Distribution of muscarinic receptors in the developing rodent cerebellum

The distribution of muscarinic receptors in the developing rodent cerebellum was studied by light microscopic autoradiography of [3H]quinuclidinyl benzilate binding sites. Muscarinic receptors were not detected in the mouse cerebellar plate until embryonic day 16, at which time they were clustered in the ventromedial region of the cerebellar anlagen. At postnatal day 1, additional areas of higher grain density became visible in the dorsolateral medullary zone, internal to the newly forming granular layer. Labeling increased throughout the entire cerebellum between postnatal days 5 and 10, becoming markedly higher in the lateral hemispheres than in the vermis. This elevated density of binding sites in the hemispheres became reduced to that of the vermis by postnatal day 13 in the mouse, and PD20 in the rat. In adult animals, the cortical grain density was highest in the granule and Purkinje cell layers, low in the molecular layer and absent from the white matter. Receptor labeling was, however, observed over many areas of white matter throughout early development; this became more restricted to specific tracts during the third postnatal week. At no time during development were binding sites observed in the external germinal layer. Microvessels and capillaries, structures which have been shown to contain [3H]quinuclidinyl benzilate binding sites, may partially account for the observed ontogenic pattern.