α2-Adrenoceptor modulation of nociception in rat spinal cord: location, effects and interactions with morphine

doi:10.1016/0014-2999(87)90430-4

European Journal of Pharmacology

Volume 138, Issue 2, 19 June 1987, Pages 169-177

https://doi.org/10.1016/0014-2999(87)90430-4 Get rights and content

Abstract

The effects of intrathecal clonidine alone and prior to intrathecal morphine were studied on electrically evoked Aβ and C fibre activity in the dorsal horn of the halothane-anaesthetised rat. Clonidine reduced C fibre-evoked activity in a dose-dependent manner, to a maximum 52% inhibition which was reversed by rauwolscine and yohimbine but not naloxone. High dose of clonidine also produced small inhibitions of A fibre-evoked activity. Clonidine potentiated the inhibitory action of intrathecal morphine on electrically evoked C fibre activity but not A fibre activity. In addition, the location of α₂-adrenoceptor and opiate binding sites in consecutive sections of rat lumbar cord was investigated using in vitro autoradiography with selective ligands, and it was demonstrated that both opiate and α₂-receptor types are present within the same superficial layers of the dorsal horn of the same animal. The results indicate that α₂-adrenoceptors and opiate receptors can interact in the modulation of nociceptive transmission in rat spinal cord.

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Citation Excerpt :
These findings, together with our current data, would suggest that the Gq-mER-mediated rapid and reversible suppression of clonidine-mediated antinociception depends primarily on non-genomic mechanisms. The α2-adrenoceptor is widely distributed in the brain and spinal cord, including the dorsal horn (Unnerstall et al., 1984; Sullivan et al., 1987; Stone et al., 1998). Consequently, epidural or i.t. clonidine treatment has been utilized to alleviate severe neuropathic or cancer pain even in patients with limited relief by and development of tolerance to opiates (Rauck et al., 1993; Eisenach et al., 1995; Hassenbusch et al., 1999; Dobrydnjov et al., 2005).
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α2-Adrenoceptor modulation of nociception in rat spinal cord: location, effects and interactions with morphine

Abstract

Brain Res.

Brain Res.

Neurosci. Lett.

Neuroscience

Pain

Trends Neurosci.

Brain Res.

Neuropeptides

Neuropharmacology

Brain Res.

Neuropharmacology

Jap. J. Pharmacol.

Brain Res.

Brain Res.

Brain Res.

European J. Pharmacol.

Lancet

Brain Res. Rev.

α₂-Adrenoceptor modulation of nociception in rat spinal cord: location, effects and interactions with morphine