A possible interaction between serotonin and cholecystokinin-8 in the ileo-colonic motor responses to feeding in rats

Cholecystokinin-8 attenuates methamphetamine-induced inflammatory activation of microglial cells through CCK2 receptor

Methamphetamine (METH) exposure reportedly promotes microglial activation and pro-inflammatory cytokines secretion. Sustained inflammation in abusers of psychostimulant drugs further induces neural damage. Cholecystokinin-8 (CCK-8) is a gut-brain peptide which exerts a wide range of biological activities in the gastrointestinal tract and central nervous system. We previously found that pre-treatment with CCK-8 inhibited behavioural and histologic changes typically induced by repeated exposure to METH. Here, we aimed to estimate the effects of CCK-8 on METH-induced neuro-inflammation, which is markedly characterized by microglia activation and increased pro-inflammatory cytokines production in vivo and in vitro. Moreover, we assessed the subtypes of the CCK receptor mediating the regulatory effects of CCK-8, and the changes in the NF-κB signalling pathway. We found that CCK-8 inhibited METH-induced microglial activation and IL-6 and TNF-α generation in vivo and in vitro in a dose-dependent manner. Furthermore, co-treatment of CCK-8 with METH significantly attenuated the activation of the NF-κB signalling pathway by activating the CCK2 receptor subtype in N9 cells. In conclusion, our findings indicated the inhibitory effect of CCK-8 on METH-induced neuro-inflammation in vivo and in vitro, and suggested the underlying mechanism may involve the activation of the CCK2 receptor, which downregulated the NF-κB signalling pathway induced by METH stimulation.

The Place of Stress and Emotions in the Irritable Bowel Syndrome

Our emotional state can have many consequences on our somatic health and well-being. Negative emotions such as anxiety play a major role in gut functioning due to the bidirectional communications between gut and brain, namely, the brain-gut axis. The irritable bowel syndrome (IBS), characterized by an unusual visceral hypersensitivity, is the most common disorder encountered by gastroenterologists. Among the main symptoms, the presence of current or recurrent abdominal pain or discomfort associated with bloating and altered bowel habits characterizes this syndrome that could strongly alter the quality of life. This chapter will present the physiopathology of IBS and explain how stress influences gastrointestinal functions (permeability, motility, microbiota, sensitivity, secretion) and how it could be predominantly involved in IBS. This chapter will also describe the role of the autonomic nervous system and the hypothalamic-pituitary axis through vagal tone and cortisol homeostasis. An analysis is made about how emotions and feelings are involved in the disruption of homeostasis, and we will see to what extent the balance between vagal tone and cortisol may reflect dysfunctions of the brain-gut homeostasis. Finally, the interest of therapeutic treatments focused on stress reduction and vagal tone enforcement is discussed.

Regional effects of cholecystokinin octapeptide on colonic phasic and tonic motility in healthy humans

The aim of this study was to assess in nine healthy subjects the effects of CCK octapeptide (CCK-8) on colonic tonic activity, measured by a barostat, and phasic activity, measured by manometry. On 2 consecutive days, recordings were performed in the unprepared proximal and distal colons during intravenous infusion of saline and CCK-8 at 5, 20, and 40 ng. kg-1. h-1. In the proximal colon CCK-8 induced, at the 20 and 40 ng. kg-1. h-1 doses, a tonic relaxation with an increase in barostat bag volume to 156 +/- 25 and 157 +/- 19% of basal (P < 0.01) and a decrease in phasic activity to 72 +/- 7 and 76 +/- 7% of basal (P < 0.01). In the distal colon, CCK-8 induced, at the 20 and 40 ng. kg-1. h-1 doses, a tonic relaxation (increase in intrabag volume to 133 +/- 12 and 149 +/- 15%, respectively; P < 0.01), whereas phasic activity increased (128 +/- 8 and 132 +/- 6%, respectively; P < 0.01). Effects of CCK-8 on tonic and phasic activities are different according to the colonic segment. Because meals induce colonic tonic contraction, our results suggest that CCK, as a hormone, is not an important mediator of the response of the colon to feeding in humans.

Peripheral neurotensin participates in the modulation of pre- and postprandial intestinal motility in rats

The present study was undertaken to determine whether neurotensin is involved in the regulation of the intestinal postprandial motor response and, if so, whether the regulatory pathway depends upon peripheral or central neurotensin secretion. Neurotensin, injected by the i.v. route (5 micrograms/kg) during the fasting state, induced firstly an increased irregular spiking activity during 30-40 min. This effect was followed by an increase of frequency of the myoelectrical complexes during 60 min. When injected by the i.c.v. route, neurotensin (0.5 microgram/kg) reinforced the fasting motility pattern of the small intestine after a latency of 70 min. Neurotensin was ineffective on the colon. The neurotensin receptor antagonist SR 48692 (200 micrograms/kg i.v.) reduced the duration of the postprandial motor response of the small intestine and blocked the late postprandial phase on the proximal colon while it suppressed the early postprandial phase on the distal colon. When administered i.c.v. (20 micrograms/kg), SR 48692 had no effect. It is concluded that neurotensin modulates intestinal postprandial motility essentially by a peripheral regulatory pathway. Endogenous neurotensin is involved in the maintenance of the postprandial motility pattern on the small intestine and the proximal colon while it is involved in the initiation of this response on the distal colon. This suggests that endogenous neurotensin acts via both endocrine and nervous mechanisms.

