Effect of Vagotomy and Sympathectomy on the Feeding Responses Evoked by Intra-Aortic Cholecystokinin-8 in Adult Male Sprague Dawley Rats

The vagus nerve and the celiaco-mesenteric ganglia (CMG) are required for reduction of meal size (MS) and prolongation of the intermeal interval (IMI) by intraperitoneal (ip) sulfated cholecystokinin-8 (CCK-8). However, recently we have shown that the gut regulates these responses. Therefore, reevaluating the role of the vagus and the CMG in the feeding responses evoked by CCK is necessary because the gut contains the highest concentration of enteric, vagal and splanchnic afferents and CCK-A receptors, which are required for reduction of food intake by this peptide, compared to other abdominal organs. To address this necessity, we injected sulfated CCK-8 (0, 0.1, 0.5, 1 and 3 nmol/kg) in the aorta, near the gastrointestinal sites of action of the peptide, in three groups of free-feeding rats (n = 10 rats per group), subdiaphragmatic vagotomy (VGX), celiaco-mesenteric ganglionectomy (CMGX) and sham-operated, and recorded seven feeding responses. In the sham group, CCK-8 reduced MS (normal chow), prolonged the intermeal interval (IMI, time between first and second meals), increased satiety ratio (SR, IMI/MS), shortened duration of first meal, reduced total (24 hrs) food intake and reduced number of meals relative to saline vehicle. Vagotomy attenuated all of the previous responses except IMI length and SR, and CMGX attenuated all of those responses. In conclusion, the feeding responses evoked by sulfated CCK-8 require, independently, the vagus nerve and the CMG.

The Vagus Nerve and the Celiaco-mesenteric Ganglia Participate in the Feeding Responses Evoked by Non-sulfated Cholecystokinin-8 in Male Sprague Dawley Rats

We have shown that non-sulfated cholecystokinin-8 (NS CCK-8) reduces food intake in adult male Sprague Dawley rats by activating cholecystokinin-B receptor (CCK-BR). Here, we tested the hypothesis that the vagus nerve and the celiaco-mesenteric ganglia may play a role in this reduction. The hypothesis stems from the following facts. The vagus and the celiaco-mesenteric ganglia contain NS CCK-8, they express and have binding sites for CCK-BR, NS CCK-8 activates CCK-BR on afferent vagal and sympathetic fibers and the two structures link the gastrointestinal tract to central feeding nuclei in the brain, which also contain the peptide and CCK-BR. To test this hypothesis, three groups of free-feeding rats, vagotomy (VGX), celiaco-mesenteric ganglionectomy (CMGX) and sham-operated, received NS CCK-8 (0, 0.5 and 1 nmol/kg) intraperitoneally prior to the onset of the dark cycle and various feeding behaviors were recorded. We found that in sham-operated rats both doses of NS CCK-8 reduced meal size (MS), prolonged the intermeal interval (IMI, time between first and second meal), increased satiety ratio (SR = IMI/MS), reduced 24-h food intake and reduced the number of meals relative to saline control. In the VGX and the CMGX groups, all of the previous responses were attenuated. Consistent with our hypothesis, the findings of the current work suggest a role for the vagus nerve and the celiaco-mesenteric ganglia in the feeding responses evoked by NS CCK-8.

Non-sulfated cholecystokinin-8 reduces meal size and prolongs the intermeal interval in male Sprague Dawley rats

The current study measured seven feeding responses by non-sulfated cholecystokinin-8 (NS CCK-8) in freely fed adult male Sprague Dawley rats. The peptide (0, 0.5, 1, 3, 5 and 10 nmol/kg) was given intraperitoneally (ip) prior to the onset of the dark cycle, and first meal size (MS), second meal size, intermeal interval (IMI) length, satiety ratio (SR = IMI/MS), latency to first meal, duration of first meal, number of meals and 24-hour food intake were measured. We found that NS CCK-8 (0.5 and 1.0 nmol/kg) reduced MS, prolonged IMI length and increased SR during the dark cycle. Furthermore, the specific CCK-B receptor antagonist L365, 260 (1 mg/kg, ip) attenuated these responses. These results support a possible role for NS CCK-8 in regulating food intake.

Non-sulfated cholecystokinin-8 increases enteric and hindbrain Fos-like immunoreactivity in male Sprague Dawley rats

Recently, we reported that non-sulfated cholecystokinin-8 (NS CCK-8) reduces food intake by cholecystokinin-B receptors (CCK-BR). To examine a possible site of action for this peptide, and based on the fact that both NS CCK-8 and CCK-BR are found centrally and peripherally, in the current study we hypothesized that NS CCK-8 increases Fos-like immunoreactivity (Fos-LI, a neuronal activation marker) in the dorsal vagal complex (DVC) of the hindbrain and the myenteric and submucosal plexuses of the small intestine. We found that intraperitoneal NS CCK-8 (0.5 nmol/kg) increases Fos-LI in the DVC, the myenteric and the submucosal plexuses of the duodenum and the myenteric plexus of the jejunum. The findings suggest, but does not prove, a potential role for the DVC and the enteric neurons in the feeding responses evoked by NS CCK-8.

Combined gastrin releasing peptide-29 and glucagon like peptide-1 reduce body weight more than each individual peptide in diet-induced obese male rats

To test the hypothesis that gastrin releasing peptide-29 (GRP-29) combined with glucagon like peptide-1 (7-36) (GLP-1 (7-36)) reduce body weight (BW) more than each of the peptides given individually, we infused the two peptides (0.5nmol/kg each) in the aorta of free feeding, diet-induced obese (DIO) male Sprague Dawley rats once daily for 25days and measured BW. We found that GRP-29 and GLP-1 reduce BW, GRP-29 reduced it more than GLP-1 and GRP-29+GLP-1 reduce BW more than each peptide given alone. This reduction was accompanied by decrease 24-hour food intake (normal rat chow), meal size (MS), duration of first meal and number of meals, and increase latency to the first meal, intermeal interval (IMI) and satiety ratio (IMI/MS, amount of food consumed per a unit of time). Furthermore, the peptides and their combination decreased 24-hour glucose levels. In conclusion, GRP-29+GLP-1 reduce BW more than each of the peptides given individually.

