Orexin-A immunoreactivity and prepro-orexin mRNA expression in hyperphagic rats induced by hypothalamic lesions and lactation.

Orexins are endogenous neuropeptides that potently facilitate appetite and food consumption. In the present study, we examined orexin immunoreactivity and prepro-orexin mRNA expression in the lateral hypothalamus by immunohistochemistry and competitive reverse transcription-polymerase chain reaction (RT-PCR) methods in different models of hyperphagia in rats. Hyperphagia was induced by lesions of either the ventromedial hypothalamus (VMHL) or the paraventricular nucleus (PVNL), and we also compared lactating rats to nonlactating controls. Both VMHL and PVNL increased food intake and body weight compared to shams. On day 7 post lesion, serum leptin and insulin concentrations exhibited 3.2- and 2.8-fold increases in VMHL rats, and nonsignificant 1.8- and 1.8-fold increases in PVNL rats; there were significant decreases (48% and 33%) in lactating rats on day 12 postpartum compared to controls, respectively. Serum glucose concentrations were not significantly changed compared to controls in these rats. Quantification by image analysis suggests that VMHL significantly decreased the number and mean staining intensity of orexin-A immunoreactive neurones compared to those in the sham-lesioned group; while PVNL did not change orexin-A immunoreactivity. Competitive RT-PCR analysis showed that VMHL significantly decreased the prepro-orexin mRNA expression compared to those in the sham-lesioned group, and PVNL did not change it. Lactating rats on days 11-12 of lactation had significantly greater number and mean staining intensity of orexin-A immunoreactive neurones, prepro-orexin mRNA expression food intake and body weight than nonlactating postpartum rats. Thus, changes in orexin-A immunoreactivity and prepro-orexin mRNA expression were not consistent between the hyperphagia models. These results suggest that the hyperphagia from VMHL or PVNL and lactating rats differ in their involvement of orexin-A, and the change in circulating leptin and insulin concentrations may be involved in the change of orexin-A immunoreactivity in these rats.