Opiate analgesics and endorphins inhibit rat dorsal root potential in vitro

The effects of endorphins and opiate analgesics on the dorsal root potential (DRP) were studied in vitro using the isolated spinal cord of newborn rat. Bath-applied beta-endorphin and [D-Ala2]-Met-enkephalinamide (D-Ala) greatly depressed the DRP and the depressant effects were abolished by prior perfusion with naloxone. The potency of Met-enkephalin, Leu-enkephalin and alpha-endorphin was much weaker than that of D-Ala. Morphine and levorphanol depressed the DRP and these effects were also antagonized by naloxone. The isolated rat spinal cord appears to be a convenient in vitro preparation for analysing the effects of opiates on synaptic transmission in the central nervous system.