The hypothalamus-amygdala axis and experimental gastric ulcers

Comparative study of perturbations of peripheral markers in different stressors in rats

Stress has been implicated in the etiopathogenesis of several diseases. In the present study, the effects of acute (AS), chronic (CS), and chronic unpredictable stress (CUS) were studied on the ulcer index, adrenal gland mass, and biochemical and hormonal changes in rats. The stress was provided in the form of immobilization-immobilization for 150 min, once only, and for 10 consecutive days in CS and CUS. In CUS, animals received variable unpredictable stressors. Immediately after stress, animals were decapitated, blood was collected, and plasma was separated for the estimation of plasma glucose, triglyceride, cholesterol, creatine kinase (CK), corticosterone, and insulin. The adrenal gland and stomach were also dissected for mass and ulcer scoring, respectively. AS significantly increased the ulcer index, plasma glucose, CK, corticosterone, and insulin. CS and CUS significantly increased the ulcer index, adrenal gland mass, and corticosterone. In CS, a significant decrease in plasma triglyceride and cholesterol levels was found, but in CUS only cholesterol was decreased significantly. High CK activity and hyperglycemia maintain the energy demands of metabolism, and elevated corticosterone desensitizes the insulin receptor in AS. In CS and CUS, prolonged elevation of corticosterone shifts metabolism to utilization of lipids as a secondary substrate by gluconeogenesis. From our experiment, it is clear that AS causes maximum activation of energy metabolism, which becomes specific after habituation in prolonged CS. These biochemical manipulations in the body by using different types of stressors are good markers that can be of great use to understand, target, and manage stress-induced etiologies.

Antiulcer activity of Utleria salicifolia rhizome extract

The effect of 50% ethanolic extract of Utleria salicifolia (USE) was assessed in different acute and chronic gastric ulcer models in rats. USE, 50-200 mg/kg administered orally, twice daily for 5 days showed dose-dependent ulcer protective effect in pylorus ligation (14.48-51.03% protection, P < 0.5 to P < 0.01), aspirin (28.80-56.52% protection, P < 0.5 to P < 0.001), ethanol (13.22-60.74% protection, P < 0.5 to P < 0.001), cold-restraint stress (21.22-77.14% protection, P < 0.05 to P < 0.001), and acetic acid (20.0-84.37% protection, P < 0.5 to P < 0.001)-induced acute and chronic ulcers. USE also significantly (P < 0.001) reduced the ulcer incidence (50 and 10%) and severity (67.83 and 91.34% protection) of duodenal ulcer, induced by cysteamine. Besides USE offered protection (53.52 and 60.58%) against ethanol-induced depletion of gastric wall mucus. However, USE reduced the ulcer index with significant decrease in plasma corticosterone (25.53 and 39.52% protection, P < 0.1 and P < 0.05), lipid peroxidation (18.75 and 47.92% protection, P < 0.01 and P < 0.001), superoxide dismutase (15.80 and 26.61% protection, P < 0.05 and P < 0.001) and increased in catalase (28.42 and 71.0% protection, P < 0.05 and P < 0.001) activity, respectively. Preliminary phytochemical screening of the USE gave the positive test for steroids, alkaloids, terpenoids, saponins and tannins. The HPTLC studies in the toluene: ethyl acetate: formic acid and the densitometric scanning at 254 nm gave three major spots with area corresponding to 28.16, 17.17, and 13.79% at 0.69, 0.78, and 0.88 R(f) values, respectively. The results indicate that USE possesses antiulcer activity.

