Interactions between ketamine and phencyclidine and dorsal root potentials (DRPs), evoked from the raphe nuclei

Dorsal root potentials (DRPs) are thought to reflect presynaptic inhibition of primary afferent activity. Electrical stimulation of sites near the nucleus raphe magnus evokes two such potentials (DRP-1 and DRP-2) along dorsal roots of the lumbar and sacral spinal cord in the anaemically decerebrated cat. Dorsal root potential-2 is thought to be serotonergically mediated, while the neurochemical mediator of dorsal root potential-1 is not known. Serotonin antagonists selectively inhibit dorsal root potential-2 while the shorter latency dorsal root potential-1, which can be elicited anywhere in the brain stem, is potentiated by these drugs. The present study showed that most general anesthetics, such as ether or barbiturates, uniformly depressed both dorsal root potentials 1 and 2. The present studies indicate that two dissociative anesthetics, ketamine and phencyclidine, selectively inhibited dorsal root potential-2. This inhibitory effect of ketamine was dose-related, such that a dose of 11 mg/kg completely blocked dorsal root potential-2, but had no effect on dorsal root potential-1. Time-course studies indicated that the effect of phencyclidine on dorsal root potential-2 lasted much longer than that of ketamine. These results suggest that the effect of dissociative anesthetics on the descending pathways is unique compared to that of other anesthetic agents and that their effect correlates well in time-course and dose-range to their sedative/anesthetic effects.