Abrupt change in the timing of the day/night negatively affects sleep behaviour and cognitive performance in diurnal zebra finches

We investigated the consequence of abrupt directional shifts in the timing of light (hence darkness) period on sleep behaviour, novel object exploration and cognitive performance in diurnal zebra finches maintained under an equinox (12:12h LD) photoperiod. To two cohorts of birds (<i>n</i> = 80), the timing of 12 h light-on (hence of the darkness) for a week was either advanced by 6 h by reducing the dark period or delayed by 6 h by lengthening the dark period, with controls maintained on LD cycle as before. The first cohort of birds were examined for the effects on 24 h activity and feeding behaviors, while the second cohorts of birds were examined for the effects on sleep, neophobia and cognitive performance; the latter two were tested by the novel object exploration and spatial learning, respectively. The abrupt LD cycle shifts negatively affected sleep behaviour and cognition, as evidenced by behavioral and gene expression assays. There was a significant decrease in the mRNA expression levels of gene coding for the tyrosine hydroxylase (<i>TH</i>, the regulatory enzyme of the dopamine synthesis), cAMP response element binding protein (<i>CREB</i>), and brain-derived neurotrophic factor (<i>BDNF</i>) in hippocampus and <i>TH</i> alone in midbrain. These results support growing evidence of negative effects on behaviour and advanced brain functions in a diurnal species exposed to abrupt shifts in 24 h LD cycles.