Intestinal intraluminal continuity is a prerequisite for the distal bowel motility response to feeding

BACKGROUND

We wanted to elucidate further the regulation of the intestinal motility response to feeding.

METHODS

After intraduodenal administration of an oleate solution, mimicking a meal, the distal bowel motility and the plasma levels of bile acids, cholecystokinin (CCK), and neurotensin were monitored in patients operated on with restorative proctocolectomy (n = 4) or low anterior resection of the rectum (n = 4). Investigations were performed both with and without a diverting loop ileostomy.

RESULTS

Intraduodenal sodium oleate elicited a prompt and significant increase in distal bowel motility. The motility response failed to appear when the luminal flow was diverted by a loop ileostomy. An increase in plasma CCK preceded the motility increase, but CCK was increased also in patients with a loop ileostomy. Whereas plasma bile acid levels were significantly increased after 30-45 min (p < 0.05), both with and without a loop ileostomy, neurotensin levels were not affected.

CONCLUSION

Intestinal continuity is a prerequisite for the distal bowel motility response, indicating that apart from other possible mechanisms, luminal factors are involved in the regulation of intestinal motility.

Effects of vagotomy on cholecystokinin- and dexfenfluramine-induced Fos-like immunoreactivity in the rat brain

This study compared the effects of bilateral subdiaphragmatic vagotomy on the Fos-like immunoreactivity (FLI), a marker of neuronal activation, in rat brain induced by two anorectic agents, cholecystokinin (CCK) and the serotonin agonist, dexfenfluramine (DFEN). In the nonvagotomized rats, both CCK (5 micrograms/kg, IP) and DFEN (2 mg/kg, IP) induced FLI in the nucleus of the solitary tract (NST), the external subdivision of the lateral parabrachial nuclei (LPBE), the lateral subdivision of the central amygdaloid nucleus (CeL), and the bed nucleus of the stria terminalis (BST). However, subregional distribution of the FLI induced by the two agents was different in most of these regions. Additionally, the area postrema and the medial subdivision of the hypothalamic paraventricular nucleus were preferentially activated by CCK but not DFEN, while the caudate-putamen was activated by DFEN but not CCK. Bilateral subdiaphragmatic vagotomy completely abolished CCK-induced FLI in all the brain regions but did not attenuate DFEN-induced FLI in any of these regions, including the NST. The results of the present study suggest that DFEN-activation of the NST-LPBE-CeL/BST neuraxis is not mediated by the vagus nerve. On the other hand, and consistent with a variety of other data, activation of various parts of the brain by peripherally administered CCK depends on a vagal pathway. These data are discussed in relation to a previously proposed interaction between CCK and serotonin in mediating satiety.

Melatonin is involved in cholecystokinin-induced changes of ileal motility in rats

The aim of this study was to determine, in the rat, the interaction between melatonin and cholecystokinin in the regulation of the ileal interdigestive motility. This was analyzed by the chronic electromyography technique. Ileal motility was defined by the presence of intermittent spike bursts corresponding to the contractile activity of the organ. In control rats, these spike bursts were organized in cyclic myoelectrical complexes. Each complex is characterized by two successive spiking activity phases: the irregular phase (ISA) followed by the regular phase (RSA). Pinealectomy suppressed the RSA phase so ileal motility was constituted only by the ISA phase. When melatonin (1 mg/kg i.v.) was injected into pinealectomized rats, RSA phases were immediately and definitively restored. RSA phases were also re-established when the "alimentary" type of cholecystokinin receptors (CCKA) were blocked by selective antagonists such as L364,718 or SR27897 (1 mg/kg i.v.). The latter had better brain accessibility than L364,718. Unlike the effects of melatonin, the effect of these antagonists was neither immediate (the latency is longer for L364,718 than for SR27897) nor definitive. In control rats, cholecystokinin (5 micrograms/kg i.v.) induced a characteristic long-lasting (29 +/- 2 min) excitomotor effect on the ileum. This effect was suppressed in pinealectomized rats and was restored after melatonin treatment. These results suggest that, via the central nervous system, melatonin is involved in the modulation of cholecystokinin action on ileal motility.