Hold-down as an alternative to unit dose in cocaine self-administration experiments: Characterization using a...

Area of Science:

• Behavioral neuroscience
• Addiction research
• Pharmacology

Background:

• Traditional cocaine self-administration studies utilize a fixed "unit dose," where subjects passively receive experimenter-determined amounts.
• This passive model limits understanding of active drug-seeking and drug-taking dynamics.

Purpose of the Study:

• To investigate the behavioral consequences of allowing subjects to actively control cocaine dose and injection speed.
• To evaluate a novel two-lever progressive ratio (PR) schedule with a hold-down (HD) cocaine delivery system.

Main Methods:

• A two-lever progressive ratio (PR) schedule was employed, where lever pressing granted access to cocaine via a hold-down (HD) mechanism.
• The HD schedule allowed subjects to determine the dose and speed of cocaine delivery by controlling the lever-hold duration.
• This procedure enabled the assessment of both drug-seeking (lever pressing) and drug-taking (lever holding) responses.

Main Results:

• Self-administered doses varied dynamically within sessions and inversely correlated with current drug levels.
• The PR-HD procedure identified distinct subpopulations exhibiting extreme drug-seeking and drug-taking behaviors.
• High-responding subjects achieved exceptionally high final ratios and self-administered substantial cocaine doses rapidly; immediacy of the cocaine bolus, not duration of access, was the primary driver of drug seeking.

Conclusions:

• Integrating a consummatory response (active drug intake) into a PR schedule offers novel insights into drug-seeking and drug-taking interactions.
• This active self-administration model provides a more nuanced understanding of addiction-related behaviors compared to passive unit-dose methods.