Long-term effect of parasympathetic or sympathetic denervation on intestinal epithelial cell proliferation and apoptosis

Intestinal epithelial tissue is constantly regenerated as a means to maintain proper tissue function. Previous studies have demonstrated that denervation of the parasympathetic or sympathetic nervous system to the intestine alters this process. However, results are inconsistent between studies, showing both increases and decreases in proliferation after denervation of the parasympathetic or sympathetic. The effect appears to correlate with (1) the timing post-denervation, (2) denervation-induced changes in food intake, (3) the denervation technique used, and (4) which intestinal segment is investigated. Thus, we proposed that parasympathetic or sympathetic denervation does not have an effect on intestinal epithelial regeneration when you (1) evaluate denervation after long-term denervation, (2) control for post-surgical changes in food intake, (3) use minimally invasive surgical techniques and (4) include a segmental analysis. To test this, adult male Sprague Dawley rats underwent parasympathetic denervation via subdiaphragmatic vagotomy, sympathetic denervation via celiacomesenteric ganglionectomy, a parasympathetic denervation sham surgery, or a sympathetic denervation sham surgery. Sham surgery ad libitum-fed groups and sham surgery pair-fed groups were used to control for surgically induced changes in food intake. Three weeks post-surgery, animals were sacrificed and tissue from the duodenum, jejunum, and ileum was excised and immunohistochemically processed to visualize indicators of proliferation (bromodeoxyuridine-positive cells) and apoptosis (caspase-3-positive cells). Results showed no differences between groups in proliferation, apoptosis, or total cell number in any intestinal segment. These results suggest that parasympathetic or sympathetic denervation does not have a significant long-term effect on intestinal epithelial turnover. Thus, intestinal epithelial regeneration is able to recover after autonomic nervous system injury. Impact statement This study investigates the long-term effect of autonomic denervation on intestinal epithelial cell turnover, as measured by proliferation, apoptosis, and total cell number. Although previous research has established that autonomic denervation can alter intestinal epithelial turnover under short-term conditions, here we establish for the first time that these changes do not persist long-term when you control for surgical-induced changes in food intake and use targeted denervation procedures. These findings add to the base of knowledge on autonomic control of tissue turnover, highlight the ability of the intestinal epithelium to recover after autonomic injury and reveal possible implications of the use of ANS denervation for disease treatment in humans.

Cholecystokinin-33, but not cholecystokinin-8 shows gastrointestinal site specificity in regulating feeding behaviors in male rats

Two separate experiments were performed to localize the gastrointestinal sites of action regulating meal size (MS), intermeal interval (IMI) length and satiety ratio (SR, IMI/MS) by cholecystokinin (CCK) 8 and 33. Experiment 1: CCK-8 (0, 0.05, 0.15, 0.25nmol/kg) was infused in the celiac artery (CA, supplies stomach and upper duodenum) or the cranial mesenteric artery (CMA, supplies small and part of the large intestine) prior to the onset of the dark cycle in free feeding, male Sprague Dawley rats and MS (normal rat chow), IMI and SR were recorded. Experiment 2: CCK-33 (0, 0.05, 0.15, 0.25nmol/kg) were infused in the CA or the CMA, under the same experimental conditions above, and MS, IMI and SR were recorded. Experiment 1 found that CCK-8 reduces MS, prolongs the IMI and increases the SR at sites supplied by both arteries. Experiment 2 found that CCK-33 reduces MS and increases the SR at sites supplied by the CMA. We conclude that in male rats the feeding behaviors evoked by CCK-33, but not CCK-8, are regulated at specific gastrointestinal sites of action.

The BB2 receptor antagonist BW2258U89 attenuates the feeding responses evoked by exogenous gastrin releasing peptide-29

This confirmatory work is aimed to test that the hypothesis that the gastrin releasing peptide (GRP) receptor - the BB2 receptor - is necessary for reduction of meal size (MS) and prolongation of the intermeal interval (IMI) by the small and the large forms of GRP in the rat, GRP-10 and GRP-29, and to confirm the sites of action regulating such responses - the vascular bed of the celiac artery (CA, supplying stomach and upper duodenum). To pursue these aims we measured first MS and IMI length in response to GRP-10 and GRP-29 (0, 0.5nmol/kg) infused in the CA (n=8 rats) and the cranial mesenteric artery (CMA, supplying the small and part of the large intestine, n=8 rats) in near spontaneously free feeding rats pretreated with the BB2 receptor antagonist BW2258U89 (0.1mg/kg) in the same arteries prior to the onset of the dark cycle. We found that GRP-29, but not GRP-10, infused by the CA reduced MS and prolonged the IMI by decreasing meal latency and meal duration and the BB2 receptor antagonist BW2258U89 infused in the same artery attenuated these responses. These results suggest that the BB2 receptor is necessary for reduction of MS and prolongation of the IMI by exogenous GRP-29, and the vascular bed of the CA, stomach and upper duodenum, contains sites of action regulating these feeding responses.

The feeding responses evoked by endogenous cholecystokinin are regulated by different gastrointestinal sites

The current study tested the hypothesis that cholecystokinin (CCK) A receptor (CCKAR) in areas supplied by the celiac artery (CA), stomach and upper duodenum, and the cranial mesenteric artery (CMA), small and parts of the large intestine, is necessary for reduction of meal size, prolongation of the intermeal interval (time between first and second meal) and increased satiety ratio (intermeal interval/meal size or amount of food consumed during any given unit of time) by the non-nutrient stimulator of endogenous CCK release camostat. Consistent with our previous findings camostat reduced meal size, prolonged the intermeal interval and increased the satiety ratio. Here, we report that blocking CCKAR in the area supplied by the celiac artery attenuated reduction of meal size by camostat more so than the cranial mesenteric artery route. Blocking CCKAR in the area supplied by the cranial mesenteric artery attenuated prolongation of the intermeal interval length and increased satiety ratio by camostat more so than the celiac artery route. Blocking CCKAR in the areas supplied by the femoral artery (control) failed to alter the feeding responses evoked by camostat. These results support the hypothesis that CCKAR in the area supplied by the CA is necessary for reduction of meal size by camostat whereas CCKAR in the area supplied by the CMA is necessary for prolongation of the intermeal interval and increased satiety ratio by this substance. Our results demonstrate that meal size and intermeal interval length by camostat are regulated through different gastrointestinal sites.

Exogenous glucagon-like peptide-1 acts in sites supplied by the cranial mesenteric artery to reduce meal size and prolong the intermeal interval in rats

Three experiments were done to better assess the gastrointestinal (GI) site(s) of action of GLP-1 on food intake in rats. First, near-spontaneous nocturnal chow meal size (MS), intermeal intervals (IMI) length and satiety ratios (SR = MS/IMI) were measured after infusion of saline, 0.025 or 0.5 nmol/kg GLP-1 into the celiac artery (CA, supplying the stomach and upper duodenum), cranial mesenteric artery (CMA, supplying small and all of the large intestine except the rectum), femoral artery (FA, control) or portal vein (PV, control). Second, infusion of 0.5 nmol/kg GLP-1 was tested after pretreatment with the GLP-1 receptor (GLP-1R) antagonist exendin-4(3-39) via the same routes. Third, the regional distribution of GLP-1R in the rat GI tract was determined using rtPCR. CA, CMA and FA GLP-1 reduced first MS relative to saline, with the CMA route more effective than the others. Only CMA GLP-1 prolonged the IMI. None of the infusions affected second MS or later eating. CA and CMA GLP-1 increased the SR, with the CMA route more effective than the CA route. CMA exendin-4 (3-39) infusion reduced the effect of CMA GLP-1. Finally GLP-1R expression was found throughout the GI tract. The results suggest that exogenous GLP-1 acts in multiple GI sites to reduce feeding under our conditions and that GLP-1R in the area supplied by the CMA, i.e., the small and part of the large intestine, plays the leading role.

