Chronic hypertension enhances the postsynaptic effect of baclofen in the nucleus tractus solitarius

Microinjection of the inhibitory neurotransmitter gamma-aminobutyric acid B-subtype receptor agonist baclofen into the nucleus tractus solitarius increases arterial blood pressure and sympathetic nerve discharge. The baclofen-induced pressor response is enhanced in chronic hypertension. We hypothesized that a postsynaptic mechanism contributes to the enhanced responses to baclofen in hypertension. We investigated the postsynaptic effect of baclofen on second-order baroreceptor neurons, identified by 1,1'-dilinoleyl-3,3,3',3'-tetra-methylindocarbocyanine, 4-chlorobenzenesulphonate labeling of the aortic nerve, in nucleus tractus solitarius slices from sham-operated normotensive and unilateral nephrectomized, renal-wrap hypertensive rats. After 4 weeks, arterial blood pressure was 153+/-7 mm Hg in hypertensive rats (n=9) and 93+/-3 mm Hg in normotensive rats (n=8; P<0.05). There was no difference in resting membrane potential (54.5+/-0.7 versus 53.3+/-0.6 mV) or input resistance (1.07+/-0.11 versus 1.03+/-0.11 GOmega) between hypertensive and normotensive neurons (both n=18). Baclofen induced a net outward current in nucleus tractus solitarius neurons in the presence of 1 micromol/L tetrodotoxin. The EC50 of the baclofen effect was greater in normotensive cells (9.1+/-3.2 micromol/L; n=5) than hypertensive cells (3.0+/-0.5 micromol/L; n=7; P<0.05), and baclofen (10 micromol/L) induced a greater decrease in input resistance in hypertensive cells (61+/-2%; n=6) than in normotensive cells (45+/-4%; n=9; P<0.05). Both potassium and calcium channels were involved in the baclofen-evoked whole-cell current. The results suggest an enhanced postsynaptic response to activation of inhibitory neurotransmitter gamma-aminobutyric acid B-subtype receptors in second-order baroreceptor neurons in the nucleus tractus solitarius in renal-wrap hypertensive rats. This enhanced inhibition could alter baroreflex function in chronic hypertension.     

High salt diet enhances cardiovascular responses from the nucleus tractus solitarius and ventrolateral medulla of Sprague-Dawley rats

High salt intake has been shown to augment the sensitivity of rostral ventrolateral medulla (RVLM) sympathoexcitatory neurons. We examined the effects of 4 weeks of high dietary salt (8%) on the sensitivity of nucleus tractus solitarius (NTS) and caudal ventrolateral medulla (CVLM) in controlling RVLM. In chloralose-anesthetized Sprague-Dawley rats, high salt intake did not elevate baseline arterial pressure or heart rate (HR). In high-salt group, NTS, CVLM, and RVLM responses to glutamate were greater. NTS responses to acetylcholine or serotonin, which is independent of baroreflex, also were greater. Phenylephrine or nitroprusside (i.v.) elicited similar changes in arterial pressure and heart rate, the baroreflex sensitivity also was similar in both groups of rats. These results suggest that high salt intake augments the sensitivity of NTS and CVLM sending inhibitory input to RVLM. This presumably may inhibit the RVLM, thereby inhibiting the elevation of arterial pressure.     

Estradiol enhances cholecystokinin-dependent lipid-induced satiation and activates estrogen receptor-alpha-expressing cells in the nucleus tractus solitarius of ovariectomized rats

Part of the mechanism through which estradiol, acting via estrogen receptor (ERalpha) signaling, inhibits feeding in rats and mice is increasing the satiating potency of cholecystokinin (CCK) acting on peripheral CCK-1 receptors. Ingested lipid is a principal secretagogue of intestinal CCK, and intraduodenal lipid infusions elicit CCK-mediated satiation in animals and humans. Here we tested whether estradiol affects the satiating potency of intraduodenal lipid infusions in ovariectomized rats and, using c-Fos immunocytochemistry, searched for potential brain sites of ERalpha involved. Food-deprived ovariectomized rats with open gastric cannulas sham fed 0.8 m sucrose 2 d after estradiol (estradiol benzoate, 10 mug, sc) or vehicle injection. Estradiol markedly increased the satiating potency of intraduodenal infusions of Intralipid but not the satiating potency of L-phenylalanine (10 min infusions, 0.44 ml/min, 0.13 kcal/ml), which in male rats satiates via a CCK-independent mechanism. Estradiol had no significant effect in rats pretreated with the CCK-1 receptor antagonist Devazepide (1 mg/kg, ip). The effect of estradiol on intraduodenal Intralipid-induced satiation was mirrored by selective increases in the number of cells expressing c-Fos immunoreactivity in a circumscribed region of the nucleus tractus solitarius (NTS), just caudal to the area postrema (cNTS) but not elsewhere in the NTS or the hypothalamic paraventricular or arcuate nuclei. In addition, a significant proportion of cNTS c-Fos-positive cells also expressed ERalpha. These data provide behavioral and cellular evidence that estradiol-ERalpha signaling in cNTS neurons increases the satiating potency of endogenous CCK released in response to ingested lipid.     

