DISTRIBUTION OF AMPA SELECTIVE GLUTAMATE RECEPTORS IN THE THALAMUS OFADULT-RATS AND DURING POSTNATAL-DEVELOPMENT - A LIGHT AND ULTRASTRUCTURAL IMMUNOCYTOCHEMICAL STUDY

The regional, cellular and subcellular distribution of AMPA receptors was demonstrated immunocytochemically within the thalamus of adult and young (from 1 to 20 days postnatal, P-1-P-20) rats. The antipeptide a ntibodies used(37) recognize individual subunit proteins of the AMPA-p referring glutamate receptor, i.e., GluR1, GluR2-3 and GluR4. Our resu lts demonstrate that these AMPA receptor subunits are generally not hi ghly expressed in the thalamus, as compared to other brain:areas and t hat they are enriched differentially within different thalamic nuclei. GluR1 is mostly found in intralaminar and midline nuclei throughout l ife, whereas GluR2-3 is moderately expressed in the thalamus, with no; major developmental changes. GluR4 is the predominant subunit expresse d in the reticular nucleus in adult rats, but not in young animals, wh ere until P-9 it is instead present in the ventrobasal complex. Sample s of paraventricular and lateral geniculate nuclei stained with GluR1 and of reticular nucleus as well as ventrobasal complex stained with G luR4 were used for the ultrastructural study; In all the samples, labe lling was in the somatic and dendritic cytoplasm, with dense patches o f reaction product apposing post-synaptic densities of terminals with round clear vesicles and asymmetric specializations. Glial staining wa s observed only with the GluR1 antiserum and there was no evidence of labelled synaptic terminals. The differential distribution of GluR sub units in the thalamus suggests that certain subunits may participate m ore than others in mediating post-synaptic responses in distinct neuro nal populations and also that other GluR types may be involved in the thalamic networks.