CB1 Blockade Disrupted New Learning More Than Practiced Performance in THC-Tolerant Rats

Rats developed tolerance to THC-related disruption of both new sequence learning and practiced responding. During chronic treatment, however, a CB1 antagonist selectively increased errors in the new-learning component, exposing a difference between the tasks.

Learning and performance were tested together

In one task component, rats learned a different three-response sequence each session. In another, the sequence stayed the same. Food reinforcement maintained responding. Acute THC reduced response rate and accuracy in both components, while the tested antagonist doses were initially ineffective.

Repeated THC changed the challenge response

Daily THC administration produced tolerance to the response-slowing and error-increasing effects of the repeated dose. When an initially ineffective antagonist dose replaced THC during chronic treatment, within-session errors increased selectively during acquisition. Performance on a familiar sequence did not show the same error pattern.

Recovery was defined by these tasks

After chronic treatment, rats were generally less sensitive to THC's disruptive effects. The finding does not establish equal recovery across all cognitive functions. Nor should a selective learning deficit be relabeled as a general memory failure without acknowledging how learning was operationally measured.

For evidence interpretation, the task distinction is central. A practiced behavior can remain stable while acquisition of new information responds differently to a pharmacological challenge. The study cannot determine whether a person is fit to drive, but it demonstrates why one intact performance measure cannot stand in for every cognitive demand.

Related: interpreting cannabis tolerance claims.

Research cited

Delatte MS; Winsauer PJ; Moerschbaecher JM. Tolerance to the disruptive effects of Delta(9)-THC on learning in rats. Pharmacology, biochemistry, and behavior (2002). doi:10.1016/s0091-3057(02)00966-8. Findings discussed from the study abstract.