Vagal afferent stimulation-evoked gastric secretion suppressed by paraventricular nucleus lesion

Traumatic stress and the autonomic brain-gut connection in development: Polyvagal Theory as an integrative framework for psychosocial and gastrointestinal pathology

A range of psychiatric disorders such as anxiety, depression, and post-traumatic stress disorder frequently co-occur with functional gastrointestinal (GI) disorders. Risk of these pathologies is particularly high in those with a history of trauma, abuse, and chronic stress. These scientific findings and rising awareness within the healthcare profession give rise to a need for an integrative framework to understand the developmental mechanisms that give rise to these observations. In this paper, we introduce a plausible explanatory framework, based on the Polyvagal Theory (Porges, Psychophysiology, 32, 301-318, 1995; Porges, International Journal of Psychophysiology, 42, 123-146, 2001; Porges, Biological Psychology, 74, 116-143, 2007), which describes how evolution impacted the structure and function of the autonomic nervous system (ANS). The Polyvagal Theory provides organizing principles for understanding the development of adaptive diversity in homeostatic, threat-response, and psychosocial functions that contribute to pathology. Using these principles, we outline possible mechanisms that promote and maintain socioemotional and GI dysfunction and review their implications for therapeutic targets.

Modulatory role of serotonin on feeding behavior

The appearance, the odor, and the flavor of foods, all send messages to the encephalic area of the brain. The hypothalamus, in particular, plays a key role in the mechanisms that control the feeding behavior. These signals modulate the expression and the action of anorexigenic or orexigenic substances that influence feeding behavior. The serotonergic system of neurotransmission consists of neurons that produce and liberate serotonin as well as the serotonin-specific receptor. It has been proven that some serotonergic drugs are effective in modulating the mechanisms of control of feeding behavior. Obesity and its associated illnesses have become significant public health problems. Some drugs that manipulate the serotonergic systems have been demonstrated to be effective interventions in the treatment of obesity. The complex interplay between serotonin and its receptors, and the resultant effects on feeding behavior have become of great interest in the scientific community.

Nicotinic acetylcholine receptor subunit mRNA expression in adult and developing rat medullary catecholamine neurons

Nicotinic acetylcholine receptors (nAChRs) mediate numerous visceral functions via medullary catecholamine (CA) neurons found in the nucleus tractus solitarius (NTS), dorsal motor nucleus of the vagus (DMV), and ventrolateral medulla (VLM). However, the nAChR subtypes involved are not known. We have therefore characterized expression of nine nAChR subunit mRNAs in adult and developing rat medullary CA nuclei using combined isotopic/nonisotopic in situ hybridization. Tyrosine hydroxylase (TH) mRNA, the CA-synthesizing enzyme, was used as a marker for CA neurons, because these nuclei consist of heterogeneous populations of cells. Subunit mRNA expression varied within and between nuclei, along the rostrocaudal axis, between cell types, and across development. All CA neurons expressed beta2 mRNA, whereas alpha2 mRNA was completely absent. alpha6 And beta3 mRNA expression were restricted mainly to the VLM. alpha4, alpha5, And alpha7 mRNA expression was significantly greater in the rostral than in the caudal VLM. alpha3 And beta4 mRNAs were highly expressed in the dorsal region of the NTS, whereas dense alpha7 mRNA expression was restricted to the DMV and ventral NTS. The remaining subunit mRNAs were detected to some degree in both DMV and NTS. Except for alpha4 mRNA, which peaked prenatally, expression levels of subunit transcripts in the NTS and DMV were lower during development compared with adults. In the VLM, alpha3, alpha4, and alpha5 mRNAs expression peaked perinatally, whereas alpha6 and beta3 levels increased with age. These variations in nAChR subunit mRNA expression suggest that different receptor subtypes may produce function-specific regulation of medullary CA systems.

