Localization of CXCR4 in the forebrain of the adult rat.

Chemokines are small secreted proteins that act as chemoattractants, and their role as neuromodulators in the brain has recently been appreciated. CXCL12 is one of the few chemokines found in neurons and expressed constitutively in the central nervous system. Previous data from our laboratory demonstrate the ability of CXCL12 to modulate the behavioral effects of cocaine, and this modulation is dependent on the central site of administration of CXCL12. The present study used single-staining immunohistochemical and dual-staining immunofluorescent methods to determine the localization of the CXCL12 receptor, CXCR4, in the caudate putamen and nucleus accumbens of the adult rat brain. Results demonstrated that individual neurons in both the caudate putamen and lateral shell of the nucleus accumbens express both CXCR4 and D1 dopamine receptors. Immunofluorescent studies showed that CXCR4 was co-expressed with ChAT, a marker for cholinergic neurons, and with GAD C38, a marker for GABAergic neurons, in the caudate putamen and lateral shell of the accumbens. No evidence of CXCR4 was found in the medial shell or core regions of the nucleus accumbens. These data demonstrate that CXCR4 is expressed by subpopulations of cholinergic and GABAergic neurons in the striatum and suggest that CXCR4 is well-positioned to modulate striatal function.