Effect of Housing and Gender on Morphine Self-Administration in Rats
Objective: Study the effect of housing and gender on morphine self-administration in rats.
Methodology:
- Experimental Design:
- Rats divided into isolated (standard cages) and social (large open box) housing conditions.
- Morphine solution (0.5 mg/ml) provided as sole fluid over 57 days.
- Following this, analyzed morphine consumption during different phases including forced consumption and abstinence periods.
Findings:
- Isolated rats showed higher morphine consumption compared to social rats, especially during choice days.
- Gender differences: Female rats consumed more morphine than males.
Phases of Experiment:
- Limited Access Period: Rats had restricted fluid access. Morphine consumption remained low.
- Forced Consumption Period: Continuous morphine access; isolated rats gradually increased their consumption.
- Nichols Cycle Period: Shift in access conditions affected morphine intake; isolated rats continued to consume more.
- Abstinence Period: Isolated rats persisted in higher morphine intake compared to social rats.
Statistical Analysis:
- Significant differences in consumption patterns (e.g., isolated vs social groups).
Conclusions:
- Housing conditions significantly influence morphine self-administration behavior.
- Environmental stress factors (isolation, confinement) may enhance the reinforcing effects of morphine.
- Challenges existing addiction theories to account for the effects of social environments.
Concerns:
- Differential mortality among female rats complicates consumption analysis.
- Study raises questions about generalizability of previous morphine self-administration studies conducted under different conditions.