Density gradients of vesicular glutamate- and GABA transporter-immunoreactive boutons in calbindinand μ-opioid receptor-defined compartments in the rat striatum.

Cortical and subcortical inputs to the striatum are functionally highly organized and they obey to some extent striatal patch-matrix topography. Whether this organization is reflected in the density of various glutamatergic endings is unknown. We therefore mapped boutons expressing the vesicular glutamate transporters VGluT1 and VGluT2, together with boutons immunoreactive for vesicular γ-aminobutyric acid (GABA) transporter (VGAT) in patch and matrix throughout the striatum. We used triple-immunofluorescence staining followed by multichannel, high-magnification confocal laser scanning and 3D object recognition. Densities of VGluT1 and VGluT2 boutons were on average higher in matrix than in patches in all striatal sectors. The dorsal one-third of the striatum contained the highest densities of VGluT1 boutons. Subsequent 3D surface plotting revealed patterns of density "valleys" in the dorsomedial striatum coinciding with patch locations in the patch-matrix mapping. The density of VGluT1 boutons increased along three axes: ventrolateral-to-dorsomedial, ventral-to-dorsal, and lateral-to-medial. In contrast, VGluT2 showed a global increase in density from lateral to medial and a relatively high density in the ventral striatum. VGAT appeared more evenly distributed in the striatal patch-matrix than the VGluTs, with a tendency of bouton density to increase from medial to lateral. We noted a good correlation between the high VGluT1 bouton density dorsomedially with inputs from dorsal medial prefrontal cortex and related thalamic regions, and the enhanced VGluT2 input ventromedially with input from ventral medial prefrontal cortex and thalamic, amygdaloid, and hippocampal sources.