Increased angiotensin II binding affinity in the nucleus tractus solitarius of spontaneously hypertensive rats.

Angiotensin II (Ang) binding kinetics were determined in discrete brainstem nuclei of 14-week-old spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) by a quantitative autoradiographic technique. Tissue sections were incubated with 125I-labeled [sarcosine-1]Ang, and results were analyzed by computerized densitometry and comparison to 125I-labeled standards. A single class of high-affinity binding sites was identified in the nucleus tractus solitarius, the area postrema, and the inferior olivary nuclei of both SHR and WKY rats. Ang binding affinity was significantly greater in the nucleus tractus solitarius of SHR compared to normotensive WKY rats (0.27 +/- 0.06 X 10(9) M-1 in WKY rats vs. 0.59 +/- 0.15 X 10(9) M-1 in SHR), with no apparent changes in the maximum binding capacity of this area. There were no changes in the Ang binding kinetics of the area postrema or the inferior olivary nuclei. Our results suggest that central Ang activity is altered in established hypertension in a brainstem area of SHR associated with peripheral cardiovascular control.     

Pressor responses to serotonin injected into the nucleus tractus solitarius of Sprague-Dawley rats and spontaneously hypertensive rats

Previous studies in rats have shown that injection of nanomoles of serotonin (5-hydroxytryptamine; 5HT) into the nucleus tractus solitarius (NTS) acts on 5HT3 receptors to increase arterial pressure (AP). We investigated the effect of 5HT in Sprague-Dawley (SD) rats and in spontaneously hypertensive rats (SHR). Injection of nanomoles of 5HT into the NTS of chloralose-anesthetized SD rats increased AP. This effect was inhibited by prior injection of 5HT3 receptor antagonist ondansetron. The GABA(A) receptor antagonist bicuculline did not inhibit the effect of 5HT. Bilateral injection of 5HT or ondansetron did not affect the baroreflex sensitivity. Bilateral injection of ondansetron did not alter AP. The pressor effect of 5HT was exaggerated in SHR. These results suggest that stimulation of 5HT3 receptors in the NTS increases AP independently of activation of GABAA receptors and the baroreflex sensitivity. Furthermore, this serotonergic system is supersensitive in the NTS of SHR.     

Delayed maturation of catecholamine phenotype in nucleus tractus solitarius of rats with glial angiotensinogen depletion

Cerebral catecholamines and angiotensins are both involved in the regulation of cardiovascular function. Recent in vitro studies have suggested that angiotensin II modulates noradrenergic neurotransmission by controlling both the expression and neuritic trafficking of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. To assess the potential existence of such mechanisms in vivo, we compared TH phenotype ontogeny in the nucleus tractus solitarius (NTS), which is the first central relay of the baroreflex, between control Sprague-Dawley rats and TGR(ASrAOGEN) rats (TG) with glial specific angiotensinogen (AOGEN) depletion. TG displayed a delayed increase in both TH-mRNA and TH protein levels, which sharply rises in the NTS of control rats within the fourth week. The delayed maturation of TH phenotype also affected the presence of TH protein in the neuropil, not only within the NTS region but also within the ventrolateral medulla. This was evidenced by a large decrease in the density of TH-containing neuronal processes in TG at 4 weeks only, without noticeable modification of the labeling of the neuritic marker MAP2, suggesting that neuritic trafficking of TH protein was transiently altered. These results indicate that glial AOGEN is crucial to coordinate within the fourth week the mechanisms driving the maturation of NTS catecholaminergic neurons and suggest that impairment of the central angiotensinergic system early in development can lead to cardiovascular dysfunction related to altered maturation of catecholaminergic neurons located in both the dorsal and the ventrolateral medulla.     