Brainstem circuits regulating gastric function

Brainstem parasympathetic circuits that modulate digestive functions of the stomach are comprised of afferent vagal fibers, neurons of the nucleus tractus solitarius (NTS), and the efferent fibers originating in the dorsal motor nucleus of the vagus (DMV). A large body of evidence has shown that neuronal communications between the NTS and the DMV are plastic and are regulated by the presence of a variety of neurotransmitters and circulating hormones as well as the presence, or absence, of afferent input to the NTS. These data suggest that descending central nervous system inputs as well as hormonal and afferent feedback resulting from the digestive process can powerfully regulate vago-vagal reflex sensitivity. This paper first reviews the essential "static" organization and function of vago-vagal gastric control neurocircuitry. We then present data on the opioidergic modulation of NTS connections with the DMV as an example of the "gating" of these reflexes, i.e., how neurotransmitters, hormones, and vagal afferent traffic can make an otherwise static autonomic reflex highly plastic.

TNFalpha-stimulation of cFos-activation of neurons in the solitary nucleus is suppressed by TNFR:Fc adsorbant construct in the dorsal vagal complex

The cytokine tumor necrosis factor alpha (TNF(alpha)) may act within the neural circuitry of the medullary dorsal vagal complex (DVC) to affect changes in gastric function such as gastric stasis, loss of appetite, nausea, and vomiting. The definitive demonstration that endogenously generated TNF(alpha) is acting within the DVC circuitry to affect these changes has been impeded by the lack of an antagonist for TNF(alpha). The present studies used localized central nervous system microinjections of the TNF-adsorbant construct (TNFR:Fc) to specifically neutralize the ability of endogenously produced TNF(alpha) to activate NST neurons. Our studies reveal that TNFR:Fc suppresses induction of cFos normally evoked by TNF(alpha). These results validate our hypothesis that circulating TNF(alpha) may act directly within the DVC to affect gastric function in a variety of pathophysiological states.

GRP mediates an inhibitory response of gut-related vagal motor neurons to PVN stimulation

We previously characterized neurons in the dorsal motor nucleus of the vagus (DMNV) that were modulated by electrical stimulation of the PVN and by gastrointestinal distention. Bombesin has been identified in a subset of PVN neurons projecting to the DMNV. It is currently unknown whether this neurotransmitter is involved in descending communication from PVN to DMNV neurons. In this study we determined whether the specific bombesin antagonist, N-acetyl-GRP(20-26), influenced (1) the basal firing rate of DMNV neurons and (2) the response to electrical current stimulation of the PVN. Our results indicate that N-acetyl-GRP(20-26), significantly attenuated the inhibitory response of DMNV neurons to PVN stimulation. These results provide a possible mechanism by which bombesin regulates gastrointestinal function, body temperature homeostasis, and feeding behaviors.

Descending influences from the infralimbic cortex on vago-vagal reflex control of gastric motor activity in the rat

In experiments on urethane anaesthetised rats the influence of electrical stimulation of ventral areas of the medial prefrontal cortex (mPFC) on spontaneous and vagally-mediated gastric motility were studied. Stimulation of the mPFC resulted in gastric relaxation manifested as a fall in intragastric pressure from a baseline value of 5.0 +/- 0.5 cm H2O. These were most prominent following a short latency when the infralimbic cortex (IL) was stimulated (27.4 +/- 2.5% fall in gastric pressure). Electrical stimulation of the central end of one cervical vagus nerve caused a comparable decrease in gastric pressure (27.1 +/- 2.9%). The cortical mediated relaxation was reduced by atropine and abolished by vagotomy. The cortically induced gastric relaxation followed a shorter latency (5.9 +/- 1.0 s), time to nadir (20.1 +/- 2.7 s) and the half recovery time (21.5 +/- 4.0 s) than vagally mediated-relaxations (9.9 +/- 2.3, 56.0 +/- 5.3 and 83.4 +/- 9.5 s, respectively). Vagally mediated relaxations were inhibited by simultaneous stimulation of the infralimbic cortex. In this case the decrease of gastric pressure, the time to nadir and the half recovery time were significantly decreased in comparison with the gastric relaxatory responses to vagal stimulation alone (P < 0.05). We conclude that one way in which the mPFC influences gastric motility is via corticofugal projections from the infralimbic cortex to the brain-stem which modulate transmission of vago-vagal reflexes.

