NGF AND BDNF ARE DIFFERENTIALLY MODULATED BY VISUAL EXPERIENCE IN THEDEVELOPING GENICULOCORTICAL PATHWAY

Neuronal activity and trophic factors have been implicated in shaping the connectivity of functional synaptic circuits. We studied the devel opment and regulation by sensory input of the neurotrophins NGF, BDNF and NT-3 in the developing rat visual system. In the occipital cortex, NT-3 mRNA was transiently expressed in the neonate. In contrast, BDNF and NGF mRNA's increased during postnatal development, and reached ma ture levels around 3 weeks of age. BDNF mRNA was ten times more abunda nt than NGF mRNA. In the lateral geniculate nucleus (LGN), NT-3 mRNA w as also transiently expressed, whereas NGF and BDNF mRNA's did not var y significantly during development. The high-affinity neurotrophin rec eptors trkB and trkC were expressed both in the developing LGN and occ ipital cortex. These receptors for BDNF and NT-3, respectively, were e xpressed at birth, with little change during development. In contrast, trkA mRNA, which encodes the high-affinity NGF receptor, was undetect able in either region. Visual experience differentially modulated expr ession of NGF and BDNF mRNA's. NGF mRNA was slightly increased after 3 weeks of light-deprivation. In contrast, BDNF mRNA expression in visu al cortex was significantly lower than normal in rats dark-reared from birth. Decreased BDNF expression after sensory deprivation was revers ible by exposure to light. Thus, all three neurotrophins were detected in visual cortex and LGN. Differences in abundance, developmental pro files, and regulation imply distinct functions for each factor in the visual system.