Biologically plausible reasons for why cannabis use and affective disorders might be related include the fact that the greatest density of cannabinoid-1 receptors in the brain are in regions that are “implicated in both cannabis use disorders but also affective disorders and other neuropsychiatric disorders,” he said. Shared risk genes is another biological explanation, he added, noting that a polymorphism in the gene that encodes for the cannabinoid-1 receptor (CNR1) gene “has been found to increase vulnerability for developing cannabis dependence, (posttraumatic stress disorder), as well as depression in Parkinson’s disease.”
The period of adolescence “does appear to be a vulnerable window specifically for the effects of cannabis use,” Dr. Hammond said, referring to preclinical data that include evidence of alterations in the maturation of the prefrontal cortex, as well as in neurotransmitter and stress-response systems in rodents exposed to exogenous cannabinoids during adolescence. Behavioral data echo “what we’re finding in the brains ... with exogenous cannabis exposure during adolescence altering emotional reactivity ... and producing in adulthood what would be considered a depressive-anxious phenotype,” in the rodent animal model, he said.
This phenotype is not evident when cannabis is administered chronically to older animals, which “suggests that there’s an age-dependent vulnerability specific to childhood and adolescence to the adverse effects of cannabinoids on the brain,” he added.
The association between cannabis use in adolescents, and anxiety disorders and bipolar disorders later in life has not been adequately studied but will be addressed in the Adolescent Brain Cognitive Development Study, Dr. Hammond said. The so-called ABCD study will enroll 10,000 subjects aged 10 through 12 years and will follow them through young adulthood, evaluating patterns of substance abuse, neurodevelopmental impact, and genetic factors. Currently, the study is in the planning stages.
Dr. Hammond disclosed receiving some research funding from a pilot research award from the American Academy of Child and Adolescent Psychiatry, and a child psychiatry fellowship award from the American Psychiatric Association.