Supraspinal Morphine Research Articles

Spinal 5-HT or NA uptake inhibition potentiates supraspinal morphine antinociception in rats.

Spinal injection of the specific uptake inhibitor of 5-hydroxytryptamine (5-HT), citalopram, or of noradrenaline (NA), desipramine, potentiated the antinociception following intracerebroventricular injection of morphine in rats tested on the hot plate. Combined spinal injection of citalopram and desipramine caused a synergistic potentiation. The unselective and less potent inhibitor of both 5-HT and NA uptake, amitriptyline, did not cause potentiation. The results support the suggested involvement of both 5-HT and NA pathways in supraspinal morphine antinociception.

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 neurons with hindpaw receptive fields. Response to C-fibre activation was conditioned by noxious heat (52°C) applied to the tail, this resulting in profound inhibition (Diffuse Noxious Inhibitory Controls - DNIC). The microinjection of 5 μg 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 μg 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.