Circadian modulation of interval timing and motivation

AGOSTINO P.V.; BUSSI I.L.; LEVÍN, G; GOLOMBEK, D.A.

Bogotá

Congreso; 17th Meeting of the International Society for Comparative Psychology; 2014

International Society for Comparative Psychology

Interval timing in the seconds-to-minute range involves the interaction of cortico-striatal circuits via dopaminergic-glutamatergic pathways, while circadian rhythms modulate physiological and behavioural functions with periods close to 24 hours. We previously reported that circadian disruption or desynchronization impaired interval timing in mice. In this work we studied the involvement of dopamine signaling in this circadian-interval timing interaction. Daily levodopa injections improved timing performance in the peak-interval (PI) procedure in C57BL/6 mice with circadian disruptions, suggesting that a daily increase of dopamine is necessary for an accurate timing performance. Moreover, the daily rhythm in striatal dopamine levels was affected by inducing circadian disruption under constant light (LL). We also demonstrated a daily oscillation in tyrosine hydroxylase (TH) levels, dopamine turnover (DOPAC/DA levels), and both mRNA and protein levels of the circadian component Period2 (Per2) in the striatum and substantia nigra, two brain areas relevant for interval timing. None of these oscillations persisted under LL conditions. We suggest that the lack of dopamine rhythmicity under constant light, probably regulated by Per2, could be responsible for impaired performance in the timing task. Also, mice under LD exhibited a significant reduction (almost 4-fold) in motivation during the daytime to lever press for food reward. Taken together, our results of diurnal rhythms in dopamine signaling and motivation may contribute to improve treatment related to psychiatric disorders or drugs of abuse. Our findings add further support to the notion that circadian and interval timing share some common processes, interacting at the level of the dopaminergic system.