Antiallodynic effect of morphine in neuropathy: role of midbrain
Research field:Central nervous system
Authors:Wei H, Linnankoski I, Pertovaara A
Address of presenting
author:		Hong Wei, Dept Physiology, Inst Biomedicine, Univ Helsinki, POB. 9, 00014-Helsinki, Finland
E-mail:wei@cc.helsinki.fi
Phone:+358-9-1918552
Fax:+358-9-1918681
Text of abstract Introduction
In the present study we investigated the efficacy of morphine in the periaqueductal gray (PAG), nucleus tractus solitarus (NTS), or after systemic or intrathecal administration in neuropathic rats.

Methods
Neuropathy was induced by unilateral ligation of the spinal nerves L5 and L6 in rats. Morphine was administered into the PAG or NTS (i.c.) or intathecally (i.t.) via a chronic cannula.
Tactile allodynia was determined by von Frey filaments, mechanical hyperalgesia was assessed by paw pressure test, and thermonociception was measured by heat-induced tail flick reflex.

Results
Morphine in the PAG or systemically produced a significant attenuation of tactile allodynia and had also antihyperalgesic and antinociceptive effects. The antinociceptive effects of systemic morphine was reversed by naloxone administered in the PAG. Intrathecally, morphine produced only a weak antihyperalgesic effect, and in the NTS it did not modulate nocifensive behaviors of the neuropathic rats.

Conclusions
Morphine attenuates pain-related responses in neuropathic rats. The effect of morphine depends on the route of administration.The antiallodynic and antinociceptive effect of systemic morphine in neuropathic animals could be explained by an action on the midbrain (PAG).


References
Kim, S.H. & Chung, J.M. 1992. Pain 50, 355-363

Keywords:morphine, chronic neuropathy, tactile allodynia, periaqueductal gray, nucleus tractus solitarus

Created 2000-05-03