Repeated exposure to high-THC Cannabis smoke during gestation alters sex ratio, behavior, and amygdala gene expression of Sprague Dawley rat offspring

Abstract

Due to the recent legalization of Cannabis in many jurisdictions and the consistent trend of increasing THC content in Cannabis products, there is an urgent need to understand the impact of Cannabis use during pregnancy on fetal neurodevelopment and behavior. To this end, we repeatedly exposed female Sprague-Dawley rats to Cannabis smoke from gestational days 6 to 20 (n=12; Aphria Mohawk; 19.51% THC, <0.07% cannabidiol) or room-air as a control (n=10) using a commercially available system. Maternal reproductive parameters, behavior of the adult offspring, and gene expression in the offspring amygdala were assessed. Body temperature was decreased in dams following smoke exposure and more fecal boli were observed in the chambers before and after smoke exposure in those dams exposed to smoke. Maternal weight gain, food intake, gestational length, litter number, and litter weight were not altered by exposure to Cannabis smoke. A significant increase in the male-to-female ratio was noted in the Cannabis-exposed litters. In adulthood, both male and female Cannabis smoke-exposed offspring explored the inner zone of an open field significantly less than control offspring. Gestational Cannabis smoke exposure did not affect behavior on the elevated plus maze test or social interaction test in the offspring. Cannabis offspring were better at visual pairwise discrimination and reversal learning tasks conducted in touchscreen-equipped operant conditioning chambers. Analysis of gene expression in the adult amygdala using RNAseq revealed subtle changes in genes related to development, cellular function, and nervous system disease in a subset of the male offspring. These results demonstrate that repeated exposure to high-THC Cannabis smoke during gestation alters maternal physiological parameters, sex ratio, and anxiety-like behaviors in the adulthood offspring. Significance statementCannabis use by pregnant women has increased alongside increased THC content in recent years. As smoking Cannabis is the most common method of use, we used a validated model of Cannabis smoke exposure to repeatedly expose pregnant rats to combusted high-THC Cannabis smoke. Our results show alterations in litter sex ratio, anxiety-like behavior, and decision making in the offspring which may relate to subtle changes in expression of amygdala genes related to development, cellular function, and nervous system disease. Thus, we believe this gestational Cannabis exposure model may be useful in delineating long-term effects on the offspring.