Multiple and interactive responses of central neurons to neurotrophic factors

The structural similarities of NGF, BDNF, NT-3 and NT-4/5, and of the Trk type tyrosine kinase receptors which act as their functional receptors, present the neurotrophins as formidable candidates to study the functions of trophic molecules in the central nervous system. Findings with neurotrophin treatment in cell cultures and adult lesion models are summarized which suggest developmentally changing, multiple and interactive roles of neurotrophic factors. It is concluded that a number of trophic molecules, including several neurotrophins, using the same transducing elements, during the perinatal period act in concert to control proper development of the nervous system. In the adult, the roles of the same trophic factors are likely to be more restricted, either activated only in specific neuronal populations or, alternatively, only during very specific physiological states of the nervous tissue.