In situ hybridization and immunohistochemistry were used to determine the presence of kainate-preferring glutamate receptor subunits GluR6 and GluR7 mRNA and protein in the median eminence of the rat. The results show that most tanycytes lining the ventral third ventricle and many astrocytes within the median eminence contain the GluR7 receptor subunit mRNA but not the GluR5 and GluR6 receptor subunit mRNA. Immunohistochemical stainings show that the GluR6/7 receptor protein was localized to tanycytic cell bodies, their basal processes and to many other astrocytes in different layers of the median eminence. The results suggest that glutamate can act directly on the glial cells in the median eminence by binding to the GluR7 subunit which may be important for the control of the secretion of releasing and inhibiting hormones from axon terminals in the external layer. In order to determine if these receptor subunits are functional, kainic acid was injected and c-fos expression monitored. Results show that kainic acid induced c-Sos synthesis in most of these glial cells. (C) 1998 Elsevier Science B.V. All rights reserved.