Figure 1. CB₁ Receptors are Present on Excitatory Terminals in the CeAL.

(A) In situ hybridization reveals the presence of CB₁ mRNA in both the CeA and the BLA of wild type mice. (B) The specificity of the riboprobe is confirmed by using CB₁^−/− animals. (C) The very high levels of CB₁ mRNA observed in a few scattered neurons in the BLA likely correspond to GABAergic interneurons. The vast majority of BLA neurons express moderate levels of CB₁ mRNA. In contrast, CB₁ mRNA expression in the CeA was only slightly above detection threshold. (D–E) Immunoperoxidase staining demonstrates the presence of the CB₁ protein in both the CeA and BLA, which was confirmed in our CB₁^−/− samples. (F) Higher magnification light micrographs reveal the dense CB₁ labeling in the neuropil throughout the CeAL. Asterisks depict CB₁-immunonegative cell bodies, whereas CB₁-immunopositive labeling appears as punctate staining indicating the compartmentalized distribution of the protein. (G₁-G₂) Serial electron micrographs illustrate the selective presynaptic accumulation of CB₁ in boutons (b+), which form mainly asymmetric (flanked by black arrowheads) and sometimes symmetric (white arrowheads) synapses with dendrites (d) and spine heads (s). CB₁ staining remained under detection threshold in a few axon terminals (b−), which highlights quantitative differences in CB₁ expression between terminal types innervating the CeAL. (H–I) The anatomical nature of the synapse type is illustrated at higher magnification. Scale bars: A, B, D, E are 200 μm; C is 50 μm; F is 20 μm; G₁, G₂, H, I are 100 nm.