Different time schedules affect conditioned place preference after morphine and morphine-6-glucuronide...

Area of Science:

• Neuroscience
• Pharmacology
• Addiction Research

Background:

• Morphine is a well-studied opioid with known reward potential, often assessed using Conditioned Place Preference (CPP).
• Morphine-6-glucuronide (M6G), a metabolite of morphine, possesses comparable analgesic effects, but its rewarding properties remain largely uncharacterized.
• Understanding the reward mechanisms of M6G is crucial, as it may contribute to the addictive potential of opioids like heroin and morphine.

Purpose of the Study:

• To investigate the reward properties of morphine and M6G using the CPP procedure in mice.
• To determine the influence of different conditioning schedules (timing and duration) on CPP induction by morphine and M6G.
• To assess the locomotor activity effects of M6G.

Main Methods:

• Utilized an unbiased, two-compartment counterbalanced CPP procedure in C57BL/6J-Bom mice.
• Administered morphine or M6G and employed varying conditioning session timings: immediate (20 or 40 min) or delayed (15 min post-injection, 20 min duration).
• Monitored locomotor activity during conditioning sessions.

Main Results:

• Morphine induced CPP with immediate 20-minute conditioning, but not with delayed conditioning.
• M6G induced CPP with delayed 20-minute conditioning, but not with immediate conditioning.
• Neither drug induced CPP with 40-minute direct conditioning sessions; M6G exhibited biphasic locomotor effects (initial decrease, then excitation).

Conclusions:

• M6G demonstrates rewarding effects, potentially contributing to opioid addiction.
• The induction of CPP by both morphine and M6G is highly dependent on the timing of drug administration relative to conditioning.
• Careful consideration of timing schedules is essential when evaluating the reward properties of M6G and related compounds.