CRF microinjected into the dorsal vagal complex inhibits TRH analog- and kainic acid-stimulated gastric contractility in rats

The effect of CRF microinjected into the dorsal vagal complex (DVC) on centrally-stimulated gastric contractility was investigated in fasted, urethane-anesthetized rats. Miniature strain gauge force transducers were acutely implanted on the corpus of the stomach and contractility was analyzed by computer. Microinjection of the stable thyrotropin-releasing hormone (TRH) analog, RX 77368, (26 pmol) into the DVC induced a 12.2-fold stimulation of gastric contractility within 30 min. Corticotropin-releasing factor (CRF) (63-210 pmol) microinjected into the DVC concomitantly with RX 77368 (26 pmol) induced a dose-related inhibition of stimulated gastric contractility. Neither CRF alone (210 pmol) nor vehicle modified basal gastric contractility. Microinjection of kainic acid (141 pmol) into the raphe pallidus nucleus induced a 3.6-fold stimulation of gastric contractility after 45 min. This stimulation was suppressed by bilateral microinjection of CRF (105 pmol/site) into the DVC. These results demonstrate that CRF acts in the DVC to inhibit centrally-stimulated gastric contractility and suggest that TRH and CRF may interact in the DVC to regulate gastric motor function.     

Raphe pallidus stimulation increases gastric contractility via TRH projections to the dorsal vagal complex in rats

The role of thyrotropin releasing hormone (TRH) in the dorsal vagal complex (DVC) in mediating the enhanced gastric contractility induced by glutamate (100 pmol) microinjected into the raphe pallidus (Rpa) was investigated in urethane-anesthetized rats acutely implanted with miniature strain gauge force transducers on the corpus of the stomach. Glutamate-induced stimulation of gastric contractility was dose-dependently inhibited by bilateral microinjection into the DVC of TRH antibody (0.17, 0.85 or 1.7 μg/100 nl/site) but not by vehicle. TRH antibody microinjected into the dorsal medullary reticular field had no effect. These data indicate that activation of Rpa neurons by glutamate increases gastric motor function through TRH release in the DVC.     

Microinjection of thyrotropin-releasing hormone analogue into the central nucleus of the amygdala stimulates gastric contractility in rats

The effect on gastric contractility following bilateral microinjection of thyrotropin-releasing hormone (TRH) analog. RX 77368, into the central nucleus of the amygdala was examined in fasted. urethane-anesthetized rats. Extraluminal force transducers were used to measure gastric corpus contractility. Bilateral microinjection of RX 77368 (0.5 μg. 1.0 μg,n = 6 each) stimulated gastric contractility for up to 120 min post-injection,P < 0.05. Gastric contractility was not significantly stimulated by microinjection of 0.1 μg RX 77368. 0.1% bovine serum albumin (BSA) into the central nucleus or RX 77368 (0.5 μg. 1.0 μg) into sites adjacent to the central nucleus. Peak responses (1.0 μg) occurred 40 min post-injection and represented a 16-26-fold increase over basal values. The frequency of gastric contraction waves was attenuated for 0–90 min in rats receiving central amygdaloid microinjection of RX 77368 (0.1. 0.5 or 1.0 μg) versus rats microinjected with the vehicle or RX 77368 into sites adjacent to the central nuclei. The stimulatory effect of RX 77368 (1.0 μg) on gastric contractility was abolished by subdiaphragmatic vagotomy. These results indicate that the TRH analog. RX 77368, acts within the central amygdala to vagally stimulate gastric contractility.     

TRH stimulation andl-glutamic acid inhibition of proximal gastric motor activity in the rat dorsal vagal complex

The importance of the dorsal vagal complex (DVC) in the control of gastric motor activity has been previously established by electrical and chemical stimulation of this region. We have further evaluated excitatory and inhibitory influences on motor activity of the gastric corpus by microinjection ofl-glutamic acid (GLU) and thyrotropin-releasing hormone (TRH) into the DVC. GLU and TRH were ejected by pressure (20–30 psi) in 1–10 nl vol. from multibarreled micropipettes and intraluminal pressure and the gastric corpus was measured using a manometric catheter placed into the stomach through the pylorus of urethane-chloralose anesthetized rats. Gastric motor activity was monitored while micropipettes were advanced from the surface of the dorsomedial medulla to a depth of 1 mm in 100 μm increments. Microinjections of GLU (1–10 pmol) at depths of 200–600 μm below the surface of the brainstem caused a decrease in tonic intraluminal pressure and amplitude of phasic contactions of the gastric corpus. Injection of TRH (1–10 pmol) at depths of 200–800 μm increased both tonic intraluminal pressure and amplitude of phasic contractions. The responses to GLU (10 pmol) and TRH (10 pmol) were abolished by hexamethonium and vagotomy; atropine abolished the effect of TRH and attenuated that of GLU. It is concluded that GLU evokes only vagally mediated inhibitory effects on tonic and phasic gastric motor activity when microinjected into the DVC. In contrast, injection of TRH at the same loci causes only vagal cholinergic increases in motor activity. Subpopulations of neurons in the DVC may, therefore, be activated by specific neurotransmitters having opposite effects on gastric motor activity.     

