title: Alpha 2-adrenoceptor modulation of nociception in rat spinal cord: location, effects and interactions with morphine.
abstract: 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.
mesh_terms: D000818:Animals; D001345:Autoradiography; D003000:Clonidine / Q000494:pharmacology; D004090:Dihydromorphine / Q000378:metabolism; D004347:Drug Interactions; D004594:Electrophysiology; D066298:In Vitro Techniques; D007278:Injections, Spinal; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000378:metabolism; D009474:Neurons / Q000187:drug effects; D009619:Nociceptors / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology*; D015016:Yohimbine / Q000378:metabolism
chemical_list: D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D009270:Naloxone; D009020:Morphine; D004090:Dihydromorphine; D003000:Clonidine