Effect of morphine-induced cortical excitation on somatosensory responses evoked in the periaqueductal grey matter.

The somatosensory cortex responses and periaqueductal grey matter responses evoked by electric peripheral nerve stimulation were studied following topical application of 1% morphine solution to the primary somatosensory area of rat cerebral cortex. Cortically applied morphine increased the negative component of cortical potentials and enhanced the peak-to-peak amplitude of the periaqueductal grey responses. It is suggested that cortical excitation induced by morphine generates descending bioelectrical impulses modulating neuronal activity at this mesencephalic level.