Jen Yu Wei

Synergistic interaction between CCK and leptin to regulate food intake

Leptin administered (either intracerebroventricularly, icv, or intraperitoneally, ip) acts in synergy with CCK to suppress food intake and body weight in lean mice or rats. The potentiating effect induced by the co-injection of ip CCK and leptin to inhibit food consumption in mice is mediated by the CCK-A receptor and capsaicin sensitive afferents. In vitro, studies in rats showed that a subset of gastric vagal afferent fibers responded to leptin injected directly into the gastric artery only after a prior intra-arterial CCK injection. Moreover, the tonic activity of gastric-related neurons in the nucleus tractus solitarius (NTS) increased when leptin was delivered into the gastric chamber of an in vitro stomach-brainstem preparation. CCK co-injected with leptin potentiated Fos expression selectively in the area postrema, NTS and paraventricular nucleus of the hypothalamus (PVN), which points to the PVN as part of the afferent and efferent limbs of the circuitry involved in the synergistic interaction between leptin and CCK. The dampening of CCK or leptin inhibitory action on ingestive behavior when either factor is not present or their receptors are non functional supports the notion that such leptin-CCK interaction may have a physiological relevance. These observations provide a mean through which leptin and CCK integrate short- and mid-term meal-related input signals into long-term control of energy balance.

CRF2 receptor activation prevents colorectal distension induced visceral pain and spinal ERK1/2 phosphorylation in rats

Background and aims: Activation of corticotropin releasing factor 1 (CRF1) receptors is involved in stress related responses and visceral pain, while activation of CRF2 receptors dampens the endocrine and some behavioural stress responses. We hypothesised that CRF2 receptor activation may influence visceral pain induced by colorectal distension (CRD) in conscious rats, and assessed the possible sites and mechanisms of action. Methods: Male Sprague-Dawley rats were exposed to CRDs (60 mm Hg, 10 minutes twice, with a 10 minute rest interval). Visceromotor responses (VMR) were measured by electromyography or visual observation. Spinal (L6–S1) extracellular signal regulated kinase 1/2 (ERK 1/2) activation following in vivo CRD and CRF2 receptor gene expression in the T13–S1 dorsal root ganglia (DRG) and spinal cord were determined. Inferior splanchnic afferent (ISA) activity to CRD (0.4 ml, 20 seconds) was assessed by electrophysiological recording in an in vitro ISA nerve-inferior mesenteric artery (intra-arterial)-colorectal preparation. Results: In controls, VMR to the second CRD was mean 31 (SEM 4)% higher than that of the first (p<0.05). The selective CRF2 agonist, human urocortin 2 (hUcn 2, at 10 and 20 μg/kg), injected intravenous after the first distension, prevented sensitisation and reduced the second response by 8 (1)% and 30 (5)% (p<0.05) compared with the first response, respectively. RT-PCR detected CRF2 receptor gene expression in the DRG and spinal cord. CRD (60 mm Hg for 10 minutes) induced phosphorylation of ERK 1/2 in neurones of lumbosacral laminae I and IIo and the response was dampened by intravenous hUcn 2. CRD, in vitro, induced robust ISA spike activity that was dose dependently blunted by hUcn 2 (1–3 μg, intra-arterially). The CRF2 receptor antagonist, astressin2-B (200 μg/kg subcutaneously or 20 μg intra-arterially) blocked the hUcn 2 inhibitory effects in vivo and in vitro. Conclusions: Peripheral injection of hUcn 2 blunts CRD induced visceral pain, colonic afferent, and spinal L6-S1 ERK 1/2 activity through CRF2 receptor activation in rats.

Chylomicron components activate duodenal vagal afferents via a cholecystokinin A receptor-mediated pathway to inhibit gastric motor function in the rat

Nutrients in the intestine initiate changes in secretory and motor function of the gastrointestinal (GI) tract. The nature of the ‘sensors’ in the intestinal wall is not well characterized. Intestinal lipid stimulates the release of cholecystokinin (CCK) from mucosal entero‐endocrine cells, and it is proposed that CCK activates CCK A receptors on vagal afferent nerve terminals. There is evidence that chylomicron components are involved in this lipid transduction pathway. The aim of the present study was to determine (1) the pathway mediating reflex inhibition of gastric motility and (2) activation of duodenal vagal afferents in response to chylomicrons. Mesenteric lymph was obtained from awake rats fitted with lymph fistulas during intestinal perfusion of lipid (Intralipid, 170 μmol h−1, chylous lymph) or a dextrose and/or electrolyte solution (control lymph). Inhibition of gastric motility was measured manometrically in urethane‐anaesthetized recipient rats in response to intra‐arterial injection of lymph close to the upper GI tract. Chylous lymph was significantly more potent than control lymph in inhibiting gastric motility. Functional vagal deafferentation by perineural capsaicin or CCK A receptor antagonist (devazepide, 1 mg kg−1, I.V.) significantly reduced chylous lymph‐induced inhibition of gastric motility. The discharge of duodenal vagal afferent fibres was recorded from the dorsal abdominal vagus nerve in an in vitro preparation of the duodenum. Duodenal vagal afferent nerve fibre discharge was significantly increased by close‐arterial injection of CCK (1‐100 pmol) in 43 of 83 units tested. The discharge of 88 % of CCK‐responsive fibres was increased by close‐arterial injection of chylous lymph; devazepide (100 μg, I.A.) abolished the afferent response to chylous lymph in 83 % of these units. These data suggest that in the intestinal mucosa, chylomicrons or their products release endogenous CCK which activates CCK A receptors on vagal afferent nerve fibre terminals, which in turn initiate a vago‐vagal reflex inhibition of gastric motor function.

