Figure 2.

CB₁ cannabinoid receptor expression during cortical development. The CB₁ receptor is present in the developing cortex, showing increasing expression levels from undifferentiated to differentiated projection neurons (PNs). The CB₁ receptor is present in Cajal–Retzius cells of the marginal zone (MZ) and apical and basal progenitors in the ventricular and subventricular (VZ/SVZ) proliferative area. Representative immunofluorescence images showing the colocalization of the CB₁ receptor in radial glial (RG) progenitors and intermediate amplifying progenitor cells (IPCs) as identified with Sox2 and Tbr2 antibodies, respectively [13] (copyright National Academy of Sciences, USA 2009). Higher expression levels of the CB₁ receptor are evident in maturing neurons that have reached the CP, that correspond to locally generated PNs. CB₁ receptor is present in certain interneuron (IN) populations that reach the pallium upon tangential migration from the ganglionic eminences. Image background corresponds to a representative in situ hybridization of the CNR1 mRNA at E.16.5 (by C. Hoffman and B. Lutz, Johannes Gutenberg University Mainz, Germany).