NEUROTROPHINS PROMOTE MOTOR-NEURON SURVIVAL AND ARE PRESENT IN EMBRYONIC LIMB BUD

Embryonic spinal motor neurons are thought to depend for survival on u nidentified factors secreted both by their peripheral targets and by c ells within the central nervous system1. The neurotrophins are a famil y of polypeptides required for survival of discrete central and periph eral neuronal populations in vivo and in vitro2,3. In spite of their a bility to reduce motor neuron death in vivo4-6, the known neurotrophin s have been thought to be without direct effect on motor neurons7-10. Here we show that picomolar concentrations of three of them, brain-der ived neurotrophic factor, neurotrophin-3 and neurotrophin-5, can preve nt the death of cultured embryonic rat spinal motor neurons. Furthermo re, messenger RNA coding for neurotrophins is present at appropriate s tages in spinal cord and limb bud, and mRNA for their receptors is fou nd in motor neurons. These neurotrophins may therefore be physiologica l motor neuron growth factors.