Chronic prenatal exposure to carbon monoxide results in a reduction in tyrosine hydroxylase-immunoreactivity and an increase in choline acetyltransferase-immunoreactivity in the fetal medulla: Implications for sudden infant death syndrome

Maternal cigarette smoking during pregnancy is associated with a significan tly increased risk of Sudden infant Death Syndrome (SIDS). This study inves tigated the effects of prenatal exposure to carbon monoxide (CO). a major c omponent of cigarette smoke, on the neuroglial and neurochemical developmen t of the medulla in the fetal guinea pig. pregnant guinea. pigs were expose d to 200 p.p.m CO for 10 h per day from day 23-25 of gestation (term = 68 d ays) until day 61-63, at which time fetuses were removed and brains collect ed for analysis. Using immunohistochemistry and quantitative image analysis , examination of the medulla of CO-exposed fetuses revealed a significant d ecrease in tyrosine hydroxylase-immunoreactivity (TH-IR) in the nucleus tra ctus solitarius. dorsal motor nucleus of: the vagus (DMV). area postrema. i ntermediate reticular nucleus. and the ventrolateral medulla (VLM). and a s ignificant increase in choline acetyltransferase-immunoreactivity (ChAT-IR) in the DMV and hypoglossal nucleus compared with controls. There was no di fference between groups in immunoreactivity for the m2 muscarinic acetylcho line receptor, substance P- or met-enkephalin in any of the medullary nucle i examined, nor was there evidence of reactive astrogliosis. The results sh ow that prenatal exposure to CO affects cholinergic and catecholaminergic p athways in the medulla of the guinea pig fetus. particularly in cardiorespi ratory centers, regions thought to be compromised in SIDS.