Conditional Inactivation of Limbic Neuropeptide Y-1 Receptors Increases Vulnerability to Diet-Induced Obesity in Male Mice.

NPY and its Y1 cognate receptor (Y1R) have been shown to be involved in the regulation of stress, anxiety, depression and energy homeostasis. We previously demonstrated that conditional knockout of Npy1r gene in the excitatory neurons of the forebrain of adolescent male mice (Npy1rrfb mice) decreased body weight growth and adipose tissue and increased anxiety. In the present study, we used the same conditional system to examine whether the targeted disruption of the Npy1r gene in limbic areas might affect susceptibility to obesity and associated disorders during adulthood in response to a 3-week high-fat diet (HFD) regimen. We demonstrated that following HFD exposure, Npy1rrfb male mice showed increased body weight, visceral adipose tissue, and blood glucose levels, hyperphagia and a dysregulation of calory intake as compared to control Npy1r2lox mice. These results suggest that low expression of Npy1r in limbic areas impairs habituation to high caloric food and causes high susceptibility to diet-induced obesity and glucose intolerance in male mice, uncovering a specific contribution of the limbic Npy1r gene in the dysregulation of the eating/satiety balance.

Enriched environment and the recovery from inflammatory pain: Social versus physical aspects and their interaction.

In this study, we aimed at comparing the effect of the social versus the physical enrichment of the environment on inflammatory pain. Hence, a rat model of carrageenan-induced knee inflammation was used. Four housing conditions were investigated: a physically enriched environment (PE), a socially enriched environment (SE), an enriched environment (EE) (i.e. physically and socially enriched) and a restricted environment (RE) (i.e. non-physically or socially enriched housing). Mechanical allodynia was assessed using the von Frey test preoperatively and at day post-operative (DPO) 1, 3, 7, 10, 14, 17, 21, 24 and 28. Besides, anxiety was evaluated at DPO29, using the Elevated Plus-Maze test. Results show that RE housing resulted in a duration of mechanical allodynia of 4 weeks and of only 3 weeks in EE housing. Housing in a physically enriched environment also resulted in a reduction of the duration of mechanical allodynia of 1 week. Finally, if housed in a SE, the mechanical allodynia lasted for 3 weeks and an half. From these data, we conclude that both physical and social aspects of the environment are involved in the reduction of inflammatory pain duration, although the PE has a larger effect than the SE in this experimental setting. Interestingly, an inter-dependent relationship was noted between the PE and SE. Moreover, no significant difference in the rat anxiety was measured between groups, suggesting that the pain outcomes are likely not biased by the mean of potential housing condition-induced anxiety.