NEUROTROPHIN-INDUCED MODULATION OF SYNAPTIC TRANSMISSION IN THE ADULTHIPPOCAMPUS

The NGF-family of neurotrophic factors including NGF, BDNF and NT-3,4/ 5 is known to be crucial for neuronal survival and differentiation dur ing development. However, recent studies suggest that the neurotrophin s are also widely expressed and play a dynamic role in the mature nerv ous system. One of the major sites of expression of the neurotrophins in the adult brain is the hippocampus which has been also popular as a n important structure for the adult plasticity. Moreover, the level of expression of the neurotrophins in the hippocampus can be regulated b y a variety of neuronal inputs, such as experimentally-induced seizure s: injection of glutamate receptor agonists, and LTP-inducing stimulat ion. The possibility that the neurotrophins modulate synaptic transmis sion in the mature brain has been investigated at the Schaffer collate ral-CA1 synapses in the adult rat hippocampus. We report that transien t application of BDNF and NT-3, but not NGF induces a long-lasting inc rease of synaptic transmission, which is likely to be mediated by Trk family of receptor tyrosine kinases. Both BDNF and NT-3 decrease paire d pulse facilitation, suggesting a possible presynaptic modification. interestingly, previous potentiation of synaptic activity by the appli cation of neurotrophic factors does not occlode the induction of long- term potentiation. These results suggest that the neurotrophins may lo cally regulate synaptic plasticity in the adult nervous system.