Effects of dl-amphetamine under concurrent VI DRL reinforcement

Area of Science:

• Behavioral pharmacology
• Neuroscience
• Animal behavior

Background:

• Understanding the behavioral effects of psychostimulants is crucial in pharmacology.
• Amphetamine derivatives are widely studied for their impact on operant conditioning and timing behavior.

Purpose of the Study:

• To investigate the effects of dl-amphetamine sulfate on timing behavior in rats under differential reinforcement of low rates (DRL) and concurrent variable interval (VI) DRL schedules.
• To determine if amphetamine disrupts internal timing mechanisms or motor activity.

Main Methods:

• Three food-deprived adult rats were administered IP injections of dl-amphetamine sulfate.
• Behavioral responses were recorded under DRL and concurrent VI DRL reinforcement schedules.
• Inter-response time (IRT) distributions and response rates were analyzed.

Main Results:

• Dl-amphetamine sulfate shifted inter-response time (IRT) distributions to the left for both DRL and VI responses, indicating faster responding.
• Temporal discrimination in DRL was partially maintained, and the distinct characteristics of VI and DRL IRT distributions persisted.
• Overall response rates increased proportionally across both schedule components.
• The frequency distribution of VI responses between DRL responses remained largely unaffected.

Conclusions:

• The primary effect of dl-amphetamine sulfate appears to be motor excitation, rather than a direct disruption of internal timing mechanisms.
• The observed alterations in timing behavior may be a secondary consequence of increased motor activity and accelerated response emission.
• Amphetamine's impact on timing is likely related to its general psychostimulant properties affecting overt behavior patterns.