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UBC Theses and Dissertations

Studies on characterized nucleus gigantocellularis neurones Harris, David Platt


Periaqueductal gray (PAG) stimulation produced antinociception may be mediated by inhibition of an ascending nociceptive pathway at the brainstem level and/or the activation of descending inhibition on spinal nociceptor-driven neurones. Experiments were performed on urethane anaesthetized rats to establish if there is a monosynaptic pathway from the PAG to the nucleus gigantocellularis (nGC). / Single units in the PAG were able to be antidromically activated by stimulation of the nGC, indicating that a direct pathway does exist. To further clarify nGC involvement in the two possibilities stated above, single units in the nGC were characterized according to their responses to natural stimuli. . About one-half of the neurones tested sere excited by noxious stimuli. Similarly, about one-half of those tested with PAG stimulation were inhibited. Of those neurones affected by both noxious peripheral stimuli and PAG stimulation, the largest group (3755) were excited by the noxious stimuli and inhibited by the PAG stimulation. Intravenous and iontophoretic fluoxetine, a specific serotonin uptake blocker, enhanced the period of inhibition and reduced the excitation of nGC neurones due to PAG stimulation. Furthermore, inhibition of nGC neurones by iontophoretic serotonin or fluoxetine was correlated with the PAG stimulation produced inhibition of these neurones, suggesting that this inhibition was mediated by serotonin. These data suggest that many nGC neurones are in an ascending nociceptive pathway and under inhibitory control of the PAG.

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