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The Journal of Neuroscience, December 15, 1999, 19(24):10993-11006
Effect of Enriched Environment Rearing on Impairments in Cortical
Excitability and Plasticity after Prenatal Alcohol Exposure
V.
Rema1, 3 and
Ford F.
Ebner1, 2, 4
1 Institute for Developmental Neuroscience, J. F. Kennedy Center for Research on Human Development, Departments of
2 Psychology, 3 Pharmacology, and
4 Cell Biology, Vanderbilt University, Nashville, Tennessee
37203
The daily ingestion of alcohol by pregnant mammals exposes the
fetal brain to varying levels of alcohol through the placental circulation. Here we focus on the lingering impact on cortical function
of 6.5% alcohol administered in a liquid diet to pregnant rats
throughout gestation, followed by 3 alcohol-free months before brain
function was analyzed in the offspring. Both spontaneous activity of
the neurons in the barrel cortex and the level of response to test
stimuli applied to the whiskers remained reduced by >75% after
alcohol exposure. Whisker pairing, a type of cortical plasticity
induced by trimming all but two whiskers in adult rats, occurred in <1
d in controls, but required 14 d to reach significance after
alcohol exposure. These long-term neuronal deficits are present in all
layers of cortex and affect neurons with both fast and slow action
potentials. Plasticity is first seen in the total sample of neurons at
14 d; however, by 7 d, neurons in layer II/III already show
plasticity, with no change in layer IV neurons, and a reverse shift
occurs toward the inactive whisker in layer V neurons. Analysis of NMDA
receptor subunits shows a persistent, ~30-50% reduction of NR1,
NR2A, and NR2B subunits at postnatal day 90 in the barrel field cortex.
Exposing the prenatal alcohol-exposed rats to enriched rearing
conditions significantly improves all measured cortical functions but
does not restore normal values. The results predict that combinations
of interventions will be necessary to completely restore cortical
function after exposure of the fetal brain to alcohol.
Key words:
synaptic plasticity; FAS; somatosensory cortex; NMDA
receptors; barrel cortex; cortical reorganization; rat neocortex
Copyright © 1999 Society for Neuroscience 0270-6474/99/192410993-14$05.00/0
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