Cocaine tolerance: acute versus chronic effects as dependent upon fixed-ratio size

Area of Science:

• Behavioral pharmacology
• Neuroscience
• Animal models

Background:

• Operant behavior is crucial for understanding drug effects.
• Tolerance to drugs like cocaine can alter behavior.
• Fixed-ratio schedules assess drug-induced changes in response rates.

Purpose of the Study:

• To investigate how fixed-ratio value influences the development of tolerance to cocaine in pigeons.
• To determine if the amount of responding required for reinforcement affects cocaine tolerance.

Main Methods:

• Pigeons were trained on a three-component multiple schedule with varying fixed-ratio values (small, medium, large).
• Cocaine was administered acutely (1.0-10.0 mg/kg) and repeatedly (5.6 mg/kg daily).
• Dose-effect functions were measured to assess changes in responding and tolerance development.

Main Results:

• Acute cocaine administration decreased response rates in a dose-dependent manner.
• Lower cocaine doses decreased responding more significantly under larger ratio schedules.
• Repeated cocaine administration led to tolerance, but this tolerance was less pronounced under the largest ratio schedule.

Conclusions:

• Tolerance to cocaine's effects on operant behavior is dependent on the fixed-ratio value.
• Reinforcement frequency reduction alone is insufficient to induce tolerance.
• The "effort" or amount of responding required for reinforcement may play a role in the development of cocaine tolerance.