Bombesin microinjected into the dorsal vagal complex inhibits vagally stimulated gastric acid secretion in the rat

Medullary sites of action for bombesin-induced inhibition of gastric acid secretion were investigated in urethane-anesthetized rats with gastric fistula. Unilateral microinjection of bombesin or vehicle into the dorsal vagal complex was performed using a glass micropipet and pressure ejection of 100 nl volume; gastric acid output was measured every 10 min by flushing the stomach. Microinjection of vehicle into the dorsal vagal complex did not alter gastric acid secretion (1.9 +/- mumol/10) from preinjection levels (2.9 +/- 0.8 mumol/10 min). Microinjection of the stable thyrotropin-releasing hormone (TRH) analog, RX 77368, at a 77 pmol dose into the dorsal vagal complex stimulated gastric acid secretion for 100 min with a peak response at 40 min (24.1 +/- 3.2 mumol/10 min). Concomitant microinjection of RX 77368 (77 pmol) with bombesin (0.6-6.2 pmol) into the dorsal vagal complex dose dependently inhibited by 35-86% the gastric acid response to the TRH analog. Bombesin (6.2 pmol) microinjected into the dorsal vagal complex inhibited by 17% pentagastrin infusion-induced stimulation of gastric acid secretion (13.2 +/- 0.8 mumol/10 min) whereas intracisternal injection induced a 69% inhibition of the pentagastrin response. These results demonstrate that the dorsal motor complex is a sensitive site of action for bombesin-induced inhibition of vagally stimulated gastric secretion. However, other medullary sites must be involved in mediating the inhibitory effect of intracisternal bombesin on pentagastrin-stimulated gastric acid secretion.     

Pancreatic polypeptide, microinjected into the dorsal vagal complex, potentiates glucose-stimulated insulin secretion in the rat

Specific binding sites for circulating pancreatic polypeptide (PP) have been found within the dorsal vagal complex (DVC) in the caudal medulla oblongata. Therefore, the effects of rat PP on pancreatic hormone secretion upon its microinjection into the DVC in halothane-anesthetized rats at doses of 0.4–40 pmol were investigated. At this range of doses, the changes in plasma concentrations of insulin, glucagon and glucose over basal levels did not differ from those after vehicle microinjection. In a separate series of experiments, vehicle and PP at doses of 0.4 and 4 pmol were microinjected into the right DVC 40 min after the continuous infusion of -glucose had been started. In animals receiving continuous infusion of -glucose, PP microinjected into the DVC (4 pmol), resulted in markedly higher insulin levels at corresponding time points compared to those with vehicle microinjected into the DVC. These data indicate, for the first time, that microinjection of PP into the DVC may potentiate glucose-stimulated insulin secretion in halothane-anesthetized rats.     

Inhibition of pulsatile luteinizing hormone release by morphine microinjected into mesencephalic dorsal raphe

Blood samples were collected via jugular catheters from ovariectomized rats at 10-minute intervals for one hour before and two hours after microinjection of 0.5 μl of either saline vehicle or morphine sulfate (10 μg) into the dorsal raphe nucleus (DNR) or adjacent peri-aqueductal gray by means of chronically-implanted guide cannulae. LH was measured by radioimmunoassay and mean pre-injec post-injection values were compared for each rat (t test) as well as for each treatment group (paired t test). Neither saline in DRN nor morphine at other sites significantly altered circulating LH. A significant decrease in LH was observed following injection of morphine into DRN. This effect of morphine was prevented by pre treatment of the animals with the narcotic antagonist naltrexone (10 mg/kg i.v.), indicating the involvement of opiate receptors. These results indicate that DRN is one site at which systemically-administered morphine might act, and suggest the possibility of participation of this mechanism in modulation of LH release by endogenous opioids.     

Effects of thyrotropin-releasing hormone (TRH) microinjected into various brain areas of conscious and pentobarbital-pretreated rabbits

Thyrotropin releasing hormone (TRH) was administered intracerebrally into various brain regions of conscious and pentobarbitalnarcotized rabbits. In conscious animals tachypnea was observed after TRH administration into all brain regions investigated. Behavioral excitation was most pronounced after TRH administration into the cerebral cortex, caudate nucleus and hypothalamus. Hyperthermia was produced only after hypothalamic injections of TRH. In pentobarbital-narcotized rabbits TRH exerted analeptic activity (shortening of narcosis) regardless of the brain area injected, although some quantitative differences were observed. These results indicate that the analeptic effect of TRH may be initiated from various areas of the brain.     

