Fig. 6.

CB₁ cannabinoid receptors are located presynaptically on glutamatergic axon terminals in the ventral tegmental area. A–B) The punctate immunostaining for CB₁ observed at the light microscopic level in Fig. 5. partly corresponds to boutons (b_CB1) giving rise to asymmetric synapses (double arrowheads) terminating on large (d in A) and small diameter (d in B) CB₁-immunonegative dendrites. C-E2) shows weak but consistent labeling for CB₁ with immunogold particles (depicted by arrows) in axon terminals (b_CB1). D and E1–E2) Two CB1-positive axon terminals (b_CB1) labeled with immunogold particles (arrows) in panel C are shown at higher magnification. These boutons form asymmetrical synapses with a robust postsynaptic density (double arrowheads) on immunonegative dendrites (d). E1-2 present two consecutive sections of the lower axon terminal in C (b_CB1-E1-2). Note that all immunogold particles (arrows) representing the localization site of the CB₁ receptors are attached to the intracellular surface of the plasma membrane in the axon terminals. Unlabeled axon terminal is indicated by ”b”. Scale bars: A-E2, 0.2μm.