Opiate withdrawal during pregnancy may occur because of voluntary or forced detoxification, or from rapid cycling associated with exposure to short-acting "street"
opiates. Thus, animal modeling of prenatal withdrawal and development of potential therapeutic interventions is important. Direct developmental effects of
opiates and/or withdrawal can be studied using a chick model. In ovo administration of the long-acting
opiate N-desmethyl-
l-alpha-noracetylmethadol (
NLAAM) induces
opiate dependence in the chick embryo. We examined activation of the hypothalamic-pituitary-adrenal (HPA) axis (assessed via serum
corticosterone) and hemodynamic changes (assessed as changes in apparent diameter of vitelline (extraembryonic) blood vessels) after chronic
NLAAM exposure and
naloxone (Nx)-precipitated withdrawal during late stages of embryogenesis. Nx-precipitated withdrawal increased
corticosterone 2- to 4.5-fold and diameters of vitelline blood vessels by 15 to 45%.
NLAAM exposure itself did not effect these measures. In a second set of experiments, isobutylmethylxanthine (
IBMX), a
phosphodiesterase inhibitor, was injected into eggs with embryos.
IBMX similarly increased
corticosterone and vitelline vessel diameter, with a similar time course and response magnitude. Previous studies found that
serotonin(2) (5-HT(2)) receptors were involved in other withdrawal manifestations, so we determined whether they were likewise involved. Pretreatment with the 5-HT(2) antagonist
ritanserin completely blocked HPA axis activation and vasodilation associated with both Nx-precipitated withdrawal and
IBMX administration. This indicates that 5-HT(2) receptors, directly or indirectly, mediate these withdrawal manifestations in the chick embryo.