Figure 3. CB₁ receptor immunolocalization in different subcellular compartments of the rodent brain.

Single pre-embedding immunogold (A) and double pre-embedding immunogold and immunoperoxidase methods (B-D). A. CB₁ receptor labeling (arrows) at a presynaptic GABAergic terminal (ter, yellow) adjacent to a dendrite (den, purple). CB₁ receptor particle is localized to a presynaptic glutamatergic terminal (ter, pink) associated with a spine (sp, purple). Mitochondria (m, red) exhibit CB₁ receptor immunolabeling in both glutamatergic (ter, pink) and GABAergic (ter, yellow) presynaptic terminals (CA1 stratum radiatum, adult mouse hippocampus). B. CB₁ receptor labeling (arrows) at a presynaptic GABAergic terminal (ter, yellow), glutamatergic terminals (ter, purple) and in one astrocyte branch (white arrowhead; as, green) in the mouse piriform cortex. Astrocytes are labeled with anti-GLAST/immunoperoxidase/DAB method (black precipitate in as). C. CB₁ receptor labeling (arrows) at a presynaptic GABAergic terminal (ter, yellow) adjacent to a dendrite (den, purple) and in one astrocyte process (white arrowhead; as, green) in the molecular layer of the mouse dentate gyrus. Astrocytes are labeled with anti-GFAP/immunoperoxidase/DAB method (black precipitate in as). D. CB₁ receptor labeling (arrows) at a presynaptic terminal (ter, yellow) combined with anti-gephyrin/immunoperoxidase/DAB method (black precipitate in den, purple) to positively identify the inhibitory postsynaptic membrane of a GABAergic synapse. White arrowhead: CB₁ receptor labeling at a thin astrocytic process filling the intercellular space (rat prelimbic cortex). E-F. Double post-embedding immunogold method revealing the localization of presynaptic CB₁ receptors (ter; 18 nm-diameter gold particles) and postsynaptic mGluR2/3 (den, sp; 10 nm-diameter gold particles) at inhibitory (ter, yellow) and excitatory (ter, pink) synapses in the mouse dentate molecular layer. Scale bars= 500 nm.