Different central areas involved in the mechanisms of morphine antinociception in the mouse and the rat.
The antinociceptive effect of morphine quantitated by the tail-flick (TF) response was studied in mice and rats with various preparations, including: precollicular transection, partial and complete anemic decerebration, vertebral artery infusion, cross-circulation, spinal ligation, spinalization with dura mater intact and spinal subarachnoid infusion. In mice, either precollicular transection or partial anemic decerebration abolished or greatly reduced the morphine antinociceptive action (MAA). However, in rats, neither precollicular transection nor complete anemic decerebration caused any significant reduction in MAA. Studies of vertebral artery infusion and cross-circulation in both species indicated that opiate-sensitive antinociceptive receptors (OSAR) were present in the hindbrain. Although, spinal ligation eliminated MAA in both species, spinalization with dura mater intact only abolished the MAA in rats. On the other hand, studies of spinal subarachnoid infusion showed that only spinal antinociceptive neurons of mice were highly sensitive to the enzyme-resistant enkephalin (Enk) analog. From all these results suggested that both pre- and post-collicular structures are necessary for MAA in the mouse, however, in the rat only the post-collicular structures are essential, furthermore, the humoral pathway seems to play a more important role than the neural pathway in the inhibition of the TF response in the mouse but just the opposite in the rat. Therefore, it is concluded that the mechanisms of MAA are different between the mouse and the rat. The possible mechanisms of MAA in both species were discussed.
Fu
T C
TC
Department of Physiology, College of Medicine, National Taiwan University, Taipei, R.O.C.
D000698:Analgesia; D000818:Animals; D001921:Brain / Q000187:drug effects*; D003655:Decerebrate State; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013045:Species Specificity
D009020:Morphine