Short-photoperiod exposure reduces @entity1951 (V1a) receptor binding but not @entity369 - @entity1951 -induced flank marking in male XXXX .

@entity251 @entity369 @entity1951 @entity329
In @entity329 , socially relevant information is communicated with a form of scent marking known as flank marking. There is substantial evidence that @entity369 - @entity1951 acting on V1a @entity1951 receptors (V1aR) in the medial preoptic-anterior hypothalamic continuum (MPOA-AH) regulates the expression of flank marking. Previous studies have shown that the expression of flank marking is also influenced by the circulating concentrations of gonadal hormones. In hamsters housed in long 'summer-like' photoperiods (i.e. >12.5 h of light/day), castration reduces flank marking and administration of @entity251 restores precastration levels of flank marking. When exposed to short 'winter-like' photoperiods (i.e. <12.5 h of light/day), hamsters undergo gonadal regression and the circulating levels of @entity251 decline. Surprisingly, flank marking induced during social encounters is not reduced in hamsters exposed to short photoperiods despite the low circulating concentrations of @entity251 . In the present study, it was hypothesized that reductions in @entity251 , caused by exposure to short photoperiod, would not reduce the ability of @entity1951 to stimulate flank marking by its actions in the MPOA-AH. The amount of flank marking induced by @entity1951 injected into the MPOA-AH did not significantly differ between hamsters housed in long and short photoperiods; however, short photoperiod-exposed males had significantly less V1aR binding in the MPOA than long photoperiod-exposed males. These results support the hypothesis that the sensitivity of the MPOA-AH to @entity1951 is not reduced in short photoperiod-exposed males, despite decreases in serum @entity251 . However, by contrast to our predictions, short photoperiod-exposed males have significantly reduced V1aR binding in the MPOA-AH compared to long photoperiod-exposed males.
