TRKB SIGNALING MODULATES SPINE DENSITY AND MORPHOLOGY INDEPENDENT OF DENDRITE STRUCTURE IN CULTURED NEONATAL PURKINJE-CELLS

Neurotrophins cooperate with neural activity to modulate CNS neuronal survival and dendritic differentiation. In a previous study, we demons trated that a critical balance of neurotrophin and neural activity is required for Purkinje cell survival in cocultures of purified granule and Purkinje cells (Morrison and Mason, 1998). Here we investigate whe ther TrkB signaling regulates dendrite and spine development of Purkin je cells. BDNF treatment of purified Purkinje cells cultured alone did not elicit formation of mature dendrites or spines. In cocultures of granule and Purkinje cells, however, continuous treatment with BDNF ov er a 2 week postnatal culture period increased the density of Purkinje cell dendritic spines relative to controls without causing a shift in the proportions of headed and filopodia-like spines. The increase in spine number was blocked by adding TrkB-IgG to the medium together wit h BDNF. Although BDNF alone did not consistently modify the morphology of dendritic spines, treatment with TrkB-IgG alone yielded spines wit h longer necks than those in control cultures. None of these treatment s altered Purkinje cell dendritic complexity. These analyses reveal a role for TrkB signaling in modulating spine development, consistent wi th recently reported effects of neurotrophins on synaptic function. Mo reover, spine development can be uncoupled from dendrite outgrowth in this reductionist system of purified presynaptic and postsynaptic neur ons.