Alpha 2-adrenoceptor modulation of nociception in rat spinal cord: location, effects and interactions with morphine

Eur J Pharmacol. 1987 Jun 19;138(2):169-77. doi: 10.1016/0014-2999(87)90430-4.


The effects of intrathecal clonidine alone and prior to intrathecal morphine were studied on electrically evoked A beta 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 doses 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 alpha 2-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 alpha 2-receptor types are present within the same superficial layers of the dorsal horn of the same animal. The results indicate that alpha 2-adrenoceptors and opiate receptors can interact in the modulation of nociceptive transmission in rat spinal cord.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Autoradiography
  • Clonidine / pharmacology
  • Dihydromorphine / metabolism
  • Drug Interactions
  • Electrophysiology
  • In Vitro Techniques
  • Injections, Spinal
  • Male
  • Morphine / pharmacology*
  • Naloxone / metabolism
  • Neurons / drug effects
  • Nociceptors / physiology*
  • Rats
  • Rats, Inbred Strains
  • Receptors, Adrenergic, alpha / physiology*
  • Spinal Cord / physiology*
  • Yohimbine / metabolism


  • Receptors, Adrenergic, alpha
  • Yohimbine
  • Naloxone
  • Morphine
  • Dihydromorphine
  • Clonidine