Altered Corticolimbic Control of the Nucleus Accumbens by Long-term Δ9-Tetrahydrocannabinol Exposure

Abstract

Background: The decriminalization and legalization of cannabis and the expansion of availability of medical cannabis in North America have led to an increase in cannabis use and the availability of high-potency strains. Cannabis potency is determined by the concentration of Δ⁹-tetrahydrocannabinol (Δ⁹-THC), a psychoactive constituent that activates cannabinoid CB₁ and CB₂ receptors. The use of high-potency cannabis is associated with cannabis use disorder and increased susceptibility to psychiatric illness. The nucleus accumbens (NAc) is part of a brain reward circuit affected by Δ⁹-THC through modulation of glutamate afferents arising from corticolimbic brain areas implicated in drug addiction and psychiatric disorders. Moreover, brain imaging studies show alterations in corticolimbic and NAc properties in human cannabis users.

Methods: Using in vitro electrophysiology and optogenetics, we examined how Δ⁹-THC alters corticolimbic input to the NAc in rats.

Results: We found that long-term exposure to Δ⁹-THC weakens prefrontal cortex glutamate input to the NAc shell and strengthens input from basolateral amygdala and ventral hippocampus. Further, whereas long-term exposure to Δ⁹-THC had no effect on net strength of glutamatergic input to NAc shell arising from midbrain dopamine neurons, it alters fundamental properties of these synapses.

Conclusions: Long-term exposure to Δ⁹-THC shifts control of the NAc shell from cortical to limbic input, likely contributing to cognitive and psychiatric dysfunction that is associated with cannabis use.

Keywords: Cannabinoid; Cannabis; Glutamate; Long-term depression; Marijuana; Medicinal marijuana; Synapse.