Delta-9-tetrahydrocannabinol (THC) history fails to affect THC's ability to induce place preferences in rats

In pre-clinical models of marijuana abuse, there is relatively limited evidence of delta-9-tetrahydrocannabinol's (THC) rewarding effects, as indexed by its general inability to induce a place preference. One explanation for this failure is that its rewarding effects are masked by its concurrently occurring aversive properties. Consistent with this explanation, THC pre-exposure, which presumably weakens its aversive effects, induces place preferences. Such demonstrations are limited to mice and given reported species differences in THC reactivity, it is unknown to what extent the same shift in affective properties would be evident in rats.

The present experiment examined the effect of THC history (3.2mg/kg) on THC (1 or 3.2mg/kg) induced place preference conditioning in rats. An assessment of taste avoidance was also run to independently characterize THC's aversive effects and any changes that occurred with drug pre-exposure. These assessments were made in a combined taste avoidance/place preference procedure in which a novel saccharin solution and environment were paired with THC (0, 1 or 3.2mg/kg).

THC did not induce place conditioning, and a history of THC was ineffective in increasing THC's ability to do so, despite the fact that this same history significantly attenuated the aversive effects of THC.

The failure of THC to consistently induce place preferences has been argued to be a function of its concurrently occurring aversive effects masking its rewarding properties. The fact that pre-exposure to THC significantly reduced its aversive effects without impacting THC's ability to induce place preferences suggests that THC has weak rewarding effects and/or its residual aversive affects may have still masked its rewarding properties. An important area for future work will be characterizing under what conditions THC is rewarding and whether its overall reinforcing effects are impacted by the relationship between its affective properties.