tractus solitarius (NTS) to study the bitter taste reaction time of neurons in the NTS. Equal volumes (0.5 mL) of denatonium benzoate (DB), a bitter tastant, or its vehicle (distilled water) were administered to rats intragastrically. The rats were sacrificed at 0, 0.5, 1, 2, 4, 8, or 16 h after treatment. In the vehicle-treated group, the number of c-Fos-positive nuclei started to increase 0.5 h after treatment and peaked 2 h after gavage. In contrast, the number of c-Fos-positive nuclei in the DB-treated group significantly increased 1 h after gavage. Thereafter, the number of c-Fos immunoreactive nuclei decreased over time. The number of c-Fos immunoreactive nuclei in the NTS was also increased in a dose-dependent manner 1 h after gavage. Subdiaphragmatic vagotomy significantly decreased DB-induced neuronal activation in the NTS. These results suggest that intragastric DB increases neuronal c-Fos expression in the NTS 1 h after gavage and this effect is mediated by vagal afferent fibers.

Nitric Oxide (NO) Inhibites the Neuronal Activities in the Rat Nucleus Tractus Solitarius

Nitric oxide (NO) system has been implicated in a wide range of physiological functions in the nervous system. However, the roleof NO in regulating the neural activity in the gustatory zone of nucleus tractus solitarius (NTS) has not been established. The present study was aimed to investigate the role of NO in the gustatory NTS neurons. Sprague-Dawley rats, weighing about 50 g, were used. Whole cell patch recording and immunohistochemistry were done to determine the electrophysiological characteristics of the rostral gustatory nucleus of the tractus solitarius and distribution of NO synthases (NOS). Neuronal NOS (nNOS) immunoreactivity was strongly detected along the solitary tract extending from rostral to caudal medulla. Resting membrane potentials of NTS neurons were -49.2+/-2 mV and action potential amplitudes were 68.5+/-2 mV with a mean duration measured at half amplitude of 1.7+/-0.3 ms. Input resistance, determined from the response to a 150 ms, -100 pA hyperpolarizing current pulse, was 385+/-15 MOmega. Superfusion of SNAP or SNP, NO donors, produced either hyperpolarization (68%), depolarization (5%), or no effect (27%). The hyperpolarization was mostly accompanied by a decrease in input resistance. The hyperpolarization caused by SNAP or SNP increased the time to initiate the first action potential, and decreased the number of action potentials elicited by current injection. SNP or SNAP also markedly decreased the number of firing neural discharges of the spontaneous NTS neural activity under zero current. Superfusion of L-NAME, a NOS inhibitor, slightly depolarized the membrane potential and increased the firing rate of NTS neurons induced by current injection. ODQ, a soluble guanylate cyclase inhibitor, ameliorated the SNAP-induced changes in membrane potential, input resistance and firing rates. 8-Br-cGMP, a non-degradable cell-permeable cGMP, hyperpolarized the membrane potential and decreased the number of action potentials. It is suggested that NO in the gustatory NTS has an inhibitory role on the neural activity of NTS through activating soluble guanylate cyclase.

Activation of Vestibular Neurons Projecting to Autonomic Brain Stem Nuclei Following Acute Hypotension in Rats

The purpose of the present study was to elucidate the possible involvement of the medial vestibular nucleus (MVN) and inferior vestibular nucleus (IVN) following acute hypotension in the vestibulo- autonomic reflex through vestibulosolitary or vestibuloventrolateral projections. Acute hypotension- induced cFos expression was assessed in combination with retrograde cholera toxin B subunit (CTb) tract tracing. After injection of CTb into the solitary region, CTb-labeled neurons were located prominently around the lateral borders of the caudal MVN and medial border of the IVN. The superior vestibular nucleus also had a scattered distribution of CTb-labeled neurons. After injection of CTb toxin into the unilateral VLM, the distributions of CTb-labeled neurons in the MVN and IVN were similar to that observed after injection into the solitary region, although there were fewer CTb-labeled neurons. In the caudal MVN, about 38% and 13% of CTb-labeled neurons were double-labeled for cFos after injection of CTb into the solitary region and the VLM, respectively. In the IVN, 14% and 7% of CTb-labeled neurons were double-labeled for cFos after injection of CTb into the solitary region and the VLM, respectively. Therefore, the present study suggests that acute arterial hypotension may result in activation of vestibulosolitary pathways that mediate behavioral and visceral reflexes, and vestibuloventrolateral medullary pathways that indirectly mediate vestibulosympathetic responses.

The Inhibition of Stress-Induced c-fos Expression by Superior Cervical Ganglion Block in Rat Brain / 대한마취과학회지

BACKGROUND: Using c-fos expression one of the immediate early gene, as a marker of altered neuronal response, we investigated the effect of superior cervical ganglion block (SCGB) exhibiting the same effect of SGB of human on the activity of several brain regions which are considered as located on autonomic neural pathway and neuroendocrine axis in rat. METHOD: The 48 Sprague-Dawley strain rats were divided into 4 groups, as saline/stress (control) group, SCGB/stress (tested) group, saline group, SCGB group. Superior cervical ganglion block was conducted in the SCGB/stress group and SCGB group while saline/stress and saline group were sham operated. After then restraint stress was imposed on the animals of SCGB/stress group and saline/stress group. And 2 hour after injection (saline, SCGB group) or restraint stress (saline/stress, SCGB/stress group), c-fos protein (Fos) was localized by immunocytochemistry. RESULTS: Much stronger Fos immunoreactivity was induced in the several brain region of control group rats compared to other three groups and the numbers of Fos positive cell count of tested group were significantly decreased in paraventricular hypothalamic nucleus (p<0.01), A5 (p<0.01), raphe pallidus (p<0.05), nucleus tractus solitaius (p<0.01) compared to control group. CONCLUSION: This study demonstrate that superior cervical ganglion block attenuates stress induced neuronal activities of paraventricular hypothalamic nucleus, A5, raphe pallidus, nucleus tractus solitarius.

THE EFFECTS OF ELECTRICAL STIMULATION OF SPINAL CORD AND NUCLEUS TRACTUS SOLITARIUS ON UNIT ACTIVITY OF PARAVENTRICULAR NEUCLEUS IN THE RAT / 第二军医大学学报

The effects of electrical stimulation of spinal cord and nucleus tractus solitarius (NTS) on unit activity of paraventricular neucleus (PVH) in the rats were studied. The results of experiments in 105 rats showed that in the 1365 units, 67 units made responses to electrical stimulation of spinal cord, and 42 units to electrical stimulation of nucleus tractus solitarius.In the 67 units responsive to electrical stimulation of spinal cord, five kinds of ffects were observed: facilitatory, excitatory, inhibitory, inhibitory-excitatory and excitatory-inhibitory. In the 42 units responsive to electrical stimulation of nucleus ractus solitarius some showed facilitatory effects and others inhibitory effects.The results indicate that the majority of spinal inputs is conveyed to the PVH along multisynaptic pathways,while a lesser part along oligo-or mono-synaptic pathways.The results also suggest that there are multisynaptic pathways from rostral part of nucleus tractus solitarius to the PVH.