Differential ontogenic pattern of metabotropic [3H]-l-glutamate receptors in normal and granule cell-deficient mouse cerebellum

Abstract

[3H]-L-glutamate binding site distribution corresponding to metabotropic receptors was studied by autoradiography during normal and altered cerebellar ontogeny in mice treated on postnatal days (PND) 5 and 6 with the antimitotic methylazoxymethanol (MAM). Quisqualate (QA)-induced and (2S,3S,4S)-alpha-(carboxycyclopropyl)-glycine (L-CCG-I)-induced [3H]-L-glutamate binding inhibition allowed us to distinguish between group I and group II metabotropic receptor binding sites. In control cerebellar cortex, the QA-sensitive binding site density increases during development, while the L-CCG-I-sensitive binding site density decreases. In the deep cerebellar nuclei (DCN), both populations of binding sites decrease during ontogeny. The antimitotic treatment induces: (1) a slight but significant increase in the QA-sensitive binding sites in the DCN at PND 10 and in the cerebellar cortex beginning from PND 20; (2) a retarded decrease in the L-CCG-I-sensitive metabotropic receptor binding site density. These differences could be due to a retarded cell maturation and/or an over-expression of some postsynaptic receptors in the adult cerebellum in response to the afference deficiency.