Celiac and the cranial mesenteric arteries supply gastrointestinal sites that regulate meal size and intermeal interval length via cholecystokinin-58 in male rats

The site(s) of action that control meal size and intermeal interval (IMI) length by cholecystokinin-58 (CCK-58), the only detectable endocrine form of CCK in the rat, are not known. To test the hypothesis that the gastrointestinal tract may contain such sites, we infused low doses of CCK-58 (0.01, 0.05, 0.15 and 0.25nmol/kg) into the celiac artery (CA, supplying stomach and upper duodenum), the cranial mesenteric artery (CMA, supplying small and most of the large intestines), the femoral artery (FA, control) and the portal vein (PV, draining the gastrointestinal tract) prior to the onset of the dark cycle in freely fed male rats. We measured the first meal size (chow), second meal size, IMI and satiety ratio (SR, IMI/meal size). We found that (1) all doses of CCK-58 given in the CA and the highest dose given in the CMA reduced the first meal size, (2) all doses of CCK-58 given in the CA reduced the second meal size, (3) a CCK-58 dose of 0.15nmol/kg given in the CA and 0.15 and 0.25nmol/kg given in the CMA prolonged the IMI, (4) CCK-58 (0.05, 0.15, 0.25nmol/kg) given in the CA and 0.25nmol/kg given in the CMA increased the SR, and (5) CCK-58 given in the FA and PV had no effect on the meal size or intermeal interval. These results support our hypothesis that the gastrointestinal tract contains sites of action that regulate meal size and IMI length via CCK-58. The stomach and upper duodenum may contain sites regulating meal size, whereas the small intestine and part of the large intestine may contain sites regulating the IMI.

Sequence analysis and feeding responses evoked by the large molecular form of gastrin releasing peptide (GRP) in the rat GRP-29

Microisolation techniques utilizing several reverse phase high performance liquid chromatography (HPLC) steps have resulted in the purification of two rat gastrin releasing peptide (GRP) forms suitable for microsequence and mass spectral analysis. The sequence of the larger form is APVSTGAGGGTVLAKMYPRGSHWAVGHLM-amide and the smaller form is GSHWAVGHLM-amide which is the carboxyl terminal decapeptide of the larger peptide. The peptides were synthesized and their feeding patterns e.g. first meal size (MS), intermeal interval (IMI) and satiety ratio (SR, IMI/MS) were determined in overnight food-, but not water deprived, male Sprague Dawley rats. The peptides were administered in the femoral vein (0, 0.21, 0.41 and 1.03 nmol/kg) immediately before presenting the rats with a 10% sucrose solution. We found that (1) GRP-10 (all doses) and GRP-29 (0.41 nmol/kg) reduced first MS, (2) both peptides prolonged IMI length and (3) both peptides increased the SR to similar extents. In conclusion, GRP-10 and GRP-29 are the two endogenous forms of GRP in the rat intestine and they reduce short term feeding to similar extents when administered intravenously.

Obese and lean Zucker rats respond similarly to intraperitoneal administration of gastrin-releasing peptides

The Zucker rat is an animal model used to study obesity and the control of food intake by various satiety peptides. The amphibian peptide bombesin (Bn) reduces cumulative food intake similarly in both obese and lean weanling Zucker rats. Here, we hypothesized that intraperitoneal (i.p) administration of gastrin-releasing peptides-10, -27 and -29 (GRP-10, GRP-27, GRP-29), which are the mammalian forms of Bn, would reduce first meal size (MS, 10% sucrose) and prolong the intermeal interval (IMI, time between first and second meals) similarly in obese and lean adult Zucker rats. To test this hypothesis, we administered GRP-10, GRP-27 and GRP-29 (0, 2.1, 4.1 and 10.3 nmol/kg) i.p. to obese and lean male Zucker rats (who were deprived of overnight food but not water) and then measured the first and second MS, IMI and satiety ratio (SR, IMI/MS). We found that in both obese and lean rats, all forms of GRP reduced the first MS, and in lean rats, they also decreased the second MS. Additionally, GRP-10 and GRP-29 prolonged the IMI in both obese and lean rats, but GRP-27 only prolonged it in lean rats. Finally, we found that all forms of GRP increased the SR in both obese and lean rats. In agreement with our hypothesis, we conclude that all forms of GRP reduce food intake in obese and lean adult Zucker rats similar to Bn in weanling rats.

The stomach and/or upper duodenum contain sites of action that control meal size and intermeal interval length by exogenous rat gastrin releasing peptide

The site(s) of action that control the reduction of food intake in response to the amphibian skin peptide bombesin (Bn) has been determined to be the area supplied by the celiac artery (CA), i.e., the stomach and the upper duodenum. Here, we investigated the gastrointestinal site(s) of action which controls meal size (MS) (normal rat chow) and intermeal interval length (IMI) by the mammalian homologues of Bn gastrin releasing peptides (GRP-10, GRP-27 and GRP-29, 0.01, 0.05, 0.1, 0.2 and 0.5 nmol/kg) infused in the CA, the cranial mesenteric artery (CMA, supplying the small and large intestine), the femoral artery (FA, control) and the portal vein (PV, draining the gastrointestinal tract, control) in freely fed rats immediately prior to the onset of the dark cycle. We found that (1) GRP-29 (0.05, 0.1, 0.2 and 0.5 nmol/kg) and GRP-27 (0.2 and 0.5 nmol/kg) in the CA and GRP-29 (0.5 nmol/kg) in the CMA reduced the MS relative to saline, (2) GRP-29 (0.1, 0.2 and 0.5 nmol/kg) and GRP-27 (0.2 and 0.5 nmol/kg) in the CA prolonged the IMI, (3) GRP-29 (0.1, 0.2 and 0.5 nmol/kg) in the CA and GRP-29 (0.5 nmol/kg) in the CMA increased the satiety ratio (SR, IMI/MS - the amount of food consumed per a given unit of time) and (4) neither peptide nor route showed any effect on the second MS. These results support an upper gastrointestinal site of action for MS and IMI length by GRP-27 and GRP-29, which is most likely the stomach and/or the duodenum.

CCK-58 prolongs the intermeal interval, whereas CCK-8 reduces this interval: not all forms of cholecystokinin have equal bioactivity

It has been accepted for decades that "all forms of cholecystokinin (CCK) have equal bioactivity," despite accumulating evidence to the contrary. To challenge this concept, we compared two feeding responses, meal size (MS, 10% sucrose) and intermeal interval (IMI), in response to CCK-58, which is the major endocrine form of CCK, and CCK-8, which is the most abundantly utilized form. Doses (0, 0.1, 0.5, 0.75, 1, 3 and 5 nmol/kg) were administered intraperitoneally over a 210-min test to Sprague Dawley rats that had been food-deprived overnight. We found that (1) all doses of CCK-58, except the lowest dose, and all doses of CCK-8, except the lowest two doses, reduced food intake more than vehicle did; (2) at two doses, 0.75 and 3 nmol/kg, CCK-58 increased the IMI, while CCK-8 failed to alter this feeding response; and (3) CCK-58, at all but the lowest two doses, increased the satiety ratio (IMI between first and second meals (min) divided by first MS (ml)) relative to vehicle, while CCK-8 did not affect this value. These findings demonstrate that the only circulating form of CCK in rats, CCK-58, prolongs the IMI more than CCK-8, the peptide generally utilized in feeding studies. Taken together, these results add to a growing list of functions where CCK-8 and CCK-58 express qualitatively different bioactivities. In conclusion, the hypothesis that "all forms of cholecystokinin (CCK) have equal bioactivity" is not supported.

