Autoradiographic localization of [3H]-L-glutamate binding sites in a model of cerebellar granule cell ectopia generated by methylazoxymethanol treatment.

The distribution of [3H]glutamate binding sites was studied in a model of altered cerebellar development obtained by injecting methylazoxymethanol (MAM) in 5-day-old mice. In these mice, at the 25th postnatal day, cerebella were smaller than normal, stratification was normal except for the presence in some lobes of a thin ectopic granule cell layer in the middle of the molecular layer, the proportion of the distribution of [3H]glutamate binding sites between molecular and internal granule cell layers was maintained but site density of both quisqualate- and NMDA-sensitive types was increased in the two layers. In the molecular layer, this increase was uniform in spite of the presence of the ectopic cell layer. In the internal granular layer, the increase of quisqualate-sensitive and NMDA-sensitive [3H]glutamate binding sites is topographically segregated and the first corresponds to areas of lesser cellular density. These results show that MAM treatment induces persistent alterations of the cerebellar glutamatergic system, which consist of receptor over-expression, possibly due to deficit of innervation, reactive gliosis and immaturity of surviving granule cells.