Appetite regulation in desert-adapted Spinifex hopping mice during water deprivation

Spinifex hopping mice, Notomys alexis, can maintain water balance without drinking. This study examined the appetite control system in hopping mice during water deprivation (WD) at five time points (2, 5, 10, 17, and 29 days) using leptin and ghrelin ELISA, and Real Time qPCR and western analysis of leptin, leptin receptor, ghrelin, ghrelin receptor, and NPY. We found that water-deprived hopping mice showed a cyclical food intake in which hypophagia is followed by sustained food intake that is greater than water-replete animals. The mice lost body weight primarily due to fat loss but then weight stabilised and increased as WD is prolonged (29 days). Plasma leptin decreased in parallel with fat loss but then increased again, which is probably due to leptin expression in tissues such as skeletal muscle. WD had no effect on central leptin receptor mRNA and protein. Plasma ghrelin decreased during the hypophagia but then increased significantly as food intake increased; it then decreased markedly despite a sustained food intake during the longer WD time points. As WD was prolonged, brain ghrelin mRNA expression was up-regulated but the receptor mRNA was down-regulated. Finally, brain NPY mRNA was up-regulated during WD. In conclusion, central control of appetite is probably critical in hopping mice for sustaining food intake to provide substrate to generate metabolic water when free water is unavailable.