Gender differences in Nociceptin/Orphanin FQ-induced food intake in strains derived from rats prone (WOKW) and resistant (Dark Agouti) to metabolic syndrome: a possible involvement of the cocaine- and amphetamine-regulated transcript system.

Our previous study found that when injected with Nociceptin/Orphanin FQ (N/OFQ) into the brain, male Dark Agouti (DA) rats, which are resistant to metabolic syndrome, have greater hyperphagia than male Wistar Ottawa Karlsburg W (WOKW) animals, which are prone to this disease. We attributed this difference to the fact that these two strains have different cocaine-amphetamine regulated transcript peptide (Cart) gene sequences and expression. In order to address this hypothesis, the present work focused on sex differences and analyzed not only male but also female N/OFQ-induced (0.25 and 0.5 nmol/rat) food intake in terms of their Cart and N/OFQ receptor gene expression in the hypothalamic area. In N/OFQ-naive WOKW females, cart gene expression is extremely elevated compared to N/OFQ-naive WOKW males. When male and female WOKW littermates are stimulated with N/OFQ, the food intake of females is significantly lower than that of the males. Granted, the N/OFQ feeding behavior experiments were not performed on the animals measured for Cart gene expression, but nonetheless, the responses observed in littermates point to an interesting avenue for further inquiry.