Anterograde transport of neurotrophins and axodendritic transfer in the developing visual system

Neurotrophic factors support the differentiation and survival of neurons(1,2) and influence properties of synaptic transmission(3,4). The neurotrophic hypothesis postulates a retrograde action of trophic factors: their production and release by target cells and their uptake by innervating axons(5). Besides the retrograde route of trophic messengers, the survival of neurons and the development of synapses is thought to be also regulated by anterograde, afferent trophic signals(6-10). We now show that exogenous neurotrophins are transported in the anterograde direction, from cell bodies to the axon terminals, and that the intact neurotrophin is released after anterograde transport, taken up and utilized by second-order visual neurons in the developing chick brain. These results suggest that anterogradely transported neurotrophins may play a role in synaptic plasticity and may have effects at more than one synapse beyond the initial release site.