Neuronal activation and corticotropin-releasing hormone expression in the brain of obese (fa/fa) and lean (fa/?) Zucker rats in response to refeeding

The present study was conducted to investigate the pattern of neuronal activation and corticotropin-releasing hormone (CRH) expression in fed, food deprived and refed lean (Fa/?) and obese (fa/fa) Zucker rats. The pattern of neuronal activation was studied by measuring the expression of the immediate-early gene c-fos. Expression of c-fos and CRH mRNA was determined by in situ hybridization histochemistry. In both lean and obese rats, one hour of refeeding led to a transient increase in c-fos mRNA levels which was detected in the paraventricular hypothalamic nucleus (PVH), the dorsomedial hypothalamic nucleus, the supraoptic nucleus, the paraventricular thalamic nucleus, the central nucleus of amygdala (CeA), the lateral and medial parabrachial nuclei, the nucleus of the solitary tract, and the area postrema. In addition, refeeding led to strong activation of the arginine-vasopressin neurons located in the magnocellular part of the PVH. Following 24 h of food deprivation, CRH expression in the parvocellular division of the PVH was significantly higher in obese rats compared to lean animals. During refeeding, PVH CRH mRNA levels in obese rats decreased to reach control values. The decrease in CRH expression in obese rats was accompanied by the alleviation of the hypercorticosteronemia that characterized obese Zucker rats. CRH mRNA levels in the central nucleus of the amygdala were significantly higher in lean rats than in obese animals, when the rats were fed ad libitum During food deprivation, CeA CRH mRNA levels decreased in lean rats and gradually returned to predeprivation values during refeeding. In refed obese rats, CeA levels of CRH mRNA were higher than those of ad libitum fed or food-deprived obese mutants. In the perifornical region of the lateral hypothalamic area (LHA), the expression of CRH mRNA rose significantly in response to refeeding in lean rats, but not in obese animals. Following the first hour of refeeding, the number of neurons expressing CRH mRNA in the LHA in lean rats almost doubled. The present results demonstrate that refeeding has a stimulating effect in obese Zucker rats in a pattern of activation similar to that seen in lean Fa/? rats. They also demonstrate differences in CRH expression between Fa/? and fa/fa rats after refeeding. The most apparent of these differences was seen in the lateral hypothalamus in which refeeding failed to up-regulate CRH expression in obese rats.