Recent studies of the central nucleus of the amygdala and stress ulcers

Increasing Aspartoacylase in the Central Amygdala: The Common Mechanism of Gastroprotective Effects of Monoamine-Based Antidepressants Against Stress

Monoamine-based antidepressants can prophylactically protect against stress-induced gastric ulcers. Although the central nucleus of amygdala (CeA) has been shown to modulate the severity of stress ulcers, little is known about the molecular mechanisms underlying the gastroprotective effect of this kind of drugs. Here, we first used proton magnetic resonance spectroscopy, a non-invasive tool, to explore the change of neurometabolites of the CeA of rats pretreated with the duloxetine of selective serotonin-norepinephrine reuptake inhibitors during 6 h of water-immersion restraint stress (WIRS). Duloxetine decreased N-acetyl-aspartate/creatine ratio (NAA/creatine) in CeA after WIRS, which was paralleled by the amelioration of gastric lesions. Meanwhile, the gastric ulcer index was negatively correlated with reduced NAA/creatine. Furthermore, the intra-CeA infusion of NAA aggravated WIRS-induced gastric mucosa damage, which suggested the crucial role of reduced NAA. Western blotting was performed to identify the specific enzymes responsible for the change of the contents of NAA at 0.5 h/3 h/6 h after WIRS, considering the preventative gastric protection of duloxetine. The NAA-catabolizing enzyme aspartoacylase (ASPA) was the only enzyme downregulated by 0.5 h WIRS and upregulated by duloxetine. Moreover, overexpressing ASPA in CeA alleviated stress ulcers. Additionally, all of the other three monoamine-based antidepressants, the fluoxetine of selective serotonin reuptake inhibitors, the amitriptyline of tricyclic agents, and the moclobemide of MAOs, increased ASPA expression in CeA. Together, these results indicate that increasing ASPA to hydrolyze NAA in CeA is a common mechanism of gastroprotective effects against stress exerted by monoamine-based antidepressants, and ASPA is a shared target more than monoamine regulation for this kind of drugs.

Cytoprotective gastric pentadecapeptide BPC 157 resolves major vessel occlusion disturbances, ischemia-reperfusion injury following Pringle maneuver, and Budd-Chiari syndrome

The stable gastric pentadecapeptide BPC 157 counteracts various venous occlusion-induced syndromes. Summarized are all these arguments, in the Robert’s cytoprotection concept, to substantiate the resolution of different major vessel occlusion disturbances, in particular ischemia-reperfusion injury following the Pringle maneuver and Budd-Chiari syndrome, which was obtained by BPC 157 therapy. Conceptually, there is a new point, namely, endothelium maintenance to epithelium maintenance (the recruitment of collateral blood vessels to compensate for vessel occlusion and reestablish blood flow or bypass the occluded or ruptured vessel). In this paper, we summarize the evidence of the native cytoprotective gastric pentadecapeptide BPC 157, which is stable in the human gastric juice, is a membrane stabilizer and counteracts gut-leaky syndrome. As a particular target, it is distinctive from the standard peptide growth factors, involving particular molecular pathways and controlling VEGF and NO pathways. In the early 1990s, BPC 157 appeared as a late outbreak of the Robert’s and Szabo’s cytoprotection-organoprotection concept, like the previous theoretical/practical breakthrough in the 1980s and the brain-gut axis and gut-brain axis. As the time went on, with its reported effects, it is likely most useful theory practical implementation and justification. Meantime, several reviews suggest that BPC 157, which does not have a lethal dose, has profound cytoprotective activity, used to be demonstrated in ulcerative colitis and multiple sclerosis trials. Likely, it may bring the theory to practical application, starting with the initial argument, no degradation in human gastric juice for more than 24 h, and thereby, the therapeutic effectiveness (including via a therapeutic per-oral regimen) and pleiotropic beneficial effects.

Effect of Electroacupuncture on the Activity of Corticotrophin-Releasing Hormone Neurons in the Hypothalamus and Amygdala in Rats Exposed to Restraint Water-Immersion Stress

Objective

To investigate the effects of electroacupuncture (EA) treatment on gastric mucosal lesions and the activity of corticotrophin-releasing hormone (CRH) neurons in the paraventricular nucleus (PVN) of the hypothalamus and the central nucleus of the amygdala (CNA) in a rat model of restraint water-immersion stress (RWIS).

Methods

24 male Wistar rats were randomly divided into three groups: normal, RWIS, and RWIS+EA (n=8 per group). Rats in the RWIS group and RWIS+EA group received RWIS for 3 hours. For rats in the RWIS+EA group, EA was applied at ST36 in the bilateral hind legs for 30 min before RWIS. Rats in the normal group did not receive stressors or EA treatment. The gastric mucosal lesions of each rat were evaluated by the erosion index (EI) according to the methods of Guth. The activity of CRH neurons in the PVN and CNA was measured by a dual immunohistochemical test for Fos and CRH in the brain sections.

Results

RWIS induced serious gastric mucosal lesions. The mean gastric EI was significantly decreased in the RWIS+EA group versus the RWIS group (P=0.005). Stress induced significant activation of CRH neurons in the PVN and CNA compared with the normal group (P<0.001 for both). The mean number of Fos+CRH immunoreactive neurons in the PVN and CNA were both decreased inRWIS+EA versusRWIS groups (P<0.001 and P=0.001).

