Feeding and stress interact through the serotonin 2C receptor in developing mice

Brain responses to high-protein diets

Proteins are suspected to have a greater satiating effect than the other 2 macronutrients. After protein consumption, peptide hormones released from the gastrointestinal tract (mainly anorexigenic gut peptides such as cholecystokinin, glucagon peptide 1, and peptide YY) communicate information about the energy status to the brain. These hormones and vagal afferents control food intake by acting on brain regions involved in energy homeostasis such as the brainstem and the hypothalamus. In fact, a high-protein diet leads to greater activation than a normal-protein diet in the nucleus tractus solitarius and in the arcuate nucleus. More specifically, neural mechanisms triggered particularly by leucine consumption involve 2 cellular energy sensors: the mammalian target of rapamycin and AMP-activated protein kinase. In addition, reward and motivation aspects of eating behavior, controlled mainly by neurons present in limbic regions, play an important role in the reduced hedonic response of a high-protein diet. This review examines how metabolic signals emanating from the gastrointestinal tract after protein ingestion target the brain to control feeding, energy expenditure, and hormones. Understanding the functional roles of brain areas involved in the satiating effect of proteins and their interactions will demonstrate how homeostasis and reward are integrated with the signals from peripheral organs after protein consumption.

Polymorphisms of the HTR2C gene and antipsychotic-induced weight gain: an update and meta-analysis

AIMS

This study aims to test for possible associations between the gene coding for the 5-HT2C receptor and antipsychotic-induced weight gain.

MATERIALS & METHODS

Four HTR2C polymorphisms (rs498207, C-759T, G-697C and Ser23Cys) were investigated in our sample of 205 chronic schizophrenia patients.

RESULTS

Significant over-representation of the C-G-Cys23 haplotype in patients with weight gain (OR: 1.93; 95% CI: 1.04-3.56; p = 0.0015) was found. Similarly, haplotype analyses of percentage weight change were also significant (p = 0.029) for the C-G-Cys23 haplotype associated with the highest average percent weight gain. Observations in the polymorphisms are consistent with previous studies. An updated meta-analysis of nine previous studies plus our current sample suggest that the -759C allele is associated with antipsychotic-induced weight gain.

CONCLUSION

Additional studies, including the resequencing of the region surrounding the HTR2C promoter, and functional studies of the promoter polymorphisms, may elucidate the mechanism underlying this genetic association.

Effects of animal care procedures on plasma corticosterone levels in group-housed mice during the nocturnal active phase

C57BL/6 mice were housed five per cage on a 12:12 h light/dark cycle. All animal care, including bed cleaning, was carried out during the nonactive phase. After 2 weeks, mean plasma corticosterone levels, collected during the nonactive (ZT6) and active (ZT18) phases, were 66.0 and 270.9 ng/ml, respectively. The values at ZT18 gradually increased in the order of the mice used for blood collection, but not at ZT6. When animal care was carried out at ZT18, the increasing pattern of plasma corticosterone levels previously observed at ZT18 was less pronounced after 2 weeks of acclimatization, and was not observed after 4 weeks. Therefore, animal care should be carried out in the active phase for at least 4 weeks before experiments involving stress responses in the active phase.

Long-term consumption of fish oil-enriched diet impairs serotonin hypophagia in rats

Hypothalamic serotonin inhibits food intake and stimulates energy expenditure. High-fat feeding is obesogenic, but the role of polyunsaturated fats is not well understood. This study examined the influence of different high-PUFA diets on serotonin-induced hypophagia, hypothalamic serotonin turnover, and hypothalamic protein levels of serotonin transporter (ST), and SR-1B and SR-2C receptors. Male Wistar rats received for 9 weeks from weaning a diet high in either soy oil or fish oil or low fat (control diet). Throughout 9 weeks, daily intake of fat diets decreased such that energy intake was similar to that of the control diet. However, the fish group developed heavier retroperitoneal and epididymal fat depots. After 12 h of either 200 or 300 μg intracerebroventricular serotonin, food intake was significantly inhibited in control group (21-25%) and soy group (37-39%) but not in the fish group. Serotonin turnover was significantly lower in the fish group than in both the control group (-13%) and the soy group (-18%). SR-2C levels of fish group were lower than those of control group (50%, P = 0.02) and soy group (37%, P = 0.09). ST levels tended to decrease in the fish group in comparison to the control group (16%, P = 0.339) and the soy group (21%, P = 0.161). Thus, unlike the soy-oil diet, the fish-oil diet decreased hypothalamic serotonin turnover and SR-2C levels and abolished serotonin-induced hypophagia. Fish-diet rats were potentially hypophagic, suggesting that, at least up to this point in its course, the serotonergic impairment was either compensated by other factors or not of a sufficient extent to affect feeding. That fat pad weight increased in the absence of hyperphagia indicates that energy expenditure was affected by the serotonergic hypofunction.

A murine model of stress controllability attenuates Th2-dominant airway inflammatory responses

Epidemiological and experimental studies suggest a positive correlation between chronic respiratory inflammatory disease and the ability to cope with adverse stress. Interactions between neuroendocrine and immune systems are believed to provide insight toward the biological mechanisms of action. The utility of an experimental murine model was employed to investigate the immunological consequences of stress-controllability and ovalbumin-induced airway inflammation. Pre-conditioned uncontrollable stress exacerbated OVA-induced lung histopathological changes that were typical of Th2-predominant inflammatory response along respiratory tissues. Importantly, mice given the ability to exert control over aversive stress attenuated inflammatory responses and reduced lung pathology. This model represents a means of investigating the neuro-immune axis in defining mechanisms of stress and respiratory disease.