Gastrin-17 injected into the hypothalamic paraventricular nucleus can induce gastric acid secretion in rats

Effects of Exogenous Hydrogen Sulfide in the Hypothalamic Paraventricular Nucleus on Gastric Function in Rats

Background: Hydrogen sulfide (H₂S) is a new type of gas neurotransmitter discovered in recent years. It plays an important role in various physiological activities. The hypothalamus paraventricular nucleus (PVN) is an important nucleus that regulates gastric function. This study aimed to clarify the role of H₂S in the paraventricular nucleus of the hypothalamus on the gastric function of rats.

Methods: An immunofluorescence histochemistry double-labelling technique was used to determine whether cystathionine-beta-synthase (CBS) and c-Fos neurons are involved in PVN stress. Through microinjection of different concentrations of NaHS, physiological saline (PS), D-2-Amino-5-phosphonovaleric acid (D-AP5), and pyrrolidine dithiocarbamate (PDTC), we observed gastric motility and gastric acid secretion.

Results: c-Fos and CBS co-expressed the most positive neurons after 1 h of restraint and immersion, followed by 3 h, and the least was at 0 h. After injection of different concentrations of NaHS into the PVN, gastric motility and gastric acid secretion in rats were significantly inhibited and promoted, respectively (p < 0.01); however, injection of normal saline, D-AP5, and PDTC did not cause any significant change (p > 0.05). The suppressive effect of NaHS on gastrointestinal motility and the promotional effect of NaHS on gastric acid secretion could be prevented by D-AP5, a specific N-methyl-D-aspartic acid (NMDA) receptor antagonist, and PDTC, an NF-κB inhibitor.

Conclusion: There are neurons co-expressing CBS and c-Fos in the PVN, and the injection of NaHS into the PVN can inhibit gastric motility and promote gastric acid secretion in rats. This effect may be mediated by NMDA receptors and the NF-κB signalling pathway.

Extragastric effects of gastrin gene knock-out mice

Gastrin is a peptide hormone that regulates both acid secretion and growth of the gastric oxyntic mucosa. Recent studies suggest that gastrin, in both its amidated, and less processed forms (glycine-extended gastrin and progastrin) may also exert biological activity in other organs in the gastrointestinal tract. This article will review the studies performed to date addressing the physiological role of gastrin outside of the gastric mucosa, with particular emphasis on the information gleaned from gastrin-deficient mice. Most of these studies address the potential role for the less processed forms of gastrin in regulating the proliferation of the colonic mucosa and colon cancers. There is also some data to support a potential role for gastrin in the regulation of the pancreas and the kidney, although the effects of gastrin deficiency on the function of these organs in mice have not yet been rigorously studied.

Neuronal expression of Fos protein in the brain after intravenous injection of gastrin in rats

The present study examined whether the central neurons are involved in the stimulatory action of gastrin on the secretion of gastric acid. Gastrin (20 microg), which was examined and ascertained to induce a marked increase in gastric acid secretion in gastric-lumen perfused rats, was intravenously injected in Wistar rats under anesthesia with pentobarbital sodium. In the experiments, 1 h after injecting gastrin, rats were perfused and fixed, the brain was removed and sectioned at 40 microm thickness. Every fourth section was treated with anti-c-Fos antiserum, and c-Fos protein was immunohistochemically stained using the avidin-biotin complex method. It was found that c-Fos protein was expressed in neurons of the lateral habenular nucleus, the central nucleus amygdala, the lateral parabrachial nucleus in the pons, and the complex area of the nucleus of the solitary tract and the dorsal motor nucleus of the vagus nerve in the medulla oblongata. The control rats were injected with saline solution, and the brain sections were processed similarly as described above. c-Fos protein was expressed in few neurons in the nuclei above in the control rats. These results suggest that gastrin released into the circulation might stimulate central neurons which, in turn, may relate to the control mechanism for the secretion of gastric acid.

Neural discharge can be modulated by carotid arterial injection of gastrin-17 in rat hypothalamic paraventricular nucleus

Neural discharge in the hypothalamic paraventricular nucleus (PVN) was examined after gastrin-17 injection into the carotid artery in anesthetized rats. Neural discharge was increased by gastrin-17 injection into the carotid artery close to the cranium, and the response due to the gastrin was dose-dependent. No discharge response was seen when gastrin was injected into the jugular vein. These results suggest that gastrin circulating in the arterial blood can penetrate the blood brain barrier, and modulate neural PVN activity which is responsible for gastric acid secretion.

