Systemic cholecystokinin amplifies vago-vagal reflex responses recorded in vagal motor neurones

Comparison of left side or right side vagotomy in the rat subjected to acute pancreatitis

PURPOSE

We aimed to evaluate the effects of unilateral vagotomy (right-VR or left-VL) on the severity of caerulein-induced acute pancreatitis (AP).

MATERIAL AND METHODS

VR or VL was done in Wistar rats 4 days before AP, except in control, sham operated group. Following 5 h administration of subcutaneous injections of caerulein, the pancreatic blood flow (PBF), serum lipase and IL-10 in caval blood samples were measured. The pancreatic specimens were taken from sacrificed rats for the assessment of MDA-4-HNE and morphology.

RESULTS

PBF decreased from 310 ± 20 ml/min/100 g of tissue in control rats to 130 ± 12 units in AP (p < 0.01). VR and VL alleviated this effect to 234 ± 22 and 229 ± 26 units, respectively, (p < 0.01). There was an immense increase of serum lipase in AP, from 100 ± 7 U/L up to 5220 ± 210 U/L (p < 0.01). Only VL limited this increase to 3469 ± 300 U/L (p < 0.01). Serum IL-10 increased uniformly in AP, without any effect of preceding VR or VL. VL performed in rats subjected subsequently to AP resulted in stronger reduction of histological changes, such as pancreatic edema and leukocyte infiltration, than the above parameters in AP rats with VR. MDA+4-HNE increased from 7.5 ± 0.1 pmol/g of tissue in control group to 30.6 ± 3 units in AP group (p < 0.01). Concentration of MDA+4-HNE in pancreatic tissue achieved 16.48 ± 3 pmol/g after VR and 13.84 ± 4 pmol/g following VL.

CONCLUSION

Our observation might suggest that protective effect of VL could be stronger than VR in the protection on AP. However changes of PBF seem to be similar in both groups of rats.

Hindbrain glucoprivation effects on gastric vagal reflex circuits and gastric motility in the rat are suppressed by the astrocyte inhibitor fluorocitrate

Fasting and hypoglycemia elicit powerful gastrointestinal contractions. Whereas the relationship between utilizable nutrient and gastric motility is well recognized, the explanation of this phenomenon has remained incomplete. A relatively recent controversial report suggested that astrocytes in the dorsal hindbrain may be the principal detectors of glucoprivic stimuli. Our own studies also show that a subset of astrocytes in the solitary nucleus (NST) is activated by low glucose. It is very likely that information about glucopenia may directly impact gastric control because the hindbrain is also the location of the vago-vagal reflex circuitry regulating gastric motility. Our in vivo single unit neurophysiological recordings in intact rats show fourth ventricular application of 2-deoxyglucose (2-DG) inhibits NST neurons and activates dorsal motor nucleus (DMN) neurons involved in the gastric accommodation reflex. Additionally, as shown in earlier studies, either systemic insulin or central 2-DG causes an increase in gastric motility. These effects on motility were blocked by fourth ventricle pretreatment with the astrocyte inactivator fluorocitrate. Fluorocitrate administered alone has no effect on gastric-NST or -DMN neuron responsiveness, or on gastric motility. These results suggest that glucoprivation-induced increases in gastric motility are dependent on intact hindbrain astrocytes.

Gut motility and enteroendocrine secretion

The motility of the gastrointestinal (GI) tract is modulated by complex neural and hormonal networks; the latter include gut peptides released from enteroendocrine cells during both the interdigestive and postprandial periods. Conversely, it is increasingly recognised that GI motility is an important determinant of gut hormone secretion, in that the transit of luminal contents influences the degree of nutrient stimulation of enteroendocrine cells in different gut regions, as well as the overall length of gut exposed to nutrient. Of particular interest is the relationship between gallbladder emptying and enteroendocrine secretion. The inter-relationships between GI motility and enteroendocrine secretion are central to blood glucose homeostasis, where an understanding is fundamental to the development of novel strategies for the management of diabetes mellitus.

Astrocytes in the hindbrain detect glucoprivation and regulate gastric motility

Glucoprivation is a strong signal for the initiation of gastrointestinal contractions. While this relationship between utilizable nutrient levels and gastric motility has been recognized for more than 100 years, the explanation of this phenomenon has remained incomplete. Using widely differing approaches, recent work has suggested that the hindbrain is responsible for this chemoreflex effect. Surprisingly, astrocytes may be the main glucodetector elements under hypoglycemic conditions. Our own work using in vitro live cell calcium imaging shows that astrocytes in the NST increase cytoplasmic calcium in a concentration dependent manner in reaction to reductions in glucose. This effect is reversed on restoration of normal glucose concentrations. In vivo single unit neurophysiological recordings show that brainstem neurons driving gastric motility are activated by glucoprivic stimuli. Studies in intact animals verify that both dorsal medullary and systemic glucoprivation significantly increases gastric motility. Astrocyte inactivation with fluorocitrate blocks the pro-motility effects of glucoprivation. Thus, it appears that intact astrocyte signaling may be essential to glucoregulatory control over gastric motility.

CXCL12 sensitizes vago-vagal reflex neurons in the dorsal medulla

Previous studies from our laboratory illustrated the potential for stromal cell-derived factor one [CXCL12; also referred to as SDF-1] to act on its receptor [CXCR4] within the dorsal vagal complex [DVC] of the hindbrain to suppress gastric motility (Hermann et al., 2008). While CXCR4 receptors are essential for normal brain development, they also play a critical role in the proliferation of the HIV virus and initiation of metastatic cell growth in the brain. Anorexia, nausea, and failed autonomic regulation of gastrointestinal function are significant causes of morbidity and are contributory factors in the mortality associated with these disease states. The implication of our previous study was that CXCL12 caused gastric stasis by acting on gastric reflex circuit elements in the DVC. This hindbrain complex includes vagal afferent terminations in the solitary nucleus, neurons in the solitary nucleus (NST) and visceral efferent motorneurons in the dorsal motor nucleus (DMN) that are responsible for the regulation of digestive functions from the oral cavity to the transverse colon. In the current study, in vivo single-unit neurophysiological recordings from physiologically-identified NST and DMN components of the gastric accommodation reflex show that while injection of femtomole doses of CXCL12 onto NST or DMN neurons has no effect on their basal activity, CXCL12 amplifies the effect of gastric vagal mechanosensory input to activate the NST and, in turn, inhibit DMN motor activity.