Localizing cell surface receptors to specific subcellular sites can be crucial for proper functioning. PDZ proteins apparently play central roles in such protein localizations. 5-HT(2C) receptors have previously been shown to interact with MUPP1, a multi PDZ domain protein, in heterologous systems and in rat choroid plexus. We now report the generation and characterization of two independent MUPP1 antisera, which recognise distinct areas of the mouse brain in agreement with previous in-situ hybridization studies. Our results indicate that MUPP1 immunoreactivity co-localizes with 5-HT(2A) or 5-HT(2C) receptor expression in all regions of the mouse brain, including the choroid plexus where 5-HT(2C) receptors are highly enriched.