Meeting Abstract

80.5  Sunday, Jan. 6  Differential expression of melatonin receptor subtypes in the song control system of European starlings UBUKA, T*; MARGULIS, J; CLEGG, S; BENTLEY, GE; Univ. of California, Berkeley ubukat@berkeley.edu

The volumes of song control nuclei of songbirds, including Area X and HVC change across the breeding seasons. Besides the effects of seasonally-changing sex steroids, the seasonal change in melatonin secretion is likely to regulate the activity of song control nuclei. Area X and HVC contain melatonin receptor (MelR), as identified by autoradiography. In laboratory-housed male European starlings, the density of MelR in Area X changes markedly according to the reproductive state. MelR are down-regulated when starlings are photostimulated (in full breeding condition) and up-regulated when starlings become photorefractory (reproductively quiescent). The functional significance of seasonal regulation of MelR in the song control nuclei remains unclear, but it is likely to involve a release of cellular inhibition by melatonin during photostimulation, with possible consequences for song learning, memory consolidation or regulation of the context of song production. It is also possible that social, physiological or environmental factors other than photoperiod contribute to the regulation of MelR in song control nuclei. Three MelR subtypes, Mel1a, Mel1b, and Mel1c, are known in birds. We have thus cloned partial Mel1a, Mel1b, and Mel1c cDNA in starlings and performed in situ hybridization analysis in Area X and HVC. All of the MelR subtypes� mRNA was clearly expressed in both Area X and HVC but Mel1b and Mel1c mRNA positive cells were more abundant than Mel1a positive cells. The cell types which express each of receptor subtype are yet to be identified but these data allow us to investigate the probability that different subtypes have different functions and are influenced by different regulatory factors.