Characterization of the Responses of Purkinje Cells to Neurotrophin Treatment

: The ability of the neurotrophins nerve growth factor (NGF), brain‐derived neurotrophic factor (BDNF), neurotrophin‐3 (NT‐3), and neurotrophin‐4/5 (NT‐4/5) to promote neuronal survival and phenotypic differentiation was examined in dissociated cultures from embryonic day 16 rat cerebellum. BDNF treatment increased the survival of neuron‐specific enolase‐immunopositive cells by 250 and 400% after 8 and 10 days in culture, respectively. A subpopulation of these neurons, the Purkinje cells, identified by calbindin staining, was increased to an equivalent extent, ∼200%, following BDNF, NT‐4/5, or NT‐3 treatment. The number of GABAergic neurons, identified by GABA immunoreactivity, was greatly increased by treatment with BDNF (470%) and moderately by NT‐4/5 (46%), whereas NT‐3 was without effect. NGF failed to increase the number of either Purkinje cells or GABAergic neurons. Addition of BDNF within 48 h of cell plating was required to obtain a maximal increase in Purkinje cell number after 8 days. In contrast, the NT‐3 responses were nearly equivalent even if treatment was delayed for 96 h after plating. BDNF, NT‐4/5, and NT‐3, but not NGF, induced the rapid expression of the immediate early gene c‐fos. Immunocytochemical double‐labeling with antibodies to c‐fos and calbindin was used to identify Purkinje cells that responded to neurotrophin treatment by induction of c‐fos. After 4 days in vitro, both BDNF and NT‐3 induced the formation of c‐fos protein in calbindin‐immunopositive neurons, whereas NT‐4/5 did not. The latter results suggest that although BDNF and NT‐4/5 have been shown to act through a common receptor, TrkB, it appears that the effects of BDNF and NT‐4/5 are not identical.