Intravenous infusion of gastrin-releasing peptide-27 and bombesin in rats reveals differential effects on meal size and intermeal interval length

We have previously shown that the intraperitoneal (i.p.) administration of gastrin-releasing peptide-27 (GRP-27) or bombesin (BN) (at 0.21, 0.41 and 1.03nmol/kg) reduces meal size (MS) and prolongs the intermeal interval (IMI). Here, we hypothesized that the intravenous (i.v.) administration of the same doses of GRP-27 and BN will be as effective as the i.p. administration in evoking these feeding responses. To test this hypothesis, we administered GRP-27 and BN i.v. and measured first MS (10% sucrose), IMI, satiety ratio (SR, IMI/MS) and second MS in overnight food-deprived but not water-deprived male Sprague Dawley rats. We found that (1) only GRP-27 reduced the first MS, (2) BN prolonged the IMI, (3) GRP-27 and BN increased the SR and (4) only BN reduced the size of the second meal. Contrary to our hypothesis, the i.v. administration of GRP-27 and BN affected the MS and IMI differently than did the i.p. administration. In conclusion, this pharmacological study suggests that the MS and IMI are regulated at different sites.

Exenatide and feeding: possible peripheral neuronal pathways

Intraperitoneal (i.p.) administration of the synthetic agonist of the glucagon like peptide-1 (GLP-1) receptor exenatide reduces food intake. Here, we evaluated possible peripheral pathways for this reduction. Exenatide (0.5 μg/kg, i.p.) was given to three, overnight food-deprived, groups of rats: total subdiaphragmatic vagotomy (VGX, severs the vagus nerve), celiaco-mesenteric ganglionectomy (CMGX, severs the splanchnic nerve) and combined VGX/CMGX. Following the injection, meal sizes (MSs) and intermeal intervals (IMIs) were determined for a total of 120 min. We found that exenatide reduced the sizes of the first two meals but failed to prolong the IMI between them, that VGX attenuated the reduction of the first MS, and that VGX, CMGX and combined VGX/CMGX attenuated the reduction of the second MS by exenatide. Therefore, the vagus nerve appears necessary for the reduction of the first MS by exenatide, whereas both nerves appear necessary for the reduction of the second MS by this peptide.

Gastrin releasing peptide-29 requires vagal and splanchnic neurons to evoke satiation and satiety

We have shown that gastrin-releasing peptide-29 (GRP-29), the large molecular form of GRP in rats, reduces meal size (MS, intake of 10% sucrose solution) and prolongs the intermeal interval (IMI). In these studies, we first investigated possible pathways for these responses in rats undergoing total subdiaphragmatic vagotomy (VGX, removal of vagal afferent and efferent innervation of the gut), celiaco-mesenteric ganglionectomy (CMGX, removal of splanchnic afferent and efferent innervation of the gut) and combined VGX and CMGX. Second, we examined if the duodenum communicates the feeding signals (MS and IMI) of GRP-29 (0, 0.3, 1.0, 2.1, 4.1, 10.3 and 17.2 nmol/kg) with the feeding control areas of the hindbrain by performing duodenal myotomy (MYO), a procedure that severs some layers of the duodenal wall including the vagal, splanchnic and enteric neurons. We found that GRP-29 (2.1, 4.1, 10.3, 17.2 nmol/kg) reduced the size of the first meal (10% sucrose) and (1, 4.1, 10.3 nmol/kg) prolongs the first IMI but did not affect the subsequent meals or IMIs. In addition, CMGX and combined VGX/CMGX attenuated reduction of MS by GRP-29 and all surgeries attenuated the prolongation of the IMI. Therefore, reduction of MS and prolongation of IMI by GRP-29 require vagal and splanchnic nerves, and the duodenum is the major conduit that communicates prolongation of IMI by GRP-29 with the brain.

The feeding responses evoked by cholecystokinin are mediated by vagus and splanchnic nerves

Total or selective branch vagotomy attenuates the reduction of cumulative food intake by cholecystokinin (CCK)-8 and CCK-33 respectively. However, the role of the sympathetic innervation of the gut and the role of the vagus nerve in feeding responses, which include meal size (MS) and intermeal interval (IMI), evoked by CCK-8 and CCK-33 have not been evaluated. Here, we tested the effects of total subdiaphragmatic vagotomy (VGX) and celiaco-mesenteric ganglionectomy (CMGX) on the previous feeding responses by CCK-8 and CCK-33 (0, 1, 3, and 5 nmol/kg given intraperitoneally). We found (1) that both peptides reduced meal size and CCK-8 (5 nmol) and CCK-33 (1 and 3 nmol) prolonged IMI, (2) that VGX attenuated the reduction of MS but failed to attenuate the prolongation of IMI by both peptides and (3) that CMGX attenuated the reduction of meal size by CCK-8 and the prolongation of IMI by both peptides. Therefore, the feeding responses evoked by CCK-8 require intact vagus and splanchnic nerves: the reduction of MS by CCK-33 requires an intact vagus nerve, and the prolongation of IMI requires the splanchnic nerve. These findings demonstrate the differential peripheral neuronal mediation of the feeding responses evoked by CCK-8 and CCK-33.

Gastrin releasing peptides increase Fos-like immunoreactivity in the enteric nervous system and the dorsal vagal complex

We and others have shown that gastrin-releasing peptide (GRP) reduces food intake. In this study, we determined the activation of the gastrointestinal and dorsal vagal complex (DVC) neurons by various forms of GRP to determine the pathway involved in this reduction. We found the following: (1) GRP-10, -27 and -29 (2.1 nmol/kg, i.p.) increased the Fos-like immunoreactivity (Fos-LI, a marker for neuronal activation) in the myenteric neurons of the stomach and the area postrema (AP) of the DVC; (2) GRP-27 and GRP-29 increased the Fos-LI in the myenteric plexus of the duodenum; and (3) only GRP-29 increased the Fos-LI in the submucosal plexus of the duodenum. In conclusion, GRP may reduce food intake by activating the area postrema. The enteric neurons may have a potential role in this reduction through the direct activation of the AP or exerting local gut actions, such as the stimulation of gut motility or secretions.

