Delta Opioid Receptor Expression Research Articles

Hypoxia decreases opioid delta receptor expression in mouse brain.

Delta opioid receptor activation is protective during hypoxic injury. Many adaptive responses occur during exposure to hypoxia to facilitate survival. It is possible that increased activity of the delta opioid receptor system is one such adaptation. We tested the hypothesis that mice exposed to prolonged hypoxia have increased expression of the delta opioid receptor in brain tissue. Prolonged exposure to hypoxia (9% oxygen, balance nitrogen) continuously for seven days selectively decreased delta opioid receptor expression in mouse brain homogenate. The same hypoxic treatment had no effects on either mu or kappa opioid receptor expression, indicating that this response was not due to non-selective degradation of protein. Shorter term hypoxic treatments (one day and three days) did not induce changes in delta opioid receptor expression in whole brain homogenate. Binding assays were also conducted in grossly dissected brain regions (cortex, midbrain, hindbrain) to determine whether the shorter term treatments would induce changes in receptor expression in more discrete areas. No consistent changes in delta opioid receptor expression were detected in these brain regions. These data demonstrate that opioid delta receptors are hypoxia sensitive and may be a part of an adaptive process to increase survival in the organism. One possible cause for the decrease in delta opioid receptor expression following seven days of hypoxic exposure may be receptor down-regulation caused by an increased release of endogenous substances acting at delta receptors. As delta opioid receptor agonists appear promising for therapeutic potential in management of hypoxic injury, changes in delta receptor expression in response to long-term hypoxia could impact potential utilization of delta agonists in patients suffering chronic hypoxia.

Increased expression of opioid delta receptors by deoxy conformation heme proteins in NG108-15 cells

Adaptations to prolonged hypoxia include an increase in the expression of proteins that may facilitate survival. One mechanism by which hypoxia increases protein expression involves a change of heme proteins from oxygenated to deoxygenated conformations. In the present study, we tested the hypothesis that treatment of NG108-15 cells with metallic cations, which are known to induce a deoxygenated conformation of heme proteins, would increase delta opioid receptor (DOR) expression. Cells were treated with cobalt and nickel, which induce deoxygenated heme protein conformation, or zinc as a control for 48 h prior to quantifying DOR expression. Cobalt and nickel, but not zinc, significantly increased DOR expression. Heme synthesis inhibitors would block the synthesis of cobalt-substituted heme proteins which are locked in a deoxygenated conformation. The cobalt-induced increase in DOR expression was blocked by the heme synthesis inhibitor, 4,6-dioxoheptanoic acid. These experiments indicate that deoxygenated conformation heme proteins, which are thought to partially mimic hypoxia, increase DOR expression. The increase in DOR expression suggests that the DOR gene may be hypoxia-sensitive. Further, the increase in DOR expression suggests a potential adaptation strategy to hypoxia and may represent one of the first findings of physiological regulation of DOR expression.

Ethanol differentially increases alpha 2-adrenergic and muscarinic acetylcholine receptor gene expression in NG108-15 cells.

Modulation of alpha 2-adrenergic and opioid neurotransmission may contribute to ethanol intoxication, tolerance, and physical dependence. We showed previously that ethanol increased the expression of functional delta-opioid receptors in NG108-15 cells (Charness, M. E., Querimit, L. A., and Diamond, I. (1986) J. Biol. Chem. 261, 3164-3169). Here we report that long-term (2 days) treatment of NG108-15 cells with ethanol increased the binding of the alpha 2-adrenergic receptor (alpha 2AR) antagonist [3H]rauwolscine and the muscarinic acetylcholine receptor (mAChR) antagonist [3H]quinuclidinyl benzilate by 2.8- and 1.4-fold, respectively. Increased receptor expression was associated with a proportionate increase in the potency of oxymetazoline and carbachol in inhibiting cAMP accumulation. Ethanol did not change the expression of G alpha i2 and reduced levels of G alpha s. Pertussis toxin pretreatment did not prevent the ethanol-induced increase in alpha 2AR, mAChR, and delta-opioid receptor expression. Ethanol caused a large (3.6-fold), dose-dependent increase in the abundance of alpha 2BAR mRNA (rat cDNA probe RNG, 4.1-kb transcript). Ethanol-induced increases in alpha 2BAR and alpha 2CAR (rat probe RG10, 2.5-kb transcript) mRNAs were first detected after 6 h of exposure to 100 mM ethanol, became maximal after 24 h, and persisted for up to 5 days. In contrast, ethanol caused only a small (1.3-fold) increase in the abundance of hm4 mAChR mRNA and did not change levels of G alpha i2 and G alpha s mRNAs. Our data indicate that clinically attainable concentrations of ethanol regulate alpha 2AR gene expression within the time frame of a single session of drinking.