Conclusions

EA at ST36 can ameliorate RWIS-induced gastric mucosal lesions and suppress the Fos expression of CRH neurons in the PVN and CNA, suggesting a potentially therapeutic role for EA in stress-related gastric disorders.

Altered Neuronal Activity in the Central Nucleus of the Amygdala Induced by Restraint Water-Immersion Stress in Rats

Restraint water-immersion stress (RWIS), a compound stress model, has been widely used to induce acute gastric ulceration in rats. A wealth of evidence suggests that the central nucleus of the amygdala (CEA) is a focal region for mediating the biological response to stress. Different stressors induce distinct alterations of neuronal activity in the CEA; however, few studies have reported the characteristics of CEA neuronal activity induced by RWIS. Therefore, we explored this issue using immunohistochemistry and in vivo extracellular single-unit recording. Our results showed that RWIS and restraint stress (RS) differentially changed the c-Fos expression and firing properties of neurons in the medial CEA. In addition, RWIS, but not RS, induced the activation of corticotropin-releasing hormone neurons in the CEA. These findings suggested that specific neuronal activation in the CEA is involved in the formation of RWIS-induced gastric ulcers. This study also provides a possible theoretical explanation for the different gastric dysfunctions induced by different stressors.

Central nervous system control of gastrointestinal motility and secretion and modulation of gastrointestinal functions

Although the gastrointestinal (GI) tract possesses intrinsic neural plexuses that allow a significant degree of autonomy over GI functions, the central nervous system (CNS) provides extrinsic neural inputs that regulate, modulate, and control these functions. While the intestines are capable of functioning in the absence of extrinsic inputs, the stomach and esophagus are much more dependent upon extrinsic neural inputs, particularly from parasympathetic and sympathetic pathways. The sympathetic nervous system exerts a predominantly inhibitory effect upon GI muscle and provides a tonic inhibitory influence over mucosal secretion while, at the same time, regulates GI blood flow via neurally mediated vasoconstriction. The parasympathetic nervous system, in contrast, exerts both excitatory and inhibitory control over gastric and intestinal tone and motility. Although GI functions are controlled by the autonomic nervous system and occur, by and large, independently of conscious perception, it is clear that the higher CNS centers influence homeostatic control as well as cognitive and behavioral functions. This review will describe the basic neural circuitry of extrinsic inputs to the GI tract as well as the major CNS nuclei that innervate and modulate the activity of these pathways. The role of CNS-centered reflexes in the regulation of GI functions will be discussed as will modulation of these reflexes under both physiological and pathophysiological conditions. Finally, future directions within the field will be discussed in terms of important questions that remain to be resolved and advances in technology that may help provide these answers.

Local protective effects of oral 45S5 bioactive glass on gastric ulcers in experimental animals

Bioactive glass has been shown to stimulate bone regeneration and soft tissue healing. In this study, we evaluated the local protective effects of bioactive glass on experimental gastric ulcers, in comparison with omeprazole and hydrotalcite. Single and multiple gavage of 45S5 bioactive glass dose-dependently protected stress ulcers in mice and chronic ulcers in rats. Multi-daily gavage of bioactive glass for 7 days prevented chronic ulcer recurrence by 50 %. Bioactive glass ionic dissolution produced marked proliferation of ethanol-injured GES-1 human gastric mucosa epithelial cells 48 and 72 h after exposure. Bioactive glass was shown to be hardly absorbed after single or multi-daily gavage. This study, for the first time, demonstrates that bioactive glass is effective in protecting against gastric ulcers, with its high efficacy comparable to omeprazole and superior to hydrotalcite. The lack of oral absorption makes bioactive glass a potential for treatment of peptic ulcers omitting systemic toxicity or side-effects.

c-Fos expression in the supraoptic nucleus is the most intense during different durations of restraint water-immersion stress in the rat

Restraint water-immersion stress (RWIS) can induce anxiety, hypothermia, and severe vagally-mediated gastric dysfunction. The present work explored the effects of different durations of RWIS on neuronal activities of the forebrain by c-Fos expression in conscious rats exposed to RWIS for 0, 30, 60, 120, or 180 min. The peak of c-Fos induction was distinct for different forebrain regions. The most intense c-Fos induction was always observed in the supraoptic nucleus (SON), and then in the hypothalamic paraventricular nucleus (PVN), posterior cortical amygdaloid nucleus (PCoA), central amygdaloid nucleus (CeA), and medial prefrontal cortex (mPFC). Moreover, body temperature was reduced to the lowest degree after 60 min of RWIS, and the gastric lesions tended to gradually worsen with the prolonging of RWIS duration. These data strongly suggest that these nuclei participate in the organismal response to RWIS to different degrees, and may be involved in the hypothermia and gastric lesions induced by RWIS.

Effects of chronic restraint stress on feeding behavior and on monoamine levels in different brain structures in rats

Monoaminergic systems are important modulators of the responses to stress. Stress may influence feeding behavior, and the involvement of monoamines in the control of food intake is well recognized. We investigated the effects induced by chronic-restraint stress, 1 h a day, for 40 days, on eating behavior and on monoamines in distinct brain structures. Increased consumption of sweet pellets, and not of peanuts, was observed. Dopamine (DA), serotonin (5-HT), and their metabolites were measured by HPLC-EC. After chronic restraint, the results observed were decreased 5-HT in hippocampus, with increased 5-HIAA/5-HT; decreased 5-HIAA levels in cortex; reduction in DA in hippocampus, and increased levels in amygdala and hypothalamus; HVA increased in cortex, as well as HVA/DA ratio, while DOPAC/DA decreased. HVA decreased in hypothalamus, as well as HVA/DA, and DOPAC/DA and HVA/DA decreased in the amygdala. These results suggest that restraint stress differentially affects the activity of central dopaminergic and serotonergic neurons, and this may be related to the effects observed in eating behavior.

