Hot Off the Press – September 3, 2019.
The expanding legalization of recreational and medical marijuana has increased its availability, and stronger strains of cannabis containing much higher levels of ∆9-tetrahydrocannabinol (THC), the primary psychoactive constituent, are now widely used. Although the effects of marijuana on the brain are often assumed to be mild, there are increasing credible reports of psychiatric disorders associated with its use. Here, using optogenetics, we show in rats exposed to THC for 14 days that large changes in discrete sets of corticolimbic synaptic inputs to the nucleus accumbens are observed. This pattern of dysregulation of nucleus accumbens inputs is consistent with changes observed in brain imaging studies in human marijuana users in which cortical control is lost and limbic control is strengthened. We hypothesize that the mechanistic changes we describe are involved in the alterations in cognition, emotion and motivation observed in heavy users of cannabis.