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 dop amine D1 and D2 receptors are segregated to striatonigral and striatop allidal neurons, respectively, The present studies investigated whethe r functional D2-like receptors are, in fact, restricted to striatopall idal neurons. Single, freshly dissociated cells from rat striatum were identified as either striatonigral or striatopallidal projection neur ons by fluorescence retrograde labeling. By using cell-attached patch- clamp recordings, neurons of each efferent group were evaluated for th e presence of a D2-like receptor-activated 85-pS K+ channel as a measu re of receptor function, We now report the presence of this D2 recepto r-mediated response on both striatal efferent populations, but we obse rved an approximately 2-fold higher Likelihood of encountering the cha nnel on pallidal- versus nigral-projecting neurons. The channel's cond uctance properties appeared identical in both groups of neurons, but t here was a significantly greater open probability for channels detecte d on striatopallidal neurons. These results indicate that functional D 2 receptors are not segregated to striatopallidal neurons, but may he expressed in a higher proportion of, or at a higher density and/or eff iciency of coupling on, pallidal- versus nigral-projecting striatal ef ferents.