Stimulation by thyrotropin-releasing hormone of vagal outflow to the thyroid gland

An intracerebroventricular (i.c.v.) injection of TRH to the urethane anesthetized rat stimulates the activity of the superior laryngeal nerve (n.sl) which is a vagal ramus terminating at the thyroid gland and adjacent muscles. The response to TRH, a tonic increase in the n.sl outflow, was dose dependent in the 0.005-5.0 micrograms/100 g B.W. range. In contrast to this, methionine-enkephalin (ENK), neurotensin (NT) and somatostatin (SRIF) (5 micrograms/100 g, i.c.v.) all caused a transient decrease in n.sl activity. SRIF showed the highest attenuating effect when injected alone and was capable of diminishing the increased activity produced by a prior injection of TRH. ENK and NT failed to affect the TRH-induced increased activity. When injected concomitantly with TRH, SRIF blocked the response to TRH while ENK and NT both failed to affect the response to TRH. Pretreatment with triiodothyronine for 5 days strongly inhibited the response of the n.sl outflow to TRH. On the other hand, pretreatment with atropine, haloperidol, propranolol, phenoxybenzamine and p-chlorophenylalanine failed to block the stimulating effect of TRH although the response was diminished by some antagonists. It therefore seemed that TRH transmission is involved in central stimulation and SRIF is antagonistic in this regulation of n.sl outflow to the thyroid gland.     

Mechanism of cardiovascular effects of nociceptin microinjected into the nucleus tractus solitarius of the rat

Microinjections (100 nl) of 0.15, 0.31, 0.62, and 1.25 mmol/l of nociceptin into the medial nucleus tractus solitarius (mNTS) elicited decreases in mean arterial pressure (11 +/- 1.8, 20 +/- 2.1, 21.5 +/- 3.1, and 15.5 +/- 1.9 mmHg, respectively) and heart rate (14 +/- 2.7, 29 +/- 5.5, 39 +/- 5.2, and 17.5 +/- 3.1 beats/min, respectively). Because maximal responses were elicited by microinjections of 0.62 mmol/l nociceptin, this concentration was used for other experiments. Repeated microinjections of nociceptin (0.62 mmol/l) into the mNTS, at 20-min intervals, did not elicit tachyphylaxis. Bradycardia induced by microinjections of nociceptin into the mNTS was abolished by bilateral vagotomy. The decreases in mean arterial pressure and heart rate elicited by nociceptin into the mNTS were blocked by prior microinjections of the specific ORL1-receptor antagonist [N-Phe(1)]-nociceptin-(1-13)-NH(2) (9 mmol/l). Microinjections of the ORL1-receptor antagonist alone did not elicit a response. Prior combined microinjections of GABA(A) and GABA(B) receptor antagonists (2 mmol/l gabazine and 100 mmol/l 2-hydroxysaclofen, respectively) into the mNTS blocked the responses to microinjections of nociceptin at the same site. Prior microinjections of ionotropic glutamate receptor antagonists (2 mmol/l NBQX and 5 mmol/l d-AP7) also blocked responses to nociceptin microinjections into the mNTS. These results were confirmed by direct neuronal recordings. It was concluded that 1) nociceptin inhibits GABAergic neurons in the mNTS, 2) GABAergic neurons may normally inhibit the release of glutamate from the terminals of peripheral afferents in the mNTS, and 3) inhibition of GABAergic neurons by nociceptin results in an increase in the release of glutamate in the mNTS, which in turn elicits depressor and bradycardic responses via activation of ionotropic glutamate receptors on secondary mNTS neurons.     

Paradoxical vagal effects on the cardiac rhythm in cats

In anaesthetised cats, an increase in the vagal burst rate resulted in a paradoxical decrease of vagal bradycardia. This seems to be due to a shift of the vagal stimulus position towards early phase of cardiac cycle. The mechanism of this paradoxical effect depends on the magnitude of vagal chronotropic effect upon the time of vagal stimulus delivery within cardiac cycle.     

