Adult experience-dependent plasticity of S1 barrel cortex in the normal and monoamine oxidase-A knockout (Tg8) mouse.

Abstract

By restricted use of D2 and D3 whiskers for 3-20 days at maturity (whisker pairing, WP), receptive field plasticity of adult D2 barrel cortex cells was compared in vivo for Tg8 mutant and normal (NOR) mice. Little plasticity was achieved until 20 days of WP in both mice. For Tg8, which lacks segregation of thalamocortical (TC) terminals into barrels, the first relay (TC) responses in layer IV to the principal whisker were potentiated more than in NOR mice by 20 days of WP. In parallel, secondary discharges were reduced more in Tg8 than NOR. It is suggested that both TC excitation and feed-forward inhibition in Tg8 are greater and potentiated more by WP than in NOR mice. Similar differences were reflected in supragranular (SG) cells. For Tg8 but not NOR mice, first latencies of one in five cells in layer IV to an adjacent surround whisker matched those of the principal whisker, increasing to one in three by 20 days of WP experience. Converse decreases occurred for the deprived surround whisker. Changes were similar but smaller for SG cells. Lack of TC segregation in Tg8, therefore, allows substantial overlapping TC terminals of immediate surround whiskers to activate neighbouring D2 column cells directly with potentiated relay to a whisker paired input and weakened relay to a deprived input. Although differing from NOR mice, experiential plasticity was not strongly compromised in Tg8 mice. Differences in WP plasticity from rat barrel cortex are discussed.