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Title: The existence of opioid receptors in the cochlea of guinea pigs
Authors: Jongkamonwiwat N.
Phansuwan-Pujito P.
Casalotti S.O.
Forge A.
Dodson H.
Govitrapong P.
Keywords: autoreceptor
beta endorphin
delta opiate receptor
kappa opiate receptor
leucine enkephalin
mu opiate receptor
opiate receptor
animal tissue
controlled study
Corti organ
guinea pig
hair cell
nucleotide sequence
priority journal
protein expression
Enkephalin, Leucine
Guinea Pigs
Microscopy, Confocal
Receptors, Opioid
Receptors, Opioid, delta
Receptors, Opioid, kappa
Receptors, Opioid, mu
Reverse Transcriptase Polymerase Chain Reaction
RNA, Messenger
Issue Date: 2006
Abstract: Several independent investigations have demonstrated the presence of opioid peptides in the inner ear organ of Corti and in particular in the efferent nerve fibers innervating the cochlear hair cells. However, the precise innervation pattern of opioid fibers remains to be investigated. In the present study the expression of opioid receptors and their peptides is demonstrated in young adult guinea pig cochlea. Opioid receptors are mainly expressed in hair cells of the organ of Corti and in inner and outer spiral bundles with different characteristics for each type of receptor. Co-localization studies were employed to compare the distribution of mu-, delta- and kappa-opioid receptors and their respective peptides, β-endorphin, leu-enkephalin and dynorphin. Additionally, immunostaining of synaptophysin was used in this study to identify the presynaptic site. Immunoreactivity for enkephalin and dynorphin was found in the organ of Corti. Leu-enkephalin was co-localized with synaptophysin prominently in the inner spiral bundle (ISB). Dynorphin was co-localized with synaptophysin in both inner and outer spiral bundles. Delta-opioid receptor was most prominently co-localized with its peptide in the ISB bundle. Kappa-opioid receptor was seemingly present with dynorphin in both inner and outer spiral bundles. The co-staining of both peptides and receptors with synaptophysin in the same areas suggests that some of the opioid receptors may act as auto-receptors. The results provide further evidence that opioids may function as neurotransmitters or neuromodulators in the cochlea establishing the basis for further electrophysiological and pharmacological investigations to understand better the roles of the opioid system in auditory function. © The Authors (2006).
ISSN: 0953816X
Appears in Collections:SCOPUS 1983-2021

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