Effects of [mu]-opioids on neurons of the medical geniculate nucleus
| Autor: | Ota, Takayo |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2000 |
| Druh dokumentu: | Text |
| Popis: | Immunohistochemical and hybridization studies have revealed the presence of μ-, but not k- and δ-opioid receptors in the medial geniculate body. Using whole-cell patch clamp techniques, I examined the effects of opioid agonists on gerbil MGB neurons (P9-P16) in vitro. The opioid effects were concentration-dependent. Opioids produced different actions on the input conductance (G[sub i]) when applied in low, compared with high concentrations. The increase in G[sub i] might be due to increase in K⁺ conductance whereas the decrease in G[sub i] might be due to l[sub H] inactivation. When Gi was increased, the reversal potential was —65 mV; this implicates opioid actions on K+, among other ion channels. In the case of decreased G[sub i], the opioid currents did not reverse from -100 mV to -50 mV, implying the involvement of cationic channels, other than K⁺. DAMGO, a μ-selective opioid agonist, had a reversal potential that was similar to that observed when morphine increased G[sub i], implying that opioids activate u-opioid receptors in MGB neurons. Tetrodotoxin altered the concentration-dependent action of morphine. Here, the suggestion is morphine's actions involve neurons that presynaptic to the patch clamped neuron. Morphine application blocked spike-frequency adaptation and reduced firing rates in response to depolarizing current pulse injection. Morphine application may block Ca²⁺-mediated K⁺ channels that inhibited spike-frequency adaptation. Such blockade may be expected to increase the spike frequency. However, the increased conductance due to morphine would shunt the Na⁺ current, resulting in a lower spike frequency. The results of this study have revealed that opioids have both excitatory and inhibitory effects on MGB neurons. Medicine, Faculty of Anesthesiology, Pharmacology and Therapeutics, Department of Graduate |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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