Figure 1.

Lack of the reinforcing effects of the selective σ1R agonists in experimentally naive rats compared with the typical acquisition of lever pressing with cocaine injections. (a) When each response on the right lever produced a cocaine injection rates of responding increased whereas rates of responding on the alternate (left) lever, which had no scheduled consequences, remained low. When cocaine injections were available only for responses on the previously inactive (left) lever, responding switched to that lever. Saline substitution decreased responding on both levers to low levels. When cocaine was again available for responses on the left lever, responding increased on that lever. (b, c) Lack of acquisition of (+)-pentazocine or PRE-084 self-administration when each response produced an injection. Response rates on the active lever were not consistently greater than those on the inactive lever throughout the course of 28 experimental sessions. *p<0.05, **p<0.01, ***p<0.001, compared with responding on the inactive lever (post-hoc Bonferroni t-test).