The dopamine D-1 receptor antagonist SCH 23390 injected into the dorsolateral bed nucleus of the stria terminalis decreased cocaine reinforcement in the rat

The effects of bilateral intracranial injections of the D-1 dopamine receptor antagonist SCH 23390 HCl (0, 0.8, 1.6, 3.2, and 6.4 microgram total bilateral dose) administered into the dorsolateral bed nucleus of the stria terminalis (dlBNST) immediately prior to a 3 h intravenous cocaine self-administration session were examined. In addition, anatomical control injections of the most effective dose of SCH 23390 HCl (6.4 micogram) were made either 1.5 mm dorsal to the dlBNST or into the lateral ventricle. Injections directly into the dlBNST, but not those dorsal to the dlBNST or into the lateral ventricle, significantly increased the rate of cocaine self-administration within the first 20 min of the self-administration session, consistent with a partial attenuation of the reinforcing effects of cocaine under a fixed-ratio schedule of reinforcement (0.25 mg cocaine iv; fixed-ratio 5, timeout 20 s). Injections into all three sites increased cocaine self-administration across the entire 3 h session. These results suggest a role for D-1 dopamine receptors in the dlBNST in the reinforcing properties of self-administered cocaine, and also support the hypothesis that D-1 dopamine receptors in the 'extended amygdala' may play a significant role in cocaine self-administration.

Central effect of melatonin against stress-induced gastric ulcers in rats

We investigated the role of melatonin in the induction of gastric lesions induced by water immersion restraint stress or centrally administered thyrotropin-releasing hormone (TRH). Melatonin (0.1-1 ng) injected intracisternally (i.c) 30 min prior to stress dose-dependently inhibited the induction of gastric lesions by water immersion restraint stress, while 100 micrograms/kg, i.p. failed to protect the gastric mucosa. Preadministration of melatonin (1 ng, i.c.) significantly reduced (83%) the severity of gastric lesions induced by a TRH analogue (500 ng, i.c.). Serum melatonin concentrations 30 min after administration of 1 ng melatonin i.c. did not differ from those of rats receiving i.c. vehicle. These results suggest that melatonin plays a protective, anti-stress, role in the gastric mucosa via a mechanism involving the central nervous system.

The effects of the medial and cortical amygdala lesions on post-stress analgesia in rats

The role of the medial, and cortical nuclei of amygdala was studied in 54 Möll-Wistar rats under two modes of foot-shock analgesia. In all but control animals bilateral electrolytic lesions were performed. Pre- and post-stress pain reactivity were measured in the hot-plate and the tail-flick tests. The damage of the medial nucleus decreases animals' primordial pain reactivity. Four minutes of continuous foot-shock produced post-stress analgesia in all control and lesioned rats, but 20 min of regularly intermittent foot-shock failed to evoke analgesia in the lesioned rats, especially in subjects with the dorsal part of the medial nucleus injuries. The results indicate that the medial and cortical nuclei are important in regulation of the post-stress antinociceptive processes evoked only by prolonged intermittent shock action. It has been previously shown that the behaviour evoked by this stressor is related to opioid mechanisms, and modulated by the hypothalamic-pituitary-adrenocortical system. Present finding is in agreement with our concept of the dorsomedial amygdala involvement in painful and stressful stimuli processing.

Use of animal models in peptic ulcer disease

Considerable progress has been made in the understanding of the formation of gastric erosions by the use of animals. The role of gastric acid secretion in their pathogenesis has been clarified. Gastric erosions are associated with the presence of acid in the stomach and slow gastric contractions. With several different experimental procedures, the animal's body temperature falls; preventing the fall averts erosions. A fall in body temperature or exposure to cold are associated with the secretion of thyrotropin-releasing hormone (TRH), and both increased and decreased concentration of corticotropin-releasing factor (CRH) in discrete regions of rat brains. Thyrotropin-releasing hormone when injected into specific sites in the brain produces gastric erosions and increases acid secretion and slow contractions, whereas CRH has the opposite effects. One of the major sites of interaction of the two peptides is in the dorsal motor complex of the vagus nerve. Thyrotropin-releasing hormone increases serotonin (5-HT) secretion into the stomach. Serotonin counter-regulates acid secretion and slow contractions. Many other peptides injected into discrete brain sites stimulate or inhibit gastric acid secretion.

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 microgram, 1.0 microgram, 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 microgram RX 77368, 0.1% bovine serum albumin (BSA) into the central nucleus or RX 77368 (0.5 microgram, 1.0 microgram) into sites adjacent to the central nucleus. Peak responses (1.0 microgram) 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 microgram) versus rats microinjected with the vehicle or RX 77368 into sites adjacent to the central nuclei. The stimulatory effect of RX 77368 (1.0 microgram) 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.

