Morphine microinjections into periaqueductal grey matter of the rat: effects on dorsal horn neuronal responses to C-fibre activity and diffuse noxious inhibitory controls.
Recording were made for dorsal horn convergent neurones with hindpaw receptive fields. Response to C-fibre activation was conditioned by noxious heat (52 degrees C) applied to the tail, this resulting in profound inhibition (Diffuse Noxious Inhibitory Controls - DNIC). The microinjection of 5 micrograms morphine into the medioventral PAG, including the n. raphé dorsalis, consistently reduced DNIC without affecting the unconditioned C-fibre responses; more lateral injections had no clear effects. Including a further study in which 20 micrograms morphine was microinjected within various PAG sites, C-fibre responses were found to be unaltered (21/51) enhanced (16/51) or reduced (4/51) with no consistent anatomical basis. The results imply that supraspinal morphine can reduce descending inhibitions and this may contribute to the consequent analgesia.
D000818:Animals; D006358:Hot Temperature; D008297:Male; D008845:Microinjections; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009619:Nociceptors / Q000502:physiology*; D010487:Periaqueductal Gray / Q000187:drug effects / Q000502:physiology*; D051381:Rats
D009020:Morphine