radolmidine and tizanidine

When administered intrathecally, alpha-2 adrenergic agonists produce spinally mediated antinociception, but also rapidly redistribute to supraspinal sites. This investigation the compared EMG effects of intrathecally administered dexmedetomidine, MPV-2426 (fadolmidine), and tizanidine in Sprague-Dawley rats, which has not been previously described.. We studied electromyographic (EMG) responses of the head and gastrocnemius muscles, antinociception using the tail-flick test, and sedation by using observer assessment. Saline, dexmedetomidine (0.5 microg, 2.5 microg and 12.5 microg), MPV-2426 (2 microg, 10 microg and 50 microg) and tizanidine (2 microg, 10 microg and 50 microg) were administered intrathecally.. Tizanidine 50 microg, MPV-2426 10 microg and 50 microg, and dexmedetomidine 2.5 microg and 12.5 microg, decreased EMG activity (P < 0.005). Dexmedetomidine 12.5 microg, MPV-2426 50 microg, and tizanidine 10 microg and 50 microg increased tail-flick latencies (P < 0.01). Dexmedetomidine alone significantly increased the magnitude of observer-assessed sedation (P < 0.0001).. We conclude that in rats, intrathecally administered dexmedetomidine, MPV-2426 and tizanidine have dose-dependent effects on EMG. At antinociceptive doses, the EMG effects of these three alpha-2 adrenergic agonists differ (dexmedetomidine > MPV-2426 > tizanidine).

Topics: Adrenergic alpha-Agonists; Animals; Behavior, Animal; Clonidine; Dexmedetomidine; Dose-Response Relationship, Drug; Electromyography; Hypnotics and Sedatives; Imidazoles; Indans; Injections, Spinal; Motor Activity; Muscle, Skeletal; Pain Measurement; Pain Threshold; Rats; Rats, Sprague-Dawley