Signaling pathways of the acute hypoxic ventilatory response in the nucleus tractus solitarius

The nucleus tractus solitarii (nTS) provides the initial central synaptic relay to peripheral chemoreceptor afferent inputs elicited by changes in oxygen tension. Insofar, the overall cumulative evidence pointing towards the N-methyl-D-aspartate (NMDA) glutamate receptor as the critical receptor underlying the early component of the hypoxic ventilatory response (HVR) is reviewed in detail. In addition, we will present recent findings supporting a role for platelet-derived growth factor (PDGF) beta receptor activation in modulation of the late phase of HVR. This evidence underscores the proposal of a working model for intracellular signaling pathways, downstream to the NMDA glutamate and PDGF-beta receptors in nTS neurons, which may contribute to both the ventilatory characteristics of the acute hypoxic response and to subsequently occurring functional adaptations and synaptic plasticity phenomena.     

Vasopressin contributes to hypertension caused by nucleus tractus solitarius lesions

Lesions of the nucleus tractus solitarius (NTS) were studied to determine whether they elevate plasma vasopressin levels and, if so, whether these elevated levels of vasopressin contribute to the hypertension caused by NTS lesions. Bilateral electrolytic lesions of the NTS caused acute, severe hypertension in rats anesthetized with chloralose and in conscious, freely moving rats. After placement of the NTS lesions there was a greater than tenfold elevation in plasma vasopressin levels. Administration of an antagonist of the vasoconstrictor action of vasopressin markedly diminished the hypertension in both conscious and anesthetized rats. Following ganglionic blockade with chlorisondamine, NTS lesions still elicited hypertension, and the magnitude of the hypertension was not different from that observed in rats not treated with chlorisondamine. The hypertension produced by lesions of the NTS in ganglionic-blocked rats was completely abolished by administration of a vasopressin antagonist. These results indicate that (1) NTS lesions elevate plasma vasopressin levels and (2) elevated plasma vasopressin contributes to the hypertension produced by such lesions.     

Peripheral pressor systems in hypertension caused by nucleus tractus solitarius lesions

The roles of vasopressin, the sympathoadrenal system, and the renin-angiotensin system in the production of hypertension after bilateral destruction of the nucleus tractus solitarius (NTS) were examined in chloralose-anesthetized rats. Since the activity of the renin-angiotensin system is high in anesthetized rats, additional studies were performed in unanesthetized, freely moving rats to evaluate the role of the renin-angiotensin system in hypertension caused by NTS lesions. Hypertension produced by bilateral electrolytic NTS lesions in rats was accompanied by elevated plasma levels of vasopressin (approximately 7-fold), norepinephrine (greater than 10-fold), and epinephrine (greater than 10-fold), but not of plasma renin activity. These results suggest that this form of hypertension is due to increased sympathoadrenal activity and increased vasopressin release into plasma and that the renin-angiotensin system is not involved. In rats with NTS lesions, blockade of vasopressin or the sympathoadrenal system, but not the renin-angiotensin system, elicited an acute decrease in arterial pressure. However, blockade of either vasopressin or the autonomic nervous system before production of the lesions had no effect on the resulting hypertension, indicating that in the absence of either one of these systems bilateral NTS lesions still result in severe hypertension. Although the renin-angiotensin system does not normally contribute to this hypertension, it does appear to contribute to the elevation in blood pressure once the actions of vasopressin have been blocked. In rats pretreated with a vasopressin antagonist, plasma renin activity increased following NTS lesions and the angiotensin converting enzyme inhibitor captopril decreased blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hindbrain administration of estradiol inhibits feeding and activates estrogen receptor-alpha-expressing cells in the nucleus tractus solitarius of ovariectomized rats

