Earlier this year, our laboratory published work demonstrating that rats whose mothers were given low-dose THC (or an analogous synthetic cannabinoid) while pregnant showed significant changes in synaptic plasticity and altered levels of several important proteins lasting well into adulthood. We found that the consequences of these changes manifested as a reduced sociability in the exposed offspring. Male rats in particular were much less likely to approach, play with, or sniff other rats.4
These findings parallel sociobehavioral changes seen in young adult humans exposed to cannabis during gestation. And scientists are now linking those effects to changes in the brain that are similar to what we observed in rats. Using functional MRI technology, for example, researchers participating in the Ottawa Prenatal Prospective Study observed a reduction in activity in the prefrontal cortices of adult offspring of mothers who smoked marijuana during pregnancy. This drop was associated with decreased working memory, echoing the attentional problems and memory dysfunction seen as early as infancy.5
Cannabis is also likely to affect the amygdala, which is critical for emotional development. In 2004, Yasmin Hurd of the Karolinska Institute and colleagues identified a significant reduction in dopamine D2 receptor mRNA in the amygdalae of fetal brains that correlated with the reported quantity of cannabis consumed by their mothers.6 (The fetuses were all between 18 and 22 weeks of gestation and donated by women who underwent voluntary abortions.) Given the known role of amygdala dopamine signaling in the regulation of mood and emotion, these findings could explain the increased depressive-like symptoms observed in children following cannabis exposure in utero, as well as these kids’ propensity towards inattention and impulsivity.
The problem of infant cannabis exposure extends well beyond pregnancy. THC and its lipophilic cannabinoid analogs are readily transferred through breast milk of humans and other mammals, and animal studies have pointed to these compounds’ influence on development throughout the pre-weaning period. Worse yet, given that these cannabinoids linger in the body for weeks, the “pump-and-dump” approach often employed to avoid feeding alcohol-laden milk to an infant isn’t as effective for cannabis users—a Friday night joint can continue to deliver active cannabinoids through breast milk throughout the weekend and into the next week.