Orexin in the chicken hypothalamus: immunocytochemical localisation and comparison of mRNA concentrations during the day and night, and after chronic food restriction

Abstract

In mammals Orexin-A and -B are neuropeptides involved in the hypothalamic regulation of diverse physiological functions including food intake and the sleep-wake cycle. This generalisation was investigated in meat-(broiler) and layer-type juvenile domestic chickens by immunocytochemical localisation of orexin A/B in the hypothalamus, and by measurements of hypothalamic hypocretin mRNA which encodes for orexin A/B after chronic food restriction, and during the sleep-wake cycle. Orexin immunoreactive fibres were observed throughout the hypothalamus with cell bodies in and around the paraventricular nucleus. No differences were observed in the pattern of immunoreactivity using anti- human orexin-A, or -B antisera. The amount of hypothalamic hypocretin mRNA in food -restricted broilers was higher than in broilers fed ad libitum, but the same as in layer- type hens fed ad libitum. Hypothalamic hypocretin mRNA was increased (P<0.01) in 12-week-old broilers fed 25% of their ad libitum intake between 6–12 weeks of age. No difference in hypothalamic hypocretin mRNA was seen in 12-week-old layer- type hens when they were awake (1–2h after lights on) or sleeping (1–2h after lights off). It is concluded that in the chicken, we could not find evidence that hypothalamic orexin plays a role in the sleep-wake cycle and it may be involved in aspects of energy balance.