ACUTE MORPHOGENIC AND CHEMOTROPIC EFFECTS OF NEUROTROPHINS ON CULTURED EMBRYONIC XENOPUS SPINAL NEURONS

Neurotrophins constitute a family of trophic factors with profound eff ects on the survival and differentiation of the nervous system. Additi on of brain-derived neurotrophic factor (BDNF) or neurotrophin-3 (NT-3 ), but not nerve growth factor (NGF), increased the survival of embryo nic Xenopus spinal neurons in culture, although all three neurotrophin s enhanced neurite outgrowth. Here we report that neurotrophins also e xert acute actions on the morphology and motility of 1-day-old culture d Xenopus spinal neurons. Bath application of BDNF induced extensive f ormation of lamellipodia simultaneously at multiple sites along the ne urite shaft as well as at the growth cone. The BDNF-induced lamellipod ia appeared within minutes, rapidly protruded to their greatest extent in about 10 min, and gradually disappeared thereafter, leaving behind newly formed thin lateral processes. When applied as microscopic conc entration gradients, both BDNF and NT-3, but not NGF, induced the grow th cone to grow toward the neurotrophin source. Our results suggest th at neurotrophic factors, when delivered to responsive neurons, may ser ve as morphogenic and chemotropic agents during neuronal development.