CB1 receptor is expressed in axonal as well as dendritic compartments of primary neurons matured over 4 wk in vitro.

(A) Coimmunostaining against CB1 receptor and dendritic marker MAP2 on 28 days in vitro (DIV) cortical neurons derived from wild-type mouse embryos (upper panels) shows the distribution of CB1 receptor in the axonal compartments (MAP2-negative) as well as dendritic compartments (MAP2-positive). The rabbit anti-CB1 antibody used throughout this experiment did not yield substantial staining in cortical neurons cultured from CB1-deficient mouse embryos at 28 DIV (lower panels). (B) Magnified images represent white boxed areas from main images. (C) CB1 receptor colocalizes with CamKII-GFP and the synaptic protein PSD95 in dendritic compartments, including several spine heads (white arrow heads), indicating postsynaptic localization. (D) Heterologously-expressed CB1-EGFP in mature cultured cortical neurons shows axonal and dentritic localization upon costaining with MAP2. Phalloidin is used to counterstain the entire actin cytoskeleton. Phall. stands for Phalloidin. (E) Dendritic (arrows) ad axonal (arrowhead) localization of endogenous CB1 in cortical neurons cultured from wild-type mice and matured at 28 DIV. White scale bars represent 20 μm and yellow scale bars represent 5 μm.