Stimulation of the paraventricular nucleus modulates the activity of gut-sensitive neurons in the vagal complex

There is good evidence that stimulation of the lateral hypothalamus excites neurons in the dorsal vagal complex (DVC), but the data regarding the role of the paraventricular nucleus (PVN) in vagal function are less clear. The purpose of this study was to clarify the effect of PVN stimulation on the activity of neurons in the DVC. We utilized extracellular and intracellular neuronal recordings with intracellular injections of a neuronal tracer to label individual, physiologically characterized neurons in the DVC of rats anesthetized with pentobarbital sodium. Most (80%) of the gut-sensitive dorsal motor nucleus of the vagus (DMNV) neurons characterized in this study exhibited a change in activity during electrical stimulation of the PVN. Stimulation of the PVN caused an increase in the spontaneous activity of 59% of the PVN-sensitive DMNV neurons, and the PVN was capable of modulating the response of a small subset of DMNV neurons to gastrointestinal stimuli. This study also demonstrated that the PVN was capable of influencing the activity of neurons in the nucleus of the solitary tract (NST). Electrical stimulation of the PVN decreased the basal activity of 66% of the NST cells that we characterized and altered the gastrointestinal response of a very small subset of NST neurons. It is likely that these interactions play a role in the modulation of a number of gut-related homeostatic processes. Increased or decreased activity in the descending pathway from the PVN to the DVC has the potential to alter ascending satiety signals, modulate vago-vagal reflexes and the cephalic phase of feeding, and affect the absorption of nutrients from the gastrointestinal tract.

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 microgram) significantly increased the force index of gastric contractions from 0 to 60 min postinjection, when compared with animals microinjected with 0.1 microgram TRH, 0.1% BSA or TRH (0.5 and 1.0 microgram 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 microgram). 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 microgram) 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.

Localization of central prostaglandin E2 antisecretory effects

Intracerebroventricular prostaglandin E2 (PGE2) inhibits stimulated gastric acid secretion; however, the central site of action is unknown. Specific PGE2 binding sites have been localized to the ventromedial hypothalamic nucleus and central amygdala (A). The nuclear accumbens has been shown to play a role in central neurotensin-induced antisecretory effects. These studies tested the hypothesis that microinjections of PGE2 into the ventromedial hypothalamic nucleus, central amygdala, and nuclear accumbens inhibit stimulated gastric acid secretion. The hippocampus served as a cerebral control region. Two days before the experiments, metal cannulas were stereotaxically positioned bilaterally into specific areas of the brain, and metal gastric cannulas were operatively implanted, under nembutal anesthesia, in male 250-g Sprague-Dawley rats. On the experimental day, the rats, fasted for 14 hours, were given saline or PGE2 (0.1-1.0 micrograms in 0.2 microL/side) through the central cannulas 10 minutes before administering pentagastrin (40 micrograms/kg SC). Gastric secretion was measured at 30-minute intervals and expressed as acid output, micromoles per hour. Acid output (mean +/- SE) in control animals was 161 +/- 14 mumol/h. Prostaglandin E2 administration at doses of 0.10, 0.50, and 1.0 micrograms/side (a) into ventromedial hypothalamic nucleus reduced acid output to 53 +/- 11,* 36 +/- 10,* and 27 +/- 11* mumol/h regularly; (b) into NACB reduced acid output to 157 +/- 36, 60 +/- 12,* and 38 +/- 12* mumol/h; and (c) into A reduced acid output to 144 +/- 31, 141 +/- 26, and 90 +/- 19* mumol/h, respectively (*P less than 0.05 by Neuman-Keuls test). Prostaglandin E2 (0.50 micrograms/side) administration into hippocampus had no significant effect on acid output (134 +/- 28 mumol/h). Although central PGE2 administration was associated with hyperthermia, this occurred at lower doses than those required to inhibit acid secretion. Prostaglandin E2 administration into specific brain areas known to have PGE2 receptors, the central amygdala and ventromedial hypothalamic nucleus, and into nuclear accumbens inhibits stimulated gastric acid secretion. These observations suggest that PGE2 may have a physiological role in the central control of gastric acid secretion.