Microinjection of thyrotropin-releasing hormone in the paraventricular nucleus of the hypothalamus stimulates gastric contractility

Changes in gastric contractility following microinjection of thyrotropin-releasing hormone (TRH) into the paraventricular nucleus of the hypothalamus (PVN) were examined in fasted, urethane-anesthetized rats. Gastric contractility was measured with extraluminal force transducers and analysed by computer. Unilateral and bilateral PVN microinjections of TRH (0.5 and 1.0 μg) significantly increased the force index of gastric contractions from 0 to 60 min postinjection, when compared with animals microinjected with 0.1 μg TRH, 0.1% BSA or TRH (0.5 and 1.0 μg TRH) in sites adjacent to the PVN. The gastric force index was also significantly elevated from 61 to 120 min postinjection in rats receiving bilateral PVN microinjections of TRH (0.5 and 1.0 μg). Peak gastric responses occurred within 10–20 min postinjection and represented an approximately eight-fold increase over basal values. In the remaining groups, the force index was not significantly altered from preinjection values. The excitatory action of TRH (1.0 μg) on gastric contractility was completely abolished by subdiaphragmatic vagotomy. These results suggest that TRH acts within the PVN to stimulate gastric contractility via vagal-dependent pathways.     

Bombesin immunoreactive neurons in the hypothalamic paraventricular nucleus innervate the dorsal vagal complex in the rat

Bombesin-like immunoreactivity has been localized within neuronal cell bodies of the hypothalamus and nerve terminals within the dorsal vagal complex. The possibility that the hypothalamus is a source for bombesin-like immunoreactive terminals within the dorsal vagal complex was examined using the combined retrograde tracing and immunohistochemical technique. After injections of retrograde tracer were made into the dorsal vagal complex, cells in the hypothalamus labeled with both retrograde tracer and bombesin immunoreactivity were localized in the parvocellular part of the paraventricular nucleus. In the paraventricular nucleus most of the vagal projecting bombesin immunoreactive neurons were located within the medial parvocellular subdivision. Approximately 30% of the bombesin immunoreactive neurons in this subnucleus projected to the dorsal vagal complex. The results suggest that the paraventricular hypothalamic nucleus is a major source of bombesin terminals within the dorsal vagal complex. This pathway may mediate some of the autonomic nervous system changes that are observed when bombesin is injected within the central nervous system. Additionally, this data adds to a growing amount of evidence supporting the role of bombesin as a peptide neurotransmitter.     

Projections between the hypothalamus and the dorsal vagal complex in the cat: An HRP and autoradiographic study

The hypothalamus is known to be intimately involved in the control of autonomic function. This study provides detailed information about pathways between the hypothalamus and the dorsal vagal complex in cat. Injection of horseradish peroxidase into the dorsomedial medulla produced retrograde neuronal labeling in the paraventricular nucleus of the hypothalamus. Injection of 3H-leucine into the paraventricular nucleus produced dense anterograde labeling in the dorsal motor nucleus of the vagus, and lighter labeling in the nucleus of the tractus solitarius, particularly in its medial subnucleus. The subnucleus gelatinous was virtually free of label, except in its medial and lateral portions. Anterograde labeling was distributed bilaterally, with an ipsilateral predominance. Injection of horseradish peroxidase into the area of the paraventricular nucleus produced retrograde neuronal labeling bilaterally in the nucleus of the tractus solitarius and the reticular formation ventrolateral to the dorsal vagal complex. anterograde terminal labeling overlapped the distribution of retrogradely labeled neurons. These findings are compared to those in rat, and discussed in relation to their functional implications.     

Tumor necrosis factor-α inhibits physiologically identified dorsal motor nucleus neurons in vivo

Our previous studies have shown that tumor necrosis factor-alpha (TNF-alpha) activates solitary nucleus neurons involved in vago-vagal reflex control of gastric motility. Here, we describe the dual role of TNF-alpha as also modulating neurons in the dorsal motor nucleus of the vagus (DMN) that respond to gastric distention. A large majority of physiologically identified DMN neurons are rapidly and completely inhibited by exposure to TNF-alpha, suggesting that TNF-alpha may induce gastric stasis by functioning as a hormone that modulates both portions of this reflex pathway during illness.     

