Delta-9-tetrahydrocannabinol during pregnancy in the rat: II. Effects on ontogeny of locomotor activity and nipple attachment in the offspring.
Either 15 or 50 mg/kg delta-9-tetrahydrocannabinol (THC) in sesame oil was administered by gastric intubation to gravid rats during the last two weeks of gestation. A pair-fed control group was administered the vehicle alone and allowed to eat and drink only the amount consumed by the 50 mg/kg group on the same gestation days. A nontreated control group was left undisturbed during pregnancy. All treated and control litters were fostered at birth to untreated dams. Intact litters from the two THC treated and the two control groups were tested at 3-day intervals from birth to 32 days of age for differences in locomotor activity. In addition, pups were tested for nipple attachment on days 2, 5, 8, 11, and 14 of age. There were no differences in locomotor activity among any of the groups although activity level varied during development. Pups from dams exposed to 50 mg/kg of THC, as well as the pair-fed controls, displayed significantly longer latencies to attach to a nipple. These results suggest that the impaired nipple attachment observed among the high-dose offspring was not a primary effect of THC, but rather was secondary to the significant reduction of food and water intake among the dams. The behavioral findings are discussed with respect to other animal and clinical reports of prenatal cannabinoid exposure.