title: Activation of delta-opioid receptors reduces excitatory input to putative gustatory cells within the nucleus of the solitary tract.
abstract: The rostral nucleus of the solitary tract (NST) is the first central relay in the gustatory pathway and plays a key role in processing and modulation of gustatory information. Here, we investigated the effects of opioid receptor agonists and antagonists on synaptic responses of the gustatory parabrachial nuclei (PbN)-projecting neurons in the rostral NST to electrical stimulation of the solitary tract (ST) using whole cell recordings in the hamster brain stem slices. ST-evoked excitatory postsynaptic currents (EPSCs) were significantly reduced by met-enkephalin (MetE) in a concentration-dependent fashion and this effect was eliminated by naltrexone hydrochloride, a nonselective opioid receptor antagonist. Bath application of naltrindole hydrochloride, a selective delta-opioid receptor antagonist, eliminated MetE-induced reduction of EPSCs, whereas CTOP, a selective mu-opioid receptor antagonist had no effect, indicating that delta-opioid receptors are involved in the reduction of ST-evoked EPSCs induced by MetE. SNC80, a selective delta-opioid receptor agonist, mimicked the effect of MetE. The SNC80-induced reduction of ST-evoked EPSCs was eliminated by 7-benzylidenenaltrexone, a selective delta1-opioid receptor antagonist but not by naltriben mesylate, a selective delta2-opioid receptor antagonist, indicating that delta1-opioid receptors mediate the reduction of ST-evoked EPSCs induced by SNC80. Single-cell reverse transcriptase-polymerase chain reaction analysis revealed the presence of delta1-opioid receptor mRNA in cells that responded to SNC80 with a reduction in ST-evoked EPSCs. Moreover, Western blot analysis demonstrated the presence of 40-kDa delta-opioid receptor proteins in the rostral NST tissue. These results suggest that postsynaptic delta1-opioid receptors are involved in opioid-induced reduction of ST-evoked EPSCs of PbN-projecting rostral NST cells.
authors.affiliation: Department of Anatomy, Southern Illinois University School of Medicine, Life Science III Room 2073, 1135 Lincoln Dr., Carbondale, IL 62901, USA.
authors.forename: Mingyan
authors.initials: M
authors.lastname: Zhu
authors.forename: Young K
authors.initials: YK
authors.lastname: Cho
authors.forename: Cheng-Shu
authors.initials: CS
authors.lastname: Li
mesh_terms: D000344:Afferent Pathways / Q000166:cytology* / Q000502:physiology*; D000818:Animals; D015153:Blotting, Western; D006224:Cricetinae; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D004558:Electric Stimulation; D004591:Electrophoresis, Polyacrylamide Gel; D004594:Electrophysiology; D004744:Enkephalin, Methionine / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D066298:In Vitro Techniques; D008647:Mesocricetus; D009292:Narcotic Antagonists / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000378:metabolism; D018408:Patch-Clamp Techniques; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D017465:Receptors, Opioid, delta / Q000819:agonists* / Q000037:antagonists & inhibitors; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017552:Solitary Nucleus / Q000166:cytology* / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D013649:Taste / Q000502:physiology*
chemical_list: D009292:Narcotic Antagonists; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D017465:Receptors, Opioid, delta; D004744:Enkephalin, Methionine