THE DOPAMINE TRANSPORTER - COMPARATIVE ULTRASTRUCTURE OF DOPAMINERGICAXONS IN LIMBIC AND MOTOR COMPARTMENTS OF THE NUCLEUS-ACCUMBENS

The dopamine transporter (DAT) regulates extracellular dopamine concen trations, transports neurotoxins, and acts as a substrate for cocaine reinforcement. These functions are known to differ in the limbic-assoc iated shell and motor-associated core compartments of the nucleus accu mbens (NAc). Previous studies have shown differential expression of DA T in the NAc shell and core but were limited in resolution to the regi onal level, Thus, it is not known whether there are differences in the amount, subcellular localization, or plasmalemmal targeting of DAT wi thin individual dopaminergic axons in the two regions. We used high-re solution electron microscopic immunocytochemistry to investigate these possibilities, We show that in both the shell and core, DAT immunogol d labeling is present in tyrosine hydroxylase-immunoreactive varicose axons that form symmetric synapses. Within these labeled axons, most D AT gold particles are located on extrasynaptic plasma membranes, but s ome are associated with intracellular membranes, Dopaminergic axons in the shell contain lower mean densities of both total DAT gold particl es (per square micron) and plasmalemmal DAT gold particles (per micron ) than those in the core. Within labeled axons in the NAc shell and co re, however, there are no detectable differences in the subcellullar d istribution of DAT or the percentage of total DAT gold particles that are located on plasma membranes. These studies are the first to examin e and compare the subcellular localization of DAT in the NAc shell and core, As a result, they identify intrinsic, cell-specific differences in the expression of DAT within dopaminergic axons in these functiona lly distinct striatal compartments.