Cholecystokinin in the control of ingestive behavior

Modulatory role of serotonin on feeding behavior

The appearance, the odor, and the flavor of foods, all send messages to the encephalic area of the brain. The hypothalamus, in particular, plays a key role in the mechanisms that control the feeding behavior. These signals modulate the expression and the action of anorexigenic or orexigenic substances that influence feeding behavior. The serotonergic system of neurotransmission consists of neurons that produce and liberate serotonin as well as the serotonin-specific receptor. It has been proven that some serotonergic drugs are effective in modulating the mechanisms of control of feeding behavior. Obesity and its associated illnesses have become significant public health problems. Some drugs that manipulate the serotonergic systems have been demonstrated to be effective interventions in the treatment of obesity. The complex interplay between serotonin and its receptors, and the resultant effects on feeding behavior have become of great interest in the scientific community.

Bicarbonate-Based Peritoneal Dialysis Solution has Less Effect on Ingestive Behavior than Lactate-Based Peritoneal Dialysis Solution

Objective

The anorexia seen in peritoneal dialysis (PD) patients may be due partially to factors of dialysis solutions, such as pH and buffering agent. We tested the effects of different PD solutions in an experimental rat model for appetite.

Design

The intraoral intake of a sucrose solution from an implanted intraoral cannula in freely moving male Wistar rats was used to evaluate appetite at 30 minutes and 120 minutes after intraperitoneal (IP) infusion of bicarbonate (25 mmol/L)/lactate (15 mmol/L)-based PD solution (P) and conventional lactate (40 mmol/L)-based PD solution (D) with different concentrations of glucose. We also tested different buffer solutions containing lactate and bicarbonate with different pH but with no glucose.

Results

The IP infusion as such and the 30 mL volume did not inhibit appetite; however, appetite was significantly less inhibited by P than by D in the 1.36%, 2.27%, and 3.86% solutions ( p < 0.05). Furthermore, intraoral intake was significantly higher in rats receiving IP solution with bicarbonate buffer (pH 7.4) than with lactate buffer ( p < 0.05), whereas there was no significant difference in intraoral intake for lactate with pH 5.5, pH 6.6, or pH 7.4.

Conclusions

The bicarbonate/lactate solution inhibited appetite less than the lactate solution; this was due partially to the use of bicarbonate. The results show possible benefit on appetite of reducing the lactate concentration in PD solutions.

A role for dopamine in feeding responses produced by orexigenic agents

Dopamine-deficient (DD) mice become hypophagic and die of starvation by 3 to 4 weeks of age unless dopamine is restored by daily treatment with l-3-4-dihydroxyphenylalanine (l-dopa). We demonstrate here that DD mice mount qualitatively normal counter-regulatory blood glucose responses to insulin and 2-deoxy-d-glucose (2-DG). However, unlike control mice, DD mice fail to eat in response to acute glucoprivation induced by insulin or 2-DG. They also have a severely blunted response to central administration of peptide YY (PYY). Viral-mediated restoration of dopamine synthesis to the central caudate putamen (CPu) of DD mice rescues feeding and survival. However, this treatment fails to restore insulin- and 2-DG-induced feeding despite normalizing feeding in response to food deprivation and PYY. Since dopamine signaling in the CPu is not sufficient for glucoprivation-induced feeding, we propose that this feeding behavior may be mediated by dopamine in an anatomically distinct brain region.

Lean (Fa/Fa) but not obese (fa/fa) Zucker rats release cholecystokinin at PVN after a gavaged meal

Neuropeptides play an important role in the integration of dietary signals. Cholecystokinin (CCK) has been implicated in regulating ingestive behavior, particularly satiety. The primary objective of this study was to examine whether the hyperphagia characteristic of obese (fa/fa) rats involves impaired neural CCK secretion. Dynamic release of CCK at the hypothalamic paraventricular nucleus (PVN) of age-matched lean (Fa/Fa) and obese Zucker rats was determined using push-pull perfusion. The gavage of a 10.3-kcal (6 ml) liquid diet during lights off was followed by increased CCK release in lean rats (from 13.6 +/- 1.1 to 22.1 +/- 1.4 fmol in the 1st postprandial period and 18.4 +/- 2.5 fmol in the 2nd postprandial period). An identical meal load resulted in no postprandial increase in CCK release in obese rats, despite the fact that high-K+ artificial cerebrospinal fluid evoked CCK outflow in all animals. Intubation of 6 ml of nonnutritive 1% carboxymethylcellulose had no effect. These results are consistent with the suggestion that hypothalamic CCK plays a physiological role in satiety, and they demonstrate that obese Zucker rats have blunted hypothalamic CCK release in response to dietary cues.

Influence of peritoneal dialysis solutions with glucose and amino acids on ingestive behavior in rats

Continuous ambulatory peritoneal dialysis (CAPD) is often associated with malnutrition; reduced intake of nutrients due to anorexia is an important factor. The glucose load from glucose-based peritoneal dialysis (PD) solutions and amino acids from amino acid-based solutions may favor suppression of the appetite. To study this matter we used a new experimental model in free-moving, unstressed male Wistar rats (300 to 350 g) with feeding catheters channeled from the top of the skull to the oral cavity. When the rats recovered from surgery they were tested under standardized conditions by giving them an intraoral infusion (1 ml/min) of a solution containing 342 g/liter of the sucrose or 97 g/liter protein solutions while recording the time (volume) of ingestion. Control rats consumed 18.8 +/- 0.9 ml of the sucrose and 39.8 +/- 0.8 ml of the protein solutions. Injections of PD solutions with 13.6, 22.7, and 38.6 g/liter of glucose reduced the ingestion of sucrose by 12.4%, 23.6% and 36.1%, respectively, but did not affect the ingestion of protein. Injections of 30 ml of PD solutions containing 11, 18 and 31 g/liter of amino acids reduced the ingestion of both sucrose by 9.7%, 17.1% and 33.2% and of protein by 13.5%, 25.9% and 33.1%, respectively. We conclude that in our experimental model, the inhibition of appetite caused by peritoneal solutions containing glucose or amino acids seems to be specific for each nutritional constituent and not simply an effect of hyperosmolality or large filling volumes.