AbstractThe role of 5‐HT2 receptors in the regulation of acetylcholine (ACh) release was examined in the medial prefrontal cortex and dorsal hippocampus using in vivo microdialysis. The 5‐HT2A/2C agonist ±1‐(2,5‐dimethoxy‐4‐iodophenyl) ‐2‐ aminopropane hydrochloride (DOI) (1 and 2 mg/kg, i.p.) significantly increased the extracellular concentration of ACh in both brain regions, and this response was attenuated in rats treated with the 5‐HT2A/2B/2C antagonist LY‐53,857 (3 mg/kg, i.p.). Treatment with LY‐53,857 alone did not significantly alter ACh release in either brain region The 5‐HT2C agonist 6‐chloro‐2‐(1‐piperazinyl)‐pyrazine) (MK‐212) (5 mg/kg, i.p.) significantly enhanced the release of ACh in both the prefrontal cortex and hippocampus, whereas the 5‐HT2 agonist mescaline (10 mg/kg, i.p.) produced a 2‐fold increase in ACh release only in the prefrontal cortex. Intracortical, but not intrahippocampal, infusion of DOI (100 μM) significantly enhanced the release of ACh, and intracortical infusion of LY‐53,857 (100 μM) significantly attenuated this response. These results suggest that the release of ACh in the prefrontal cortex and hippocampus is influenced by 5‐HT2 receptor mechanisms. The increase in release of ACh induced by DOI in the prefrontal cortex, but not in the hippocampus, appears to be due to 5‐HT2 receptor mechanisms localized within this brain region. Furthermore, it appears that the prefrontal cortex is more sensitive than the dorsal hippocampus to the stimulatory effect of 5‐HT2 agonists on ACh release. Synapse 53:202–207, 2004. © 2004 Wiley‐Liss, Inc.