Please cite this article in press as: Yadav, S.K., et al., Variation in melatonin receptors (Mel 1a and Mel 1b ) and andro- gen receptor (AR) expression in the spleen of a seasonally breeding bird, Perdicula asiatica. J. Reprod. Immunol. (2011), doi:10.1016/j.jri.2011.08.003 ARTICLE IN PRESS G Model JRI-2080; No. of Pages 8 Journal of Reproductive Immunology xxx (2011) xxx–xxx Contents lists available at SciVerse ScienceDirect Journal of Reproductive Immunology j o ur nal homep age : w w w.elsevier.com/locate/jreprimm Variation in melatonin receptors (Mel 1a and Mel 1b ) and androgen receptor (AR) expression in the spleen of a seasonally breeding bird, Perdicula asiatica S.K. Yadav, C. Haldar ∗ , S.S. Singh Department of Zoology, Banaras Hindu University, Varanasi 221005, India a r t i c l e i n f o Article history: Received 5 April 2011 Received in revised form 20 July 2011 Accepted 9 August 2011 Available online xxx Keywords: Melatonin receptors Androgen receptor Immunity Reproduction Tropical quail a b s t r a c t 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 24 h time scale. Therefore, to understand the relationship between immune function and reproductive phases in a seasonally breeding bird, Perdicula asiatica, the Indian jun- gle 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 4 h, suggesting that the expression of the recep- tors 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. All rights reserved. 1. Introduction Both immune function and reproductive function are considered of eminent importance in various vertebrate groups. However, only a few studies have investigated the immune capacity and reproduction of birds in relationship to environmental variables under natural conditions (Sorci et al., 1997; Singh and Haldar, 2005). It has been reported that melatonin, an endocrine modulator of the photope- riodic inductions, plays a pivotal role in the seasonal ∗ Corresponding author at: Pineal Research Laboratory, Department of Zoology, Banaras Hindu University, Varanasi 221005, India. Tel.: +91 542 2307149x125; fax: +91 542 2368174; mobile: +91 9415222261. E-mail address: chaldar2001@yahoo.com (C. Haldar). adjustment of immunity in diurnal birds (Skwarlo-Sonta, 1999). Daily variations in the immune response have been positively correlated with pineal function in terms of melatonin secretion and negatively with circulatory testos- terone by several researchers in birds (Rodriguez et al., 1999; Brennan et al., 2002). Melatonin binding and receptor mRNA levels vary on a circadian basis, with expression lev- els affected by light and melatonin concentration in plasma (Bartness et al., 1993). Further, the actions of melatonin are considered to vary with time of the day due to the varia- tions in the availability of melatonin binding sites on target tissues in several vertebrate species (Gauer et al., 1993; Bayarri et al., 2004). Testosterone has traditionally been considered immunosuppressive (Grossman, 1984; Folstad and Karter, 1992). Testosterone fluctuates on a daily basis being high 0165-0378/$ – see front matter © 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.jri.2011.08.003