Locus coeruleus projections to the dorsal motor vagus nucleus in the rat

The origin of the noradrenergic innervation of the preganglionic autonomic nuclei in the medulla oblongata and spinal cord is still controversial. In this investigation descending connections of the locus coeruleus to the dorsal motor vagus nucleus in the rat are studied with Phaseolus vulgaris leucoagglutinin and horseradish peroxidase as neuroanatomical tracers. Locus coeruleus projections in the motor vagus nucleus are found in the medial part at rostral levels and in the lateral part at intermediate levels of this nucleus. The terminal labeling in the lateral intermediate part of the vagus nucleus appears in an area where possibly preganglionic parasympathetic cardiac neurons are located, suggesting that the locus coeruleus might be involved in regulation of cardiovascular functions. After small iontophoretic injections of horseradish peroxidase in the motor vagus nucleus, retrogradely labeled cells are found in the ventral part of the locus coeruleus and occasionally in the dorsal part of the nucleus. The results show that the locus coeruleus-dorsal motor vagus nucleus pathway may participate in the inhibition of the cardiac preganglionic neurons in the dorsal motor vagus nucleus by the hypothalamic paraventricular nucleus.

Simultaneous labeling of vagal innervation of the gut and afferent projections from the visceral forebrain with dil injected into the dorsal vagal complex in the rat

The vagal innervation of the different layers of the rat gastrointestinal wall was identified with the fluorescent carbocyanine dye Dil, injected into the dorsal motor nucleus of the vagus (dmnX). Multiple, bilateral injections were used to label all dmnX preganglionic motoneurons, and as a consequence, most of the vagal primary afferents that terminate in the adjacent nucleus of the solitary tract (nts) were also retrogradely and transganglionically labeled. With Fluorogold used to label the enteric nervous system completely and specifically, the Dil-labeled vagal profiles could be visualized and quantified in their anatomical relation to the neurons of the myenteric and submucous ganglia. In the myenteric plexus, vagal fibers and terminals were found throughout the gastrointestinal tract as far caudal as the descending colon, but there was a general decreasing proximodistal gradient in the density of vagal innervation. All parts of the gastric myenteric plexus (fundus, corpus, antrum), as well as the proximal duodenum, were extremely densely innervated, with vagal fibers and terminals in virtually every ganglion and connective. Further caudally, both the percentage of innervated myenteric ganglia and the average density of label within the ganglia rapidly decreased, with the exception of the cecum and proximal colon, where up to 65% of the ganglia were innervated. In the gastric and duodenal submucosa very few and in the mucosa no vagal fibers and terminals were found. With both normal epifluorescence and laser scanning confocal microscopy, highly varicose or beaded terminal structures of various size and geometry could be identified. The Dil injections, which impregnated the dmnX as well as the adjacent nts, resulted in retrograde and anterograde labeling of all the previously reported forebrain connections with the dorsal vagal complex. We conclude that the myenteric plexus is the primary target of vagal innervation throughout the gastrointestinal tract, and that its innervation is more complete than previously assumed. In contrast, vagal afferent (and efferent) innervation of mucosa and submucosa seems conspicuously sparse or absent. Furthermore, the use of more focal injections of Dil offers the prospect to simultaneously identify specific subsets of vagal preganglionics and their central nervous inputs.

