PARACRINE INTERACTIONS OF BDNF INVOLVING NGF-DEPENDENT EMBRYONIC SENSORY NEURONS

The expression of BDNF mRNA by a proportion of embryonic dorsal root g anglion neurons has led to the proposal that BDNF acts by an autocrine loop on these neurons. To clarify the role of BDNF expression in deve loping sensory neurons, we measured the level of BDNF mRNA in purified populations of cranial sensory neurons that depend on either NGF or B DNF for survival. When neuronal death is taking place, the highest lev els of BDNF mRNA were detected in NGF-dependent cutaneous sensory neur ons. BDNF mRNA was expressed at lower levels in BDNF-dependent cutaneo us sensory neurons and was undetectable in BDNF-dependent propriocepti ve neurons. In coculture, NGF-dependent neurons promoted the survival of BDNF-dependent neurons by the production and release of BDNF. Depol arizing levels of KCl increased the expression of BDNF mRNA in culture d sensory neurons and this effect was partially inhibited by calcium c hannel antagonists. Our results suggest that during the phase of natur ally occurring neuronal death, BDNF acts by a paracrine mechanism in s ensory neurons and that BDNF expression is regulated by neural activit y.