CHARACTERIZATION OF THE RESPONSES OF PURKINJE-CELLS TO NEUROTROPHIN TREATMENT

The ability of the neurotrophins nerve growth factor (NGF), brain-deri ved neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophi n-4/5 (NT-4/5) to promote neuronal survival and phenotypic differentia tion was examined in dissociated cultures from embryonic day 16 rat ce rebellum. BDNF treatment increased the survival of neuron-specific eno lase-immunopositive cells by 250 and 400% after 8 and 10 days in cultu re, respectively. A subpopulation of these neurons, the Purkinje cells , identified by calbindin staining, was increased to an equivalent ext ent, similar to 200%, following BDNF, NT-4/5, or NT-3 treatment. The n umber of GABAergic neurons, identified by GABA immunoreactivity, was g reatly increased by treatment with BDNF (470%) and moderately by NT-4/ 5 (46%), whereas NT-3 was without effect, NGF failed to increase the n umber 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 pl ating. BDNF, NT-4/5, and NT-3, but not NGF, induced the rapid expressi on of the immediate early gene c-fos. Immunocytochemical double-labeli ng with antibodies to c-fos and calbindin was used to identify Purkinj e 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 n ot. 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 eff ects of BDNF and NT-4/5 are not identical.