Localization of glial cell line-derived neurotrophic factor receptor alpha and c-ret mRNA in rat central nervous system

Glial cell line-derived neurotrophic factor (GDNF) is a neurotrophic factor that influences the survival and function of several neuronal populations in the central (CNS) and peripheral nervous systems. The actions of GDNF are mediated by a multicomponent receptor complex composed of the tyrosine kinase product of c-ret and the ligand-binding protein GDNF receptor alpha (GDNFR-α). In the present study, we used in situ hybridization to localize cells expressing the mRNA for these GDNF receptor subunits in rat CNS. As reported previously, GDNFR-α and c-ret mRNA are present in the substantia nigra and ventral tegmental area, regions containing GDNF- responsive dopamine neurons. However, both mRNA were found in motor neurons of spinal cord and brainstem nuclei that innervate skeletal muscle. These areas include alpha motor neurons in the ventral horn of spinal cord and neurons in hypoglossal, facial, trigeminal, and abducens nuclei. In areas rostral to the substantia nigra, c-ret mRNA is not detected, whereas GDNFR- α is found in numerous brain structures, including the hippocampus, cortex, medial geniculate, and the medial habenula, the latter area expressing the highest levels of GDNFR-α mRNA in brain. These results provide evidence that c-ret and GDNFR-α mRNA are expressed in neuronal populations involved in motor function and provides further support for GDNF as a target-derived neurotrophic for these motor neurons. The observation that GDNFR-α mRNA is localized in several brain structures that do not contain detectable levels of c-ret mRNA indicates that either GDNFR-α utilizes signal transduction molecules other than c-ret in these areas or that other GDNF-like ligands that utilize GDNFR-α as a receptor may be present.