Stress-induced activation of prefrontal cortex dopamine turnover: blockade by lesions of the amygdala

Stress consistently has been found to activate peripheral and central catecholamine systems. Dopamine (DA) turnover in the prefrontal cortex is especially sensitive to stress produced by relatively mild footshock, conditioned fear, or exposure to a novel cage. Because lesions of the central nucleus of the amygdala block the effects of both stress and fear in many experimental paradigms, the present study evaluated whether such lesions would block stress-induced increases in prefrontal dopamine turnover using either mild footshock or novelty as stressors. In Experiment 1 electrolytic lesions of the central nucleus of the amygdala attenuated the increase in the dopamine metabolite homovanillic acid (HVA) in the prefrontal cortex evaluated in post-mortem tissue normally produced by footshock. In Experiment 2 similar lesions attenuated the increase in dopamine turnover in the prefrontal cortex using a different stressor, novelty, and a different measure of dopamine turnover, DOPAC/DA ratios. These data provide further evidence for the critical role of the amygdala in stress.

Role of the central nucleus of the amygdala and bed nucleus of the stria terminalis in experimentally-induced salt appetite

The contributions of the central nucleus of the amygdala (CeA) and the bed nucleus of the stria terminalis (BST) to salt appetite were evaluated with two treatments which induce sodium chloride (NaCl) ingestion. Cumulative 3 h intakes of 2% NaCl after sodium depletion using furosemide, or subcutaneous (s.c.) injections of yohimbine (YOH), were measured in male, Sprague-Dawley rats both before and after electrolytic lesions of the CeA or the BST. Before surgery, sham-lesion and lesion groups drank equivalent amounts of 2% NaCl in response to furosemide depletion and YOH treatment. After surgery, rats with sham lesions increased their intakes of 2% NaCl following YOH while rats with CeA or BST lesions showed significant decreases. Rats with CeA or BST lesions also showed significant decreases in their intake of 2% NaCl after furosemide depletion, while intakes of the sham lesion groups remained unchanged. Lesions of either nucleus virtually eliminated 24 h need-free salt intake. Before and after surgery, all groups drank equivalent amounts of water in response to s.c. angiotensin II and to s.c. hypertonic saline, indicating the lesions specifically affected salt appetite. The results indicate that the CeA and the BST may be important sites for processing inputs mediating salt appetite.

The amygdaloid complex, corticotropin releasing factor and stress-induced gastric ulcerogenesis in rats

The amygdaloid complex and corticotropin releasing factor (CRF) are both important in stress reactions and we thus evaluated the effects of intra-amygdalar CRF on stress ulceration in rats. Bilateral micro-applications of CRF (0.05, 0.5 or 5.0 micrograms) into the central amygdala (CEA) attenuated cold restraint-induced gastric mucosal lesions in a dose-related manner. Similar gastric cytoprotective effects were seen with intra-CEA noradrenaline (NA; 3.0 micrograms), whereas the NA neurotoxin, DSP-4 (25 micrograms), or the beta-adrenoceptor antagonist, propranolol (1 microgram), aggravated stress ulcer pathology. Intra-CEA pretreatment with DSP-4 or propranolol clearly reversed the ulceroprotective effects of CRF during stress. These results indicate that the CEA is a neural substrate for CRF effects, and CRF-NA interactions in this limbic area are crucial for the regulation of stress ulcerogenesis.

Effects of amygdaloid lesions on gastric erosion formation during exposure to activity-stress

To examine the role of the amygdala in the production of gastric ulcers induced by activity-stress, electrolytic lesions were placed in the centromedial (CENT) and medial (MED) amygdaloid nuclei, as well as in the intra-amygdaloid division of the bed nucleus of the stria terminalis (BNST). As compared to sham-operated controls (CONT), gastric ulceration was attenuated in rats with CENT lesions and exacerbated in rats with lesions located in the BNST or MED. Wheel running did not differ significantly between control animals and lesioned rats, but did differ within lesioned groups. Rats with MED lesions ran more than rats with CENT or BNST lesions. Results support the view that the integrity of the centromedial amygdala is critical for the maintenance of the viscera and demonstrate that neurogenic factors contribute to the development of gastric erosions during exposure to activity-stress.

Colocalization of fos- and glucocorticoid receptor-like immunoreactivities in the rat amygdaloid complex after immobilization stress

In the present paper we demonstrate the effect of immobilization stress on c-fos-like immunoreactivity (Fos-LI) in the rat amygdaloid complex. Furthermore, since the subnuclei of the amygdaloid complex contain numerous glucocorticoid receptor-immunoreactive (GR-IR) neurons, we also studied the possible colocalization of GR- and Fos-LI ie. Fos-Lls and the action of a synthetic glucocorticoid, dexamethasone, and an anti-glucocorticoid, RU 38486, on Fos-LI. Immobilization stress caused a remarkable increase in the number of the Fos-IR neurons in all the subnuclei of the amygdaloid complex except in the lateral nucleus. The majority of Fos-IR neurons also contained GR-LI, with the highest colocalization in the central amygdaloid nucleus. A similar induction of Fos-LI after immobilization was seen in the hypothalamic paraventricular nucleus and almost all the Fos-IR neurons in this nucleus also exhibited GR-LI. Treatments with dexamethasone or RU 38486 prior to stress did not have any marked effect on Fos-LI when compared to stress alone. The present findings suggest that Fos may function as a transcriptional regulator in the amygdaloid complex after stress and affect the synthesis of neurotransmitters and receptors in the amygdaloid neurons. Since we did not observe any effect of dexamethasone or RU 38486 on Fos-LI, it is likely that glucocorticoids do not directly regulate the expression of the c-fos gene or the formation of Fos protein. In view of the fact that Fos is capable of forming a stabile complex with GR and repress the transactivational capacity of GR, Fos may inhibit the negative feedback effect of circulating glucocorticoids and thus maintain elevated plasma glucocorticoid levels in stress.

