Mechanism of Intrathecally Administered Morphine Analgesia
The effects of intrathecally administered morphine on the activity of single units in Rexed lamina V of the transected feline lumbar spinal cord were studied in order to investigate the mechanisms of intrathecally administered morphine analgesia. The activity of single units in Rexed lamina V was sampled utilizing an extracellular microelectrode recording technique. These cells respond preferentially to noxious peripheral stimuli. The results of the present study demonstrate a well-defined suppression of the activity of lamina V nociceptive neurons after intrathecally administered morphine (0.1 mg) on the spinal cord. The results also demonstrate that the degree and duration of this suppression by intrathecally administered morphine 0.1 mg were significantly greater than those by intravenously administered morphine 2.0 mg/kg. The suppressive effect continued for more than 2 and half hours. Naloxone promptly reversed the suppression effect of intrathecally administered morphine. Onset time of the suppressive effect was significantly slower in morphine intrathecally administered than in morphine intravenously administered.
Considering our results, it may be concluded that the analgesic effect of intrathecally administered morphine is due to the morphine penetration through the cord dorsum and the suppression of activity of cells in Rexed lamina V.
KeywordsDorsal Horn Morphine Sulfate Spinal Cord Function Lamina Versus Gallamine Triethiodide
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