Oxytocin excites gastric-related neurones in rat dorsal vagal complex

1. Dorsal medullary injections of oxytocin (OT) influence gastric motor and secretory function via a vagally mediated mechanism. Thus, it was hypothesized that OT altered the firing rate of brain stem vagal neurones that were specifically related to gastric function. 2. To study this, glass microelectrode/injection pipette arrays were used to record the activity of gastric-related neurones in the dorsal vagal complex (DVC), which includes vagal sensory neurones in the nucleus tractus solitarius (NTS) and motor neurones in the dorsal motor nucleus (DMN). After identifying such a neurone, spontaneous activity was monitored before and after micropressure injection of OT and vehicle solutions from the pipettes. 3. Two methods were used to identify neurones that were related to gastric function. One method employed a gastric balloon to identify DVC neurones that were responsive to gastric inflation. The second method employed a gastric vagal stimulating electrode, which permitted the identification of gastric-related NTS and DMN cells via orthodromic or antidromic activation, respectively. 4. Twenty-four of forty-two gastric-inflation-related neurones responded to administration of OT (100-400 fmol in 100-400 pl). The majority of those responding to OT were activated by this peptide (21/24). All the cells tested (n = 13) remained sensitive to gastric inflation after administration of OT. Also, OT was found to excite the majority of cells that were identified as gastric-related NTS (nine excited; one no effect) or DMN cells (eleven excited; two no effect). 5. These studies support the hypothesis that central oxytocinergic neurones influence gastric motility and secretion by increasing the excitability of central vagal neurones in the NTS and DMN that are related to gastric function.

The role of the hypothalamus and dorsal vagal complex in gastrointestinal function and pathophysiology

A foregone conclusion is that central neural and endocrine control of gastrointestinal functions is based on a complex array of interconnecting brain structures, neurochemical systems, and hormonal modulators. As might be expected, a considerable degree of redundancy is seen not only in the manner in which certain brain structures appear to participate in the regulation of GI functions, but also in the extent to which certain neurotransmitters or brain-gut peptides, when injected centrally, alter these functions. Despite the seemingly ambiguous nature of brain-gut interactions, a picture is beginning to unfold that suggests that GI properties are based on certain reflexes (e.g., vago-vagal). These reflexes, in turn, appear to be influenced by brain structures in a hierarchical manner, not all that dissimilar to the system described by Papez and expanded on by MacLean several years ago. For example, the perceptual or cognitive aspects of both external and internal stimuli are monitored at various brain levels, but obviously higher cortical processes are intimately involved. Aversive events provide sensory information, which is integrated primarily by the limbic system (e.g., amygdala) and translated into the expression of emotional behavior and associated autonomic response patterns. Various hypothalamic structures, in turn, appear most strongly to influence physiological changes associated with aversive events by virtue of the direct connections to the autonomic and endocrine systems. Ultimately, the visceral outcome can be seen as being based on the integrated convergence of information from cortical, limbic, and hypothalamic structures onto medullary nerve nuclei as well as other efferent systems. With respect to animal models of neurogenic or stress ulcer, activity of the dorsal vagal complex and vagal efferents appears to be the final common pathway for pathologic changes in the gut.

Effects of stimulation of the hypothalamic area on pancreatic exocrine secretion in dogs

The effects of electrical or chemical (0.1 M dl-homocysteic acid) stimulation of the hypothalamus on pancreatic exocrine secretion were studied in chloralose-anesthetized and hemispherectomized dogs whose pyloric sphincter had been ligated. Excitatory pancreatic flow responses with frequently increased antral contractility and small changes in blood pressure were induced by stimulation of the ventral and dorsal portions of the anterior hypothalamic area, the lateral part of the middle hypothalamus, and the mamillary body. The inhibitory pancreatic responses with reduced antral and corpus contractility and elevated blood pressure were elicited by stimulation of the posterior hypothalamic area, the middle portion of the anterior hypothalamus and the most dorsal area of the hypothalamus. Both excitatory and inhibitory responses were obtained even in dogs with cervical cord transection. The excitatory responses and some of the inhibitory ones were abolished by vagotomy or atropine, but some inhibitory responses remained even after vagotomy. These results indicate that hypothalamic stimulation induced both excitatory and inhibitory responses in pancreatic exocrine secretion via the vagus and other routes.

