Figure 1.
Injection of AAV2/1-EGFP into the basal pons labels ponto-cerebellar mossy fibers in the adult rat. a, A diagram of the cortico-cerebellar circuit. Cortical layer 5/6 pyramidal cells provide ipsilateral input to neurons of the basal pons. Pontine axons travel in the contralateral middle cerebellar peduncle (mcp) and branch throughout the white matter and granule cell layer of the cerebellar hemisphere. b, The granule cell layer microcircuit. Each mossy fiber axon branches over multiple lobules and gives rise to 100–200 terminals. A mossy fiber terminal forms a glomerular synapse with the dendrites of 30–40 granule cells. Granule cells are also innervated by inhibitory Golgi cells. c, EGFP expression in the basal pons revealed by native EGFP fluorescence in a fixed coronal brain slice prepared ∼2 months after the virus injection. This image is a montage of several maximal z-projections, each encompassing ∼30 µm of depth. Note the broad distribution of infected cells within the basal pons. The right portion of the panel shows the labeled boundaries of the basal pontine nuclei and surrounding fiber tracts corresponding to approximately −8.0 mm AP from bregma. d, Immunohistochemistry using an antibody directed against EGFP reveals pontine mossy fibers in Crus IIa of the cerebellar hemisphere contralateral to the injection site. The rat was killed, and slices were prepared ∼2 months after viral injection. bp, Brachium pontis; Go, Golgi cell; gcl, granule cell layer; gr, granule cell; mel, medial lemniscus; mft, mossy fiber terminal; ml, molecular layer; lfp, lateral fasciculus of the pons; P, Purkinje cell; pf, parallel fiber; pn, pontine nuclei. Scale bar, 100 μm.