Morphine pretreatment increases opioid inhibitory effects on maternal behavior

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Pharmacology

Background:

• Opioid drugs inhibit ongoing maternal behavior in rats.
• Drug abuse can lead to lasting enhancements in drug-reinforcing effects.
• The impact of puerperal morphine treatment on opioid sensitivity and maternal behavior is understudied.

Purpose of the Study:

• To investigate if abrupt withdrawal from repeated morphine chlorhydrate (MC) treatment during late pregnancy and early lactation influences maternal behavior in rats.
• To determine if MC-induced changes in sensitivity to opioid inhibition of maternal behavior persist postpartum.
• To test if naloxone can reverse MC-induced inhibition of maternal behavior.

Main Methods:

• Female Wistar rats received daily subcutaneous injections of MC (5.0 mg/kg) or saline from day 17 of pregnancy for 7 days.
• Following abrupt discontinuation, rats were acutely challenged with MC (5.0 mg/kg) or saline.
• Maternal behavior was tested on postpartum days 5, 10, and 17, with naloxone (1.0 mg/kg) used in one experiment.

Main Results:

• Rats repeatedly treated with MC during late pregnancy and acutely challenged with MC (MM group) exhibited significantly longer latencies for all maternal behaviors compared to other groups.
• This heightened inhibition of maternal behavior in the MM group persisted until day 17 postpartum.
• Acute pretreatment with naloxone reversed the inhibitory effects of MC on maternal behavior.

Conclusions:

• Repeated administration of MC during late pregnancy sensitizes female rats to the inhibitory effects of opioids on maternal behavior.
• This sensitization is long-lasting, persisting postpartum without continuous drug reinforcement.
• Opioid antagonist naloxone can reverse these MC-induced behavioral changes.