Spontaneous physical activity (SPA) describes activity outside of formal exercise and shows large inter-individual variability. The hypothalamic orexin/hypocretin peptides are key regulators of SPA. Orexins drive SPA within multiple brain sites, including rostral lateral hypothalamus (LH) and nucleus accumbens shell (NAcSh). Rats with high basal SPA (high activity, HA) show higher orexin mRNA expression and SPA after injection of orexin-A in rostral LH compared to low activity (LA) rats. Here we explored the contribution of orexin signaling in rostral LH and NAcSh to the HA/LA phenotype. We found that HA rats have higher sensitivity to SPA after injection of orexin-A in rostral LH, but not in NAcSh. HA and LA rats showed similar levels of orexin receptor expression in rostral LH and activation of orexin producing neurons after orexin-A injection in rostral LH. Also, in HA and LA rats the co-injection of orexin-A in rostral LH and NAcSh failed to further increase SPA beyond the effects of orexin-A in rostral LH. Pre-treatment with muscimol, a GABA(A) receptor agonist, in NAcSh potentiated SPA produced by orexin-A injection in rostral LH in HA but not in LA rats. Our results suggest that a feedback loop from orexin responsive neurons in rostral LH to orexin neurons and a NAcSh - orexin neuron - rostral LH circuit regulate SPA. Overall, our data suggest that differences in orexin sensitivity in rostral LH and its modulation by GABA afferents from NAcSh contribute to individual SPA differences.
- physical activity
- lateral hypothalamus
- Copyright © 2016, American Journal of Physiology-Regulatory, Integrative and Comparative Physiology