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number of studies have shown that the electrical activity of neurons may be
involved in the modulation of the target-derived neurotrophic factors prob-
ably through the control of the uptake of trophic factors ( Houenou,
McManaman, Prevette, & Oppenheim, 1991; Oppenheim, 1991 ). In the
visual system, it is well documented that both spontaneous synaptic activity
before eye opening and light-evoked retinal activity after eye opening are
critical for the normal development of the synaptic circuitry in the higher
centers of the brain. Visual experiences regulate the growth, stabilization,
and elimination of immature thalamocortical connections from each eye
and the response properties of cortical neurons ( Hubel, Wiesel, &
Stryker, 1997; Sherman & Spear, 1982 ). The strength of developing cortical
synapses can be increased or weakened depending on the level of presynaptic
axonal activity and postsynaptic neuronal depolarization ( Bienenstock,
Befus, Pearce, Denburg, & Goodacre, 1982; Miller, Chapman, &
Stryker, 1989 ).
The neurotrophins, including brain-derived neurotrophic factor (BDNF),
have been proposed to be the retrograde signaling molecules that contribute to
the bidirectional synaptic communication that modulates the efficacy and sta-
bility of the connections ( Domenici, Berardi, Carmignoto, Vantini, &Maffei,
1991; Snider & Lichtman, 1996 ). These molecules control many other devel-
opmental events, including neuronal survival and differentiation ( Lewin &
Barde, 1996 ). Neurotrophins also selectively modify the growth of develop-
ing axons ( Cohen-Cory & Fraser, 1995; Inoue & Sanes, 1997 ) and dendrites
( Horch, Kr¨ ttgen, Portbury, & Katz, 1999; Schwartz, Borghesani, Levy,
Pomeroy, & Segal, 1997 ).
Blocking the spontaneous or light-evoked retinal activity can disturb the
development of eye-specific segregation of the axons of the retinal ganglion
cells
(RGCs)
in the dorsal
lateral geniculate nucleus
(dLGN; Penn,
Riquelme, Feller, & Shatz, 1998 ; Shatz & Stryker, 1988).
Visual stimuli regulate the synthesis of the mRNA of BDNF by their
effects on neural activity. The expression of the mRNA of BDNF is reduced
in the primary visual cortex (V1) of rodents and carnivores after dark rearing
(DR; Castr´n, Zafra, Thoenen, &Lindholm, 1992 ) or after blocking the gen-
eration of retinal impulses by intraocular injections of tetrodotoxin ( Bozzi
et al., 1995; Castr´n et al., 1992 ). The rapid increase of the cortical mRNA
of BDNF induced inV1 of DRanimals that are later exposed to light ( Castr´n
et al., 1992; Schoups, Elliott, Friedman, & Black, 1995 ) showed that BDNF
synthesis in V1 is tightly regulated by sensory activity. Repeating visual stim-
uli were able to upregulate the transcription of the plasticity-related gene in
the Xenopus optic tectum ( Schwartz, Schohl, & Ruthazer, 2009 ). Sensory
stimulation activates the BDNF exon IV promoter, and the subsequent
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