Dextromethorphan reduces sign-tracking but not goal-tracking in male Sprague-Dawley rats.

Sign-tracking is a well-known phenomenon in appetitive Pavlovian conditioning in which subjects approach the site of a conditioned stimulus (CS) associated with an appetitive unconditioned stimulus (US) even when the two are located separately. Control of sign-tracking may be important in rehabilitation from drug dependence to help ward off relapse. Recent studies have found success in using ketamine to reduce sign-tracking. In this study, we employed a similar but unscheduled drug, dextromethorphan (DXM), which affects many of the same molecular targets as ketamine, in an attempt to reduce sign-tracking in a standard paradigm. DXM was found to reduce sign-tracking at the doses examined in this study, while goal-tracking (approaching the site of the US rather than CS) was relatively unaffected. DXM offers advantages over ketamine in terms of use with patients and may have some utility in rehabilitation.

Acute caffeine enhances sign-tracking in male Sprague-Dawley rats.

Sign-tracking, as a classically conditioned behavior, is of interest due to its relation to impulsivity and addiction. Caffeine affects the activity of neurotransmitters linked to sign-tracking such as dopamine and acetylcholine. As such, acute caffeine administration may enhance sign-tracking behavior. Caffeine was found to enhance measures of sign-tracking behavior in Sprague-Dawley rats in a sign/goal-tracking procedure. It is suggested that part of caffeine's effects on cognition may be due to its ability to enhance incentive salience in conditioned stimuli.