Ileal interposition attenuates the satiety responses evoked by cholecystokinin-8 and -33

One of the possible mechanisms by which the weight-reducing surgical procedure ileal interposition (II) works is by increasing circulating levels of lower gut peptides that reduce food intake, such as glucagon like peptide-1 and peptide YY. However, since this surgery involves both lower and upper gut segments, we tested the hypothesis that II alters the satiety responses evoked by the classic upper gut peptide cholecystokinin (CCK). To test this hypothesis, we determined meal size (MS), intermeal interval (IMI) and satiety ratio (SR) evoked by CCK-8 and -33 (0, 1, 3, 5nmol/kg, i.p.) in two groups of rats, II and sham-operated. CCK-8 and -33 reduced MS more in the sham group than in the II group; CCK-33 prolonged IMI in the sham group and increased SR in both groups. Reduction of cumulative food intake by CCK-8 in II rats was blocked by devazepide, a CCK(1) receptor antagonist. In addition, as previously reported, we found that II resulted in a slight reduction in body weight compared to sham-operated rats. Based on these observations, we conclude that ileal interposition attenuates the satiety responses of CCK. Therefore, it is unlikely that this peptide plays a significant role in reduction of body weight by this surgery.

The short term satiety peptide cholecystokinin reduces meal size and prolongs intermeal interval

Camostat mesilate (or mesylate) releases endogenous cholecystokinin (CCK) or CCK-58, the only detectable endocrine form of CCK in the rat, and reduces cumulative food intake by activating CCK(1) receptor. However, the literature lacks meal pattern analysis and an appropriate dose-response curve for this peptide. Therefore, the current study determines meal size (MS), intermeal interval (IMI) and satiety ratio (SR) by orogastric gavage of camostat (0, 12.5, 25, 50, 100, 200, 300, 400, 800mg/kg) and compares them to those previously reported by a single dose of CCK-8 (1nmol/kg, i.p), the most utilized form of CCK. We found that camostat (200, 300, 400 and 800mg/kg) and CCK-8 reduced cumulative food intake and the size of the first meal, but only camostat prolonged IMI and increased SR. There was no change in the duration of the first two meals or in rated behaviors such as feeding, grooming, standing and resting in response to camostat and CCK-8, but there was more resting during the IMI in response to camostat. This study provides meal pattern analysis and an appropriate dose-response curve for camostat and CCK-8. Camostat reduces food intake by decreasing MS and prolonging IMI, whereas CCK-8 reduces food intake by reducing only meal size.

Cholecystokinin-33 inhibits meal size and prolongs the subsequent intermeal interval

There are various forms of the satiety gut-brain peptide cholecystokinin (CCK), a short, widely utilized form or CCK-8, and a long, putatively more effective form or CCK-33. The issue of which of these forms is a more effective satiety peptide is not resolved. Here, we compared the satiety responses, including the sizes of the first three meals (MS) and intermeal intervals (IMI) as well as their calculated satiety ratios (SR), evoked by both peptides. CCK-8 and 33 (1, 3 and 5 nmol/kg, i.p) reduced the size of the first meal similarly, only CCK-33 prolonged the first IMI and increased SR and both peptides failed to affect second and third MS and IMI. As such, CCK-33 is a more effective satiety peptide than CCK-8. The current results confirm previous findings which showed that both peptides reduce food intake by inhibiting meal size, whereas only CCK-33 reduces food intake by prolonging the intermeal interval.

Gastrin releasing peptide-29 evokes feeding responses in the rat

In mammals, gastrin releasing peptide (GRP) 10 and 27 reduce food intake. In the current work, we test the hypothesis that GRP-29, the large molecular form of GRP in the rat, also evokes feeding responses consistent with a possible role in satiety. Here, we measured three feeding responses, size of first meal, intermeal interval (IMI, time between first and second meal) and satiety ratio (SR, satiation period for every unit of food consumed in the first meal), in overnight food deprived rats following GRP-10, 27 or 29 (0, 0.3, 1.0, 2.1, 4.1, 10.3, 17.2nmol/kg) intraperitoneally and presentation of a 10% sucrose test diet. GRP-29 and GRP-27 reduced the size of the first meal, prolonged IMI and increased SR, but GRP-10 failed to exhibit similar feeding responses. The order of potency was GRP-29=GRP-27>GRP-10. The current data support a role for GRP-29 in the short-term regulation of food intake.

Cholecystokinin-8 activates myenteric neurons in 21- and 35-day old but not 4- and 14-day old rats

Cholecystokinin (CCK) activates the myenteric neurons of adult rats. The goal of this work is to determine the ontogeny of this activation by CCK-8 in the myenteric plexus of the duodenum (2cm immediately following the pyloric sphincter aborally) and compare it with that of the dorsal vagal complex (DVC) - which occurs in 1-day old pups. Despite the existence of both of the CCK receptors, CCK(1) and CCK(2), in 4, 14, 21 and 35 day old rats, CCK-8 (0, 5, 10, 20 and 40μg/kg, i.p.) increased Fos-like immunoreactivity (Fos-LI, a marker for neuronal activation) in the myenteric neurons of 21- and 35-day old rats but in the DVC of all age groups. As such, this belated activation of myenteric neurons by CCK-8 compared to the DVC may reflect a delayed role for these neurons in CCK-related functions.

Activation of submucosal but not myenteric plexus of the gastrointestinal tract accompanies reduction of food intake by camostat

It has been shown in the rat that endogenous cholecystokinin (CCK), released in response to the non-nutrient trypsin inhibitor camostat, reduces food intake at meals and increases Fos-like immunoreactivity (Fos-LI; a marker for neuronal activation) in the dorsal vagal complex (DVC) of the hindbrain but not the myenteric plexus of the duodenum and jejunum. Experiment 1: We examined Fos-LI in the myenteric and the submucosal plexuses of the gut in response to orogastric gavage of camostat in rats. As we reported previously, camostat failed to increase Fos-LI in the myenteric plexus. We show here that camostat increased Fos-LI in the submucosal plexus of the duodenum and jejunum. Camostat also increased Fos-LI in the DVC. Experiment 2: Pretreatment with devazepide, a specific CCK(1) receptor antagonist abolished camostat-induced Fos-LI in the submucosal plexus and the DVC. Experiment 3: Bilateral subdiaphragmatic vagotomy reduced camostat-induced Fos-LI in the submucosal plexus approximately 40% and abolished it in the DVC.

CONCLUSIONS

Activation of the submucosal plexus by cholecystokinin at the CCK(1) receptor accompanies stimulation of the dorsal vagal complex of the hindbrain and inhibition of food intake. Unlike the submucosal plexus, activation of the myenteric plexus is not necessary for cholecystokinin's influence on the dorsal vagal complex and food intake. The lack of activation in the myenteric plexus after camostat stimulation, in contrast to nutrient releasers of CCK such as oleate, suggests that intestinal stimulants can either release different amounts of CCK or cause release of CCK from I cells with different molecular forms of CCK. This would suggest that CCK-8 is released by camostat and is not able to travel to the myenteric plexus while a more stable form of CCK such as CCK-58 can travel to this site that is further away from the I cell.

