Endomorphin-1 is more potent than endomorphin-2 in inhibition of synaptic transmission in substantia gelatinosa of adult rat spinal cord.
Effects of endomorphin-1 (EM-1) and endomorphin-2 (EM-2) on synaptic trans-mission were investigated on neurons in substantia gelatinosa (SG) of the spinal dorsal horn. Both EM-1 (1 microM) and EM-2 (1 microM) remarkably reduced the frequency but not the amplitude of miniature excitatory postsynaptic currents (mEPSCs) and miniature inhibitory postsynaptic currents (mIPSCs). These effects were antagonized by beta-funaltrexamine (beta-FNA, 10 microM), a selective mu-opioid receptor antagonist. Noticeably, EM-1 showed higher potency in decreasing the frequency of mEPSCs and mIPSCs than that of EM-2. These results indicate that EMs suppress both excitatory and inhibitory synaptic transmission by activating presynaptic mu-opioid receptors in the SG and EM-1, compared with EM-2, might be a more potent endogenous analgesic at the spinal cord level.
Leng
Dong-Ni
DN
Department of Anatomy and K. K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, PR China.
Feng
Yu-Peng
YP
Li
Yun-Qing
YQ
D000701:Analgesics, Opioid / Q000494:pharmacology*; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D004347:Drug Interactions; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D066298:In Vitro Techniques; D009433:Neural Inhibition / Q000187:drug effects* / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D009842:Oligopeptides / Q000494:pharmacology*; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D013376:Substantia Gelatinosa / Q000166:cytology / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects* / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D000701:Analgesics, Opioid; D000779:Anesthetics, Local; D009842:Oligopeptides; C105293:endomorphin 1; C105294:endomorphin 2; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid