Actions of endomorphins on synaptic transmission of Adelta-fibers in spinal cord dorsal horn neurons.
The effects of endogenous mu-opioid ligands, endomorphins, on Adelta-afferent-evoked excitatory postsynaptic currents (EPSCs) were studied in substantia gelatinosa neurons in spinal cord slices. Under voltage-clamp conditions, endomorphins blocked the evoked EPSCs in a dose-dependent manner. To determine if the block resulted from changes in transmitter release from glutamatergic synaptic terminals, the opioid actions on miniature excitatory postsynaptic currents (mEPSCs) were examined. Endomorphins (1 microM) reduced the frequency but not the amplitude of mEPSCs, suggesting that endomorphins directly act on presynaptic terminals. The effects of endomorphins on the unitary (quantal) properties of the evoked EPSCs were also studied. Endomorphins reduced unitary content without significantly changing unitary amplitude. These results suggest that in addition to presynaptic actions on interneurons, endomorphins also inhibit evoked EPSCs by reducing transmitter release from Adelta-afferent terminals.
Yajiri
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Marine Biomedical Institute, Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston, Tex. 77555-1069, USA.
Huang
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LY
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000344:Afferent Pathways / Q000187:drug effects; D000818:Animals; D001681:Biological Assay; D004594:Electrophysiology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D008962:Models, Theoretical; D009412:Nerve Fibers / Q000502:physiology*; D009842:Oligopeptides / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D020671:Posterior Horn Cells / Q000502:physiology*; D051381:Rats; D020318:Rats, Long-Evans; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology; D013376:Substantia Gelatinosa / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects*
D018691:Excitatory Amino Acid Antagonists; D009842:Oligopeptides; C105293:endomorphin 1; C105294:endomorphin 2; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate