Distributions of synaptic vesicle proteins and GAD65 in deprived and nondeprived ocular dominance columns in layer IV of kitten primary visual cortexare unaffected by monocular deprivation

Two days of monocular deprivation (MD) of kittens during a critical period of development is known to produce a loss of visual responses in the primar y visual cortex to stimulation of the nondeprived eye, and 7 days of depriv ation results in retraction of axon branches and loss of presynaptic sites from deprived-eye geniculocortical arbors. The rapid loss of responsiveness to deprived-eye visual stimulation could be due to a decrease in intracort ical excitatory input to deprived-eye ocular dominance columns (ODCs) relat ive to nondeprived-eye columns. Alternatively, deprived-eye visual response s could be suppressed by an increase in intracortical inhibition in deprive d columns relative to nondeprived columns. We tested these hypotheses in cr itical period kittens by labeling ODCs in layer IV of primary visual cortex with injections of the anterograde tracer Phaseolus vulgaris-leucoagglutin in (PHA-L) into lamina A of the lateral geniculate nucleus (LGN). After eit her 2 or 7 days of MD, densities of intracortical excitatory presynaptic si tes within deprived relative to nondeprived ODCs were estimated by measurin g synaptic vesicle protein (SVP) immunoreactivity (IR). Because most of the synapses within layer IV of primary visual cortex are excitatory inputs fr om other cortical neurons, levels of SVP-IR provide an estimate of the amou nt of intracortical excitatory input. We also measured levels of immunoreac tivity of the inhibitory presynaptic terminal marker glutamic acid decarbox ylase (GAD)65 in deprived relative to nondeprived ODCs. Monocular deprivati on (either 2 or 7 days) had no effect on the distributions of either SVP- o r GAD65-IR in deprived and nondeprived columns. Therefore, the rapid loss o f deprived-eye visual responsiveness following MD is due neither to a decre ase in intracortical excitatory presynaptic sites nor to an increase in int racortical inhibitory presynaptic sites in layer TV of deprived-eye ODCs re lative to nondeprived columns. (C) 2000 Wiley-Liss, Inc.