EFFECTS OF ENKEPHALIN ANALOG AND NALOXONE ON CAT SPINAL-CORD DORSAL-ROOT POTENTIALS

A systemically active enkephalin analogue, FK33824, given intravenously depressed dorsal root potentials in cat spinal cord. The negative DR V and positive DR VI, measured by computer, were both decreased; this effect was reversed by small doses of intravenous naloxone. Naloxone, given alone, with no previous analogue produced no changes in dorsal root potentials suggesting the absence of a basal enkephalin tone. A second injection of FK33824 was much less effective than the first dose. The results were discussed in relation to presynaptic mechanisms for analgesia: we proposed that FK33824 causes presynaptic inhibition by modulation rather than by depolarization of primary afferent fibers. © 1979.