Expression of a dopamine D2 receptor-activated K+ channel on identified striatopallidal and striatonigral neurons

One view of the efferent circuitry of the basal ganglia holds that dopamine D1 and D2 receptors are segregated to striatonigral and striatopallidal neurons, respectively. The present studies investigated whether functional D2-like receptors are, in fact, restricted to striatopallidal neurons. Single, freshly dissociated cells from rat striatum were identified as either striatonigral or striatopallidal projection neurons by fluorescence retrograde labeling. By using cell-attached patch-clamp recordings, neurons of each efferent group were evaluated for the presence of a D2-like receptor-activated 85-pS K+ channel as a measure of receptor function. We now report the presence of this D2 receptor-mediated response on both striatal efferent populations, but we observed an approximately 2-fold higher likelihood of encountering the channel on pallidal- versus nigral-projecting neurons. The channel's conductance properties appeared identical in both groups of neurons, but there was a significantly greater open probability for channels detected on striatopallidal neurons. These results indicate that functional D2 receptors are not segregated to striatopallidal neurons, but may be expressed in a higher proportion of, or at a higher density and/or efficiency of coupling on, pallidal- versus nigral-projecting striatal efferents.