Postnatal nicotine and/or intermittent hypercapnic hypoxia effects on apoptotic markers in the developing piglet brainstem medulla.

The most important risk factors currently identified for the sudden infant death syndrome (SIDS) are prone sleeping and cigarette smoke exposure. In this study, we investigated the neuropathological sequelae of these risk factors by exposing piglets to intermittent hypercapnic-hypoxia (IHH) and/or nicotine (nic) in the early postnatal period. Our hypothesis was that either nic or IHH exposure could increase neuronal cell death, and that combined exposure (nic+IHH) would be additive. Four exposure patterns were studied: controls (n=14), IHH (n=10), nic (n=14), and nic+IHH (n=14). All groups had equal gender ratios. Nic exposure via an implanted osmotic minipump commenced within 48 h of birth and continued until age 13-14 days when animals were killed and brains collected. A total of 48 min of hypercapnic-hypoxia was delivered on the day immediately prior to killing in a pattern comprising 6 min of HH (8% O(2), 7% CO(2), balance N(2)) alternating with 6 min of air. Immunohistochemistry was performed to identify neurons positive for active caspase-3 and DNA fragmentation (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, TUNEL) in seven nuclei of the caudal medulla. Staining quantification showed that: 1. IHH induced neuronal death (increased both TUNEL and casapse-3) in more brainstem nuclei than nicotine. 2. Females were more severely affected by IHH than males. 3. Where IHH and nicotine were combined, TUNEL expression was approximately 5% less than IHH alone, but changes in caspase-3 were variable. We conclude that acute exposure to IHH in the postnatal period is more neurotoxic than exposure to nicotine alone. Combined exposure to IHH and nicotine produced variable responses with some results suggesting that nicotine can be neuroprotective. These results indicate that environmental insults attributable to prone sleeping can produce neurotoxic sequelae in SIDS, with some regional specificity in the response. However, no consistent relationship is evident when combining the two insults.