Profile of NE, DA and 5-HT activity shifts in medial hypothalamus perfused by 2-DG and insulin in the sated or fasted rat

This study was carried out in the unrestrained rat to determine the nature of the in vivo profile of monoamine neurotransmitters within the medial hypothalamus in response to the presence of a glucoprivic or metabolic challenge to neurons within this region. In these experiments, insulin or 2-deoxy-D-glucose (2-DG) was applied locally to the paraventricular nucleus (PVN), dorsomedial nucleus (DMN) and ventromedial hypothalamus (VMH). In each of 11 Sprague-Dawley rats, a guide cannula was implanted stereotaxically to rest just above these structures. Upon recovery, a concentric push-pull cannula system was used to perfuse an artificial CSF within a medial hypothalamic site. The CSF was perfused at a rate of 20 microliters/min with a 5.0 min interval intervening between the collection of each 100 microliters sample. After the rat was fasted for 20-22 hr, either 10 micrograms/microliters 2-DG or 4.0 mU/microliters of insulin was incorporated into the control CSF medium and perfused at the same locus. The aliquots of hypothalamic perfusate were assayed by high performance liquid chromatography with electrochemical detection (HPLC-EC) for the respective concentration in pg/microliter of norepinephrine (NE), dopamine (DA), serotonin (5-HT) and each of their major metabolic products. When the rat was sated, 2-DG enhanced significantly the mean efflux of NE from the medial hypothalamus in comparison to control CSF values. However, under the fasted condition, 2-DG augmented the turnover of both the catecholamine and 5-HT as reflected by elevated levels of MHPG and 5-HIAA, respectively. On the other hand, insulin perfused within the same medial hypothalamic sites evoked a significant increase in the synthesis and release of DA from the sated rat, but did not alter its turnover. Following the interval of fast, insulin produced no immediate alteration in transmitter activity; however, in the interval following insulin's perfusion, DA and 5-HT turnover were enhanced while the efflux of 5-HT was suppressed. An analysis of the proportional values of the levels of the amines to each other revealed marked shifts in the relationships between the catechol- and indoleamine transmitters following local perfusion with both 2-DG and insulin. Overall, NE synthesis and turnover exceeded that of 5-HT following 2-DG, whereas DA predominated over NE and 5-HT during insulin's perfusion.(ABSTRACT TRUNCATED AT 400 WORDS)

Interactions of thyrotropin-releasing hormone (TRH) with neurotensin and dopamine in the central nucleus of the amygdala during stress ulcer formation in rats

Bilateral microinjections of thyrotropin-releasing hormone (TRH; 1, 3 and 10 micrograms) into the central nucleus of the amygdala produced a dose-related aggravation of cold restraint-induced gastric ulcers in rats. TRH (10 micrograms) also induced gastric erosions in non-stressed animals. Pretreatment with atropine methyl nitrate attenuated the TRH-induced ulcers in both stress and non-stress situations. TRH (10 micrograms) also antagonized the gastric cytoprotection of intra-amygdalar neurotensin (10 micrograms) and was ineffective in altering the stress ulcer-attenuating effects of dopamine (10 micrograms). Pretreatment with i.p. clozapine, however, prevented the inhibitory effects of dopamine on the TRH-induced aggravation of the gastric stress pathology. The results suggest an interaction of TRH, neurotensin and dopamine in the central amygdalar nucleus during stress, and indicate peripheral cholinergic pathways in the mediation of the ulcerogenic effects of TRH.

