Conditioned suppression and opioid kappa receptor in mice

Area of Science:

• Neuroscience
• Pharmacology
• Behavioral Science

Background:

• Stress can induce behavioral changes, such as conditioned suppression of motility in mice.
• Opioid receptors, particularly mu and kappa subtypes, play complex roles in stress and pain responses.

Purpose of the Study:

• To investigate the role of different opioid receptor subtypes in stress-induced conditioned suppression of motility in mice.
• To examine how chronic administration of mu and kappa opioid agonists affects stress-related behavioral and neurochemical changes.

Main Methods:

• Mice were pretreated with chronic morphine (mu agonist), ethylketocyclazocine (kappa agonist), pentazocine (kappa agonist), or vehicle.
• Conditioned suppression of motility was assessed by placing mice in a familiar environment previously associated with electric footshock.
• Specific binding of radioligands ([3H]phencyclidine, [3H]naloxone, [3H]ethylketocyclazocine) to synaptic membranes was measured.

Main Results:

• Chronic morphine and vehicle pretreatment resulted in conditioned suppression of motility.
• Chronic kappa agonist (ethylketocyclazocine, pentazocine) pretreatment blocked conditioned suppression.
• In mice showing conditioned suppression, [3H]phencyclidine and [3H]naloxone binding increased, while [3H]ethylketocyclazocine binding remained unchanged.
• In mice without conditioned suppression, [3H]phencyclidine and [3H]naloxone binding were unaltered, and [3H]ethylketocyclazocine binding decreased in the pentazocine group.

Conclusions:

• Different opioid receptor subtypes are differentially affected by stress.
• Kappa opioid receptors appear to be critical for the expression of conditioned suppression of motility in mice.
• Stress may alter the binding function of opioid receptors, influencing behavioral responses.