A new endogenous form of PYY isolated from canine ileum: Gly-extended PYY(1-36)

We purified and identified the peptide YY (PYY) forms present and determined their levels from a portion of the canine ileum directly adjacent to the cecum by a new extraction method designed to prevent and evaluate degradation of endogenous peptides. We used three reverse phase chromatography steps with radioimmunoassay of fractions for PYY-like-immunoreactivity (PYY-LI). The purified fractions underwent intact protein/peptide mass spectrometry identification and sequencing (i.e. "top-down" MS analysis). This analysis confirmed the identity of a new form of PYY, PYY(1-36)-Gly, which co-elutes with PYY(1-36)-NH(2) through all three of separation steps used. The PYY(1-36)-Gly form represents approximately 20% of the total PYY found in this region of the canine intestine. In addition, we also found that the PYY(3-36)-NH(2) form represents 6% of the total PYY in the canine ileo-cecal junction. The physiological implication of the Gly-extended form of PYY(1-36) warrants further investigation.

Cholecystokinin-33 is more effective than cholecystokinin-8 in inhibiting food intake and in stimulating the myenteric plexus and dorsal vagal complex

We compared the abilities of cholecystokinin-33 (CCK-33) and CCK-8 to reduce food intake and to activate feeding-related areas of the nervous system. (1) Overnight food-deprived rats were presented with a 10% sucrose solution, and intake was measured at 5-min intervals throughout a 90-min test beginning immediately after intraperitoneal injections of 1, 3, or 5 nMol/kg of CCK-33, CCK-8, or the vehicle control. In the initial 20 min (first meal), both peptides were equally effective, producing large reductions of food intake. Thereafter, however, CCK-33 was more effective than CCK-8, producing much more sustained reductions. Overall, both peptides reduced total food intake, but CCK-33 was more effective than CCK-8. (2) Possible roles for the myenteric plexus of the duodenum and the dorsal vagal complex (DVC) of the brainstem in the differential satiety effects of CCK-33 and CCK-8 were examined by quantifying CCK-33- and CCK-8-stimulated Fos-like immunoreactivity (Fos-LI) in each site. Consistent with the greater ability of CCK-33 to produce sustained inhibitions of food intake, CCK-33 produced more Fos-LI than CCK-8 in nearly every section of the sampled sites. The results demonstrate: (1) Different forms of CCK have different efficacies in reducing food intake; (2) CCK-33 produces a much more prolonged satiety action than CCK-8; and (3) the myenteric plexus and DVC may play roles in these differential satiety actions.

Endogenous cholecystokinin reduces food intake and increases Fos-like immunoreactivity in the dorsal vagal complex but not in the myenteric plexus by CCK1 receptor in the adult rat

We hypothesized that endogenous CCK reduces food intake by activating the dorsal vagal complex (DVC) and the myenteric neurons of the gut. To test this hypothesis, adult rats were given camostat mesilate; a nonnutrient releaser of endogenous CCK, by orogastric gavage, and Fos-like immunoreactivity (Fos-LI) was quantified in the DVC and the myenteric plexus. The results for endogenous CCK were compared with those for exogenous CCK-8. Exogenous CCK-8 reduced food intake and stimulated Fos-LI in the DVC and in myenteric neurons of the duodenum and jejunum. In comparison, endogenous CCK reduced food intake and increased DVC Fos-LI but did not increase Fos-LI in the myenteric plexus. Similar to CCK-8, devazepide, a specific CCK1 receptor antagonist, and not L365,260, a specific CCK2 receptor antagonist, attenuated the reduction of food intake by camostat. In addition, Fos-LI in the DVC in response to both exogenous CCK-8 and camostat administration was significantly attenuated by vagotomy, as well as by blocking CCK1 receptors. These results demonstrate for the first time that reduction of food intake in adult rats by endogenous CCK released by a nonnutrient mechanism requires CCK1 receptors, the vagus nerve, and activation of the DVC, but not the myenteric plexus.

Effect of adrenalectomy on cholecystokinin-8–induced Fos-like immunoreactivity in myenteric neurons and the dorsal vagal complex in rats

OBJECTIVE

To investigate the effect of adrenalectomy on cholecystokinin-8 (CCK-8)-induced Fos-like immunoreactivity (Fos-LI) in the myenteric neurons of the dorsal vagal complex (DVC) in rats.

ANIMALS

16 male Sprague Dawley rats.

PROCEDURES

Rats were allocated to 1 of 2 groups and underwent adrenalectomy or a sham adrenalectomy procedure. Rats were challenged with a supraphysiologic dose of CCK-8 (40 microg/kg) or physiologic saline (0.9% NaCl) solution (0.5 mL) administered IP; after 90 minutes, rats were euthanized, and Fos-LI was quantified in the DVC (at the levels of the area postrema, nucleus tractus solitarii, and dorsal motor nucleus of the vagus) and the myenteric neurons of the duodenum and jejunum by use of a diaminobenzidine reaction enhanced with nickel. The Fos-LI-positive cells were counted by use of an automated system and manually in the DVC and intestinal samples, respectively. Counts of Fos-LI in the different hindbrain levels and myenteric neurons were compared between the adrenalectomy--and shamtreated groups and between the CCK-8- and saline solution-treated groups.

RESULTS

After adrenalectomy, CCK-8-induced Fos-LI was attenuated only in the myenteric neurons of the duodenum.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicate that the adrenal gland has a role in the activation of myenteric neurons by CCK-8 in rats.

Atropine methyl nitrate increases myenteric but not dorsal vagal complex Fos-like immunoreactivity in the rat

Atropine methyl nitrate (AMN, 0.05, 0.5 and 25 mg/kg) intraperitoneally increased Fos-like immunoreactivity (Fos-LI) in the myenteric plexus, but not the dorsal vagal complex (DVC, the area postrema (AP), nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus (DMV)) in adult, male Sprague-Dawley rats. A 3 mg/kg AMN dose decreased intake of 15% sucrose, but failed to increase Fos-LI in both locations. In conclusion, the myenteric plexus may play a local role in the behavioral response evoked by AMN.

Effect of sympathectomy and demedullation on increased myenteric and dorsal vagal complex Fos-like immunoreactivity by cholecystokinin-8

Chemical sympathectomy with daily, intraperitoneal (IP) injections of guanethidine sulfate to adult rats, attenuated myenteric, but not dorsal vagal complex (DVC) Fos-like immunoreactivity (Fos-LI) by cholecystokinin-8 (CCK). This technique destroys only 60-70% of the sympathetic neurons, and spares the hormonal source of catecholamines, the adrenal medulla. The goal of the current study is to evaluate the effect of complete sympathectomy or destroying 100% of the sympathetic neurons by injecting guanethidine to 1-day-old pups (40 mg/kg daily for 5 weeks), and surgically removing the adrenal medulla. In the DVC, demedullation and sympathectomy-demedullation increased Fos-LI by CCK in the area postrema and nucleus of the solitary tract, but sympathectomy-demedullation increased it only in the area postrema. In the myenteric plexus, sympathectomy increased this response in the duodenum, and demedullation increased it in the duodenum and jejunum. On the other hand, sympathectomy-demedullation attenuated myenteric Fos-LI in the jejunum. These results indicate that catecholamines may play an inhibitory role on the activation of the DVC neurons by CCK. In the myenteric neurons, however, catecholamines may have both inhibitory and excitatory roles depending on the level of the intestine e.g., duodenum vs. jejunum. This may also indicate that CCK activates the enteric neurons by different mechanisms or through different pathways.

