The effect of naloxone on the inhibition of nociceptor driven neurones in the cat spinal cord.
The functional role of the opiate receptors and enkephalins found in high concentration in the superficial dorsal horn of the spinal cord has not been ascertained but may be the modulation of transmission in nociceptive pathways. In cats anaesthetized with alpha-chloralose the nacrotic antagonist, nalozone, was tested on various types of inhibitory input to spinal cord neurones which responded to both noxious and non-noxious stimulation of their receptive fields (Class 2 neurones). Naloxone (0.3-2.0 mg/kg i.v.) failed to alter the response of these neurones to noxious radiant heat, to tonic descending inhibition or to inhibition evoked by stimulation of the dorsal columns or contralateral plantar nerve. Thus the endorphins do not appear to be involved in mediating the types of inhibition examined. On the other hand, i.v. morphine reduced the response of Class 2 neurones to noxious heating of the skin that was reversed by naloxone.
D000818:Animals; D002415:Cats; D004305:Dose-Response Relationship, Drug; D005727:Ganglia, Spinal / Q000187:drug effects; D006614:Hindlimb / Q000294:innervation; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology*; D009433:Neural Inhibition / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects; D009619:Nociceptors / Q000187:drug effects*; D011957:Receptors, Opioid / Q000187:drug effects; D013116:Spinal Cord / Q000187:drug effects*
D011957:Receptors, Opioid; D009270:Naloxone; D009020:Morphine