THC-Tolerant Rats Showed Withdrawal-Related Changes Without Greater Morphine Self-Administration
A rat study found behavioral and molecular responses to CB1 blockade after repeated THC exposure, but no increase in morphine self-administration. The withdrawal-related findings and the null reinforcement result answer different questions and should be reported together.
An antagonist precipitated the challenge
Researchers administered SR141716 to THC-tolerant and control rats. The antagonist increased behaviors including tremor, turning and retropulsion more clearly in the tolerant animals. This was an experimentally precipitated withdrawal model, rather than simply observing what happened when cannabis use stopped.
Plasma hormones and brain signals diverged
Prolactin and corticosterone increases in plasma were smaller in tolerant rats than in controls. By contrast, the direction of hypothalamic CRF-mRNA response differed between groups. The antagonist also reversed some regional brain endocannabinoid changes but not those in every region examined. Hormone concentrations in plasma and lipid measurements in brain tissue are different evidence streams.
The morphine result was not positive
THC-tolerant and control rats self-administered morphine to a similar extent. The abstract also reported similar dopaminergic activity in relevant regions. Consequently, this experiment does not support claiming that the tested THC history increased morphine's reinforcing properties. It also cannot exclude every possible effect of other cannabis exposures or conditions.
The study provides evidence of adaptation to repeated THC while limiting a broader prediction about subsequent opioid reinforcement. Treating withdrawal signs as automatic proof of increased vulnerability to another drug would skip a comparison that the investigators actually performed and that did not show the proposed increase.
Related: interpreting cannabis tolerance claims.
Research cited
González S; Fernández-Ruiz J; Di Marzo V; Hernández M; Arévalo C; Nicanor C; Cascio MG; Ambrosio E; Ramos JA. Behavioral and molecular changes elicited by acute administration of SR141716 to Delta9-tetrahydrocannabinol-tolerant rats: an experimental model of cannabinoid abstinence. Drug and alcohol dependence (2004). doi:10.1016/j.drugalcdep.2003.12.011. Findings discussed from the study abstract.
