Morphine: conditioned increases in self-administration in rhesus monkeys

Area of Science:

• Behavioral neuroscience
• Pharmacology
• Primate research

Background:

• Operant conditioning is a fundamental learning process.
• Opioid drugs like morphine are frequently self-administered.
• Understanding drug reinforcement is crucial for addiction research.

Purpose of the Study:

• To investigate the effects of nalorphine on morphine-reinforced operant responding in non-human primates.
• To examine how repeated nalorphine administration influences the pattern and timing of drug self-administration.
• To assess the development of conditioned drug-seeking behavior.

Main Methods:

• Three rhesus monkeys were trained to respond for intravenous morphine infusions.
• Nalorphine was administered to assess its effects on ongoing morphine-reinforced behavior.
• Response latency and the effects of saline substitution were recorded over successive daily injections.

Main Results:

• Nalorphine reliably increased the rate of morphine-reinforced responding.
• Successive daily nalorphine injections led to a decreased latency in self-administration responding for morphine.
• Saline injections, substituted for nalorphine, elicited conditioned increases in morphine-reinforced responding.

Conclusions:

• Nalorphine acts as a modulator of morphine reinforcement.
• Repeated exposure to nalorphine can alter the temporal dynamics of drug seeking.
• Conditioned responses to drug-associated cues, like saline, can emerge and influence drug self-administration.