High-fat diet exacerbates cognitive rigidity and social deficiency in the BTBR mouse model of autism.

The global increase in rates of obesity has been accompanied by a similar surge in the number of autism diagnoses. Accumulating epidemiological evidence suggest a possible link between overweight and the risk for autism spectrum disorders (ASD), as well as autism severity. In laboratory animals, several studies have shown a connection between various environmental factors, including diet-induced obesity, and the development of autism-related behaviors. However, the effect of high-fat or imbalanced diet on a pre-existing autism-like phenotype is unclear. In this study, we employed the BTBR inbred mouse strain, a well-established mouse model for autism, to assess the impact of inadequate fattening nutrition on the autism-related behavioral phenotype. Male mice were fed by high-fat diet (HFD) or control balanced diet (control) from weaning onward, and tested in a series of behavioral assays as adults. In addition, we measured the hypothalamic expression levels of several genes involved in oxytocin and dopamine signaling, in search of a possible neurobiological underlying mechanism. As an internal control, we also employed similar metabolic and behavioral measures on neurotypical C57 mice. Compared to control-fed mice, BTBR mice fed by HFD showed marked aggravation in autism-related behaviors, manifested in increased cognitive rigidity and diminished preference for social novelty. Moreover, the total autism composite (severity) score was higher in the HFD group, and positively correlated with higher body weight. Finally, we revealed negative correlations associating dopamine signaling factors in the hypothalamus, to autism-related severity and body weight. In contrast, we found no significant effects of HFD on autism-related behaviors of C57 mice, though the metabolic effects of the diet were similar for both strains. Our results indicate a direct causative link between diet-induced obesity and worsening of a pre-existing autism-related behavior and emphasize the need for adequate nutrition in ASD patients. These findings might also implicate the involvement of hypothalamic dopamine in mediating this effect.

Urocortin 3 transgenic mice exhibit a metabolically favourable phenotype resisting obesity and hyperglycaemia on a high-fat diet.

AIMS/HYPOTHESIS: Urocortins are the endogenous ligands for the corticotropin-releasing factor receptor type 2 (CRFR2), which is implicated in regulating energy balance and/or glucose metabolism. We determined the effects of chronic CRFR2 activation on metabolism in vivo, by generating and phenotyping transgenic mice overproducing the specific CRFR2 ligand urocortin 3. METHODS: Body composition, glucose metabolism, insulin sensitivity, energy efficiency and expression of key metabolic genes were assessed in adult male urocortin 3 transgenic mice (Ucn3(+)) under control conditions and following an obesogenic high-fat diet (HFD) challenge. RESULTS: Ucn3(+) mice had increased skeletal muscle mass with myocyte hypertrophy. Accelerated peripheral glucose disposal, increased respiratory exchange ratio and hypoglycaemia on fasting demonstrated increased carbohydrate metabolism. Insulin tolerance and indices of insulin-stimulated signalling were unchanged, indicating these effects were not mediated by increased insulin sensitivity. Expression of the transgene in Crfr2 (also known as Crhr2)-null mice negated key aspects of the Ucn3(+) phenotype. Ucn3(+) mice were protected from the HFD-induced hyperglycaemia and increased adiposity seen in control mice despite consuming more energy. Expression of uncoupling proteins 2 and 3 was higher in Ucn3(+) muscle, suggesting increased catabolic processes. IGF-1 abundance was upregulated in Ucn3(+) muscle, providing a potential paracrine mechanism in which urocortin 3 acts upon CRFR2 to link the altered metabolism and muscular hypertrophy observed. CONCLUSIONS/INTERPRETATION: Urocortin 3 acting on CRFR2 in skeletal muscle of Ucn3(+) mice results in a novel metabolically favourable phenotype, with lean body composition and protection against diet-induced obesity and hyperglycaemia. Urocortins and CRFR2 may be of interest as potential therapeutic targets for obesity.

Prolonged and site-specific over-expression of corticotropin-releasing factor reveals differential roles for extended amygdala nuclei in emotional regulation.

Corticotropin-releasing factor (CRF) has a key role in the central stress response, and altered levels of this neuropeptide are linked to stress-related psychopathologies such as anxiety and depression. These disorders are associated with the inability to properly regulate stress response, specifically following exposure to prolonged stressful stimuli. Therefore, the current study assessed the effects of prolonged and site-specific over-expression of CRF, which mimics the state of chronic production, in extended amygdala nuclei that are known to be involved in mediating anxiety-like states. We first constructed and generated lentiviruses that overexpress (OE) CRF in a robust and stable manner, and then generated two male mouse models continuously over-expressing CRF, either at the central nucleus of the amygdala (CeA), or at the dorsolateral subdivision of the bed nucleus of the stria terminalis (BNSTdl). After 4 months, behavioral assessments were conducted for anxiety and depressive indices on these mice. Surprisingly, prolonged CRF OE at the CeA attenuated stress-induced anxiety-like behaviors, whereas prolonged CRF OE in the BNSTdl increased depressive-like behaviors, without affecting anxiety levels. These results show possible differential roles for CRF expressed by distinct loci of the extended amygdala, in mediating stress-induced emotional behaviors.

The anxiolytic effect of environmental enrichment is mediated via amygdalar CRF receptor type 1.

Environmental enrichment (EE) is known to have an anxiolytic effect in several animal models; however, the molecular mechanisms underlying these behavioral changes are not understood. In this study, we have shown that the anxiolytic effect of EE is associated with alterations in the corticotropin-releasing factor receptor type 1 (CRFR1) expression levels in the limbic system. We found that the decrease in anxiety-like behavior after housing in enriched conditions was associated with very low levels of CRFR1 mRNA expression in the basolateral amygdala of C57BL/6 mice. We further showed using a lentiviral-based system of RNA interference, that knockdown of CRFR1 mRNA expression in the basolateral amygdala induces a significant decrease in anxiety levels, similar to those achieved by EE nurture. Our data strongly suggest that reduced expression of CRFR1 mRNA levels in the basolateral amygdala mediates the effect of EE on anxiety-like behavior.