Selective activation of mesoamygdaloid dopamine neurons by conditioned stress: attenuation by diazepam

Populations of dopamine (DA) neurons in the rat brain are selectively activated by stress, and the response is attenuated by the administration of anxiolytics. Given the role of the component nuclei of the amygdaloid complex in conditioned associations, stress responses and the anxiolytic effects of benzodiazepines, we hypothesized that particular mesoamygdaloid DA projections might be especially sensitive to the effects of conditioned stress and to diazepam (DZ). We mapped the effect of a conditioned stressor on the concentration of the DA metabolite homovanillic acid (HVA) in distinct amygdaloid nuclei and other brain nuclei and areas and the effect of DZ (1 or 3 mg/kg) on the conditioned response in drug-experienced subjects. The conditioned stress paradigm resulted in significant elevations in classical indices of stress, including serum corticosterone and plasma epinephrine. Conditioned stress-induced increases in the estimated activity of DA neurons were specific for DA neurons projecting to the central, basolateral and lateral amygdaloid nuclei, and for DA projections to the dorsal septal nucleus. Conditioned stress-induced increases in the HVA concentration of responsive amygdaloid nuclei were antagonized by low, anxiolytic doses of DZ. These results indicate a role for a subset of mesoamygdaloid DA projections in transducing the impact of perceived stressors on the output of the amygdaloid complex. A role for particular amygdaloid DA projections in the formation of conditioned fear or anticipatory anxiety and its modulation by anxiolytics is also suggested.

Subtotal lesions of the amygdala: the rostral central nucleus in passive avoidance and ulceration

Rats received small bilateral electrolytic or ibotenate lesions of the rostral part of the amygdaloid central (rACE) or lateral (rAL) nuclei, or caudal part of the basolateral nuclei (cBL), or electrolytic lesions of the dorsal hippocampus (HIPP). All groups were tested in a drinking passive avoidance (PA) task that appears less sensitive to deficits in acquisition/retention or activity/spatial perception than are many other PA tasks, and more specifically sensitive to deficits in generation of fear. Consistent with this interpretation, performance in the task was facilitated, not deficient, in the HIPP group. Electrolytic lesions of rAL produced a mild deficit in PA, but ibotenate lesions did not, and neither did the more caudal lesions of the cBL groups. Ibotenate lesions of rACE did produce a deficit in PA, consistent with views of a role of this part of the amygdala in fear. Electrolytic lesions of rACE produced a very profound PA deficit and also blocked the rapid development of gastric erosions by water-restraint stress, effects that were not found with ibotenate lesions in this location. This suggests a particular contribution of fibers passing through rACE to some of the more marked effects of electrolytic lesions of rostrodorsal portions of the amygdala.

The amygdala. Emotions and gut functions

Studies are reviewed that indicate that the amygdala, and its temporal lobe pathways connecting it with entorhinal cortex and hippocampus, modulates the effects of stressful conditions on the development of gastric pathology. The amygdala integrates aversive stimulus conditions with the defensive behaviors and visceral reactions seen under such circumstances. The transmitter mechanisms for these effects include dopamine, gamma-aminobutyric acid, thyrotropin-releasing hormone, neurotensin, enkephalins, and endorphins. Recording data also show that distinct neural "signatures" in this temporal lobe region correlate with the vulnerability to stressful experiences. The efficacy of synaptic transmission, as represented by potentiation or suppression of recorded neuronal responses, is an indication of coping adjustments, ie, habituation or behavioral helplessness. Glutamate receptors in this brain region, activated by N-methyl-D-aspartate, are implicated in these behavioral strategies. It is proposed that the neurophysiology of these limbic system structures produces individual differences in stress ulcer severity.

Rat central amygdaloid nucleus projections to the bed nucleus of the stria terminalis

The projections from the central amygdaloid nucleus (Ce) to different subdivisions of the bed nucleus of the stria terminalis (BNST) were investigated using retrograde transport of fluorescent dyes. Iontophoretic injections of either Fast Blue (FB) or bisbenzimide (BB) were applied to the anterior medial, posterior medial, anterior lateral and posterior lateral parts of the bed nucleus of the stria terminalis. The anterior medial BNST receives projections from caudal part of medial Ce (CeM). The posterior medial BNST receives projections specifically from the intermediate subdivision of Ce, though in some cases projections from the ventral subdivision (CeV) of Ce were seen. The anterior lateral BNST receives projections primarily from the caudal lateral Ce (CeL) as well as middle and caudal part of CeM. The posterior lateral BNST receives projection from rostral CeL as well as the CeV and lateral capsular Ce. In general, the results indicate that the major subdivisions of the BNST receive projections from Ce subdivisions having similar connections with diencephalic or brainstem cell groups. Additional evidence is presented suggesting that Ce-BNST projections are part of an extensive system of intrinsic connections linking similar groups of neurons in both the Ce and BNST as well as within Ce.

