Affective Responses of Early Life Photoperiod in Male Wistar Rats

Behavior changes season dependant are probably linked to change in day length or photoperiod. Although much research on seasonality in small mammals has focused on photoperiod manipulations in adults, early life photoperiod is also an important source of seasonal information and can establish individual’s developmental trajectory by regulating somatic and reproductive development and affective responses to day lengths later in life. The experiments developed in this work are based on the hypothesis that early life photoperiod affect emotionality in adult rats. To cheek this hypothesis, male rats were exposed at birth to different photoperiods (LP: 16L/8D; SP: 8L/16D). 8, 16 or 24 weeks later, rats were subjected to different behavioral tests to quantify anxiety-like behavior. Independently of duration, rats exposed to SP exhibited higher levels of anxious-like behavior than rats raised in LP, in an open field test (OFT) and in elevated plus maze (EPM). Repeated comparisons showed that photoperiod effect was accentuated after 16 weeks of treatment. 24 weeks of treatment failed to induce any effect on emotionality in male rats. Our results indicate that changes in day length are associated with different levels of anxious-like behaviors; consistent with the conjecture that early life photoperiod may influence affective behavior in adult male rats.