IONOTROPIC GLUTAMATE-RECEPTOR GENE-EXPRESSION IN HYPOTHALAMUS - LOCALIZATION OF AMPA, KAINATE, AND NMDA RECEPTOR RNA WITH IN-SITU HYBRIDIZATION

In situ hybridization and Northern blots were used to study the ionotr opic subtypes of the glutamate receptor in the rat hypothalamus. Wides pread expression of AMPA, kainate, and NMDA receptor RNA was found in the hypothalamus with the transcripts the same size and number as foun d in other regions of the brain. Most of the glutamate-receptor subuni ts studied were expressed in greater amounts in hippocampus than in hy pothalamus; GluR5, on the other hand, showed a greater expression in h ypothalamus than in hippocampus. On the basis of Northern blot analysi s, all regions of the brain examined, including hypothalamus, cerebral cortex, cerebellum, olfactory bulb, and hippocampus, expressed all ei ght of the subunits studied. Each subunit showed different relative ex pressions in the different regions. In the hypothalamus, GluR1 and Glu R2 were among the most widely expressed of the non-NMDA ionotropic rec eptors. Other AMPA-preferring receptors, GluR3 and -R4, were also foun d, but to a lesser extent. Scattered cells expressed the kainate-prefe rring receptors GluR5, -R6, and -R7. The NMDA receptor NMDAR1 was dete cted throughout the hypothalamus. In many regions of the hypothalamus, only scattered cells showed detectable expression of the glutamate-re ceptor mRNA as detected by autoradiographic silver grains over neurons ; unlabeled cells were mixed among labeled cells. Every region of the hypothalamus had several different glutamate receptors. The expression of many different types of ionotropic glutamate receptors throughout the hypothalamus suggests that multiple modes of ion channel regulatio n by glutamate probably operate here and provides further support for the importance of the excitatory transmitter glutamate in hypothalamic regulation. (C) 1994 Wiley-Liss, Inc.