Vesicular and cytoplasmic localization of neurotensin-like immunoreactivity (NTLI) in neurons postsynaptic to terminals containing NTLI and/or tyrosine hydroxylase in the rat central nucleus of the amygdala

Neurotensin and catecholamines in the central nucleus of the amygdala (CNA) have both been implicated in the integration of autonomic responses to stress. We examined whether there might be a cellular substrate for interactions involving these putative neurotransmitters in the CNA. Sections of acrolein-fixed rat brain were processed either (1) for the ultrastructural localization of a rat antiserum against neurotensin using the peroxidase-antiperoxidase (PAP) method, or (2) for the dual localization of rat neurotensin antiserum and rabbit antiserum against the catecholamine-synthesizing enzyme, tyrosine hydroxylase (TH), using the PAP method and immunoautoradiography. The rat polyclonal antiserum against neurotensin was shown in immunoblots to recognize neuromedin N and Lys-Arg-neurotensin (LANT-6) in addition to neurotensin. In single and dual labeling studies, the neurotensin-like immunoreactivity (NTLI) was detected in perikarya and processes. The NTLI was localized predominantly to dense core vesicles in one group of perikarya and dendrites, while a second group had labeling both in dense core vesicles and more diffusely throughout the cytoplasm. Terminals also showed NTLI, particularly in association with dense core vesicles. The labeled terminals formed primarily symmetric junctions with both cell bodies and dendrites. In the dual labeling study, perikarya contained only NTLI while terminals contained TH and/or NTLI. Terminals containing TH or NTLI separately innervated cell bodies and dendrites displaying NTLI, and formed separate or convergent inputs onto unlabeled neuronal targets. Terminals colocalizing both TH and NTLI formed junctions only on unlabeled dendrites. These findings show that in the rat CNA two populations of neurons differ with respect to their distribution of NTLI, and that the output from neurons containing NTLI is modulated by direct synaptic input from terminals containing neurotensin and/or catecholamines. Release of neurotensin and catecholamines, most likely dopamine, from the same or separate terminals on common targets in the CNA may account for certain similarities in their stress-related functions.

The basolateral amygdala, dopamine and gastric stress ulcer formation in rats

Bilateral microinjections of dopamine (DA, 0.3, 3.0 or 30.0 micrograms) or the DA-agonist, bromocriptine (3.0 micrograms) into the basolateral amygdala (BLA) dose-dependently attenuated cold restraint stress (3 h at 4 degrees C)-induced gastric ulcer formation in rats. On the other hand, intra-BLA injections of the neurotoxin, 6-hydroxydopamine (10 micrograms) of the DA-antagonist, haloperidol (0.1 or 1.0 micrograms) aggravated such stress ulcer formation. All these effects were seen only when the injection sites were localized in the posterior (and not the anterior) BLA. Further, pretreatment of rats with haloperidol (0.1 micrograms) clearly antagonized the gastric cytoprotective effects of DA or bromocriptine (both at 3.0 micrograms), when both chemicals were injected in the posterior BLA. The results indicate that DA-ergic mechanisms in the posterior BLA are important for the regulation of gastric mucosal integrity during cold restraint stress.

The neurobiology of stress ulcers

We have reviewed the neurobiology of stress ulcers from animal models to potential pharmacotherapeutic mechanisms. The evidence strongly supports the hypothesis that certain stress-related gastric lesions are 'brain-driven' events which may be more effectively managed through central manipulations than by altering local, gastric factors. Recent advances in the use of anxiolytic and antidepressant drugs in the management of stress-related gastric mucosal injury further supports the contention that a brain-gut axis, which may have nervous, peptidergic and classic monoaminergic components, modulates the intricate and complicated pattern of communication between the brain and the stomach. Delineation of the precise pathways which make up this communication as well as their manipulation by various pharmacological agents will be the focus of future research endeavour.

Gastric cytoprotection by intracisternal interleukin-1 beta in the rat

The effects of intracisternal (ic) injection of recombinant interleukin-1 beta (IL-1) on absolute ethanol-induced gastric necrotic lesions were studied in conscious rats. IL-1 given ic inhibited ethanol-induced gastric lesions. The cytoprotective effect was dose dependent (ED175 ng/rat), long lasting with a maximal action when given 1-3 h prior to ethanol, blocked by ic injection of a IL-1 receptor antagonist protein (IRAP), and by intraperitoneal injection of indomethacin. IL-1, injected ic, was detected in the peripheral blood. However, IL-1 serum levels were lower after IL-1 injection ic than after ip at a dose giving equal gastric protection. These data show that ic IL-1 induces long lasting gastric protection mediated by interaction with IL-1 receptors and prostaglandin pathways at central and/or peripheral sites that remain to be localized.

Organization of peptidergic and catecholaminergic efferents from the nucleus of the solitary tract to the rat amygdala

