Selectively bred diet-induced obese (DIO) rats become obese on a high fat diet and are leptin resistant before becoming obese. As compared to diet-resistant (DR) neonates, DIO neonates have impaired leptin-dependent arcuate (ARC) neuropeptide Y/agouti-related peptide (NPY/AgRP) and α-melanocyte-stimulating hormone (αMSH; from pro-opiomelanocortin (POMC) neurons) axon outgrowth to the paraventricular nucleus (PVN). Using phosphorylation of STAT3 (pSTAT3) as a surrogate, we show that reduced DIO ARC leptin signaling develops by postnatal day 7 (P7) and is reduced within POMC, but not NPY/AgRP neurons. Since amylin increases leptin signaling in adult rats, we treated DIO neonates with amylin during the postnatal hypothalamic development and assessed leptin signaling, leptin-dependent ARC-PVN pathway development and metabolic changes. DIO neonates treated with amylin from P0-6 and from P0-16 increased ARC leptin signaling and both AgRP and αMSH ARC-PVN pathway development, but increased only POMC neuron number. Despite ARC-PVN pathway correction, P0-16 amylin-induced reductions in body weight did not persist beyond treatment cessation. Since amylin enhances adult DIO ARC signaling via an IL-6-dependent mechanism, we assessed ARC-PVN pathway competency in IL-6 knockout mice and found that the AgRP, but not αMSH, ARC-PVN pathway was reduced. These results suggest that both leptin and amylin are important neurotrophic factors for the postnatal development of the ARC-PVN pathway. Amylin might act as a direct neurotrophic factor in DIO rats to enhance both the number of POMC neurons and their αMSH ARC-PVN pathway development. This suggests important and selective roles for amylin during ARC hypothalamic development.
- Copyright © 2016, American Journal of Physiology-Regulatory, Integrative and Comparative Physiology