Fig. 5.

M2-immunogold and CB1 immunoperoxidase labeling in small axons and axon terminals. a and b) Plasmalemmal and cytoplasmic M2R immunogold is localized to small unmyelinated axons (M2-a) that are apposed to similar sized small axons that show immunoperoxidase labeling for the CB1 receptor (CB1-a). c and d) Images respectively illustrate M2R immunogold in separate axon terminals convergent on an unlabeled dendritic spine (us) and co-expressed in a single terminal presynaptic to a dendrite that also contains M2R-immunogold particles (M2-d). e and f) Presynaptic plasmalemmal and cytoplasmic distribution of M2R-immunogold particles in axon terminals forming asymmetric synapses with unlabeled dendritic spines. g) M2R immunogold is located on the plasma membrane and nearby large dense core vesicles (dcv) along the perimeter of an axon terminal without recognizable synaptic membrane specializations. Pictures in (b) and (g) were taken from THC-injected mice; all others were taken from vehicle-injected animals. Small straight arrows and black block arrows respectively indicate cytoplasmic and plasmalemmal M2R-immunogold particles in varying sizes of dendritic spines (M2-s). Black curved arrows—Asymmetric axospinous synapses; tv = tubulovesicle. Scale bars = 500 nm.