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  • Title: Morphine microinjections into periaqueductal grey matter of the rat: effects on dorsal horn neuronal responses to C-fibre activity and diffuse noxious inhibitory controls.
    Author: Dickenson AH, Le Bars D.
    Journal: Life Sci; 1983; 33 Suppl 1():549-52. PubMed ID: 6664236.
    Abstract:
    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.
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