Congenital behavioral effects in mature rats prenatally exposed to levo-alpha-acetylmethadol (LAAM)

Male and female rats exposed prenatally to LAAM (0.2 mg/kg maternal body weight per day, PO) or water were tested for congenital effects on their performance of various unconditioned and conditioned behaviors. No differences were found in neuromuscular development or in exploratory activity. Although they acquired and performed an autoshaped lever-touch response like controls, the LAAM rats responding under this paradigm were less affected by dextroamphetamine than were controls, suggesting an alteration in catecholamine neurotransmission in these subjects. Furthermore, when required to respond on a progressive fixed-ratio (FR) procedure, in which the response requirement for reinforcement was doubled each day from FR1 to a maximum of FR128, LAAM rats made more responses at the higher ratios than did controls. Although these data suggest that LAAM may be a behavioral or functional teratogen, the possibility that early postnatal toxicity or withdrawal are responsible for these findings is discussed.