Immunocytochemical localization of mGluR5 and CB1R in the prelimbic prefrontal cortex (prPFC).
(A) Double confocal immunofluorescence showed no colocalization of both proteins. mGluR5 immunoreactivity was distributed in the neuropil throughout cortical layers, but the staining was more evident in apical dendrites of layers V/VI pyramidal neurons heading for the superficial layers. High CB1R immunoreactivity was in layers II/III, deeper part of layer V and throughout layer VI (Á: enlargement of A). The lack of CB1R labeling showed mGluR5 immunoreactivity in layers I, IV and in the upper part of layer V. (B–F). Electron microscopy of the localization of mGluR5 (DAB immunoreaction product) and CB1R (silver-intensified gold particles) in prPFC cortical layers V/VI. mGluR5 immunoreactivity was in dendritic profiles and spines (s). Typically, CB1R immunopositive synaptic terminals (T) made asymmetric synapses with mGluR5-immunoreactive dendritic spines (s). Note metal particles localizing CB1R (arrows) at perisynaptic and extrasynaptic sites relative to presynaptic membrane specializations of axonal synaptic boutons. Scale bars in A,A': 100 µm; B,C,E,F: 0.33 µm; D:0.20 µm.