Microinjection of TRH analogs into the raphe pallidus stimulates gastric acid secretion in the rat

The effects of microinjection of the stable thyrotropin-releasing hormone (TRH) analog, RX 77368, [pGlu-His-(3,3'-dimethyl)-Pro-NH2] into the raphe pallidus on gastric acid secretion were studied in urethane-anesthetized rats with gastric fistula. RX 77368 microinjected into the raphe pallidus at doses of 0.07, 0.7 and 7.7 pmol induced a dose-dependent net stimulation of gastric acid secretion (7 +/- 4, 50 +/- 7 and 61 +/- 12 mumol/h respectively). The peak acid response was reached within 30 min and returned to basal level 90 min post-injection. The stimulatory effect was abolished by bilateral cervical vagotomy and pirenzepine pretreatment (1 mg/kg, i.v.). RX 77368 (7.7 pmol) microinjected into the inferior olive or pyramidal tract induced smaller or no gastric acid secretory response. These results demonstrate that chemical stimulation of the raphe pallidus increases gastric acid secretion through vagal pathways and peripheral muscarinic receptors. These data suggest that the nucleus raphe pallidus may be involved in vagal modulation of gastric acid secretion in the rat.     

弥漫性颅脑外伤对DVC及内脏活动的作用

目的观察弥漫性脑损伤（DBI）大鼠延髓内脏带（MVZ）中背侧迷走神经复合体（DVC）的神经元放电频率的变化以及观察内脏活动的变化，为临床防治DBI引起的并发症提供理论依据。方法在成功建立DBI大鼠模型基础上，应用电生理学方法，观察DBI发生后1h、2h、6h、12h、24h，大鼠MVZ中DVC神经元放电频率的变化以及DBI大鼠心率、呼吸频率和胃电活动的变化。结果DBI1h，DVC神经元放电频率、胃电、心率和呼吸频率开始出现变化；DBI2h，上述指标出现较为显著的变化，呈现第一次变化高峰。DBI6h时其变化与DBI2h时相类似；而在DBI12h时，上述指标呈现第二次更为显著的变化高峰，直至DBI24h时仍然呈现相对高水平的改变，但较DBI12h时为低。结论DBI发生后，MVZ的DVC中神经元的激活是导致内脏活动发生改变的原动力。     

Lateral hypothalamus modulates gut-sensitive neurons in the dorsal vagal complex

The lateral hypothalamus (LH) regulates metabolic, behavioral and autonomic functions. The influence of the LH on gastrointestinal function and feeding behavior may be mediated by the dorsal vagal complex (DVC). In the present experiment, we used tract tracing and neurophysiologic techniques to evaluate the interrelationship between the LH and DVC. Using the tracer DiI, we demonstrated that the LH projects to both the nucleus of the solitary tract (NST) and the dorsal motor nucleus of the vagus (DMNV). We determined the effects of electrical stimulation of the LH and/or distention of the gastrointestinal tract on the firing rates of 107 DMNV neurons and 68 NST neurons. As previously reported, the majority of the DMNV neurons were inhibited and the majority of the NST neurons were excited by gastrointestinal distention. Electrical stimulation of the LH significantly changed the spontaneous activities of 71% of the DMNV neurons (46 excited and 30 inhibited). Of the 68 NST neurons characterized, 25 neurons were inhibited and 8 were excited by LH stimulation. In a separate experiment, we characterized the effects of both electrical and chemical stimulation of the LH on 36 DMNV and 14 NST neurons. Glutamate (0.8 nM) induced similar responses in the DVC neurons as electrical stimulation of the LH. The results indicate that the LH influences the electrical activity of DVC neurons. This effect may be the mechanism by which the LH modulates gastrointestinal function and feeding behavior.     

Olanzapine treatment decreases the density of muscarinic M2 receptors in the dorsal vagal complex of rats

In this study, we investigated the effects of antipsychotic drugs, olanzapine and haloperidol, on the density of the muscarinic M2 receptors in the dorsal vagal complex (DVC) and hypoglossal nucleus (HN). Female Sprague Dawley rats were treated with olanzapine, haloperidol or vehicle (control) for 1 (short-term) or 12 weeks (long-term). Quantitative autoradiography was used to investigate the M2 receptor density in the DVC and HN using a muscarinic antagonist [(3)H] AF-DX384. Olanzapine, but not haloperidol, treatment induced a significant decrease in the binding density of M2 receptors in the DVC compared to control groups. Although the HN showed a higher density of [(3)H] AF-DX384 binding than the DVC, treatment with both olanzapine and haloperidol did not induce any significant changes in [(3)H] AF-DX384 binding in the HN. These results suggest that olanzapine-induced body weight gain may be associated with functional changes in the muscarinic neurotransmission in the DVC.     

