Differential appetite regulation in lines of chickens selected for high and low juvenile body weight: the role of beta-MSH
Smith, Marissa L.
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Melanocortins play a key role in appetite regulation across species. One such melanocortin, beta-melanocyte stimulating hormone (beta-MSH) is receiving increasing attention for its anorexigenic effects. In chicks selected for low (LWS) and high (HWS) juvenile body weight, beta-MSH differentially decreased food intake and HWS chicks may be more sensitive to its effects. Both lines responded similarly to beta-MSH with decreased water intake. While whole blood glucose concentrations and ingestive and non-ingestive behaviors (sit, stand, preen, perch, deep rest, jumps, escape attempts, feed pecks, defecations, and total distance traveled) were not affected in either line, beta-MSH increased corticosterone in LWS chicks but not HWS chicks. However, despite the increase in corticosterone concentration in LWS, astressin, a corticotrophin releasing hormone (CRH) receptor antagonist, did not attenuate the effects of beta-MSH in either line suggesting that the altered stress response may not be acting via CRH receptors. When beta-MSH was co-administered with HS014, a highly selective antagonist for the melanocortin 4 receptor, only LWS responded with an attenuated response to beta-MSH suggesting that the differential response may in part be due to altered receptor affinity or binding resulting from the selection process. To investigate the roles of the hypothalamus and hindbrain in the differential food intake response, an experiment was designed where chicks were injected targeting either the lateral or 4th ventricle utilizing a novel freehand injection procedure. Chicks from both lines responded similarly to beta-MSH following both lateral and 4th ventricle injections. Together, these data suggest that alterations in the b-melanocortinergic appetite regulation system may be in part responsible for the differential body weights of the LWS and HWS lines. [Adaptations of chapters II, III, and IV have been published in Neuroscience Letters, Journal of Neuroendocrinology, and Behavioural Brain Research, respectively]
- Doctoral Dissertations