This 2017 Italian rodent study found:
“THC [delta9-tetrahydrocannabinol, the psychoactive compound of cannabis] exposure affects histone modifications in the brain of female rats in a region- and age-specific manner. Specifically, THC acts on different targets depending on the considered brain area and, remarkably, the adolescent brain is generally more sensitive to THC than the adult brain.
Adolescent exposure to THC, or to synthetic cannabinoids, induced sex-dependent brain and behavioral alterations at adulthood. In female rats, the phenotype was more complex, as both depressive-like and psychotic-like signs were present.
Development of the depressive/psychotic-like phenotype is restricted to adolescent THC exposure. Not only the behavioral phenotype developed after adolescent, and not adult, exposure, but also changes in both histone modifications and gene expression were more widespread and intense after adolescent treatment, further confirming a specific adolescent susceptibility.
The primary effect in the adolescent brain was represented by changes leading to transcriptional repression, whereas the one observed after adult treatment led to transcriptional activation. Moreover, only in the adolescent brain, the primary effect was followed by a homeostatic response to counterbalance the THC-induced repressive effect, except in the amygdala.”
The authors’ interpretation of the brain area results was:
“The amygdala is more responsive in adult than adolescent animals. Since it has been established that the amygdala is activated during exposure to aversive stimuli, functioning as a “behavioral brake”, different response between adult and adolescent animals could represent the biological bases of the adolescent propensity for risk-taking and novelty-seeking behaviors. Also in adolescent humans, neuroimaging studies have shown a weaker involvement of the amygdala, and a greater contribution of the NAc [nucleus accumbens], in response to negative and positive stimuli compared to adults.”
http://www.mdpi.com/1422-0067/18/10/2094 “Chronic Δ9-THC Exposure Differently Affects Histone Modifications in the Adolescent and Adult Rat Brain”