Fetal nicotine or cocaine exposure:
which one is worse?
by
Slotkin TA
Department of Pharmacology and Cancer Biology,
Duke University Medical
Center,
Durham, North Carolina, USA.
J Pharmacol Exp Ther 1998 Jun; 285(3):931-45
ABSTRACT
Despite extensive adverse publicity, tobacco use continues in approximately
25% of all pregnancies in the United States, overshadowing illicit drugs of
abuse, including cocaine. The societal cost of maternal smoking is seen most
readily in underweight newborns, in high rates of perinatal morbidity, mortality
and Sudden Infant Death Syndrome and in persistent deficits in learning and
behavior. We have designed animal models of nicotine exposure to prove that
nicotine itself is a neuroteratogen, thus providing a causative link between
tobacco exposure and adverse perinatal outcomes. In particular, nicotine
infusion paradigms that, like the transdermal patch used in man, produce drug
exposure without the confounds of other components of tobacco or of episodic
hypoxic-ischemic insult, have enabled a mechanistic dissection of the role
played by nicotine in fetal brain damage. Nicotine targets specific
neurotransmitter receptors in the fetal brain, eliciting abnormalities of cell
proliferation and differentiation, leading to shortfalls in the number of cells
and eventually to altered synaptic activity. Because of the close regulatory
association of cholinergic and catecholaminergic systems, adverse effects of
nicotine involve multiple transmitter pathways and influence not only the
immediate developmental events in fetal brain, but also the eventual programming
of synaptic competence. Accordingly, defects may appear after a prolonged period
of apparent normality, leading to cognitive and learning defects that appear in
childhood or adolescence. Comparable alterations occur in peripheral autonomic
pathways, leading to increased susceptibility to hypoxia-induced brain damage,
perinatal mortality and Sudden Infant Death. Identifying the receptor-driven
mechanisms that underlie the neurobehavioral damage caused by fetal nicotine
exposure provides a rational basis for decisions about nicotine substitution
therapy for smoking cessation in pregnancy. In contrast to the effects of
nicotine, animal models of crack cocaine use in pregnancy indicate a more
restricted spectrum of effects, a reflection of differences both in
pharmacokinetics and pharmacodynamics of the two drugs. Notably, although
cocaine, like nicotine, also targets cell replication, its effects are
short-lived, permitting recovery to occur in between doses, so that the eventual
consequences are much less severe. To some extent, the effects of cocaine on
brain development resemble those of nicotine because the two share
cardiovascular actions (vasoconstriction) that, under some circumstances, elicit
fetal hypoxia-ischemia. In light of the fact that nearly all crack cocaine users
smoke cigarettes, the identification of specific developmental effects of
cocaine may prove difficult to detect. Although scientists and the public
continue to pay far more attention to fetal cocaine effects than to those of
nicotine or tobacco use, a change of focus to concentrate on tobacco could have
a disproportionately larger impact on human health.
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