Injection of neuropeptide Y into the paraventricular nucleus of the hypothalamus inhibits gastric acid secretion in the rat

Neuropeptide Y (NPY) was injected into the paraventricular nucleus (PVN) of the hypothalamus of anesthetized rats in order to assess its effect on gastric acid secretion. NPY evoked a dose-dependent decrease of interdigestive gastric acid output when injected directly into the PVN or immediately ventral to it. Intracerebroventricular NPY and saline injections did not alter acid output. Injection of NPY into adjacent non-PVN hypothalamic areas resulted in either an elevated acid output or had no effect depending on the site of injection. Mean arterial blood pressure and heart rate were not consistently affected by NPY. These results show that injection of NPY into the PVN of anesthetized rats inhibits interdigestive gastric acid output in a dose-dependent manner.

Dynamism of chemoarchitecture in the hypothalamic paraventricular nucleus

The hypothalamic paraventricular nucleus (PVN) has been implicated in a remarkable number of functions including control of pituitary-adrenocortical activity in response to stress, body fluid homeostasis, milk ejection reflex, prolactin secretion, thyroid hormone secretion, analgesia, food intake, gastrointestinal functions, cardiovascular functions, and control of pineal melatonin synthesis. Paraventricular neurons produce hormones of key importance in neuroendocrine regulation such as vasopressin (VP), oxytocin (OX), 41-residue corticotropin releasing factor (CRF), thyrotropin releasing hormone (TRH), somatostatin (SOM) and the putative prolactin releasing factor vasoactive intestinal polypeptide (VIP). Three recent advances pertinent to the organization of the PVN include: (1) the evidence that the structure of the PVN is compartmental in nature, topographically segregated cellular units seem to carry out different functions; (2) the discovery that paraventricular neurons are capable of expressing a multitude of neuromediators simultaneously, thus cellular units can be best specified by a certain combination of neuromediators; (3) evidence that the composition of the neuromediator "cocktail" in individual neurons is variable and depends on the physiological status of the animal. Hence, the PVN may be best considered as a dynamic mosaic of chemically specified subgroups of neurons. The flexibility of neurotransmitter status in paraventricular neurons may play a central role of a functional plasticity of fixed anatomical circuits.

Direct connections between the central nucleus of the amygdala and the nucleus of the solitary tract: an electrophysiological study in the rat

Reciprocal connections between the central nucleus of the amygdala (CNA) and the nucleus of the solitary tract (NST) have been implied from anatomical studies in the rat and physiological studies in other species. Our work supports this conclusion in that microstimulation of the NST caused both antidromic and orthodromic activation of neurons in the CNA. The distribution of CNA neurons activated by NST stimulation suggests that the dorsomedial portion of the CNA provides input to the dorsal medulla while the ventrolateral CNA receives input from the NST.

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.

Central control of gastric acid secretion by extralateralhypothalamic nuclei

Whether secretion of gastric acid (GAS) is in response to peripheral and/or central administration of chemical or electrical stimuli can be differentiated by vagotomy. GAS has been shown to be controlled by specific lateral hypothalamic (LHA) neurons. Application of 2-deoxy-D-glucose (2-DG) or insulin to the LHA by microinjection or iontophoresis has experimentally induced GAS. The paraventricular nucleus (PVN) has now been found to also affect GAS. GAS was produced more copiously and more quickly by rostral PVN lesion than by lesion of the ventromedial (VMH) or dorsomedial (DMH) nucleus, and nearly as much by caudal PVN lesion. Microinjection of 2-DG into the LHA induced GAS more potently in animals with rostral PVN lesions than in those with caudal PVN, VMH or DMH lesions, or in intact animals. Results indicate that the PVN may be an additional central site from which GAS is affected.

