Altered monoamine metabolism in the hypothalamus of the genetically obese yellow (Ay/a) mouse

Bombesin receptor subtype-3 modulates plasma insulin concentration

Mice lacking a functional bombesin receptor subtype-3 (BRS-3) develop mild obesity. However, the origin of obesity in BRS-3 knockout (KO) mice remains unclear. We used a strain-crossing strategy to investigate the physiological role of the BRS-3 pathway. We crossed female heterozygous BRS-3 KO mice (X-/X) and male KK-Ay mice (Ay/+) to obtain BRS-3 KO/KK-Ay hybrid animals. In X-/Y:Ay/+ mice, plasma insulin concentrations were significantly higher, and on the oral glucose tolerance test, the additional secretion of insulin was impaired compared to other genotypes. Our results indicate that the BRS-3 pathway contributes to the regulation of plasma insulin concentrations.

Neonatal MSG reduces hypothalamic DA, beta-endorphin, and delays weight gain in genetically obese (A viable yellow/alpha) mice

Neonatal treatment with monosodium glutamate (MSG) decreases proopiomelanocortin (POMC) peptides and results in obesity. The yellow mouse is a model of obesity induced by the viable yellow (Avy) gene at the agouti locus on Chromosome 2, which results in overproduction of a POMC receptor antagonist. Thus we hypothesized that MSG, when imposed on the genetically susceptible model, would alter the development of obesity. Both yellow obese (Avy) and black lean (alpha/alpha) males were injected on Postnatal Days 1, 3, 5, 7, and 9 with 2.0 mg/g body weight MSG or saline SC. Their food intake, growth parameters, and neurochemical status were examined. Paradoxically, MSG interacted with the yellow phenotype to delay the rapid rate of weight gain characteristic of this model (p < 0.05). Food intake was decreased (p < 0.05) in both phenotypes treated with MSG, as was hypothalamic content of dopamine (p < 0.05) and of the POMC peptide, beta-endorphin (p < 0.001). The yellow obese phenotype was more sensitive than the black lean phenotype to the neurochemical effect of early postnatal MSG administration. Recent reports suggest the agouti locus protein is an antagonist of the receptor for another POMC peptide, melanocyte-stimulating hormone (MSH). Therefore, the balance of functional activity between various POMC peptides appears to be an important factor in the development of both acquired and genetic obesity.