Retrograde degeneration within the dorsal motor vagal nucleus following bilateral vagotomy in rabbits

The effects of unilateral and bilateral intrathoracic vagotomy on the neuronal structure of the dorsal motor nucleus of the vagus were studied in rabbits. Degeneration affected mainly the small neurones which disintegrated and vanished from dorsal motor nucleus relative to the survival time after operation. A substantial proportion of large neurones was lost or degenerated, but some were preserved unchanged. In unilaterally vagotomized rabbits the dorsal motor nucleus of the intact side showed scattered neurones with axonal reaction which stands up for peripheral crossing of the vagi. The degree of retrograde degeneration was largely determined by the survival time. The nucleus ambiguus was bilaterally preserved unchanged.     

The role of vagal afferents and carbon dioxide in the respiratory response to thyrotropin-releasing hormone

Rats treated neonatally with pargyline and 5,7-dihydroxytryptamine to decrease central serotonin-containing neurons have an accentuated respiratory response to i.c.v. thyrotropin-releasing hormone (TRH). Since these treated rats also evidence an elevated PaCO2, we sought to evaluate the importance of CO2 in determining the magnitude of the respiratory response to TRH. Neonatal treatment with capsaicin or acute vagotomy also produced adult animals whose basal PaCO2 was elevated and whose respiratory response to TRH was greater than that seen in control rats with lower PaCO2 values. In normal rats, however, administration of CO2 immediately before and after TRH administration does not alter the subsequent response to TRH. Thus, it appears that TRH facilitates the processing of CO2-dependent afferent impulses, and that CO2 does not alter disposition or pharmacokinetics of TRH.     

Thyrotropin-releasing hormone in the dorsal vagal complex stimulates pancreatic blood flow in rats

Central administration of thyrotropin-releasing hormone (TRH) enhanced pancreatic blood flow in animal models. TRH nerve fibers and receptors are localized in the dorsal vagal complex (DVC), and retrograde tracing techniques have shown that pancreatic vagal nerves arise from the DVC. However, nothing is known about the central sites of action for TRH to elicit the stimulation of pancreatic blood flow. Effect of microinjection of a TRH analog into the DVC on pancreatic blood flow was investigated in urethane-anesthetized rats. After measuring basal flow, a stable TRH analog (RX-77368) was microinjected into the DVC and pancreatic blood flow response was observed for 120 min by laser Doppler flowmetry. Vagotomy of the several portions, or pretreatment with atoropine methyl nitrate or N(G)-nitro-l-arginine-methyl ester was performed. Microinjection of RX-77368 (0.1-10 ng) into the left or right DVC dose-dependently increased pancreatic blood flow. The stimulation of pancreatic blood flow by RX-77368 microinjection was eliminated by the same side of cervical vagotomy as the microinjection site or subdiaphragmatic vagotomy, but not by the other side of cervical vagotomy. The TRH-induced stimulation of pancreatic blood flow was abolished by atropine or N(G)-nitro-l-arginine-methyl ester. These results suggest that TRH acts in the DVC to stimulate pancreatic blood flow through vagal-cholinergic and nitric oxide dependent pathways, indicating that neuropeptides may act in the specific brain nuclei to regulate pancreatic function.     

迷走背核微量注射P物质抑制大鼠胃肌电活动和胃运动

本工作观察到大鼠迷走背核微量注射Ｐ物质（Ｓｕｂｓｔａｎｃｅ Ｐ,ＳＰ）抑制胃肌电快波和胃运动。该效应可分别迷走背核注射ＳＰ抗血清,ＳＰ受体拮抗剂「Ａｒｇ＾６,Ｄ－Ｔｒｐ＾７,９,Ｎ－Ｍｅ－Ｐｈｅ＾８」－ＳＰ６－１１或切断迷走神经所消除。用利血平耗竭交感神经递质则不影响该效应。     

Inhibition of affective aggression and dominance in rats after thyrotropin-releasing hormone (TRH) microinjection into the nucleus accumbens

The effect of 10 micrograms TRH injected bilaterally into the nucleus accumbens septi on two models of affective aggression and on dominance in a water-competition task was investigated in pairs of male Wistar rats. TRH significantly suppressed affective shock-induced and apomorphine-induced fighting. It also decreased dominance when administered to dominant rats while no effect was noted upon injection into subordinate animals. The peptide influenced neither water consumption in thirsty rats nor the pain threshold in a hot plate test.     

