Time-dependent effect of morphine and time-independent effect of MK-801, an NMDA antagonist, on the thermal hyperesthesia induced by unilateral constriction injury to the sciatic nerve in the rat.

Abstract

BACKGROUND:

It is known that peripheral nerve injury induces time-dependent changes in dorsal horn function. The current study investigated the time dependency of the effects of intrathecal morphine and MK-801, an N-methyl-D-aspartate antagonist, on the thermal hyperesthesia evoked by unilateral constriction injury to the sciatic nerve in the rat.

METHODS:

In rats with a unilateral constriction injury to the sciatic nerve, paw withdrawal latency against thermal stimulation for the injured paw was typically 3 s less than that for the uninjured paw during the first 5 weeks after the injury. Drugs were administered intrathecally 1 or 5 weeks after the nerve injury.

RESULTS:

Intrathecal morphine increased the paw withdrawal latencies of both the injured paw and the uninjured paw in an equally dose dependent manner in the 1-week study. In the 5-week study, morphine increased the paw withdrawal latency of the uninjured paw in a dose-dependent manner, but not that of the injured paw. Intrathecal MK-801 increased the paw withdrawal latency of the injured paw to the level of the uninjured paw in a dose-dependent manner in both the 1- and 5-week studies.

CONCLUSIONS:

These data indicate that (1) an N-methyl-D-aspartate receptor-mediated spinal facilitation may be the common mechanism maintaining the thermal hyperesthesia evoked by the constriction injury, and (2) the effects of intrathecal morphine on this thermal hyperesthesia are time-dependent.

• Authors: T Yamamoto, N Shimoyama, H Asano, T Mizuguchi
• Journal: Anesthesiology (Anesthesiology) Vol. 80 Issue 6 Pg. 1311-9 (Jun 1994) ISSN: 0003-3022 [Print] United States
• PMID: 8010478 (Publication Type: Journal Article)

Chemical References

• Naloxone
• Dizocilpine Maleate
• Morphine

Topics

• Animals
• Constriction, Pathologic
• Dizocilpine Maleate (administration & dosage, pharmacology)
• Dose-Response Relationship, Drug
• Hot Temperature
• Hyperesthesia (etiology, physiopathology)
• Injections, Spinal
• Male
• Morphine (administration & dosage, pharmacology)
• Naloxone (pharmacology)
• Rats
• Rats, Sprague-Dawley
• Reflex (drug effects)
• Sciatic Nerve (injuries)
• Time Factors