The effects of reduced climbing and parallel fibre input on Purkinje cell dendritic growth.

The effects of afferent fibre depletion on the development of the dendritic trees of Purkinje cells in the cerbellum were investigated. Parallel fibres were reduced by postnatal administration of a schedule of low level X-irradiation. Climbing fibers were prevented from innervating the cerebellum by lesioning the olivo-cerebellar tract. Network analysis was performed on Purkinje cells in Golgi-Cox preparations of the vermis of 30-day-old animals. tin the irradiated cerebella Purkinje cells with a 'weeping willow' type morphology predominated. Purkinje cells devoid of their climbing fibre contact exhibited large spines on their main dendritic trunks. In both experimental situations the size of the dendritic tree was reduced. This diminution was the result of a decrease in the total number of dendritic segemnts. Individual segment lengths were largely unalteral. Topological type analysis revealed that the trees had arisen in a manner indistinguishable from terminal dichotomous branching and that the 'weep-willow' pattern was produced by a deviation of branching from a purely random form. The interaction of intrinsic and extrinsic factors in the formation of segments and on the nature of branching were discussed.