Abstract

This dissertation investigated the response of female rats in varying reproductive states to the administration of anorexigenic and orexigenic hormones and how behavioural and neural responses to such compounds might be influenced by reproductive state. The first set of experiments examined cycling, early or late stage lactation rats after treatment with various anorexigenics and measured food intake, body, and litter weight. The ability of central leptin administration to induce the phosphorylation of STAT3 in hypothalamic nuclei was also compared in these groups. Central leptin administration reduced food intake and body weight in all animals tested in a dose dependent way, however this effect was attenuated for food intake in early lactation. Litters of dams receiving the highest dose of leptin weighed less than those receiving the lowest dose or saline. Chronic peripheral leptin administration had no effect on any measures in lactating rats. Central administration of 1µg leptin produced increased PSTAT3-IR in ARC and the VMH across all groups tested, with trend in the PVN. MTII resulted in a dose dependent suppression of food intake and body weight across all reproductive states, with the higher dose being more pronounced. MTII administration at both doses reduced litter growth. The second chapter investigated intracerebroventricular (ICV) administration of ghrelin (0, 0.25 µg, 0.5 µg, 1 µg) and its effects on food intake in cycling and mid-lactation females. In the second experiment the food intake of cycling rats following the ICV administration of ghrelin (0.25 µg or 1 µg) was compared to rats in early and late lactation. These same reproductive states were compared with regard to food intake following administration of a ghrelin antagonist (JMV 3002, 0.4 µg). Central ghrelin administration resulted in a dose dependent increase in food intake in cycling rats while rats in mid-lactation showed a peak effect at the lowest dose of ghrelin administered. Cycling, early, and late lactating all responded to ghrelin with increased food intake. Ghrelin antagonist administration produced greater food intake reductions in late lactation compared to cycling or early lactation rats. Findings are discussed in relation to other neuropeptides and energy balance during lactation.