Gastric acid secretion caused by gastrin-17 injection into both sides of the hypothalamic paraventricular nucleus in rats

Gastric acid outputs were examined after gastrin-17 (gastrin) injection into either side of the hypothalamic paraventricular nucleus (PVN) or both sides of the PVN in bilaterally adrenalectomized rats. The acid output increased when 40 pM gastrin was unilaterally injected (10 s, 500 nl) into the PVN through a 28-gauge stainless steel tube. The acid output was also increased when 80 pM gastrin was iontophoretically injected (2 min, -50 nA) into the PVN through a glass tube. An additive increase in the acid output was elicited when an effective concentration of gastrin was simultaneously injected into both sides of the PVN. It was also noted that there was a significant increase in acid output when an ineffective concentration of gastrin was simultaneously injected into both sides of the PVN. Almost the same magnitude of acid response due to PVN gastrin was reproduced in normoglycemia, but it was diminished in hyperglycemia. These results suggest that PVN neurons sensitive to gastrin form a neural circuit in both sides of the nucleus, and the circuit acts to potentiate the stimulation of gastric acid which is dependent on the glycemic condition.

Control of motor and secretory functions of the stomach by a portal glucose signal

D-glucose solution injected into the portal vein influences efferent tonic activities of the vagal nerve innervating the stomach. This suggested the existence of a neural connection between hepatic vagal branch afferents and gastric vagal efferents in the brain. Considering this observation together with findings indicating that electrical stimulation of the proximal cut end of the hepatic vagal branch changes acidity in the gastric perfusing fluid or pressure within the stomach, it has been presumed that hepatic afferent signals related to glucose may regulate the motor or secretory function of the stomach through a change in central nervous activity. Recently active interaction between the portal and medullary glucose signals in gastric function was discovered, and analysis of the characteristic features of the system is in progress.

Enhanced gastric acid secretion induced by gastrin can be suppressed by glucose injected into the portal vein in rats

Gastric acid secretion induced by tetragastrin was examined after glucose injection into the portal vein in rats. The enhancement of acid secretion caused by gastrin was inhibited by glucose injection into the portal vein, and the acid response was dose dependent. The acid response due to portal glucose injection was not reproduced when the hepatic vagal branch was sectioned. These findings suggest that the portal glucose signal modulates gastric acid secretion controlled by gastrin.

Enhanced gastric acid secretion induced by gastrin can be suppressed partially by glucose injection into the medullary nuclei in rats

Gastric acid outputs after glucose injection into the nucleus of the vagus nerve (X) or into the nucleus of the tractus solitarius (SOL) were examined in rats with tetragastrin. The enhanced acid output caused by gastrin was partially inhibited by glucose injection into the X or SOL. Glucose injection into the X depressed acid output in a dose-dependent fashion, but a non-dose-dependent response in acid output was seen when glucose was injected into the SOL. There was no interaction between the X and SOL in acid response due to glucose. These findings suggest that glucose modulates gastric acid secretion stimulated by gastrin at the medullary level, and that such a modulation is characterized by the medullary X or SOL, separately.

The efferent connections of the lateral septal nucleus in the guinea pig: projections to the diencephalon and brainstem

The anterograde Phaseolus vulgaris-leucoagglutinin (PHA-L) tracing technique was used to determine the distribution of efferent fibers originating in the lateral septal nucleus of the guinea pig. For complementary detection of the chemical identity of the target neurons, double-labeling immunocytochemistry was performed with antibodies to PHA-L and to vasopressin, oxytocin, vasoactive intestinal polypeptide, serotonin or dopamine beta-hydroxylase, respectively. The hypothalamus received the majority of the PHA-L-stained septofugal fibers. Here, a specific topography was observed. (1) The medial and lateral preoptic area, (2) the anterior, lateral, dorsal, posterior hypothalamic and retrochiasmatic area, (3) the supraoptic, paraventricular, suprachiasmatic, dorsomedial, caudal ventromedial and arcuate nuclei, and (4) the tuberomammillary, medial and lateral supramammillary, dorsal and ventral premammillary nuclei always contained PHA-L-labeled fibers. The rostral portion of the ventromedial nucleus and the medial and lateral mammillary nucleus only occasionally showed weak terminal labeling. In other diencephalic areas, termination of PHA-L-labeled fibers was observed in the epithalamus and the nuclei of the midline region of the thalamus. In the mesencephalon, terminal varicosities occurred in the ventral tegmental area, interfascicular and interpeduncular nucleus, and periaqueductal gray. In addition, the dorsal and medial raphe nuclei of the metencephalon, together with the locus coeruleus and the dorsal tegmental nucleus, received lateral septal efferents.