Short and long-term effects of pre-natal cannabis inhalation upon rat offspring

Pregnant rats were exposed to Cannabis smoke or smoke from material with cannabinoids removed on Days 1-19 of gestation. The number of resorptions was greater in the experimental than the control group. The litter size, length of gestation, sex ratio, live births, and external appearance of the offspring did not differ between the two groups. However, the birth weights of both the male and female offspring of the experimental rats were significantly reduced. Cross-fostering controls were utilized. Those rats born to control mothers but raised by experimental rats (C-E) were consistently lighter than offspring born and raised by controls (C-C) during the last 15 days of nursing but one month after weaning they were indistinguishable from the C-C group. Those animals born to experimental mothers but raised by controls (E-C) were initially 6-8% lighter than control offspring but by weaning the difference was 3% and one month later than E-C animals were indistinguishable from C-C animals. Progeny born and raised by experimental mothers (E-E) were consistently higher than controls during nursing and, even two months after weaning, were still significantly smaller. The E-C and E-E groups had reduced activity at 9 days of age and showed delayed incisor eruption and eye opening. When the offspring were chronically injected with THC commencing at 100 days of age, the C-E animals developed tolerance sooner than controls whereas the E-C and, less clearly, the E-E groups too, longer to develop tolerance.