Cholecystokinin-8 increases Fos-like immunoreactivity in myenteric neurons of the duodenum and jejunum more after intraperitoneal than after intravenous injection

The objective of this study was to measure the relative efficacy and potency of cholecystokinin-8 (CCK-8) given by intraperitoneal (i.p.) and intravenous (i.v.) injection to stimulate Fos-like immunoreactivity (Fos-LI) in neurons of the myenteric plexus in the duodenum and jejunum. The subjects for his experiment were 40 male Sprague-Dawley rats divided into eight treatment groups (n=5 rats per treatment). Four groups of rats were injected with 5, 10, and 40 microg/kg sulfated CCK-8 and saline (control) i.p., and the remaining groups with the same treatments i.v. We then detected Fos-LI, a marker for neuronal activation, in the myenteric plexus of the duodenum and jejunum, in response to the previous doses and routes. All of the CCK-8 doses administered by both routes increased Fos-LI in the myenteric plexus of the duodenum and jejunum significantly more than saline did. Although both routes were efficacious in increasing Fos-LI, CCK-8 i.p. was significantly more potent than CCK-8 i.v. These data provide immunohistochemical evidence that i.p. administration of CCK-8 is a more potent stimulant of Fos-LI in the neurons of the myenteric plexus of the duodenum and jejunum than i.v. injection.

Chemical sympathectomy attenuates myenteric but not dorsal vagal complex Fos-like immunoreactivity induced by cholecystokinin-8 in the rat

Vagotomy and capsaicin treatment attenuate dorsal vagal complex (DVC) but not myenteric Fos-like immunoreactivity (Fos-LI) induced by cholecystokinin-8 (CCK-8). The goal of this experiment is to test the role of the sympathetic nervous system in the pathway by which CCK-8 increases myenteric Fos-LI. Adult male Sprague-Dawley rats were pretreated with guanethidine sulfate (40 mg/kg daily for 5 weeks) or vehicle intraperitoneally (IP), and injected with CCK-8 (40 microg/kg) or saline IP. Fos-LI was then quantified in the DVC and the myenteric neurons of the duodenum and jejunum using a diaminobenzidine reaction. Guanethidine pretreatment attenuated myenteric but not DVC Fos-LI induced by CCK-8. These findings demonstrate that sympathetic neurons play a role in mediating the myenteric Fos-LI response to CCK. They also suggest differential mediation of myenteric and DVC responses to CCK.

Strain differences in myenteric neuron number and CCK1 receptor mRNA expression may account for differences in CCK induced c-Fos activation

We utilized a diaminobenzidine reaction enhanced with nickel to compare dorsal vagal complex (DVC) and myenteric neuronal Fos-Like immunoreactivity (Fos-LI), in response to sulfated cholecystokinin-8 (CCK-8) (5, 10, 20, 40 microg/kg), among Sprague-Dawley (SD), Standard Long-Evans (SLE), Otsuka Long-Evans Tokushima Fatty (OLETF), and Long-Evans Tokushima Otsuka (LETO) rats. All rat strains but OLETF expressed Fos-LI in response to CCK-8. In addition, SD rats expressed more Fos-LI in the area postrema and myenteric neurons than SLE and LETO rats. To investigate the basis for these differences, we utilized cuprolinic blue staining, which stains neuronal cell bodies, to quantify the number of myenteric neurons, and a reverse transcriptase chain polymerase reaction to measure the gene expression of CCK(1) receptor in the gut. We found that SD rats have significantly more duodenal myenteric neurons than the other strains. In addition, this strain expressed significantly higher levels of the CCK(1) gene in both the duodenum and jejunum than the other strains. In conclusion, SD rats may express more myenteric Fos-LI in response to CCK due to increased numbers of myenteric neurons or more intestinal CCK(1) receptors than the other strains of rats.

Cholecystokinin-8 increases Fos-like immunoreactivity in the brainstem and myenteric neurons of rats through CCK1 receptors

To examine the role of cholecystokinin1 receptor (CCK1) in the activation of brainstem and myenteric neurons by CCK, we compared the ability of exogenous CCK-8 to induce Fos-like immunoreactivity (Fos-LI) in these neurons in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, lacking CCK1 receptors, and Long-Evans Tokushima Otsuka (LETO) controls. Five groups (n=4 rats per group) of OLETF rats, and five LETO control groups, were injected intraperitoneally (IP) with 5, 10, 20, and 40 microg/kg CCK-8 or saline. Forty-micrometer brainstem sections containing the area postrema, nucleus of the solitary tract, and the dorsal motor nucleus of the vagus, and myenteric neurons of the duodenum, jejunum, and ileum underwent a diaminobenzidine reaction enhanced with nickel to reveal Fos-LI. CCK-8 did not increase Fos-LI in any of the tested neurons in the OLETF rats. CCK-8 increased Fos-LI in the brainstem of the LETO rats in a dose dependent manner. In the LETO rats only 40 microg/kg CCK-8 increased Fos-LI in the myenteric plexus of the jejunum. This study demonstrates that CCK-8 activates the brainstem and myenteric neurons through the CCK1 receptor.

Cholecystokinin1 receptors mediate the increase in Fos-like immunoreactivity in the rat myenteric plexus following intestinal oleate infusion

Intestinal infusion of nutrients, such as glucose and oleic acid, increase Fos-like immunoreactivity (Fos-LI) in both the enteric nervous system and neurons of the dorsal vagal complex (DVC) of the hindbrain. To test the hypothesis that increased Fos-LI in enteric neurons and the DVC, following intestinal nutrient infusions is mediated by cholecystokinin(1) receptors (CCK(1)), we counted enteric and DVC neurons that expressed Fos-LI following intestinal infusion of oleate or glucose, with and without pretreatment with the CCK(1) receptor antagonist, lorglumide. Both oleate and glucose infusions increased Fos-LI in the DVC. Oleate also increased Fos-LI in the myenteric and submucosal plexuses of the duodenum and the jejunum, but not the ileum, while glucose only increased Fos-LI in the submucosal plexus of the ileum. The CCK(1) receptor antagonist, lorglumide, abolished Fos-LI in the DVC following infusions of either oleate or glucose. In addition, lorglumide attenuated oleate-induced Fos-LI in the myenteric and submucosal plexuses of the duodenum and jejunum. However, lorglumide failed to attenuate glucose-induced Fos-LI in the submucosal plexus of the ileum. These data confirm previous reports indicating that CCK(1) receptors mediate increased DVC Fos-LI following intestinal infusion of oleate or glucose. CCK(1) receptors also contribute to increased Fos-LI in enteric neurons following intestinal oleate infusion. However, failure of lorglumide to attenuate the increase of Fos-LI in the ileal submucosal plexus following intestinal glucose suggests that some intestinal nutrients trigger Fos-LI induction via CCK(1) receptor-independent pathways.

Effects of cholecystokinin-receptor antagonists on Fos-like immunoreactivity stimulated by sulfated cholecystokinin-8 in neurons of the myenteric plexus and hindbrain of rats

OBJECTIVE

To evaluate the role of cholecystokinin (CCK)-receptor antagonists in the activation of enteric and hindbrain neurons by sulfated CCK-8.

