Variation in melatonin receptors (Mel 1a and Mel 1b) and androgen receptor (AR) expression in the spleen of a seasonally breeding bird, Perdicula asiatica

Abstract

Daily variation in the peripheral level of melatonin plays a major role in integrating reproduction and environmental information for seasonally breeding birds. However, the variation in immunity and reproduction has never been assessed in any avian species on a 24h time scale. Therefore, to understand the relationship between immune function and reproductive phases in a seasonally breeding bird, Perdicula asiatica, the Indian jungle bush quail, we studied the daily variation of melatonin and testosterone levels along with expression of their receptors Mel 1a, Mel 1b, and androgen receptor in the spleen during the reproductively active phase. Immunocytochemistry for the melatonin receptors Mel 1a and Mel 1b presented a differential distribution pattern. Western blot of splenic protein suggested a daily rhythm of melatonin receptors, while acrophases for the two melatonin receptors Mel 1a and Mel 1b differed by 4h, suggesting that the expression of the receptors may peak at different times, causing more of either Mel 1a or Mel 1b to be available at a particular time to mediate function. The circulatory melatonin level correlated with percentage stimulation ratio of splenocytes and plasma interleukin-2 level, but did not correlate with testosterone or androgen receptor, suggesting that melatonin could be a major hormone imparting a time-of-day effect on the modulation of immune function in a seasonally breeding bird during the reproductively active phase. © 2011 Elsevier Ireland Ltd.