Small GTPases of the Rho-family, like Rho, Rac and Cdc42, are involved in neuronal morphogenesis by regulating growth cone morphology or dendritic spine formation. G-proteins of the G12-family, G12 and G13, couple G-protein-coupled receptors (GPCRs) to the activation of RhoA. Recently, two novel Rho-specific guanine nucleotide exchange factors (RhoGEFs), PDZ-RhoGEF and LARG, have been identified to interact with the activated alpha-subunits of G12/G13 and are thus believed to mediate GPCR-induced Rho activation. Although studies in neuronal cell lines have shown that G12/G13 and PDZ-RhoGEF mediate GPCR-induced neurite retraction, the role, as well as the expression of this signalling pathway, in intact brain has not been adequately studied. In the present study, we have characterized systematically the expression of G(alpha)12, G(alpha)13, PDZ-RhoGEF and LARG in various murine tissues as well as their subcellular localization in the central and peripheral nervous systems. By performing immunohistochemistry, using polyclonal antibodies raised against the above proteins, we observed that G(alpha)12, G(alpha)13 and their RhoGEF-effectors are distributed widely in the mammalian nervous system. Moreover, these proteins localize to distinct morphological compartments within neurons. While LARG and G(alpha)12 were mainly found in somata of the neurons, PDZ-RhoGEF and G(alpha)13 were predominantly localized in the neuropil of central neurons. Interestingly, PDZ-RhoGEF is a neural-specific protein, whereas LARG is nearly ubiqoutous. Our data provide evidence that the G12/13-RhoGEF-mediated pathway is present throughout the adult brain and may be involved in regulation of neuronal morphogenesis and function via GPCRs.