Quantitative Analysis of the Expression of Dopamine D1 and D2 Receptors in Pyramidal and GABAergic Neurons of the Rat Prefrontal Cortex

Mesocortical dopamine (DA) is a key neurotransmitter in cognitive processes and is involved in schizophrenia and antipsychotic drug action. DA exerts a highly complex modulation of network activity in prefrontal cortex (PFC), possibly due to the recruitment of multiple signaling pathways and to specialized cellular localizations of DA receptors in cortical microcircuits. Using double in situ hybridization, we quantitatively assessed the expression of D-1 and D-2 receptor messenger RNAs (mRNAs) in pyramidal and gamma-aminobutyric acidergic (GABAergic) neurons of rat PFC. The proportion of pyramidal and GABA cells expressing these transcripts shows great regional variability in PFC, with little overlap (layer V). More pyramidal and GABA cells express D-1 than D-2 receptors. D-1 receptors are expressed by a greater proportion of GABA than pyramidal neurons, yet the number of D-1-positive pyramidal cells outnumbers D-1-positive interneurons due to the greater abundance of pyramidal neurons. Occasional PFC cells show high levels of mRNA, similar to those in striatal neurons. Finally, pyramidal and GABAergic cells expressing the same transcript were almost never found in close apposition, yet D-2-containing pyramidal neurons were often found close to non-D-2 GABA neurons. Thus, cellular and network DA actions in PFC are region and layer specific and may depend on precise cellular interactions.