Autoradiographic localization of thyrotropin-releasing hormone and substance P receptors in the rat dorsal vagal complex

We utilized quantitative autoradiography to localize receptors for thyrotropin-releasing hormone (TRH) and substance P in individual subnuclei of the rat nucleus tractus solitarii (NTS) and the dorsal vagal complex. Within the NTS, TRH receptor concentrations were highest within the gelatinosus and centralis subnuclei and the medial subnucleus rostral to the area postrema, moderate within the intermediate subnucleus and the medial subnucleus adjacent to the area postrema, and low within the ventrolateral and commissural subnuclei and the medial subnucleus caudal to the area postrema. In contrast, substance P receptor concentrations were high throughout the medial subnucleus, moderate in all other subnuclei medial to the tractus solitarius, and relatively low in subnuclei lateral to the tractus solitarius. The dorsal motor nucleus of the vagus contained high concentrations of both TRH and substance P receptors, whereas we observed low TRH and moderate substance P receptors in the area postrema. High TRH and moderate substance P receptors were observed in the adjacent hypoglossal nucleus. In addition, we compared the concentrations of TRH receptors between chloroform-defatted and nondefatted tissue sections, and noted little effect of white matter tritium quench upon the observed TRH receptor concentrations. These results suggest that neurotransmitter receptors within the rat dorsal vagal complex are organized in a manner consistent with previous cytoarchitectural and hodological partitioning of the NTS and that the distribution of an individual neurotransmitter receptor in the NTS may correspond to the role of that transmitter in modulating autonomic function.     

Dopamine microinjected into the nucleus ambiguus elicits vagal bradycardia in spinal rats.

To investigate the effects of dopamine (DA) on vagal efferent activity, DA was microinjected into the right nucleus ambiguus (NA) in rats. Experiments were done in 19 urethane anaesthetized, artificially ventilated spinal (C1) rats. Sites in the right NA containing cardioinhibitory neurons were identified by observing a marked and reproducible decrease in heart rate (HR; 64.9 + 2.8 bpm; n = 36) elicited by microinjecting L-glutamate (GLU; 1.5. nmol in 10 nl). No decreases in arterial pressure (AP) were obtained at these sites. Microinjection of DA (1-15 nmol in 10 nl) into 24 of these 36 sites caused a dose-dependent decrease in HR. The responses to 1 nmol and 3 nmol DA were blocked by (+/-)-sulpiride, a specific D2 receptor antagonist (0.1 nmol in 10 nl). A higher dose of (+/-)-sulpiride (1 nmol in 10 nl) was required to block the responses to 15 nmol of DA. Bradycardia elicited by even the lowest amount of DA (1 nmol) was not blocked by SCH-23390, a specific D1 receptor antagonist. These experiments demonstrate that the bradycardia caused by microinjection of DA into the NA is due to the excitation of dopamine D2 receptors present on vagal preganglionic cardioinhibitory neurons controlling HR.     

Bombesin microinjection into the basolateral amygdala influences feeding behavior in the rat

It has been demonstrated that the basolateral amygdala (ABL) represents a satiety mechanism. Experimental data indicate that peripheral or central applications of neuropeptide bombesin (BN) and BN-like peptides inhibit feeding. Since the amygdala (AMY) is rich in BN-like immunoreactive elements, the present study was performed to determine whether 10 or 40 ng doses of BN microinjected bilaterally into the ABL could modify solid food intake. Twenty nanograms of BN (10 ng per injection site) in 24-h deprived rats caused transient inhibition of food intake and 80 ng resulted in a significant reduction of food consumption for 1 h. This inhibitory effect of BN on feeding was eliminated by prior BN antagonist treatment. Results of behavioral tests showed that BN microinjections into the ABL specifically reduced food intake without altering behavioral patterns or influencing the body temperature. Present results suggest that BN-like peptides may act as a complex satiety signal in the ABL.     

