Opioid peptides modulate GABA(A) receptor responses in neurons of bullfrog dorsal root ganglia.
Effects of enkephalin and selective opioid-receptor agonists on GABA-induced current were examined in dissociated neurons of bullfrog dorsal root ganglia (DRG) by using whole-cell patch-clamp method. Leucine- (Leu)-enkephalin and methionine- (Met)-enkephalin depressed GABA(A) receptor-mediated currents. DPDPE, DAMGO and dynorphin-A (Dyn-A) also depressed the inward current produced by GABA; the order of agonist potency was DPDPE > DAMGO > Dyn-A. Naloxone blocked the inhibitory effects of enkephalins and other opioid agonists on the GABA current. Naltrindole (NTI), a delta-receptor antagonist, prevented the DPDPE-induced depression of the GABA current. beta-Funaltrexamine (beta-FNA), a mu-receptor antagonist, reduced the DAMGO-induced depression of GABA currents. Nor-binaltorphimine (nor-BNI), a kappa-receptor antagonist, reduced the effects of Dyn-A in depressing the GABA current. The results suggest that enkephalin down-regulates GABA(A) receptor function through mainly delta- and mu-opioid receptors in bullfrog DRG neurons.
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Department of Physiology, Kurume University School of Medicine, Asahi-machi, Japan.
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D000700:Analgesics / Q000494:pharmacology; D000818:Animals; D004305:Dose-Response Relationship, Drug; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004745:Enkephalins / Q000494:pharmacology*; D005727:Ganglia, Spinal / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects*; D011892:Rana catesbeiana; D011963:Receptors, GABA-A / Q000187:drug effects*
D000700:Analgesics; D004745:Enkephalins; D011963:Receptors, GABA-A; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-