Endogenous Serotonin 5-HT 2A and 5-HT 2C Receptors Associate in the Medial Prefrontal Cortex.

The 5-HT2A receptor (5-HT2A R) and 5-HT2C R are localized to the same neurons within the medial prefrontal cortex (mPFC), which regulates executive function, decision-making, and reward-guided learning and memory processes. The 5-HT2A R and 5-HT2C R co-immunoprecipitate in the mPFC of male, Sprague-Dawley rats, while in vitro studies demonstrate the presence of a physical interaction between the 5-HT2A R and 5-HT2C R. The purpose of this study was to identify mPFC subregions in which the 5-HT2A R and 5-HT2C R physically interact ex vivo in the male Sprague-Dawley rat. We established the expression patterns of 5-HT2A R and 5-HT2C R in layers I-VI of the anterior cingulate cortex (ACC), prelimbic (PL), and infralimbic (IL) subregions using double-label fluorescence immunohistochemistry in male rats. We then employed the proximity ligation assay (PLA) to test the hypothesis that the 5-HT2A R and 5-HT2C R form a close, physical association within these mPFC subregions. Our results demonstrate subregion- and layer-specific expression of the 5-HT2A R and 5-HT2C R proteins using immunofluorescence and single recognition PLA, and a spatially close (within 40 nm) interaction between the 5-HT2A R and 5-HT2C R that occurs along a dorsal-ventral gradient in the rat mPFC.