Prenatal nicotine exposure alters glycinergic and GABAergic control of respiratory frequency in the neonatal rat brainstem-spinal cord preparation.

Bath application of GABA-A receptor agonists in neonatal rat brainstem-spinal cord preparations (BSSC) reduces respiratory frequency, an effect that is enhanced by prenatal nicotine exposure. Here we test the hypothesis that these effects can be reproduced by microinjection of GABAergic and glycinergic agonists into the pre-Botzinger complex region (PBC). We recorded the activity of phrenic motor axons from the fourth cervical ventral root in 1-3 days old BSSC that were exposed to either nicotine (6 mg/(kg day)) or saline prenatally. Microinjection of glycine or muscimol into the PBC caused abrupt, reversible apnea in all experiments. Apnea duration with glycine averaged 50.3+/-5 s in saline-exposed (N=12), and 95.7+/-9.9 s in nicotine-exposed (N=12) neonates (P<0.001). Apnea duration with muscimol averaged 51+/-5.1 s in saline-exposed (N=10), and 86+/-10.6 s in nicotine-exposed (N=12) neonates (P<0.05). These data show that prenatal nicotine exposure alters development of central ventilatory control, and that neurons in the PBC region are involved.