Fig. 2. CXCR4 is distributed in a non-uniform manner both in the somatodendritic and axonal domains, but is preferentially associated with axons. Hippocampal neurons at day 10 in culture were fixed and immunostained for CXCR4 (A1,B1) and either the dendritic marker MAP2 (A2) or the synaptic marker SV2 (B2). CXCR4 immunoreactivity was detected within neuronal cell bodies and a subset of nerve cell processes identified as MAP2-positive and -negative processes, indicating a somatodendritic and axonal localization of CXCR4 (A1-A3). The extent of axonal CXCR4 immunostaining was however more prominent than the dendritic labelling. CXCR4 immunoreactivity was not uniformly distributed but was often observed in large clusters along the cell body and processes (arrows in insets corresponding to higher magnification of boxed regions in A3). Double labelling with SV2 (B3) shows that these CXCR4 clusters did not overlap with the synaptic marker, indicating that CXCR4 clusters were localized at nonsynaptic sites. Bar, 20 µm.