The role of paraventricular nucleus of hypothalamus in stress-ulcer formation in rats

The rat stress model of restraint and cold water immersion was used to investigate the effect of stimulating the paraventricular nucleus (PVN) of hypothalamus on the development of stress-induced gastric ulceration. The results were (1) electric stimulation of the PVN increased the stress ulceration, while electrolytic lesion of the PVN decreased it; (2) intracerebroventricular injection (i.c.v.) of acetylcholine (Ach) enhanced the effect of PVN stimulation on stress ulcers, and the M-receptor was involved; (3) i.c.v. norepinephrine (NE) attenuated the effect of PVN stimulation on stress ulcers in a dose-dependent manner, and the beta-receptor was involved; (4) i.c.v. 5-hydroxytryptamine (5-HT) enhanced the effect of PVN stimulation on stress ulcers; (5) electrolytic lesions of dorsal raphe nucleus (DR) attenuated the effect of PVN stimulation on stress ulcers, while electrolytic lesions of the locus ceruleus (LC) aggravated the effect; (6) thyroidectomy, adrenalectomy, ovariectomy, vagotomy and sympathectomy all attenuated the effect of PVN stimulation on stress ulcers; (7) electric stimulation of the PVN produced no effect on gastric juice volume, acidity, total acid output, pepsin activity or the gastric barrier mucus; but greatly reduced gastric mucosal blood flow. These results indicate that the PVN is an important brain site regulating the development of stress-induced gastric ulcers, that the classical neurotransmitters Ach, NE and 5-HT are involved, and that in the periphery, both the parasympathetic and sympathetic nervous systems and the three endocrine glands (thyroid, adrenal and gonad) take part in the effect.

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.

Role of dopaminergic mechanisms in the regulation of stress responses in experimental animals

The effects of some dopaminergic agents were evaluated on stress responses in normal and immunized experimental animals. Restraint stress (RS) consistently induced gastric mucosal lesions and elevated plasma corticosterone in rats. Pretreatment with alpha-methyltyrosine (alpha-MT), haloperidol, or sulpiride aggravated both responses, whereas bromocriptine attenuated them. In rats immunized with sheep red blood cells (SRBCs), RS prevented the booster-induced rise in anti-SRBC antibody titre. This response was further suppressed by alpha-MT, haloperidol, or sulpiride pretreatment, whereas bromocriptine potentiated the humoral immune response. In mice immunized with SRBCs, antigen challenge-induced increase in footpad thickness was inhibited by RS. Similar inhibitions in this response were also seen after alpha-MT or haloperidol treatment. The results are discussed in light of complex dopaminergic mechanisms in the regulation of visceral, endocrinological, and immune responses during stress.

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.

Vulnerability to stress ulcerogenesis in rats differing in anxiety: a dopaminergic correlate

Dopamine and its agonists, acting through D1/DA1 receptors, have been shown to be effective protective factors against stress ulcerogenesis. Since anxiety has been related to stress ulcer development, we chose to examine dopaminergic activity in rats screened for the extremes of behaviorally manifest anxiety. High anxious rats develop more stress ulcers and more ethanol ulcers, relative to low anxious animals. High anxious rats require greater amounts of dopaminergic agonists for 50% protection against stress ulcer formation. In conditions of exposure to a stressor, high anxious rats lose amygdalar dopamine at a faster rate than do low anxious rats. These results suggest that anxiety is a significant factor in stress ulcer development and that central dopaminergic function is critically involved in mediating this pathogenetic factor.

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.

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.

Role of histaminergic mechanisms in the regulation of some stress responses in rats

The involvement of histaminergic mechanisms in the regulation of some stress responses was studied in rats. The brain neuronal histamine (HA) depletor, alpha-fluoromethyl histidine (alpha-FMH), at doses (50 or 100 mg/kg) which markedly lower brain HA, significantly attenuated the gastric ulcer formation and the elevation in plasma corticosterone in response to cold restraint stress (CRS). alpha-FMH also appreciably reduced gastric mucosal HA content. The H1-antagonist, pheniramine (25 mg/kg), attenuated both the gastric mucosal and endocrine response to CRS, while the effects of the H2-antagonist, cimetidine (200 mg/kg), were on the plasma corticosterone levels. These results are discussed in light of complex HA-ergic mechanisms in the maintenance of physiological homeostasis during stress.

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.