17beta-estradiol (E2), acting via estrogen receptor (ER)-alpha, inhibits feeding in animals. One mechanism apparently involves an increase in the satiating potency of cholecystokinin (CCK) released from the small intestine by ingested food. For example, the satiating potency of intraduodenal lipid infusions is increased by E2 in ovariectomized rats; this increased satiation is dependent on CCK, and it is accompanied by increases in the numbers of ERalpha-positive cells that express c-Fos in a subregion of the caudal nucleus tractus solitarius (cNTS) that receives abdominal vagal afferent projections. To test whether direct administration of E2 to this area of the hindbrain is sufficient to inhibit food intake, we first implanted 0.2 microg estradiol benzoate (EB) in cholesterol or cholesterol alone either sc or onto the surface of the hindbrain over the cNTS. Food intake was significantly reduced after hindbrain EB implants but not after sc EB implants. Next we verified that equimolar hindbrain implants of E2 and EB had similar feeding-inhibitory effects and determined that only small amounts of E2 reached brain areas outside the dorsal caudal hindbrain after hindbrain implants of (3)H-labeled E2. Neither plasma estradiol concentration nor plasma inflammatory cytokine concentration was increased by either hindbrain or sc EB implants. Finally, hindbrain EB implants, but not sc implants, increased c-Fos in ERalpha-positive cells in the cNTS after ip injection of 4 microg/kg CCK-8. We conclude that E2, acting via ERalpha in cNTS neurons, including neurons stimulated by ip CCK, is sufficient to inhibit feeding.     

Modulation of carotid sinus afferent input to nucleus tractus solitarius by parabrachial nucleus stimulation

There is increasing evidence that the parabrachial nucleus (PBN) may be integrally involved in cardiovascular reflex regulation. In cats in which anesthesia was induced with pentobarbital and maintained with alpha-chloralose, we studied the effects of PBN stimulation on cardiovascular afferent inputs to nucleus tractus solitarius (NTS), the site of first central termination for cardiovascular afferent fibers. Electrical stimulation of PBN resulted in an initial excitation followed by prolonged inhibition of the spontaneous activity of NTS neurons activated by ipsilateral carotid sinus nerve (CSN) stimulation. In 53 units recorded extracellularly in and around NTS, the number of action potential responses to ipsilateral CSN stimulation was reduced 73 +/- 3% by a prior conditioning stimulus to PBN at an interval of 30-60 msec. CSN input to 10 units excited by selective baroreceptor stimulation was inhibited by the PBN conditioning stimulus, as were convergent inputs from contralateral CSN, vagus, and renal nerves. The inhibitory influence of the PBN stimulus lasted as long as 450 msec. We examined the mechanism for these phenomena in additional intracellular recording experiments. In 57 units, PBN stimulation evoked a long lasting (65-359 msec) membrane potential hyperpolarization. In 42 cells, the PBN evoked inhibitory postsynaptic potential (IPSP) was preceded by an excitatory postsynaptic potential (EPSP). CSN and convergent inputs were inhibited when timed to occur during the PBN induced IPSP. Conversely, CSN and convergent afferent nerves inhibited PBN input to NTS neurons with no associated change in membrane potential (n = 9 of 14). These data demonstrate for the first time a potent modulatory influence of PBN on NTS neurons processing cardiovascular afferent input.     

Roles of periaqueductal gray and nucleus tractus solitarius in cardiorespiratory function in the rat brainstem

Periaqueductal gray (PAG) and nucleus tractus solitarius (NTS) are important centres for regulation of cardiorespiratory function in cats. We aimed to study the effects of specific PAG stimulation on cardiorespiratory parameters in the rat. Microinjection of D, L-homocysteic acid (DLH) into dorsolateral PAG of anaesthetised rats, led to: marked increases in respiratory frequency (RF) and amplitude of diaphragmatic electromyogram, decreases in inspiratory and expiratory durations, and increased blood pressure and heart rate. Following injection of propranolol (150 pmol, 30 nl), a beta-adrenergic antagonist, into the commissural subnucleus of NTS, the DLH-induced increase in RF was markedly attenuated. Inspiratory neurones (late I cells) in NTS were excited upon stimulation of PAG and their increased activity was accompanied by increased RF. The changes in activity of the late I cells in response to stimulation of dorsolateral PAG provide physiological evidence of a link, possibly noradrenergic, between the two nuclei and involvement of the NTS in control of respiratory functions orchestrated by the PAG.     

