| Research Abstract |
The neostriatum is known to receive glutamatergic projections from the cerebral cortex and thalamic nuclei. Vesicular glutamate transporters 1 and 2 (VGluT1 and VGluT2) are located on axon terminals of corticostriatal and thalamostriatal inputs, respectively, whereas VGluT3 is found in axon terminals of cholinergic interneurons in the neostriatum. In the present study, the presynaptic localization of ionotropic glutamate receptors was examined in rat neostriatum by the post-embedding immunogold method for double labeling of VGluT and glutamate receptor. Immunoreactive gold particles for AMPA receptor subunits, GluR1-3, were frequently found on presynaptic profiles immunopositive for VGluT1 and VGluT2 in the neostriatum. Quantitative analysis revealed that about 1/4 and 2/5 of GluR2/3-immunopositive particles found in VGluT-positive synapses were associated with presynaptic profiles of VGluT1-and VGluT2-positive axon terminals, respectively, in the neostriatum. In contrast, almost no GluR2/3-immunopositive particles were observed on presynaptic profiles of VGluT3-positive terminals, which made asymmetric synapses in the neostriatum, or on those of VGluT1-or VGluT2-positive terminals in the neocortex. Furthermore, in contrast to GluR1-3, almost no immunoreactivity for GluR4 or NMDA receptor subunit, or only a little immunoreactivity for kainate receptor subunit was found in presynaptic profiles in the neostriatum. The present results suggest that glutamate released from corticostriatal and thalamostriata axon terminals controls the activity of the axon terminals through presynaptic AMPA-type glutamate autoreceptors.
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