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

Studies are reviewed which indicate that the multiple-unit activity of the central nucleus of the amygdala differentiates stress-susceptible from stress-resistant rats, highly emotional from less emotional animals, and genetically-selected Roman High-Avoidance and Low-Avoidance rats. Kindling of this region increases the susceptibility to stress ulcer formation. Dopamine, neurotensin, and the endogenous opiates in the central nucleus are cytoprotective, whereas thyrotropin-releasing hormone aggravates the stress pathology. It is suggested that the amygdala codes the stressfulness of aversive inputs, the central nucleus being the point of output to areas controlling visceral responses to such information.

Effects of intra-amygdalar dopamine agonists and antagonists on gastric stress lesions in rats

Microinjections of dopamine (DA, 3 and 30 micrograms) or its agonist apomorphine (3 micrograms) into the central amygdala (CEA) attenuated cold restraint (3 h at 4 degrees C)-induced gastric ulcer formation in rats. Pretreatment with DA antagonists, haloperidol and metoclopramide (both i.p. and intra-amygdalar) reversed the stress ulcer attenuating effect of DA. It is suggested that the CEA is one of the central sites for this DA cytoprotection and that D2 receptors are possibly involved in this effect.

Central dopamine systems and gastric stress pathology in rats

Acute treatments with haloperidol (1 mg/kg), clozapine (10 mg/kg) and metoclopramide (10 mg/kg) significantly facilitated cold-restraint-induced gastric ulcer formation in rats. In addition, haloperidol and clozapine also produced gastric mucosal erosions in non-stressed rats. Bilateral lesions of the ventral tegmental area (VTA) and substantia nigra also aggravated stress ulcerogenesis--VTA lesions also being effective in inducing gastric ulcers in non-stressed rats. Long-term treatment with dopaminergic blockers showed variable effects. Clozapine potentiated the gastric stress pathology, whereas no significant facilitation was observed with haloperidol or metoclopramide. In addition, withdrawal from haloperidol did not influence the gastric ulcer formation when compared to controls. The role of central dopaminergic involvement in gastric stress pathology is discussed in light of the present results.

Restraint stress in biomedical research: a review

The use of restraint or immobilization for investigations of animal physiology, pathology and pharmacology has an extensive history. The major use of this technique has been as a "stressor" for the induction of stress response syndromes in animals. Many such syndromes have been characterized from the behavioral level to the neurochemical concomitants of stress. As a consequence of this particular use of the restraint procedure, much information concerning drug effects on stress response syndromes has been obtained. Indeed, many researchers in the area of gastrointestinal drugs routinely screen their new compounds in a restraint model of gastric stress ulcer. The purpose of this review is to present for researchers, a summary of the methods for, the parameters of, and known drug effects on, restraint-induced pathology. In our experience, this technique has proven to be a very useful one for the examination of both central and peripheral mechanisms of stress-related disorders, as well as for studying drug effects upon these disorders.

Neuroendocrine mechanisms of stress ulceration: focus on thyrotropin-releasing hormone (TRH)

It is generally accepted that stress ulceration, a multifactorial or pluricausal gastrointestinal disorder, may be the result of mechanistic interrelationships between mucosal, vascular, hormonal and neurogenic factors. The relative importance of each of these independent mechanisms remains unclear. This minireview represents an attempt to interpret many recent studies on certain neurogenic mechanisms and to integrate these observations into the existing body of knowledge. A variety of in vitro techniques and animal models to manipulate actual structures, organ systems, and certain well-defined hormonal influences have been utilized. The peripheral studies have followed, for the most part, the established observation that the stomach is under reciprocal control by sympathetic inhibitory and parasympathetic excitatory autonomic fibers. As a result, several autonomic adrenergic neurotransmitter substances have been found to promote mucosal resistance. Some of these include dopamine, epinephrine, and norepinephrine. Others in contrast, appear to promote vulnerability of the mucosa, and of these, the most well-studied include acetylcholine and histamine.

