Figure 8.

Muscarinic M₁ receptor is preferentially expressed in the somatodendritic compartments of D₁- and D₂-positive MS neurons. A, Triple labeling for M₁ (red), D₁ (green), and D₂ (blue) receptors. Note colabeling of M₁ with D₁ or D₂ receptors in thin perikaryal rims and neuropils. Scale bar, 10 μm. B–D, Arrows indicate interneurons expressing PV (B), high-affinity CHT (C), or neuronal NOS (D). Note vacant M₁ staining in these interneurons in contrast to abundant M₁ expression in perikarya of putative MS neurons (asterisks). Scale bars, 10 μm. E–G, Silver-enhanced immunogold microscopy for M₁ receptor. Note preferential M₁ labeling in spines (Sp), dendritic shafts (Dn), and cell bodies (CB) of putative MS neurons, in contrast to negative labeling in nerve terminals (NT) forming asymmetrical (Asy) and symmetrical (Sym) synapses. Scale bars, 1 μm. H, The mean number of metal particles per 1 μm of the cell membrane on spines (measured length, 177.5 μm), total dendrites (173.9 μm), dendrites within 500 nm from the edge of symmetrical synapses (12.0 μm), soma (29.8 μm), nerve terminals (71.5 μm), and myelin sheath (33.4 μm).