Long term depression is expressed during postnatal development in rat visual cortex: a role for visual experience

Long term forms of synaptic plasticity and in particular LTD/LTP are both p resent in the mammalian visual cortex. However, while LTP is not inducible in adulthood LTD can be elicited in the mature brain, but its developmental pattern is unknown. Aim of this work was to investigate whether LTD is exp ressed during postnatal development and if it is modulated by visual experi ence. To investigate these points we have used rat primary visual cortex sl ices taken at different stages of functional maturation process, i.e., post natal day 17 (P17), P23 and P30-35. LTD was assessed by measuring the ampli tude of extracellular field potentials recorded in cortical layers 2/3 and elicited by low frequency stimulation to the white matter. LTD was expresse d at all ages investigated without significant differences between age grou ps. These data indicate that LTD developmental expression is not temporally related with the period of functional maturation of rat visual cortex. Dar k rearing from birth to P23 resulted in a reduction of LTD amplitude while light deprivation from P17 to P30 did not affect LTD expression in comparis on to age matched control values. We suggest that light imprinting is essen tial for a normal LTD expression during postnatal development. (C) 1999 Els evier Science B.V. All rights reserved.