Corticosterone microinjected into nucleus pontis oralis increases tonic immobility in rats

Tonic immobility (TI) is also known as “immobility response”, “immobility reflex”, “animal hypnosis”, etc. It is an innate antipredatory behavior characterized by an absence of movement, varying degrees of muscular activity, and a relative unresponsiveness to external stimuli. Experimentally, TI is commonly produced by manually forcing an animal into an inverted position and restraining it in that position until the animal becomes immobile. Part of the neural mechanism(s) of TI involves the medullo-pontine reticular formation, with influence from other components of the brain, notably the limbic system. It has been observed that TI is more prolonged in stressed animals, and systemic injection of corticosterone (CORT) also potentiates this behavior. At present, the anatomical brain regions involved in the CORT modulation of TI are unknown. Thus, our study was made to determine if some pontine areas could be targets for the modulation of TI by CORT. A unilateral nucleus pontis oralis (PnO) microinjection of 1 μL of CORT (0.05 μg/1 μL) in rats resulted in clear behavioral responses. The animals had an increased duration of TI caused by clamping the neck (in this induction, besides of body inversion and restraint, there is also clamping the neck), with an enhancement in open-field motor activity, which were prevented by pretreatment injection into PnO with 1 μL of the mineralocorticoid-receptor antagonist spironolactone (0.5 μg/1 μL) or 1 μL of the glucocorticoid-receptor antagonist mifepristone (0.5 μg/1 μL). In contrast, these behavioral changes were not seen when CORT (0.05 μg/1 μL) was microinjected into medial lemniscus area or paramedian raphe. Our data support the idea that, in stressful situations, glucocorticoids released from adrenals of the prey reach the PnO to produce a hyper arousal state, which in turn can prolong the duration of TI.     

神经降压素对迷走运动背核神经元兴奋作用的离体的研究

Intracellular recordings were made from neurons of the dorsal motor nucleus of the vagus (DMV) in rat brain slices. Most of DMV neurons (88%) were depolarized by droplets or perfusion of neurotensin (NT) in a dose-dependent manner. The depolarization, accompanied by an increase in membrane resistance, depended on extracellular K+ concentration and reversed polarity at about -82 mV. Perfusion with Ca(2+)-free/high-Mg2+ solution or with 1 mumol/L TTX solution, which blocked synaptic activities, did not eliminate NT-induced depolarization. The results indicate that NT excites DMV neurons through postsynaptic mechanism and this exciting depolarization may result from a decrease in K+ conductance.     

Gastric erosions induced by intracisternal thyrotropin-releasing hormone (TRH) in rats

Intracisternal injection of TRH (1 microgram) under light ether anesthesia induced within 4 hr gastric lesions in 24-hr fasted rats maintained unrestrained at room temperature. Saline, ovine corticotropin-releasing factor (oCRF, 10 micrograms), or human pancreatic growth hormone-releasing factor [hpGRF(1-40), 10 micrograms] tested under the same conditions did not modify the integrity of the gastric mucosa. TRH injected intravenously (100 micrograms/kg) proved to be ineffective. The production of gastric erosions elicited by intracisternal TRH (0.1-1 microgram) or by a stabilized TRH analog, RX 77368 [pGlu-His-(3,3'-dimethyl)-ProNH2, (0.01-0.1 microgram)] was dose-dependent. RX 77368 shows an enhanced potency over TRH. TRH action on gastric mucosa was reversed by atropine, omeprazole and cimetidine. These results demonstrate that TRH, unlike the other hypothalamic releasing factors CRF or GRF, is able to act within the brain to cause the formation of gastric erosions probably through mechanisms involving changes in gastric acid secretion. Intracisternal injection of TRH or its potent analog RX 77368 appears also as a new, simple method to produce centrally mediated experimental gastric erosions in 24 hr-fasted rats.     

Noradrenergic alpha 2 binding sites in vagal dorsal motor nucleus and nucleus tractus solitarius: autoradiographic localization

The distribution in the canine medulla oblongata of binding sites for p-[3H]aminoclonidine, a ligand specific for alpha 2-adrenergic receptors, was studied with light microscopic autoradiographic methods. Specific labelling was determined using unlabelled phentolamine as a displacer. The greatest density of sites was localized in the dorsal motor nucleus of the vagus nerve, the area postrema, and in several regions of the nucleus tractus solitarius. Less dense binding of the radioligand was also seen in the inferior olivary nucleus. Dorsomedial regions of the nucleus tractus solitarius were the most densely labelled in this nucleus, and dorsolateral and ventral regions were much less densely labelled. The region of the nucleus tractus solitarius shown in this study to be heavily labelled with alpha 2-adrenergic binding sites has been implicated in the autonomic control of blood pressure. The dorsal motor nucleus of the vagus, together with the nucleus tractus solitarius, may thus represent the site of the antihypertensive action of the drug clonidine, an alpha 2-adrenoreceptor agonist.     

