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J Neurophysiol 101: 258-268, 2009. First published November 19, 2008; doi:10.1152/jn.90648.2008
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Activation of {delta}-Opioid Receptors Reduces Excitatory Input to Putative Gustatory Cells Within the Nucleus of the Solitary Tract

Mingyan Zhu1, Young K. Cho1,2 and Cheng-Shu Li1

1Department of Anatomy, Southern Illinois University School of Medicine, Carbondale, Illinois; and 2Department of Physiology and Neuroscience, Kangnung National University College of Dentistry, Kangnung, Kangwon, Korea

Submitted 5 June 2008; accepted in final form 12 November 2008

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 µ-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 {delta}1-opioid receptor antagonist but not by naltriben mesylate, a selective {delta}2-opioid receptor antagonist, indicating that {delta}1-opioid receptors mediate the reduction of ST-evoked EPSCs induced by SNC80. Single-cell reverse transcriptase–polymerase chain reaction analysis revealed the presence of {delta}1-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 {delta}1-opioid receptors are involved in opioid-induced reduction of ST-evoked EPSCs of PbN-projecting rostral NST cells.

Address for reprint requests and other correspondence: C.-S. Li, Department of Anatomy, Southern Illinois University School of Medicine, Life Science III Room 2073, 1135 Lincoln Dr., Carbondale, IL 62901 (E-mail: cli{at}siumed.edu)






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