Is there any Cross‐Antagonism between μ‐Opioid and α2‐Adrenergic Receptors in the Rat Spinal Cord?

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Abstract
A functional connection, evidenced by synergism and cross‐tolerance, seems to exist between the μ‐opioid and the α2‐adrenergic receptors in the superficial dorsal horn of the rat spinal cord. In this study possible cross‐antagonism between these systems was studied by intrathecal administration of morphine 2.5 μg or dexmedetomidine 1.25 μg 15 min. after subcutaneous injection of naloxone 1.0 mg/kg or atipamezole 3.0 mg/kg in the morphine group and 4.0 mg/kg or 1.0 mg/kg in the dexmedetomidine group, respectively. No cross‐antagonism of the antinociceptive effect was seen either in the tail flick or in the hot plate test at 15, 30, 45 and 60 min. from the pretreatment.