Lesions of the mesolimbic dopamine system disrupt signalled escape responses in the rat

Classically conditioned shuttling and escape responses of 14 rats with 6-hydroxydopamine lesions of the ventral tegmental area (VTA) were compared with those of 16 sham-lesioned control rats in an aversive classical conditioning paradigm. Although the 6-OHDA lesion did not enhance classically conditioned shuttling, it eliminated the facilitation of escape responses by the conditioned stimulus. Thus, whereas the classically conditioned sham-lesioned rats were faster to escape shock than were the pseudoconditioned sham-lesioned rats, the 6-OHDA classically conditioned and pseudoconditioned rats were equally slow to escape. This suggests that the ability of the rat to respond appropriately to the motivational or informational content of the warning signal was disrupted following damage to the mesolimbic dopamine system.