Opioid receptor subtype involvement in maternal behavior in lactating rats

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Pharmacology

Background:

• Opioid administration, particularly morphine, is known to disrupt maternal behavior in rats.
• Morphine acts as a mu-opioid receptor agonist, but its effects may involve other opioid receptor subtypes.
• Understanding the specific opioid receptor subtypes involved is crucial for characterizing the neurobiological underpinnings of maternal behavior.

Purpose of the Study:

• To investigate the role of different opioid receptor subtypes in modulating maternal behavior in female rats.
• To determine which specific opioid receptor subtype(s), when activated, disrupt maternal behavior.
• To compare the potency of various selective opioid receptor agonists in affecting maternal behavior.

Main Methods:

• Virgin Sprague-Dawley rats were mated and surgically implanted with cannulae for intracerebroventricular (i.c.v.) infusions.
• On postpartum day 5, maternal behavior was assessed after vehicle infusion.
• On postpartum day 6, rats received i.c.v. infusions of various opioid receptor agonists (beta-endorphin, DAGO, morphine, DPDPE, U50488H, SKF10047) at different doses before behavioral testing.

Main Results:

• Intracerebroventricular administration of mu-opioid receptor agonists dose-dependently disrupted maternal behavior in lactating rats.
• Selective delta (DPDPE), kappa 1 (U50488H), and sigma (SKF10047) receptor agonists did not significantly affect maternal behavior.
• The highly selective mu-opioid agonist DAGO was more potent than beta-endorphin and morphine in disrupting maternal behavior.

Conclusions:

• Maternal behavior in female rats is primarily regulated by the activation of mu-opioid receptors.
• The mu-opioid receptor is the key subtype involved in the disruption of maternal behavior by opioids.
• These findings emphasize the critical role of the mu-opioid system in the neurobiological control of maternal care.