Orexin and MCH neurons express c-Fos differently after sleep deprivation vs. recovery and bear different adrenergic receptors

Though overlapping in distribution within the posterior hypothalamus, neurons containing orexin (Orx) and melanin concentrating hormone (MCH) may play different roles in the regulation of behavioural state. In the present study in rats, we tested whether they express c-Fos differently after total sleep deprivation (SD) vs. sleep recovery (SR). Whereas c-Fos expression was increased in Orx neurons after SD, it was increased in MCH neurons after SR. We reasoned that Orx and MCH neurons could be differently modulated by noradrenaline (NA) and accordingly bear different adrenergic receptors (ARs). Of all Orx neurons (estimated at approximate to 6700), substantial numbers were immunostained for the alpha(1A)-AR, including cells expressing c-Fos after SD. Yet, substantial numbers were also immunostained for the alpha(2A)-AR, also including cells expressing c-Fos after SD. Of all MCH neurons (estimated at approximate to 12 300), rare neurons were immunostained for the alpha(1A)-AR, whereas significant numbers were immunostained for the alpha(2A)-AR, including cells expressing c-Fos after SR. We conclude that Orx neurons may act to sustain waking during sleep deprivation, whereas MCH neurons may act to promote sleep following sustained waking. Some Orx neurons would participate in the maintenance of waking during deprivation when excited by NA through alpha(1)-ARs, whereas MCH neurons would participate in sleep recovery after deprivation when released from inhibition by NA through alpha(2)-ARs. On the other hand, under certain conditions, Orx neurons may also be submitted to an inhibitory influence by NA through alpha(2)-ARs.