Previous studies have focused on the role of the central nucleus of the amygdala (CeA) in cardiovascular and other amygdaloid functions. The combined retrograde tracing/immunohistochemical method was used to test for the presence of enkephalin, neurotensin, neuropeptide Y, and catecholamine neurons within the nucleus of the solitary tract that send efferents to the CeA. After injections of retrograde tracer into the CeA, retrogradely labeled neurons were observed within the caudal, medial nucleus of the solitary tract. Most CeA-projecting neurons were located ipsilaterally within the medial nucleus of the solitary tract at the level of the area postrema. Retrogradely labeled enkephalin- and neurotensin-immunoreactive neurons were found within the medial nucleus of the solitary tract at this level, while retrogradely labeled neuropeptide Y-immunoreactive neurons were found within the medial nucleus of the solitary tract rostral to the area postrema. About 60-74% of CeA-projecting cells were also immunoreactive for tyrosine hydroxylase. Approximately 9% of retrogradely neurons were phenylethanolamine-N-methyltransferase immunoreactive. The results provide evidence that within the nucleus of the solitary tract, peptidergic CeA-projecting neurons have a topographic distribution. In addition, noradrenergic neurons within the A2 group, rather than adrenergic neurons of the C2 group, provide the bulk of catecholaminergic input to the CeA from the nucleus of the solitary tract. Cell counts indicate that each of these peptides may be colocalized (to varying extents) within catecholamine-producing neurons. Also the catecholaminergic and enkephalinergic contribution to the ascending pathway from the nucleus of the solitary tract to the CeA distinguishes it neurochemically from the descending pathway. Thus, although there are afferent and efferent connections between the nucleus of the solitary tract and CeA, their peptidergic/neurotransmitter connections are not necessarily reciprocal. Input from nucleus of the solitary tract peptidergic and catecholaminergic neurons to the CeA may be important in the etiology of a number of pathophysiological conditions including hypertension, gastric ulcers, and schizophrenia.

Potentiation of inputs from the posterolateral amygdala to the dentate gyrus and resistance to stress ulcers formation in rats

Physical restraint was found to increase the activity of a number of multiple units in the lateral amygdala of rats. High-frequency electrical stimulation of units in the posterolateral amygdala increased the amplitudes of granule cell potentials in the dentate gyrus. This bilateral long-term potentiation (LTP) of inputs from posterior areas of the lateral amygdala also attenuated the severity of stress ulcers produced by physical restraint. This effect was reversed by intraventricular injections of the selective N-methyl-D-aspartate receptor blocker, aminophosphonovaleric acid. LTP in this pathway also reduced "struggling" behaviour during restraint. The data were interpreted to indicate that LTP in this temporal lobe pathway increased the coping ability because of faster habituation to stressors.

Hippocampal pathway to the amygdala and stress ulcer development

The objective of the first study was to localize the reported aggravation of stress ulcers found after large bilateral hippocampal lesions in rats. Lesions in the ventral hippocampus produced a similar increase in the severity of gastric erosions after cold-restraint, as was seen after large bilateral lesions. Dorsal hippocampal damage produced no differential effects. In the second experiment, high-frequency electrical stimulation of the ventral CA1 region of the hippocampus, a procedure known to induce long-term potentiation, increased the evoked potentials in the lateral central nucleus of the amygdala, and in adjacent parts of the lateral and basolateral nuclei. The increase in the efficacy of synaptic transmission in this pathway attenuated stress ulcer development. It was concluded that the ventral hippocampus is part of a coping system, and a strengthening of synaptic connections with the central amygdala increases the coping ability of rats under stress conditions.

Brain ACTH prevents stress gastric lesions in rats

This study evaluated the effect of ACTH and several ACTH fragments on the development of gastric glandular lesions induced by cold-restraint stress in rats. Intracerebroventricular administration of ACTH1-39 dose-dependently (0.1-10 micrograms) inhibited stress gastric lesion formation. Studies with smaller molecular weight forms of ACTH (in a dose equimolar to 10 micrograms of ACTH1-39) revealed that ACTH1-13 and ACTH1-10 were also protective. The ACTH fragments ACTH5-10, ACTH34-39 and ACTH1-17 were without effect. Immunoneutralization of endogenous brain ACTH1-39 significantly increased stress gastric lesion severity. Antisera raised against synthetic somatostatin, gonadotropin-releasing hormone, and L-enkephalin were ineffective. These results with ACTH coupled with our previous demonstration of a protective effect of beta-endorphin suggest that specific brain pro-opiomelanocortin gene products modulate gastric mucosal integrity in response to stress.

Contrasting effects of centromedial and basolateral amygdaloid lesions on stress-related responses in the rat

The effects of lesions in the centromedial and basolateral amygdala were examined using three different tests sensitive to the following stress-related responses: exploratory behavior, pain reactivity, and immune responses. The most clear-cut results were found with exploratory behavior. Rats with lesions of the centromedial amygdala tended to explore a radial-arm maze more quickly and entered more novel arms of the maze than controls. Those with lesions of the basolateral amygdala were generally too hesitant to explore at all. No significant differences were found between groups on measurements of natural killer cell activity. In tests of pain perception, rats in the control group displayed an analgesic response on the hot plate following an injection of the anxiogenic drug, RO 15-1788, whereas rats with centromedial lesions tended to exhibit a blunted response. These findings provide modest support for the view that the central and lateral regions of the amygdala play complementary roles in aversively motivated behaviors and in stress-related response patterns.

The central amygdala is involved in the conditioned but not in the meal-induced cephalic insulin response in the rat

The central nucleus of the amygdala (CEA) is considered to be involved in the regulation of autonomic correlates of fear. Its involvement in the control of autonomic functions other than elicited by fear has received little attention. The effects of a bilateral electrolytical lesion of the CEA on feeding related insulin responses have been analyzed in male Wistar rats. The cephalic phase of the insulin response is a vagally mediated elevation of plasma insulin concentration during the first minute after meal onset, before any increase in plasma glucose can be noticed. This response can also be entrained to environmental stimuli. The insulin response elicited under these conditions is due to conditioning. CEA lesioning abolished the conditioned insulin response but not the early insulin elevation during the presentation of food. The CEA lesion failed to affect plasma glucose levels in both the meal-induced and conditioned test situations. To our knowledge this is the first study that shows that the CEA is also involved in the organization of conditioned metabolic endocrine responses.