Functional interaction between nucleus tractus solitarius NK1 and 5-HT3 receptors in the inhibition of baroreflex in rats

OBJECTIVE: Previous data showed that in the nucleus tractus solitarius (NTS), 5-HT(3) receptors are critically involved in the inhibition of cardiac baroreceptor reflex response occurring during the defense reaction. Since stimulation of NTS NK(1) receptors has been found to inhibit the baroreflex bradycardia, we examined in this study whether this reflex response is inhibited during the defense reaction via an interaction between NK(1) and 5-HT(3) receptors. METHODS: For this purpose, we analyzed in urethane-anaesthetized rats the effects of intra-NTS GR205171, a selective NK(1) receptor antagonist, on the baroreflex bradycardia inhibition observed either during the defense reaction triggered by electrical stimulation of the dorsal periaqueductal grey matter (dPAG) or after NTS 5-HT(3) receptor activation. RESULTS: Intra-NTS GR205171, reversed, in dose-dependent manner, the inhibitory effect of dPAG stimulation on baroreflex bradycardia. This reversion was of 49% when both sinus carotid and aortic baroreceptors were stimulated by phenylephrine, and of 84% when aortic depressor nerve was stimulated. Similarly, intra-NTS GR205171 reversed partially or almost totally the inhibitory effect of local microinjections of phenylbiguanide, a 5-HT(3) receptor agonist, on baroreflex bradycardia induced either by phenylephrine administration or aortic nerve stimulation, respectively. CONCLUSION: These results strongly suggest that NK(1) receptors contribute downstream to the 5-HT(3) receptor-mediated inhibition of the aortic but not carotid cardiac baroreflex response occurring during the defense reaction, therefore implying that baroreceptor afferent inputs may be differentially modulated depending on their origin. This differentiation may be useful for a better understanding of baroreflex dysfunction in disease-induced conditions.     

Nucleus tractus solitarius mediates hyperalgesia induced by chronic pancreatitis in rats

BACKGROUND Central sensitization plays a pivotal role in the maintenance of chronic pain induced by chronic pancreatitis(CP). We hypothesized that the nucleus tractus solitarius(NTS), a primary central site that integrates pancreatic afferents apart from the thoracic spinal dorsal horn, plays a key role in the pathogenesis of visceral hypersensitivity in a rat model of CP.AIM To investigate the role of the NTS in the visceral hypersensitivity induced by chronic pancreatitis.METHODS CP was induced by the intraductal injection of trinitrobenzene sulfonic acid(TNBS) in rats. Pancreatic hyperalgesia was assessed by referred somatic pain via von Frey filament assay. Neural activation of the NTS was indicated by immunohistochemical staining for Fos. Basic synaptic transmission within the NTS was assessed by electrophysiological recordings. Expression of vesicular glutamate transporters(VGlu Ts), N-methyl-D-aspartate receptor subtype 2 B (NR2 B), and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subtype 1(Glu R1) was analyzed by immunoblotting. Membrane insertion of NR2 B and Glu R1 was evaluated by electron microscopy. The regulatory role of the NTS in visceral hypersensitivity was detected via pharmacological approach and chemogenetics in CP rats.RESULTS TNBS treatment significantly increased the number of Fos-expressing neurons within the caudal NTS. The excitatory synaptic transmission was substantially potentiated within the caudal NTS in CP rats(frequency: 5.87 ± 1.12 Hz in CP rats vs 2.55 ± 0.44 Hz in sham rats, P 0.01; amplitude: 19.60 ± 1.39 p A in CP rats vs14.71 ± 1.07 p A in sham rats; P 0.01). CP rats showed upregulated expression of VGlu T2, and increased phosphorylation and postsynaptic trafficking of NR2 B and Glu R1 within the caudal NTS. Blocking excitatory synaptic transmission via the AMPAR antagonist CNQX and the NMDAR antagonist AP-5 microinjection reversed visceral hypersensitivity in CP rats(abdominal withdraw threshold: 7.00± 1.02 g in CNQX group, 8.00 ± 0.81 g in AP-5 group and 1.10 ± 0.27 g in saline group, P 0.001). Inhibiting the excitability of NTS neurons via chemogenetics also significantly attenuated pancreatic hyperalgesia(abdominal withdraw threshold: 13.67 ± 2.55 g in Gi group, 2.00 ± 1.37 g in Gq group, and 2.36 ± 0.67 g in m Cherry group, P 0.01).CONCLUSION Our findings suggest that enhanced excitatory transmission within the caudal NTS contributes to pancreatic pain and emphasize the NTS as a pivotal hub for the processing of pancreatic afferents, which provide novel insights into the central sensitization of painful CP.     

