BDNF ENHANCES THE DIFFERENTIATION BUT NOT THE SURVIVAL OF CNS STEM CELL-DERIVED NEURONAL PRECURSORS

We have previously reported the isolation of an EGF-responsive precurs or from the embryonic and adult mouse striatum. This precursor exhibit s self renewal and the ability to produce a sphere of undifferentiated cells which can be induced to differentiate into neurons and glia. RT -PCR analysis of these spheres of undifferentiated cells revealed the expression of mRNA for the trkB neurotrophin receptor, both with and w ithout the catalytic domain, and little or no expression of trkA or tr kC. We examined the actions of BDNF on the fate of EGF-generated neura l precursors. Ten days after a one-time exposure to BDNF, single EGF-g enerated spheres showed a twofold increase in neuron number and a mark ed enhancement in neurite outgrowth. Examination of neuronal nuclei wi th immunochemical probes for c-fos and bromodeoxyuridine revealed that the actions of BDNF were directly upon neuronal cells and did not inv olve division of neuronal precursors. The twofold increase in neuronal number due to BDNF, observed after 10 d in vitro, was significantly r educed after 21 d in vitro and was not apparent at 27 d in vitro. Quan titative analyses revealed that while repeated application of BDNF did not prevent the loss of neuron number over time, it did result in a s ignificant increase in neurite numbers. Moreover, delayed addition of BDNF mimicked the increase in neuronal numbers seen when BDNF was pres ent throughout. These BDNF actions did not appear to involve the enhan cement of a novel neuronal phenotype, with all effects being due to in crease in the numbers and neurite outgrowth of neurons that colocalize GABA and substance P. These findings suggest that BDNF markedly enhan ces the antigenic and morphologic differentiation of EGF-generated neu ronal precursors. BDNF alone does not appear to act as a survival fact or for neuronal precursors nor is it sufficient for preventing their d eath over time.