Effects of photoperiod regimen on emotional behaviour in two tests for anxiolytic activity in Wistar rat.

Seasonal changes are often gone with mood and behaviour changes which are probably linked to change in day length or photoperiod. The experiments developed in this work are based on the hypothesis that changes in photoperiod affect emotionality in rats. To check this hypothesis, female rats were exposed to four different photoperiods (LP: 16L/8D; MP: 12L/12D; SP: 8L/16D; SP-F: 8L/16D with a light pulse in midpoint of the dark phase). Eight or 14 weeks later, rats were subjected to two behavioural tests to quantify anxiety level. Independently of duration, rats exposed to SP exhibited higher levels of anxious-like behaviour than rats raised in LP and SP-F, in an open field test (OFT) and in elevated plus maze (EPM). Significant differences in EPM are obtained only after 14 weeks of treatment. Moreover rats treated more long time showed greater suprarenal gland mass. Compared to all other groups, females exposed to SP had greater suprarenal gland. Our results indicate that changes in day length are associated with different levels of anxious-like behaviours consistent with the conjecture that short days may have an anxiogenic effect in female rats.