Sleep in unnatural times: illuminated night negatively affects sleep and associated hypothalamic gene expressions in diurnal zebra finches

We investigated the effects of exposure at ecologically relevant levels of dim light at night (dLAN) on sleep and the 24 h hypothalamic expression pattern of genes involved in the circadian timing (per2, bmal1,reverb-beta,cry1,ror-alpha,clock) and sleep regulatory pathways (cytokines:tlr4,tnf-alpha,il-1 beta,nos; Ca2+-dependent pathway:camk2,sik3,nr3a; cholinergic receptor,achm3) in diurnal female zebra finches. Birds were exposed to 12 h light (150 lux) coupled with 12 h of absolute darkness or of 5 lux dim light for three weeks. dLAN fragmented the nocturnal sleep in reduced bouts, and caused sleep loss as evidenced by reduced plasma oxalate levels. Under dLAN, the 24 h rhythm ofper2, but notbmal1orreverb-beta, showed a reduced amplitude and altered peak expression time; however,clock,ror-alpha andcry1expressions showed an abolition of the 24 h rhythm. Decreasedtlr4,il-1 beta andnos, and the lack of diurnal difference inachm3messenger RNA levels suggested an attenuated inhibition of the arousal system (hence, awake state promotion) under dLAN. Similarly, changes incamk2,sik3andnr3aexpressions suggested dLAN-effects on Ca2+-dependent sleep-inducing pathways. These results demonstrate dLAN-induced negative effects on sleep and associated hypothalamic molecular pathways, and provide insights into health risks of illuminated night exposures to diurnal animals.