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Stimulus and response factors affecting the development of behavioral sensitization to apomorphine
B A Mattingly1, C Koch, F H Osborne
1Department of Psychology, Morehead State University, KY 40351-1689, USA.
Psychopharmacology
|March 1, 1997
Summary
Behavioral sensitization to apomorphine in rats depends on response factors, not just stimulus cues. Environmental context is critical for developing this drug-induced hypersensitivity.
Area of Science:
- Neuroscience
- Behavioral Pharmacology
- Psychopharmacology
Background:
- Behavioral sensitization, a form of neuroplasticity, involves progressively enhanced behavioral responses to repeated drug administration.
- The context-dependency of sensitization suggests that environmental cues associated with drug exposure can influence its expression.
- Direct dopamine agonists, like apomorphine, are commonly used to study sensitization due to their potent effects on motor activity.
Purpose of the Study:
- To investigate the roles of stimulus and response factors in the context-dependency of behavioral sensitization to apomorphine.
- To determine if changing external stimulus cues affects the development and expression of apomorphine-induced sensitization.
- To examine the impact of response-contingent environmental factors on behavioral sensitization.
Main Methods:
- Male Wistar rats received repeated subcutaneous injections of apomorphine (5 mg/kg) or vehicle at 24- to 72-h intervals.
- Locomotor activity was assessed in either an open-field activity drum or a running wheel.
- Experiment 1: Rats were tested in alternate environments to assess sensitization transfer. Experiment 2: Rats were trained in either a mobile or immobilized running wheel before a challenge injection.
Main Results:
- Apomorphine induced progressive increases in locomotor activity (sensitization) in both tested environments.
- Sensitization to apomorphine completely transferred between different test environments, indicating stimulus cues did not impede expression.
- Rats trained in a mobile running wheel showed significantly greater activity after an apomorphine challenge compared to those trained in an immobile wheel, suggesting response factors are critical.
Conclusions:
- The expression of behavioral sensitization to apomorphine is not dependent on specific external stimulus cues associated with drug exposure.
- Environmental factors related to the response (e.g., motor output) are critical for the development of behavioral sensitization to apomorphine.
- These findings highlight the importance of response-contingent learning in mediating drug-induced neuroplasticity.