QUANTITATIVE IMMUNOCYTOCHEMISTRY OF DARPP-32-EXPRESSING NEURONS IN THE RAT CAUDATOPUTAMEN

DARPP-33, a dopamine and cAMP-regulated phosphoprotein with an apparen t molecular weight of 32 kD, is enriched in dopaminoceptive brain regi ons. Chief among these regions is the caudatoputamen which contains a large number of DARPP-32-containing medium sized spiny neurons. Since medium spiny neurons are a heterogeneous population with respect to co nnections and chemical neuroanatomy, it seemed of interest to determin e whether DARPP-32 is present in all medium-sized neurons, or only wit hin a specific subpopulation. The present study used immunocytochemist ry and quantitative analysis to address this issue. We demonstrate tha t DARPP-32 is contained in almost all medium-sized neurons (96.4%) and is not detected in large neurons. Taken together with previous observ ations that the DARPP-32-containing medium-sized neurons project heavi ly to all neostriatal targets, these data demonstrate that DARPP-32 is present in virtually all neostriatal output neurons. Thus, the DARPP- 32 cascade represents a final common pathway through which convergent efferent fibers using a variety of neurotransmitter agents may modulat e striatal outflow. (C) 1998 Elsevier Science B.V. All rights reserved .