The peptidergic brain-gut axis: influence on gastric ulcer formation

The existence of a relationship between the brain and the formation of gastric ulcers has been suspected since the last century. The advancement of stereotaxic procedures and the use of electrical lesion or stimulation have allowed localization within the limbic system, hypothalamus and brain stem, of discrete nuclei that influence the formation of gastric ulceration in experimental animals. Recently, further progress in the understanding of how the brain may influence gastric pathogenesis has been made by the demonstration that specific peptides act in the central nervous system to induce or prevent the formation of gastric ulcers and to markedly alter gastric secretory and motor function. Peptides established to have a centrally mediated protective effect are bombesin, calcitonin, corticotropin-releasing factor, neurotensin and opioid peptides. Growing evidence suggests a possible role for endogenous thyroptropin-releasing hormone in mediating cold-restraint stress induced gastric lesions. Circadian variations of the content and release of these peptides have been demonstrated in specific brain structures. To what extent such rhythms of peptide secretion are potentially linked to the circadian changes in the susceptibility to ulcer formation is worth investigating.

Hypothalamic paraventricular nucleus stimulation-induced gastric acid secretion and bradycardia suppressed by oxytocin antagonist

Unilateral microstimulation of the medial parvocellular division of the hypothalamic paraventricular nucleus (PVNmp) elicits significant increases in gastric acid secretion and bradycardia. An injection of 25 picomoles of the oxytocin antagonist dET2Tyr(Et)Orn8 Vasotocin (ETOV), suspended in 5 nanoliters of artificial of cerebrospinal fluid (CSF), into the dorsal motor nucleus of the vagus (DMN) immediately preceding microstimulation of the PVNmp suppresses this change in gastric acid secretion and heart rate. The injection of an equal volume (5 nanoliters) of artificial CSF vehicle solution into this region of the DMN, prior to PVNmp microstimulation, has no effect on either the subsequent stimulation-evoked changes in acid secretion or cardiac activity. This suppression of PVNmp stimulation-evoked changes in gastric acid levels and heart rate by the presence of the oxytocin antagonist, ETOV, within the DMN supports the hypothesis that oxytocin may be a neurotransmitter used for descending communication from the PVNmp to neurons within the DMN that regulates these two functions.

Gastric-vagal solitary neurons excited by paraventricular nucleus microstimulation

Electrophysiological studies were performed to determine whether neurons of the nucleus of the solitary tract (NST) which receive sensory input from the stomach via vagal afferents are activated by microstimulation of the medial parvocellular division of the paraventricular nucleus of the hypothalamus (PVHmp). We found that 37% of the NST neurons orthodromically activated by gastric vagal nerve stimulation are also orthodromically excited by PVHmp microstimulation. Not only do these NST neurons receive convergent input from the PVHmp as well as gastric afferent input (vagal), but this input from the PVHmp may also bias the responsiveness of these NST neurons to incoming afferent information. This PVHmp influence on NST excitability is probably mediated by a direct, monosynaptic projection between these two nuclei. These data support the hypothesis that neurons in the PVHmp can control gastric function by altering the sensitivity of neurons which form the sensory limb of gastric vago-vagal reflexes. This ability of the PVHmp to bias the responsiveness of NST neurons to incoming vagal afferent information is probably mediated by a direct, monosynaptic projection between these two nuclei.

Dorsal medullary oxytocin, vasopressin, oxytocin antagonist, and TRH effects on gastric acid secretion and heart rate

Injections of oxytocin and TRH (11 picomoles), centered on the dorsal motor nucleus of the vagus, substantially increased gastric acid secretion. Additionally, oxytocin, but not TRH, simultaneously produced a consistent reduction in heart rate. Vasopressin injected into the same locus, at doses of 11 and 110 picomoles, had no effect on either function. Both the gastric and cardiac effects of oxytocin were eliminated by the central injections of oxytocin antagonist dEt2Tyr(Et)Orn8Vasotocin (ETOV; 6 picomoles) or peripheral administration of atropine (300 micrograms/kg, IP). Application of oxytocin or TRH to the area postrema, at double the dosage (22 picomoles) yielded no consistent effects on either gastric secretion or heart rate. These findings indicate that oxytocin in the dorsal motor nucleus of the vagus may act as a regulator of vagally-mediated gastric and cardiovascular functions while TRH effects, in this medullary area, seem limited to the regulation of gastric function.