A light and electron microscopic study of glutamate receptors in the monkey subthalamic nucleus

The distribution of glutamate receptors in the monkey subthalamic nucleus w as studied using affinity purified polyclonal antibodies to GluR1, phosphor ylated GluR1, GluR2/3, NMDAR1, mGluR1a and mGluR5. Intense staining for bot h the unphosphorylated and the phosphorylated forms of the AMPA receptor su bunit GluR1 was observed in the cell bodies and proximal dendrites of neuro ns in this nucleus. In comparison to GluR1, less intense staining for GluR2 /3 was observed in the cell bodies and processes. NMDAR1 immunoreactivity w as present in cell bodies and large numbers of small diameter dendrites. Li ght staining was observed in cell bodies with mGluR1a and no staining was o bserved on cell bodies with mGluR5. The neuropil, however, contained many p rocesses that were labeled for mGluR1a or mGluR5. Electron microscopy showe d that label was present in cytoplasmic locations in cell bodies and dendri tes, in addition to components of the synaptic region, in sections stained for GluR1, GluR2/3 and NMDAR1. In contrast, very lightly labeled or unlabel ed cell bodies but labeled dendrites and axon terminals, was observed in se ctions stained for mGluR1a and mGluR5. In addition to neural processes, occ asional astrocytic processes were also labeled for mGluR5. Of the immunogol d particles that were associated with components of the synaptic region, la bel for ionotropic glutamate receptors was mostly present on postsynaptic d ensities, whilst that for metabotropic glutamate receptors was mostly prese nt in a perisynaptic location. The ratio of GluR1/GluR2 messenger RNAs has been reported to increase in the aged hippocampus (PAGLIUSI, S. R., GERRARD , P., ABDALLAH, M., TALABOT, D. & CATSICAS, S. (1994) Neuroscience 61, 429- 433.), and it is possible that a similar change in the ratio of GluR1 and G luR2 may occur in neurons of the subthalamic nucleus with age. It is postul ated that this could result an increase in calcium permeability via AMPA re ceptors, and an enhancement of excitatory transmission in this nucleus.