Intracisternal TRH and RX 77368 Potently Activate Gastric Vagal Efferent Discharge in Rats

The influence of intracisternal (ic) TRH and the stable TRH analog, RX 77368, on gastric vagal efferent discharge (GVED) was investigated in urethane-anesthetized rats. Consecutive IC injections of TRH (3, 30, and 300 ng) at 60 min intervals stimulated dose dependently multi-unit GVED with a peak increase of 90 +/- 21%, 127 +/- 18% and 145 +/- 16% respectively. In two separate studies, IC injection of RX 77368 at 1.5 or 15 ng stimulated multi-unit GVED by 142 +/- 24% and 244 +/- 95% respectively. Saline injection IC had no effect on GVED. RX 77368 (1.5 ng, ic) action was long lasting (84 +/- 13 min) compared with TRH (3 ng: 44 +/- 7 min). Single-unit analysis also showed that 13 of 13 units responded to ic RX 77368 (1.5 ng) by an increase in activity. These data indicate that low doses of TRH injected ic stimulate vagal efferent outflow to the rat stomach and that RX 77368 action is more potent than TRH.

Central and Peripheral Actions of Calcitonin Gene-Related Peptide on Gastric Secretory and Motor Function

CGRP exerts a potent central action to inhibit gastric acid secretion in rats and dogs and gastric emptying, contractility and ulcer formation in rats. The site of action to inhibit acid secretion has been localized in the dorsal vagal complex. The inhibition of acid secretion is related primarily to the decrease in vagal efferent activity whereas the inhibition of gastric motor functions involves increases in sympathetic outflow. The central action of CGRP to prevent ethanol-induced lesions is unique to this peptide and not shared by other centrally acting inhibitors of gastric function. It may be related to the increase in gastric mucosal blood induced by central CGRP. The presence of CGRP-like immunoreactivity and receptors in medullary nuclei receiving visceral information and influencing vagal outflow suggests a possible role of the peptide in the vagal regulation of gastric secretion. Peripheral injection of CGRP also inhibits acid secretion when administered peripherally in rats, dogs, rabbits and humans. Its antisecretory effect is unlikely to be related to a direct action on the parietal cells. It involves specific and marked release of gastric somatostatin through an interaction with CGRP receptors characterized on D cells and coupled with cAMP. In addition, CGRP induces a decrease in acetylcholine transmission in the enteric nervous system which may contribute to the inhibition of acid. Peripheral CGRP inhibits gastric emptying and motility by a direct action on smooth muscles through receptors linked with cAMP. The release of CGRP from spinal afferents innervating the stomach in response to stimulation of capsaicin-sensitive fibers suggests a role of the peptide in the regulation of gastric function.

Intracisternal sauvagine is more potent than corticotropin-releasing factor to decrease gastric vagal efferent activity in rats☆

Consecutive intracisternal (ic) injections of corticotropin-releasing factor (CRF) (21, 63, and 126 pmol, ic) or sauvagine (2.1, 6.3, and 21 pmol, ic) decreased gastric vagal efferent multiunit discharge (GVED) to 82%, 75% and 69% and 71%, 40% and 21%, respectively, from preinjection basal levels (taken as 100%). The inhibitory action was dose related (magnitude and duration of the response, 7-45 min). The CRF antagonist, [D-Phe12,Nle21,38,Calpha-MeLeu37]-rCRF12-4 1 (6.25 nmol, ic) increased GVED by 43.5+/-4.3% and blocked the decrease in GVED induced by CRF (21 pmol, ic) for >90 min with a complete recovery after 3 h. Vehicles (injected intracisternally) had no effect. These data indicate that: 1) CRF injected intracisternally decreases GVED through the activation of CRF receptors and sauvagine is more potent than CRF to inhibit GVED; and 2) endogenous CRF exerts an inhibitory tone on basal GVED in urethane-anesthetized rats undergoing surgery.

Bombesin acts in the brain to decrease gastric vagal efferent discharge in rats

The central nervous system action of bombesin to influence basal gastric vagal efferent discharge (GVED) was investigated in urethane-anesthetized rats. Bombesin (62, 620, and 6200 pmol) injected intracisternally (IC) decreased GVED to 78 +/- 10%, 50 +/- 4%, and 43 +/- 3% of preinjection levels, respectively. Bombesin (620 pmol) injected IV also reduced GVED to 36 +/- 6%. Pretreatment with bombesin monoclonal antibody 2A11 completely prevented the decrease in GVED induced by bombesin (620 pmol) given IV but not IC. These data indicate that both IC and IV injections of bombesin decrease basal GVED, and that the inhibitory effect of IC injection represents a central nervous system-mediated action.