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 intra-amygdalar thyrotropin releasing hormone (TRH) and its antagonism by atropine and benzodiazepines during stress ulcer formation in rats

Bilateral intra-amygdalar (i/am) microinjections of TRH (1 and 10 micrograms) and physostigmine (10 micrograms) into the central nucleus (CEA) aggravated cold restraint stress (3 hr at 4 degrees C) induced gastric ulcer formation in rats, whereas atropine (1, 5 and 10 micrograms) attenuated this phenomenon. Similar stress ulcer reducing effects were seen with chlordiazepoxide (CDP, 10 mg/kg, IP) and midazolam (1, 3 and 10 micrograms, i/am). Pretreatment of rats with atropine or CDP antagonized the ulcerogenic effects of both TRH and physostigmine. Further, when administered intra-CEA, midazolam neutralized the effects of TRH in a dose-related manner. These results are discussed in light of TRH-acetylcholine-benzodiazepine/GABA interactions within the amygdaloid complex during stress ulcer formation.

Administration of thyrotropin-releasing hormone into the central nucleus of the amygdala induces gastric lesions in rats

Studies utilizing microinjections of thyrotropin-releasing hormone (TRH) were performed to determine potentially sensitive limbic brain sites to the ulcerogenic effect of TRH. Administration of TRH into the central nucleus of the amygdala (CEA) produced a high (80%) incidence of gastric lesions and also significantly stimulated acid secretion. Microinjections of TRH into other brain sites including superior colliculus, medial septum, substantia nigra and the hippocampus (CA1 area) were ineffective. Intra-CEA TRH-induced gastric lesions and acid secretion were prevented by vagotomy. These results indicate that the amygdala is of importance for mediating the ulcerogenic effect of brain TRH through peripheral vagal pathways.

Localization of DARPP-32 immunoreactive neurons in the bed nucleus of the stria terminalis and central nucleus of the amygdala: co-distribution with axons containing tyrosine hydroxylase, vasoactive intestinal polypeptide, and calcitonin gene-related peptide

The distribution and morphology of neurons containing the dopamine- and cyclic AMP-regulated phosphoprotein, DARPP-32, were investigated in the bed nucleus of the stria terminalis (BST) and the central nucleus of the amygdala (CeA). DARPP-32 immunoreactive neurons are numerous in both regions, but are restricted to the lateral dorsal and the lateral juxtacapsular subdivisions of the BST, and the central lateral and lateral capsular subdivisions of the CeA. Immunoreactive neurons in the lateral dorsal BST, and the central lateral and lateral capsular CeA are similar morphologically, while those in the juxtacapsular BST appear to be a subpopulation of striatal medium-sized spiny neurons. The distribution of DARPP-32 immunoreactive neurons in the BST and CeA overlaps considerably with axonal plexuses containing tyrosine hydroxylase (TH), vasoactive intestinal polypeptide (VIP), and calcitonin gene-related peptide (CGRP). These studies provide further evidence of the close relationship between the CeA and BST, and also provide anatomical evidence for possible interactions between neurotransmitters, neuropeptides, and phosphoproteins.

Granule cell potentials in the dentate gyrus of the hippocampus: coping behavior and stress ulcers in rats

Evoked population potentials of the granule cells in the dentate gyrus of the hippocampus were increased in stress-resistant rats and decreased in stress-susceptible rats, as indexed by restraint-induced gastric ulcers. Inescapable, uncontrollable shock stimulation also suppressed granule cell population spikes and interfered with subsequent coping responses when escape was possible, i.e. the so-called helplessness effect. The data were interpreted to indicate that the hippocampus is part of a coping system in stressful situations.

Synaptic efficacy in the entorhinal-dentate pathway and stress ulcers in rats

High-frequency electrical stimulation in the entorhinal-dentate pathway of male Wistar rats was found to increase the amplitudes of the population spikes recorded from granule cells located in the dentate gyrus of the hippocampal formation. This increase in synaptic efficacy attenuated the gastric ulceration produced by cold restraint. It was suggested that this limbic system structure modulates the ability to cope with environmental demands.

The GABA/benzodiazepine receptor complex in the central amygdalar nucleus and stress ulcers in rats

The effects of bilateral microinjections of chlordiazepoxide and GABA into the central amygdalar nucleus on gastric ulcer formation induced by cold-restraint were examined in chronically implanted Wistar rats. Higher doses of chlordiazepoxide (20 and 30 micrograms/amygdala) significantly reduced stress ulcer development, whereas a lower dose (2.5 micrograms) produced a nonsignificant increase in ulcer severity. A similar dose/response pattern was observed following GABA administration. The benzodiazepine receptor antagonist Ro15-1788, applied to the amygdala, abolished the protective effects of both chlordiazepoxide and GABA. In addition, when Ro15-1788 (10 micrograms) was injected into the amygdala by itself, it aggravated the gastric stress pathology. However, a lower dose (5 micrograms) had an attenuating effect, opposite to the pattern of effects produced by chlordiazepoxide and GABA. The role of the amygdalar GABA-benzodiazepine receptor complex in stressful conditions is discussed.