Cross-tolerance between D-amino acids and morphine in mice

Area of Science:

• Neuroscience
• Pharmacology
• Genetics

Background:

• Morphine is a potent analgesic with known side effects.
• Opioid receptors and their downstream signaling pathways are complex.
• Genetic differences between mouse strains can influence drug responses.

Purpose of the Study:

• To investigate the effects of D-amino acids (D-AA) on morphine-induced analgesia and locomotor activity.
• To determine if D-AA pretreatment induces cross-tolerance to morphine in different mouse strains.
• To explore strain-specific interactions in opioid pharmacodynamics.

Main Methods:

• DBA/2 (DBA) and C57BL/6 (C57) mice were injected with D-amino acids (D-AA) for 5 consecutive days.
• Following D-AA pretreatment, mice were administered morphine.
• Analgesia and running activity were measured to assess drug effects.

Main Results:

• In DBA mice, D-AA pretreatment resulted in a clear cross-tolerance to morphine's analgesic effects.
• In C57 mice, D-AA pretreatment did not alter the stimulating effect of morphine on running activity.
• These findings highlight differential effects of D-AA on opioid responses based on mouse genetic background.

Conclusions:

• D-amino acids exhibit strain-dependent cross-tolerance with morphine in mice.
• The interaction between D-AA and opioid systems is specific to analgesia in DBA mice.
• Genetic factors in C57 mice may mediate distinct pathways for opioid-induced activity, unaffected by D-AA.