Nicotine exposure during a postnatal critical period alters NR2A and NR2B mRNA expression in rat auditory forebrain

Chronic nicotine exposure (CNE) can alter brain development and is thought to produce deficits in auditory function. Previously, we found that CNE during the second postnatal week, but not before or after, increases the duration of excitatory postsynaptic potentials (EPSPs) mediated by N-methyl-D-aspartate receptors (NMDARs) in rat auditory cortex. It was proposed that a potential mechanism underlying increased EPSP duration could be over-stimulation of presynaptic nicotinic acetylcholine receptors, leading to prolonged glutamate release. Since glutamatergic activity regulates levels of postsynaptic NMDAR subunits, here we examine the effects of CNE on mRNA expression for the NR2A and NR2B subunits in auditory cortex and thalamus. Two days of CNE (postnatal days 8-9), produced no effects, but 5 days (postnatal days 8-12) enhanced cortical NR2A mRNA levels and reduced thalamic NR2B mRNA levels for up to 2 weeks. These effects are consistent with the hypothesis that CNE during a postnatal critical period disrupts auditory cortex development by over-stimulating glutamatergic synapses.