损毁孤束核对电针足三里穴抗大鼠应激性胃溃疡作用的影响

目的:探讨孤束核(NTS)在电针(EA)足三里穴抗大鼠应激性胃溃疡中的作用.方法:健康♂SD大白鼠56只随机分为应激组、EA 应激组、NTS电损毁组、NTS假损毁组.通过脑立体定向仪电损毁大鼠孤束核,采用束缚-浸水制备大鼠应激性胃溃疡模型,分别测定各组胃黏膜损伤指数(UI)、超氧化物歧化酶(SOD)活性、丙二醛(MDA)含量.结果:与应激组比较,EA 应激组UI明显减少(t=9.5071,P<0.01),SOD活性升高(t=3.8729,P<0.01),MDA降低(t=2.3578,P<0.05).NTS电损毁组分别与假损毁组和EA 应激组比较UI提高(t=4.4223,7.2579,均P<0.01),SOD活性降低(t=3.5625,3.7242,均P<0.01),MDA含量升高(t=2.9045,2.4960,均P<0.05).结论:电损毁孤束核后,电针足三里穴对应激性胃黏膜损伤的保护作用减弱.     

An association between ethanol-evoked enhancement of c-jun gene expression in the nucleus tractus solitarius and the attenuation of baroreflexes

BACKGROUND: An increased expression of Fos, the protein product of the immediate early gene c-fos, in the nucleus tractus solitarius (NTS) is associated with dysfunction in baroreceptor reflex control of heart rate. Our previous studies demonstrated that ethanol attenuates baroreflex sensitivity (BRS) in rats and humans. In this study, we tested the hypothesis that enhanced expression of the immediate early gene c-jun (an index of neuronal activity) in the NTS contributes to the baroreflex dysfunction caused by ethanol. METHODS: Conscious male spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats were used to measure blood pressure, heart rate, and baroreflex sensitivity (Oxford method). The c-jun messenger RNA (mRNA) expression in NTS was measured by in situ hybridization. RESULTS: Ethanol elicited dose-dependent attenuation in BRS in WKY rats, which was associated with significant increases in c-jun mRNA in the NTS. In contrast, ethanol had no effect on BRS or c-jun mRNA in the NTS of the SHRs; the latter exhibited significantly lower BRS and higher c-jun mRNA in the NTS compared with WKY rats. CONCLUSIONS: An increased basal level of c-jun mRNA in the NTS may contribute to the reduced BRS in the SHR, and ethanol enhancement of neuronal activity of the NTS, expressed as increased c-jun mRNA expression, may contribute to its attenuation of BRS, which highlights the NTS as a neuroanatomical target for ethanol action on baroreflexes.     

Refeeding-activated glutamatergic neurons in the hypothalamic paraventricular nucleus (PVN) mediate effects of melanocortin signaling in the nucleus tractus solitarius (NTS)

We previously demonstrated that refeeding after a prolonged fast activates a subset of neurons in the ventral parvocellular subdivision of the paraventricular nucleus (PVNv) as a result of increased melanocortin signaling. To determine whether these neurons contribute to satiety by projecting to the nucleus tractus solitarius (NTS), the retrogradely transported marker substance, cholera toxin-β (CTB), was injected into the dorsal vagal complex of rats that were subsequently fasted and refed for 2 h. By double-labeling immunohistochemistry, CTB accumulation was found in the cytoplasm of the majority of refeeding-activated c-Fos neurons in the ventral parvocellular subdivision of the hypothalamic paraventricular nucleus (PVNv). In addition, a large number of refeeding-activated c-Fos-expressing neurons were observed in the lateral parvocellular subdivision (PVNl) that also contained CTB and were innervated by axon terminals of proopiomelanocortin neurons. To visualize the location of neuronal activation within the NTS by melanocortin-activated PVN neurons, α-MSH was focally injected into the PVN, resulting in an increased number of c-Fos-containing neurons in the PVN and in the NTS, primarily in the medial and commissural parts. All refeeding-activated neurons in the PVNv and PVNl expressed the mRNA of the glutamatergic marker, type 2 vesicular glutamate transporter (VGLUT2), indicating their glutamatergic phenotype, but only rare neurons contained oxytocin. These data suggest that melanocortin-activated neurons in the PVNv and PVNl may contribute to refeeding-induced satiety through effects on the NTS and may alter the sensitivity of NTS neurons to vagal satiety inputs via glutamate excitation.     

Systemic administration of lipopolysaccharide induces release of nitric oxide and glutamate and c-fos expression in the nucleus tractus solitarii of rats.

