Study of photic versus non-photic cues as entrainers of circadian running activity in rats

Though relative dominance of photic/non-photic cues on rodent circadian running activity is known, the exclusive role of non-photic entrainers in rats deprived of photic entrainers is not demonstrated and hence present work using retino-hypothalamic pathway blocked male rats (n = 10) was initiated. Blocking is done by enucleation of eyeballs. Circadian running activity is studied before enucleation and after enucleation towards instinctual social cues, food, water and sexual cues provided in activity cage. Twenty four hour activity of rats was recorded kymographically for a fifteen day period before enucleation and for a similar period after enucleation. Analysis of the records revealed that eight animals had predominant diurnal rhythm whereas two animals had predominant nocturnal rhythm. Enucleation of diurnal rats neither altered total running activity pattern nor caused any significant change in the goal compartments thus showing absence of entrainment by photic cues. In contrast nocturnal rats showed gradual shift of activity towards day time on enucleation thus indicating that nocturnal animals were entrained by photic cues. The overriding influence of non-photic entrainers on photic entrainers is discussed.