Fig. 4.

Mechanisms that might account for the accumulation of BDNF protein in V1 of dark-reared animals. A, A reduction in the removal of BDNF by LGN or other afferents (arrow across the synapse). Only axodendritic synapses are depicted, but axosomatic connections are also present.B, An accumulation of BDNF delivered to LGN or other afferent presynaptic terminals by anterograde axonal transport.C, An increase in the retention of locally synthesized BDNF within cortical networks by transsynaptic, autocrine, or paracrine secretion (arrows between cells). Increased cortical BDNF could also arise by reduced anterograde transport or increased retrograde transport in the axons of cortical efferent neurons (arrow in axon).