Differential Localization of Ionotropic and Metabotropic Glutamate Receptors in the Rat Substantia Nigra

Parkinson’s disease is characterized by a depletion of dopaminergic neurons in the substantia nigra pars compacta (SNc). Although the cause for the neuronal degeneration is largely unknown, ionotropic glutamate receptor-mediated excitocytotoxicity is suggested. The localization of different ionotropic glutamate receptors in the substantia nigra (SN) is therefore of critical importance in relation to glutamate excitocytotoxicity and Parkinson’s disease. In the present study, rats were perfuse-fixed under deep anesthesia. Sections of the SN were obtained using a vibrating microtome. Receptor immunocytochemistry using commercially available antibodies against ionotropic and metabotropic glutamate receptors was performed. Results were analyzed in a light microscope. Immunoreactivity for GluRl, GIuR2. GluR2/3, NMDAR1 and NMDAR2B subunits was mainly localized in the perikarya and proximal dendrites of the compacta neurons and also in a number of substantia nigra pars reticulata (SNr) neurons. In contrast, GIuR4-immunoreactivity was mainly found in the reticulata neurons. Less immunoreactivity for NMDAR2A and NMDAR2C subunits was detected. Immunoreactivity for mGluRla and mGluR2/3 was primarily detected in the neuropilar elements in the SNr. Occasionally some mGluRla-immunoreactive perikarya were seen in the SNr. The present results indicate that there is a differential localization of ionotropic and metabotropic glutamate receptor subunits in the SN. Acknowledgement: Supported by HKBU 2006/97M, Hong Kong Research Grant Council.