Electrical stimulation of the medial forebrain bundle-posterior lateral hypothalamus attenuates gastric lesions

The major purpose of Experiment 1 was to see if electrical stimulation of the brain in an area that supports self-stimulation can act during stress to attenuate the severity of gastric lesions produced by six hours of tailshock and restraint. It was found that rats receiving electrical stimulation of the medial forebrain bundle-posterior lateral hypothalamus had significantly less gastric pathology than control subjects not receiving stimulation. Further experiments sought to examine characteristics of the stimulation that would account for this finding. Experiments 2 and 3 studied signal and analgesic properties, respectively, of the brain stimulation, but did not find evidence for their involvement in the effect.

Some behavioral factors related to the effects of cold-restraint stress in rats: a factor analytic-multiple regression approach

Recently, some individual differences in rats have been shown to be related to stress-induced physiological responses. As yet there has been no attempt to incorporate measurement techniques from the psychometric field to this line of research. The present study was conducted to examine the utility of applying such methods to animal research. Physiological responses to cold-restraint stress in 26 male rats were investigated using a factor analytic-multiple regression procedure. Nineteen behavioral and physiological measures obtained during open-field testing, motor activity monitoring, and passive avoidance learning were subjected to a principle components factor analysis. Five factors were extracted which reflected exploratory behavior, general activity level, metabolic rate, behavioral reactivity, and autonomic reactivity. The obtained factor scores were used to predict physiological responses to four hours of supine cold-restraint using a step-wise multiple regression procedure. General activity level was the best predictor of adrenal weight and temperature loss. Autonomic reactivity was the best predictor of ulcer incidence and severity. Applications of these statistical procedures are discussed.

The bed nucleus of the stria terminalis and immobilization-stress: unit activity, escape behaviour, and gastric pathology in rats

Multiple unit-activity in the bed nucleus of the stria terminalis was increased or decreased, relative to baselines, during physical restraint in rats. Changes in unit-activity were also obtained by presenting an auditory stimulus that had been paired with the immobilization treatment. The animals escaped from that stimulus in behavioural tests, and bilateral lesions in the bed nucleus reduced the latencies of escape responses. The lesion also increased the severity of restraint-induced mucosal erosions. The latter effect was most pronounced when the damage was in the lateral portion of the bed nucleus. It was concluded that the bed nucleus of the stria terminalis is part of a coping system which responds when the organism is placed in a stressful situation.

Effects of catecholamine agonist and antagonist drugs on acute stomach ulceration induced by medial hypothalamic lesions in rats

In order to investigate the involvement of catecholamines (CAs) in acute stomach ulceration induced by hypothalamic lesions, rats were given bilateral electrolytic anodal lesions in the medial hypothalamus followed by a single subcutaneous injection of CA agonist or antagonist drugs. As in previous studies, lesioned rats that received no post operative drug treatment showed extensive gastric damage when examined 24 hr after the brain lesion. Chlorpromazine, amphetamine, desipramine and isoproterenol caused significant reductions in the extent (total length) and/or number of erosions induced by the brain lesion. Haloperidol and propranolol did not seem to affect ulcer formation. Clozapine increased the number but not the total length of ulcers. Phentolamine, alone or in combination with propranolol, significantly increased both the number and total length of lesion-induced ulcers. Similarities between these results and those reported for most of these drugs in the context of ulcers induced by various experimental stress procedures suggest a degree of commonality between acute stress ulcers and ulcers induced by hypothalamic lesions. The overall pattern of results obtained is also consistent with evidence indicating a protective role for catecholamines in acute ulcer formation.

Mucosal damage following electrical stimulation of the anterior cingulate cortex and pretreatment with atropine and cimetidine

Bipolar electrical stimulation of a restricted area of the anterior cingulate cortex in anesthetized rats produced stomach erosions. Pretreatment with atropine sulfate prevented the pathological effects of stimulation. Cimetidine was not effective in preventing the gastric damage. It was concluded that the pathological effects of electrical stimulation were cholinergically mediated, whereas, histamine-2 receptors were not involved.

