D2αPan receptors co-localize with synapsin in the fine neuropil. A: Illustration of a filled PD neuron in a sagittal section of the STG. A single primary process extends from the soma and exits the STG via the dvn. Before leaving the STG, the primary neurite branches to produce 9–10 large-diameter secondary neurites, that can continue to branch beyond the 16th branch order. Large-diameter neurites are found in the central, coarse neuropil. Small-diameter neurites and synapses lie in the fine neuropil. B: STG synaptic terminal drawn to scale. The presynaptic varicosity contains six release sites, indicated by vesicle clusters. A fingerlike postsynaptic twig extends from the presynaptic compartment and ends in a bulbous postsynaptic spine. C,D: A merged, 18-μm confocal projection (C) and an individual merged 1-μm optical slice (D) from a double-label IHC experiment indicate that D2αPan (red) and synapsin (green) can be either juxtaposed (red and green puncta) or co-localized (yellow puncta). Isolated D2αPan can also be observed (arrowhead). Magenta-green panels for C and D may be seen in Supplementary Figure 4. (Illustration by Sonia Hilliard, DVM.) Scale bar = 10 μm in C,D.