Vaporized Cannabis Extracts Have Reinforcing Properties and Support Conditioned Drug-Seeking Behavior in Rats
Authors: Freels Timothy G. , Baxter-Potter Lydia N. , Lugo Janelle M. , Glodosky Nicholas C. , Wright Hayden R. , Baglot Samantha L. , Petrie Gavin N. , Yu Zhihao , Clowers Brian H. , Cuttler Carrie , Fuchs Rita A. , Hill Matthew N. , McLaughlin Ryan J. 
Published: January 2020

Recent trends in cannabis legalization have increased the necessity to better understand the effects of cannabis use. Animal models involving traditional cannabinoid self-administration approaches have been notoriously difficult to establish and differences in the drug used and its route of administration have limited the translational value of preclinical studies. To address this challenge in the field, we have developed a novel method of cannabis self-administration using response-contingent delivery of vaporized Δ9-tetrahydrocannabinol-rich (CANTHC) or cannabidiol-rich (CANCBD) whole-plant cannabis extracts. Male Sprague-Dawley rats were trained to nose-poke for discrete puffs of CANTHC, CANCBD, or vehicle (VEH) in daily 1 h sessions. Cannabis vapor reinforcement resulted in strong discrimination between active and inactive operanda. CANTHCmaintained higher response rates under fixed ratio schedules and higher break points under progressive ratio schedules compared with CANCBDor VEH, and the number of vapor deliveries positively correlated with plasma THC concentrations. Moreover, metabolic phenotyping studies revealed alterations in locomotor activity, energy expenditure, and daily food intake that are consistent with effects in human cannabis users. Furthermore, both cannabis regimens produced ecologically relevant brain concentrations of THC and CBD and CANTHCadministration decreased hippocampal CB1 receptor binding. Removal of CANTHCreinforcement (but not CANCBD) resulted in a robust extinction burst and an increase in cue-induced cannabis-seeking behavior relative to VEH. These data indicate that volitional exposure to THC-rich cannabis vapor has bona fide reinforcing properties and collectively support the utility of the vapor self-administration model for the preclinical assessment of volitional cannabis intake and cannabis-seeking behaviors.

SIGNIFICANCE STATEMENTThe evolving legal landscape concerning recreational cannabis use has increased urgency to better understand its effects on the brain and behavior. Animal models are advantageous in this respect; however, current approaches typically used forced injections of synthetic cannabinoids or isolated cannabis constituents that may not capture the complex effects of volitional cannabis consumption. We have developed a novel model of cannabis self-administration using response-contingent delivery of vaporized cannabis extracts containing high concentrations of Δ9tetrahydrocannabinol (THC) or cannabidiol. Our data indicate that THC-rich cannabis vapor has reinforcing properties that support stable rates of responding and conditioned drug-seeking behavior. This approach will be valuable for interrogating effects of cannabis and delineating neural mechanisms that give rise to aberrant cannabis-seeking behavior.