摘要
The results of studying SPA (stimulation produced analgesia) and analgesia produced by intracerebral injection of morphine have shown that the mechanism of morphine analgesia may be due to activation of periaqueductal or periventricular gray which in turn inhibits the centripetal inflow of noxious messages. However, direct iontophoresis of morphine into midbrain reticular formation, including central gray, causes inhibitory effects on them in most instances. Obviously, this inhibitory effect could hardly be in harmony with the proposed mechanism. Some recent studies