ANIMALS

81 male Sprague-Dawley rats.

PROCEDURE

Rats were allocated to 10 groups (5 to 22 rats/group). Each rat received 2 IP injections (15 minutes between injections). The first injection consisted of a specific CCK2-receptor (CCK2R) antagonist (L365,260; 150, 500, or 1,000 microg/kg), a specific CCK1-receptor (CCK1R) antagonist (devazepide; 150 microg/kg), or 1% dimethyl sulfoxide (DMSO [ie, vehicle]), and the second injection consisted of sulfated CCK-8 (10 microg/kg) or saline (0.9% NaCl) solution. Rats were anesthetized and perfused with 500 mL of Krebs saline solution, and the myenteric plexuses of the duodenum and jejunum were collected. Rats were then perfused with 500 mL of phosphate-buffered 4% formaldehyde solution; rats were then euthanatized, and the hindbrain of each was harvested. Tissues were stained by use of a diaminobenzidine reaction enhanced with nickel to reveal Fos-like immunoreactivity (Fos-LI), a marker of neuronal activation, in the aforementioned neurons.

RESULTS

Sulfated CCK-8 significantly increased Fos-LI in the myenteric and hindbrain neurons, compared with values for the DMSO injections. All dosages of L365,260 failed to attenuate this increase; however, injection of devazepide attenuated the increase in Fos-LI.

CONCLUSIONS AND CLINICAL RELEVANCE

Analysis of the results of this study reveals that sulfated CCK-8 activates myenteric and hindbrain neurons of rats primarily through CCK1 R. It provides evidence that CCK2R are lacking or not functional in the gastrointestinal tract of rats.

Gastrointestinal neuroendocrinology

There exists individual enteroendocrine cells spread throughout the gastrointestinal mucosa that release specific peptide, as well as nonpeptide, hormones to have various endocrine action on target cells bearing cell surface receptors selectively sensitive to these regulatory substances. Following receptor activation, a series of events is set into motion that serves to transduce the information imparted to the target cell. Such transduction mechanisms are numerous, and may be excitatory or inhibitory to the cell depending upon which G-protein subunits the receptor is coupled.

Intestinal infusions of oleate and glucose activate distinct enteric neurons in the rat

Nutrients entering the small intestine trigger a variety of neural and endocrine reflexes that involve specific afferents, efferents and interneurons, many of which are located within the enteric nervous system (ENS). We hypothesized that intestinal nutrient stimuli might activate specific subpopulations of these neurons. To test this hypothesis, we utilized immunohistochemical detection of nuclear c-fos expression in the myenteric and submucosal plexuses of the rat small intestine following intraintestinal infusions of oleate or glucose. Additionally, we used dual label methods to detect both Fos-immunoreactivity and immunoreactivity for five phenotypic neuronal markers: neurokinin-1 receptor (NK-1R), neurofilament-M (NF-M), neuronal nitric oxide synthase (NOS), calbindin (Cal) and calretinin (Calr), to characterize neurons that were activated by intestinal infusion of oleate and glucose. We found that oleate and glucose activated myenteric neurons in the duodenum and jejunum, but not the ileum. Oleate and glucose infusions significantly increased the number of Fos-immunoreactive nuclei in the submucosal plexus of the duodenum and jejunum, however, only glucose increased Fos-immunoreactivity in the ileum. Oleate and glucose infusions were associated with a small increase in Fos-immunoreactivity in NOS-immunoreactive neurons in the myenteric plexus. In the submucosal plexus, the majority of neurons activated by intestinal infusion of oleate or glucose were immunoreactive to Cal and Calr. In the rat, many of these neurons have Dogiel Type II-like morphology, which is consistent with the possibility that these neurons function as mucosal afferents in reflexes activated by nutrient stimuli.

Morphology and distribution of nitric oxide synthase-, neurokinin-1 receptor-, calretinin-, calbindin-, and neurofilament-M-immunoreactive neurons in the myenteric and submucosal plexuses of the rat small intestine

Characterization of the enteric neurons is vital for understanding their physiological role. We have used single and dual label fluorescence and peroxidase-based immunohistochemistry in myenteric and submucosal whole mounts from the rat small intestine to evaluate the morphology and distribution of enteric neurons immunoreactive for the following phenotypic antigens: neuronal nitric oxide synthase (NOS), neurokinin-1 receptor (NK-1R), calretinin (Calr), calbindin (Cal), and neurofilament-M (NF-M). NOS-immunoreactive neurons had Dogiel type I morphology, were abundant in the myenteric plexus compared to the submucosal plexus, and never coexpressed NK-1R immunoreactivity. NK-1R- and Calr-immunoreactive neurons had Dogiel type II morphology and were distributed comparably in both plexuses. NK-1R and Calr-immunoreactivity were coexpressed in many of the same neurons. Calbindin-immunoreactive neurons exhibited four distinct morphologies: small and large Dogiel type II neurons, Dogiel type I neurons, and small elongated neurons. These neurons were significantly fewer in number in the myenteric plexus compared to the submucosal plexus. Neurofilament-M-immunoreactive neurons had three morphologies, Dogiel type II neurons, small Dogiel type II neurons, and a less common subpopulation of small, elongated, multipolar neurons. These neurons were also fewer in number in the myenteric plexus compared to the submucosal plexus. The distribution of these phenotypic markers may assist future work that elucidates the functional activities of these enteric neurons such as control of intestinal motility and adaptation to the entry of gastric contents.

Cholecystokinin activates specific enteric neurons in the rat small intestine

Cholecystokinin (CCK) is a peptide hormone released from the I-cells of the upper small intestine. CCK evokes a variety of physiological responses, such as stimulation of pancreatic secretion, reduction of food intake and inhibition of gastric emptying. Previously, we reported that CCK activates enteric neurons in the rat. However the specific subpopulations of enteric neurons activated by CCK have not been identified. In the work reported here, we utilized immunohistochemical detection of nuclear Fos, a marker for neuronal activation, and selected phenotypic markers to identify some of the neuronal subpopulations activated by CCK. The phenotypic markers that we examined were: nitric oxide synthase (NOS), neurokinin-1 receptor (NK-1R), calbindin (Cal), Calretinin (Calr), and neurofilament-M (NF-M). We found that in the myenteric plexus of the rat duodenum and jejunum, CCK activated NOS immunoreactive neurons. In the submucosal plexus of duodenum and jejunum, CCK activated Cal, Calr and NF-M immunoreactive neurons. CCK failed to activate NK-1R immunoreactive neurons in either plexus. Our results indicate that CCK activates distinct enteric neurons in the rat upper small intestine. Furthermore the fact that NOS immunoreactive neurons were activated suggests that CCK modulates the activity of inhibitory motor neurons in the myenteric plexus. Expression of Fos immunoreactivity in Calr and Cal immunoreactive neurons is consistent with a role for CCK in modulation of intrinsic sensory and/or secretomotor neuronal activity in the submucosal plexus.