Differences in ultrastructural localization of dopaminergic D1 receptors between dorsal striatum and nucleus accumbens in the rat.

Dopaminergic receptors of the D1 type are highly expressed in the dorsal striatum and nucleus accumbens. In the dorsal striatum, they are rarely observed on presynaptic terminals. However, their subcellular localization in the nucleus accumbens core and shell had not been compared to that of dorsal striatum. Here we investigated the subcellular localization of D1 receptors in these three brain regions using immunogold labeling and electron microscopy. We showed that, among all presynaptic terminals forming asymmetric contact with dendritic processes, the percentage of D1R immunoreactive terminals was low in the dorsal striatum (8.2%), but reached in the nucleus accumbens core and shell 25.5 and 29%, respectively. These observations are consistent with electrophysiological studies, which showed that D1 stimulation inhibits the response of target neurons to glutamatergic input via presynaptic mechanisms in the nucleus accumbens but not in the dorsal striatum.