In vitro studies of the effects of naloxone on the root potentials in the frog spinal cord: enkephalin-like effect on the recurrent presynaptic inhibition.
Specific binding of [3H]naloxone was demonstrated in the frog spinal cord. In isolated and perfused frog spinal cord, naloxone increased the spontaneous discharges of the ventral root. Naloxone decreased the ventral root-dorsal root potential (VR-DRP) in a dose-dependent manner, and inhibited presynaptic inhibition of the ventral root reflex. Methionine-enkephalin also decreased the VR-DRP, and naloxone partially antagonized this effect. These results suggest the existence of enkephalinergic control of spinal motor activities and that naloxone has a partial agonistic effect in the frog spinal cord.
D000818:Animals; D004744:Enkephalin, Methionine / Q000494:pharmacology*; D004745:Enkephalins; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009270:Naloxone / Q000378:metabolism / Q000494:pharmacology*; D011892:Rana catesbeiana; D011957:Receptors, Opioid / Q000378:metabolism; D012018:Reflex / Q000187:drug effects; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D013570:Synaptic Membranes / Q000378:metabolism
D004745:Enkephalins; D011957:Receptors, Opioid; D009270:Naloxone; D004744:Enkephalin, Methionine