Pyramidal neurons in rat prefrontal cortex projecting to ventral tegmental area and dorsal raphe nucleus express 5-HT2A receptors

Abstract

The prefrontal cortex (PFC) is involved in higher brain functions altered in schizophrenia. Classical antipsychotics modulate corticolimbic circuits mainly through subcortical D2 receptor blockade, whereas second generation (atypical) antipsychotics preferentially target cortical 5-HT receptors. Anatomical and functional evidence supports a PFC-based control of the brainstem monoaminergic nuclei. Using a combination of retrograde tracing experiments and in situ hybridization we report that a substantial proportion of PFC pyramidal neurons projecting to the dorsal raphe (DR) and/or ventral tegmental area (VTA) express 5-HT2A receptors. Choleratoxin B application into the DR and the VTA retrogradely labeled projection neurons in the medial PFC (mPFC) and in orbitofrontal cortex (OFC). In situ hybridization of 5-HT2A receptor mRNA in the same tissue sections labeled a large neuronal population in mPFC and OFC. The percentage of DR-projecting neurons expressing 5-HT2A receptor mRNA was ~60% in mPFC and ~75% in OFC (n 5 3). Equivalent values for VTA-projecting neurons were ~55% in both mPFC and ventral OFC. Thus, 5-HT2A receptor activation/blockade in PFC may have downstream effects on dopaminergic and serotonergic systems via direct descending pathways. Atypical antipsychotics may distally modulate monoaminergic cells through PFC 5-HT2A receptor blockade, presumably decreasing the activity of neurons receiving direct cortical inputs.