Unit-activity in the central amygdalar nucleus of rats in response to immobilization--stress

Multiple-unit activity in the central nucleus of the amygdala of rats was measured during immobilization and during presentations of a white-noise stimulus that had been paired with the restraint treatment. Results showed that some units responded with an increase, others with a decrease in firing rate during immobilization. Several units also showed "conditioned" rate changes to the auditory stimulus. A behavioral assessment of the presumed conditioned aversive properties of the stimulus showed that the rats which had experienced the pairing of restraint and the noise stimulus escaped faster when presented with the stimulus than the unpaired controls. It is suggested that the central amygdala might be part of a system in which stressful inputs influence autonomic functions.

Gastric mucosal damage induced by lateral hypothalamic lesions in rats: the potential contribution of bile

The present study was conducted to investigate the potential contribution of bile to gastric mucosal damage induced by lesions of the lateral hypothalamic area in rats. In two separate experiments it was found that (1) lateral hypothalamic lesions did not alter the rate of bile flow in the acute preparation, but (2) bile duct ligation significantly reduced the incidence of gastric mucosal damage. Based on these and previous findings it is suggested that the reflux of bile interacts with the weakened gastric mucosal barrier to elicit ulceration.

The telencephalic limbic system and experimental gastric pathology: a review

The effects of lesions and stimulations of the telencephalic limbic system on experimental gastric ulcers and erosions are reviewed. It is concluded that the centromedial amygdala and the anterior cingulate gyrus are facilitatory structures, whereas the medial prefrontal cortex, posterior cingulate cortex, entorhinal cortex, hippocampus and posterolateral amygdala are inhibitory areas during stressful experiences, e.g., immobilization. Both the centromedial amygdala and the anterior cingulate gyrus may be part of an "ancillary" pain system, mediating the affective components of aversive experiences. The inhibitory structures, on the other hand, are assumed to be part of a "preventive" mechanism which is initiated by the selective nuclear binding of glucocorticoids when under stress.

Hippocampal deafferentation and deefferentation and gastric pathology in rats

Previous studies have shown that large hippocampal lesions increase the gastric pathology found in restrained and unrestrained animals. The present experiments investigated the effects of lesions in the two major afferent and efferent pathways of the hippocampus, i.e., the dorsal pathway through the fimbria-fornix and the ventral pathway in the entorhinal region, on gastric pathology in restrained and unrestrained rats. Result demonstrated that lesions in the ventral pathway produced an increased incidence of pathology whereas lesions in the fimbria-fornix did not. Neuroanatomical pathways which may mediate these effects are described

Afferent projections to the dorsal motor nucleus of the vagus

The afferent projections to the dorsal motor nucleus of the vagus (DMN) were investigated by iontophoretically infusing horseradish peroxidase (HRP) into that neural region of the rat. After the tetramethylbenzidine histochemical procedure was performed on the HRP-injected brains, projections to the DMN from several areas were observed including the nucleus reticularis parvocellularis and gigantocellularis, the nucleus of the solitary tract, the nucleus raphe obscuris, the principal sensory trigeminal nucleus, and the paraventricular nucleus of the hypothalamus. The pathway originating in the paraventricular nucleus was the only forebrain projection to the DMN, a finding compatible with observation of other investigators.

Physiological and morphological changes in the gastrointestinal tract induced by hypothalamic intervention: an overview

Neural control and modulation of gastric secretion is well established. The role of the parasympathetic vagal system as a final motor pathway in gastric acid secretion is clearer than the involvement of the sympathetic nervous system. Both portions of the autonomic nervous system, however, appear to play an important role in the pathogenesis of at least experimentally induced gastric erosions. With respect to higher neural control there are numerous reports of hypothalamic effects on gastric secretion, motility, and morphology, yet the results of many of these reports appear equivocal. This ambiguity can be attributed in part to species differences, time course of observations, and differences in stimulation and lesion parameters. However, a mcal description of the sites of central lesions and stimulation. Implications of several of the studies concerning hypothalamic involvement in gastric functions are reviewed and recent methodological advances including neural fiber transection, relatively specific neural cell damage with neurotoxins (e.g., 6-OHDA, kainic acid), histochemistry and intracerebral infusions of gut hormones are suggested as alternative approaches to studying brain-gut relationships.