Attenuation of ascending nociceptive signals to the rostroventromedial medulla induced by a novel alpha2-adrenoceptor agonist, MPV-2426, following intrathecal application in neuropathic rats.
BACKGROUND
In the current study, the potency and spread of the antinociception induced by MPV-2426, a novel alpha2-adrenoceptor agonist, was characterized in neuropathic and non-neuropathic animals.


METHODS
Neuropathy was induced by unilateral ligation of two spinal nerves in the rat. After lumbar intrathecal or systemic administration of MPV-2426, thermally and mechanically evoked responses of nociceptive neurons of the rostroventromedial medulla were recorded during pentobarbitone anesthesia. To obtain a behavioral correlate of neurophysiologic findings, nocifensor reflex responses evoked by thermal and mechanical stimuli were assessed in unanesthetized neuropathic and control animals.


RESULTS
After intrathecal administration, MPV-2426 and dexmedetomidine produced a dose-related antinociceptive effect, independent of the submodality of the noxious test stimulus or the pathophysiologic condition. This antinociceptive effect was spatially restricted to the inputs from the lower half of the body, and it was reversed by atipamezole, an alpha2-adrenoceptor antagonist. After systemic administration in non-neuropathic animals, MPV-2426 had no antinociceptive effect on responses to rostroventromedial medulla neurons, whereas systemically administered dexmedetomidine produced a dose-related suppression of nociceptive signals to the rostroventromedial medulla, independent of the site of test stimulation. In a behavioral study, intrathecal MPV-2426 produced a dose-dependent suppression of nocifensor responses evoked by noxious mechanical or heat stimuli, whereas systemic administration of MPV-2426 had no effects.


CONCLUSIONS
Intrathecal MPV-2426 has spatially limited antinociceptive properties in neuropathic and non-neuropathic conditions because of its action on spinal alpha2-adrenoceptors. These properties may be advantageous when designing therapy for spatially restricted pain problems.
Pertovaara
A
A
Department of Physiology, Institute of Biomedicine, University of Turku, Finland. Pertovaa@penger.helsinki.fi
Wei
H
H
D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D020927:Dexmedetomidine / Q000494:pharmacology; D004594:Electrophysiology; D006358:Hot Temperature; D007093:Imidazoles / Q000008:administration & dosage / Q000494:pharmacology*; D007189:Indans / Q000008:administration & dosage / Q000494:pharmacology*; D007278:Injections, Spinal; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects*; D010146:Pain / Q000503:physiopathology*; D010523:Peripheral Nervous System Diseases / Q000503:physiopathology*; D010812:Physical Stimulation; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects*
D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists; D007093:Imidazoles; D007189:Indans; D020927:Dexmedetomidine; C400294:radolmidine