Identification of NPY-induced c-Fos expression in hypothalamic neurones projecting to the dorsal vagal complex and the lower thoracic spinal cord

Neuropeptide Y exerts profound effects on body weight and glucose homeostasis. We have investigated the effect of centrally administered neuropeptide Y on the activity of descending neurones of the hypothalamic paraventricular nucleus by combining retrograde tract tracing with c-Fos immunocytochemistry. Male rats were injected with True Blue into the dorsal vagal complex and with FluoroGold into the intermediolateral column of the lower thoracic spinal cord. One week after the last surgical procedure, animals were injected centrally with an orexigenic dose of neuropeptide Y (5 microg) and sacrificed 60 to 240 minutes following this injection. Temporal analysis of NPY-induced c-Fos expression showed a peak at 90 minutes, which was nearly returned to basal levels between 120 and 240 minutes. Expression of c-Fos was prominent in several of the subnuclei of the paraventricular nucleus and in the adjacent perifornical nucleus. Neurones projecting to the spinal cord were prominent in the dorsal, lateral, and ventral portion of the medial parvicellular subnuclei of the PVN. About 15% of IML projecting neurones of the medial parvicellular subnucleus were Fos-positive, whereas less than 5% of IML projecting neurones from other subnuclei were Fos-positive. Hardly any PVN neurones projecting to the dorsal vagal complex were concomitantly Fos-positive. A considerably larger (>10%) proportion of perifornical neurones projecting to the nucleus of the solitary tract were c-Fos-immunopositive. In conclusion, NPY induces c-Fos in paraventricular neurones projecting to intermediolateral column of the spinal cord and in neurones of the perifornical nucleus projecting to the dorsal vagal complex.     

High metabolic activity in the dorsal vagal complex of Brattleboro rats

Receptor densities for angiotensin II and atriopeptin are particularly high in the dorsal vagal complex (DVC) of the caudal medulla oblongata. Measurements of glucose metabolism in individual components of the DVC, compared with those in Long-Evans rats, revealed that the area postrema was activated selectively both in water-sated and water-deprived Brattleboro rats, which have high circulating levels of angiotensin II. Other parts of the DVC, including subnuclei of the nucleus of the solitary tract and the dorsal motor nucleus of the vagus nerve, as well as brainstem structures within efferent trajectories of the DVC, had elevated rates of glucose metabolism in Brattleboro rats deprived of water overnight and in Sprague-Dawley rats dehydrated for 120 h. The findings are consistent with neural activation by angiotensin II, as either a hormone or neurotransmitter, within subregions of the dorsal medulla oblongata having high densities of putative receptors and immunoreactive perikarya and fibers containing both angiotensin II and atriopeptin.     

Units in tegmental nuclei responding to stimulation of gastric vagal and greater splanchnic fibers in the cat

The response of neurons in the ventral and dorsal tegmental nuclei during electrical stimulation of the gastric vagal fibers which serve the proximal stomach and the left greater splanchnic fibers were evaluated in chloralose-anesthetized cats. The mean latency of 181 gastric vagally evoked unitary responses recorded in the tegmental nuclei was 352.2 ms, whereas the latency of the left greater splanchnic-evoked tegmental response was significantly less (63.2 ms). The unitary responses to the gastric vagal and greater splanchnic fibers stimulation were bilaterally distributed in the ventral and dorsal tegmental nuclei. Convergence of the gastric vagal input from the proximal stomach and the left greater splanchnic input was observed in 151 units (83 percent). Stimulation of the greater splanchnic nerve usually resulted in a short latency excitation followed by an inhibitory effect on gastric vagally evoked responses. The results suggested that some convergent splanchnic inhibition of gastric vagally evoked responses was mediated via an interneuron. Projections from the nucleus tractus solitarius and the parabrachial nucleus to the tegmental nuclei were also identified electrophysiologically by direct microstimulation of the two former areas. The significant number of gastric vagal and splanchnic evoked unitary responses recorded in the ventral and dorsal tegmental nuclei suggested that they may serve as an important pontine site for processing of visceral information between the nucleus tractus solitarius and forebrain sites.     

Bombesin microinfusion into the paraventricular nucleus suppresses gastric acid secretion in the rat

Bombesin is a particularly potent inhibitor of gastric acid secretion when injected intracisternally in the rat. Because bombesin-like immunoreactivity is found in several forebrain regions implicated in gut regulation, the ability of bombesin to affect gastric secretion was tested in these areas by direct microinfusion. Bombesin significantly and dose-relatedly suppressed gastric acid secretion when it was infused into the hypothalamic paraventricular nucleus. Bombesin microinfusion into the ventromedial or lateral hypothalamic areas, or the caudate-putamen, had no significant effect. A further experiment using glass micropipets showed that back-diffusion of bombesin along the cannula track to a distant site of action was unlikely to account for the results obtained, and provided further evidence that the active site is limited to the paraventricular nucleus and possibly the ventralmost nucleus reuniens. The results suggest that the bombesin receptors and immunoreactive terminals previously identified in this region may be involved in the central regulation of gastric secretion.