Coordinated Expression of Dopamine Receptors in Neostriatal Medium Spiny Neurons

Abstract

The expression of dopamine (DA) receptors in individual neostriatal neurons has been examined using patch-clamp and single-cell reverse transcriptionpolymerase chain reaction (RT-PCR) techniques. To determine the molecular identity of the receptors mediating the responses to the dopaminergic ligands in individual neurons, single-cell RT-PCR techniques have been used. Several neurons have been found to express detectable levels of D2 and D1b mRNA, but not D1a mRNA; these cells consistently had robust responses to D1-class agonists. In other cells, D3 or D4 mRNA has been detected but not D2 mRNA; these cells consistently had responses to D2-class agonists. It suggests that these mRNAs are capable of being translated and properly processed. This inference allowed the equation of responsiveness to D1-class agonists with the presence of D1a receptors and responsiveness to D2-class agonists with the presence of D2 receptors. The demonstration that D1- and D2-class receptors are coexpressed by a significant percentage of medium spiny neurons, particularly those within the striatonigral pathway, establishes a cellular and molecular foundation for the well-known physiological and biochemical responses of these neurons to D1- and D2-class agonists. It has been also demonstrated that single-cell RT-PCR techniques yield a picture compatible with that derived from in situ hybridization if attention is restricted to only the most abundant receptor mRNAs.