PHOTOPERIODIC REGULATION OF MT1 AND MT2 MELATONIN RECEPTOR EXPRESSION IN SPLEEN AND THYMUS OF A TROPICAL RODENTFUNAMBULUS PENNANTIDURING REPRODUCTIVELY ACTIVE AND INACTIVE PHASES

Jun 8, 2010Chronobiology international

Day Length Effects on Melatonin Receptors in Immune Organs of a Tropical Rodent During Reproductive and Non-Reproductive Phases

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Abstract

Differential expression of melatonin receptors MT1 and MT2 in the spleen and thymus is associated with changes in photoperiod in the seasonal breeder Funambulus pennanti.

Long photoperiod (16L:8D) decreased melatonin receptor expression and circulatory melatonin levels in lymphatic tissues.
Short photoperiod (10L:14D) increased melatonin receptor expression and circulatory melatonin levels in both spleen and thymus.
Melatonin and testosterone levels vary seasonally, potentially influencing immunity and reproductive physiology.
The study suggests that slight changes in daylength can significantly impact the reproductive and immune systems of tropical seasonal breeders.

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Photoperiodic regulation of melatonin receptor types on target tissues, such as lymphatic organs, has never been explored for any seasonal breeder. In the present study, we accessed the high affinity membrane melatonin receptors MT1 and MT2 expression dynamics in lymphoid organs (i.e., spleen and thymus) of a seasonally breeding rodent Funambulus pennanti during two major reproductive phases (i.e., active and inactive), when the internal hormonal (melatonin and gonadal steroid) as well as the ecological conditions were entirely different. Photoperiod regulates circulatory melatonin level; hence, we noted the effect of different photoperiodic regimes (long; 16L:8D and short; 10L:14D photoperiod) equivalent to summer and winter daylength on membrane melatonin receptor MT1 and MT2 expression in spleen and thymus. We have correlated the melatonin receptor expression with two major hormones varying seasonally (i.e., melatonin and testosterone) also being responsible for modulation of immunity of a seasonal breeder. Differential immunoreactivity of MT1 and MT2 receptor in spleen and thymus of F. pennanti suggests an involvement of both the receptor types in signal transduction of photoperiod for seasonal immunomodulation, because in the tropical zone, a slight difference (1:45-2 h) in daylength may change reproductive physiology and immunity of animals for adaptation. Our above suggestion receives strong support from the experiment of photoperiodic exposure on MT1 and MT2 expression at the translational level, where long daylength decreased the circulatory melatonin level and melatonin receptor expression in both lymphatic tissues. On the other hand, under short daylength, expression of MT1 and MT2 receptor increased in both spleen and thymus along with concomitant increase in circulatory melatonin level. Differential hormonal level of melatonin and gonadal hormones during reproductively active and inactive phase and its direct relation with melatonin receptor expression dynamics in lymphoid organs could be responsible for seasonal adjustment of immunity and reproduction.

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PHOTOPERIODIC REGULATION OF MT1 AND MT2 MELATONIN RECEPTOR EXPRESSION IN SPLEEN AND THYMUS OF A TROPICAL RODENTFUNAMBULUS PENNANTIDURING REPRODUCTIVELY ACTIVE AND INACTIVE PHASES

Abstract

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