Neuroactive substances in the dorsal vagal complex of the medulla oblongata: nucleus of the tractus solitarius,area postrema,and dorsal motor nucleus of the vagus

The distributions of classical and putative neurotransmitters within somata and fibres of the dorsal vagal complex are reviewed. The occurrence within the dorsal medulla oblongata of receptors specific for some of these substances is examined, and possible functional correlations of the specific neurochemicals with respect to their distribution within the dorsal vagal complex are discussed.Many of the known transmitters and putative transmitters are represented in the dorsal vagal complex, particularly within various subnuclei of the nucleus of the solitary tract, the main vagal afferent nucleus. In a few cases, some of these have been examined in detail, particularly with respect to their possible mediation of cardiovascular or gastrointestinal functions. For example, the catecholamines, substance P and angiotensin II in the nucleus of the solitary tract have all been strongly implicated as playing a role in the central control of cardiovascular function. Other neurotransmitters or putative transmitters may be involved as well, but probably to a lesser extent. Similarly, the roles in the dorsal vagal complex of dopamine, the endorphins and cholecystokinin in control of the gut have been studied in some detail.Future investigations of the distributions of and electrophysiological parameters of neurotransmitters at the cellular level should provide much needed clues to advance our knowledge of the correlations between anatomical distributions of specific neurochemicals and physiological functions mediated by them.     

Quantitation and characterization of thyrotropin-releasing hormone in vagal nuclei and other regions of the medulla oblongata of the rat

Abstract: Since evidence is now available to support a nonendocrine autonomic function for thyrotropin-releasing hormone (TRH), quantitative measurements of TRH were made in nuclei of the vagal complex and other areas of the caudal medulla oblongata of the rat. Regions containing the dorsal motor nucleus of the vagus (DMN), nucleus tractus solitarius (NTS), hypoglossal nucleus, dorsal column nuclei, descending nucleus V (DNV), nucleus ambiguus (NA), raphe nuclei (MR) dorsomedial and ventromedial reticular formation, and inferior olivary nuclei were isolated from 300-μm-thick frozen sections of medulla by the micropunch technique. Each region was pooled bilaterally, homogenized in 0.1 M HCl, and vacuum-dried. Extracts were assayed for TRH by specific radioimmunoassay (RIA). TRH levels varied 100-fold among medulla nuclei. Highest content (ng/mg protein ± SEM) was found in DMN (14 ± 1.38) and NTS (4.7 ± 0.68), whereas lowest levels occurred in the DNV and MR (0.13, 0.06). Nearly 65% of the total medullary TRH was localized in nuclei associated with vagal complex (DMN, NTS, NA). Characterization of tissue immunoreactivity (TRHi) in these regions suggests the presence of TRH, since (1) medullary tissue extracts competed with ¹²⁵I-TRH for antibody binding sites with the same affinity as authentic TRH; (2) TRHi in tissue extracts co-migrated with synthetic TRH when subjected to reverse-phase high performance liquid chromatography and Sephadex G-10 chromatography; and (3) rat serum TRH peptidases degraded TRHi and authentic TRH at similar rates. Another group of rats was subjected to unilateral (right side) vagotomy. At 33 weeks post-vagotomy, the vagal preganglionic cell population in the ipsilateral DMN was depleted 50–75%, while the contralateral side was unaffected. Interestingly, the content of TRH in the ipsilateral (right) DMN remained unchanged, whereas TRH in the contralateral DMN increased by 50%. In contrast, TRH was significantly elevated in the NA on the ipsilateral side of the lesion. TRH in both ipsi- and contralateral NTS was unchanged when compared with sham-operated controls. These results indicate that (1) TRH is present in several specific loci of the medulla; (2) very high levels are found in the vagal complex; and (3) vagotomy may alter TRH in the contralateral DMN and ipsilateral NA.