Opioids Hyperpolarize β-Endorphin Neurons via μ-Receptor Activation of a Potassium Conductance
Autor: | Oline K. Rønnekleiv, Michael D. Loose, Martin J. Kelly |
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Rok vydání: | 1990 |
Předmět: |
medicine.medical_specialty
Potassium Channels Endocrinology Diabetes and Metabolism Voltage clamp Guinea Pigs Receptors Opioid mu Action Potentials Fluorescent Antibody Technique Neuropeptide Membrane Potentials Cellular and Molecular Neuroscience chemistry.chemical_compound Endocrinology Bacterial Proteins Internal medicine medicine Animals Endorphins Fluorescent Dyes Neurons Membrane potential Naloxone Endocrine and Autonomic Systems Lysine Cell Membrane beta-Endorphin Enkephalins Enkephalin Ala(2)-MePhe(4)-Gly(5) Hyperpolarization (biology) Fluoresceins Potassium channel Electrophysiology Microscopy Fluorescence chemistry Receptors Opioid Female Streptavidin Fluorescein-5-isothiocyanate Thiocyanates |
Zdroj: | Neuroendocrinology. 52:268-275 |
ISSN: | 1423-0194 0028-3835 |
Popis: | Intracellular recordings were made from hypothalamic arcuate (ARC) neurons with biocytin-filled electrodes under current- and voltage-clamp in slices prepared from ovariectomized guinea pigs which were pretreated with estradiol. Forty-three neurons were identified after linking the intracellular biocytin with streptavidin-FITC and subsequently were examined for beta-endorphin immunoreactivity. Ten of these neurons were immunoreactive for beta-endorphin. beta-Endorphin neurons displayed the following passive membrane properties: RMP:-56 +/- 2 mV; Rin: 439 +/- 66 M omega; tau: 17.5 +/- 2.4 ms; and often fired spontaneously (5.9 +/- 2.2 Hz). These membrane characteristics were not different from identified neurons in the ARC that were not immunoreactive for beta-endorphin. beta-Endorphin neurons exhibited instantaneous inward rectification and time-dependent rectification. The mu-opioid agonist Tyr-D-Ala-Gly-MePhe-Gly-ol (DAGO) decreased spontaneous firing, induced membrane hyperpolarization (12 +/- 2 mV; range 6-22 mV) and decreased the Rin (38 +/- 4%) of the beta-endorphin neurons. These effects of DAGO were blocked by the opioid antagonist naloxone (1 microM) and were not blocked by 1 microM TTX. DAGO-responsive cells were unaffected by either kappa- or delta-receptor opioid agonists. These results indicate that mu-receptors may be autoreceptors on ARC beta-endorphin neurons and that activation of opioid mu-receptors hyperpolarizes beta-endorphin neurons via an increase in K+ conductance. Therefore, opioid peptides may modulate opioid tone through an 'ultra-short loop' feedback control mechanism. |
Databáze: | OpenAIRE |
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