There is increasing recognition that communication pathways exist between the immune system and brain, which allows bidirectional regulation of immune and brain responses to infection. The endotoxin lipopolysaccharide (LPS) has been reported to elicit release of cytokines and expression of inducible nitric oxide synthase (iNOS) in peripheral organs. Whereas LPS given systemically causes endotoxic shock, little is known about its central nervous system action, particularly the induction of iNOS. Nitric oxide (NO) and glutamate in the nucleus tractus solitarii (NTS) are important mediators of central cardiovascular regulation. We have previously demonstrated that intravenous injections of LPS increased the NO precursor L-arginine-induced depressor effect in the NTS. The present study investigated further the effects of LPS on the release of NO and glutamate in the NTS and the expression of c-fos, an immediate early response gene product, in neural substrates for central cardiovascular control. In vivo microdialysis coupled with chemiluminescence and electrochemical detection techniques were used to measure extracellular levels of NO and glutamate in the rat NTS. Immunohistochemistry was used for the examination of c-fos protein expression. We found that intravenous infusion of LPS (10 mg/kg) produced a biphasic depressor effect, with an early, sharp hypotension that partially recovered in 15 minutes and a secondary, more prolonged hypotension. In the NTS, a progressive increase of extracellular glutamate and NO levels occurred 3 and 4 hours after LPS was given, respectively. The effects of LPS on the induction of delayed hypotension and NO formation in the NTS were abolished by pretreatment with the iNOS inhibitor aminoguanidine. Finally, c-fos protein expression in the NTS and related structures for cardiovascular regulation was observed after LPS challenge. Taken together, these data suggest that an endotoxin given systemically can elicit delayed increases of glutamate release and iNOS-dependent NO production in the NTS and activate the central neural pathway for modulating cardiovascular function.     

Interaction of carbon monoxide and adenosine in the nucleus tractus solitarii of rats

Carbon monoxide has been identified as an endogenous biological messenger in the brain. Heme oxygenase catalyzes the metabolism of heme to carbon monoxide and biliverdin. Previously, we have shown the involvement of carbon monoxide in central cardiovascular regulation, baroreflex modulation, and glutamatergic neurotransmission in the nucleus tractus solitarii of rats. We also showed that adenosine increased the release of glutamate in the nucleus tractus solitarii. In this study, we investigated the possible interactions of carbon monoxide and adenosine in the nucleus tractus solitarii. Male Sprague-Dawley rats were anesthetized with urethane, and blood pressure were monitored intra-arterially. Unilateral microinjection of increasing doses of hemin (0.01 to 3.3 nmol), a heme molecule cleaved by heme oxygenase to yield carbon monoxide, produced a significant decrease in blood pressure and heart rate in a dose-dependent manner. In addition, similar cardiovascular effects were observed after injection of adenosine (2.3 nmol). These cardiovascular effects of hemin were attenuated by prior administration of the adenosine receptor antagonist 1,3-dipropyl-8-sulfophenylxanthine. Similarly, pretreatment of the heme oxygenase inhibitor zinc protoporphyrin IX or zinc deuteroporphyrin 2,4-bis glycol also attenuated the depressor and bradycardic effects of adenosine. These results indicate that the interaction between carbon monoxide and adenosine may contribute to the activation of heme oxygenase in central cardiovascular regulation.     

短波胃电刺激对大鼠孤束核及下丘脑c-fos表达的影响及其机制

目的 探讨肠肌间神经丛及中枢神经系统相关核团(孤束核及下丘脑)是否参与介导外源性短波胃电刺激调控中枢感觉功能.方法 雄性Wistar大鼠15只,分为对照组、胃电刺激组、去肠肌间神经丛组,均于胃底、胃体交界处植入一对电极,去肠肌间神经丛组大鼠同时胃浆膜面予苯扎氯胺处理,后两组均予短波胃电刺激,持续30 min.SP免疫组化法观察延髓孤柬核及下丘脑c-fos表达.结果 胃电刺激组和去肠肌间神经丛组大鼠每高倍视野下孤束核处c-fos阳性神经元数量分别为(71.6±7.4)和(63.4±10.8)个,下丘脑处则分别为(224.2±47.3)和(249.1±44.0)个,两组间差异无统计学意义(P＞0.05),但均显著高于对照组[(36.4±8.6)和(90.2±47.3)个,P值均＜0.05].结论 孤束核及下丘脑可能是介导短波胃电刺激治疗作用的中枢核团,而肠神经系统不参与介导此作用.