Fate of grafted embryonic purkinje cells in the cerebellum of the adult “purkinje cell degeneration” mutant mouse. II. Development of synaptic responses: An in vitro study

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Abstract
Solid pieces of cerebellar primordia from 12‐day‐old C57Bl embryos were implanted in the cerebellar vermis of 3–4‐month‐old “Purkinje cell degeneration” mutant mice. Ten to 22 days after grafting, mutant mice were sacrificed, and synaptic responses of grafted Purkinje cells were studied by intracellular recordings performed in 400 μm thick sagittal slices in vitro.As early as 10 days after transplantation, grafted Purkinje cells have already completed their migration from the implant into the host molecular layer. Accordingly, inhibitory as well as excitatory responses were already elicited in these cells by electrical stimulation of the host subcortical white matter. Furthermore, a transient stage of multiple innervation of Purkinje cells by climbing fibers exists between 10 and 15 days after grafting, as revealed by the stepwise variation in amplitude of the climbing fiber‐mediated excitatory postsynaptic potentials recorded before 15 days after grafting. Thirteen days after transplantation, typical all‐or‐none climbing fiber‐mediated responses, parallel fiber‐mediated excitatory postsynaptic potentials, and inhibitory postsynaptic potentials were also already present. Finally, normal adult‐type synaptic responses were observed in all tested cells 15 to 17 days after grafting.Together with the companion paper (Sotelo et al., 1990), these results demonstrate that grafted Purkinje cells are able to impose on host afferents a pattern of synaptogenesis which closely follows that occuring during normal development, in particular, the transient stage of multiple innervation of Purkinje cells by climbing fibers.