Chronic exposure to antibodies directed against anti-opiate peptides alter delta-opioid receptor levels

Regulation of the rat brain endothelin system by endogenous beta-endorphin

Several lines of evidence indicate that the central endogenous opioid and endothelin (ET) system regulate each other. To explore this idea further, we determined the effect of intracerebroventricular (i.c.v.) administration of anti-beta-endorphin IgG (rabbit) on the expression level of the opioid, corticotropin-releasing hormone and endothelin receptors, and tissue concentration of ET-1. Three days after implanting cannula into the lateral ventricle, male Sprague-Dawley rats were administered 10 microl (i.c.v.) of either control rabbit IgG (2.5 microg/microl) or anti-beta-endorphin IgG (2.5 microg/microl) on days 1, 3 and 5. On day 6, animals were euthanized and caudate, cortex and hippocampus collected for Western blot analysis. Anti-beta-endorphin IgG down-regulated ET-A receptor protein expression in the caudate (51%), but had no effect on the expression of mu, delta, kappa opioid, ET-B, CRH-1 and CRH-2 receptors in any brain region. Anti-beta-endorphin IgG increased tissue ET-1 levels in the caudate by 30.3%. [35S]GTP-gamma-S binding assays demonstrated that anti-beta-endorphin IgG increased the efficacy of [D-Ala2-MePhe4, Gly-ol5]enkephalin without altering its potency in caudate. Control experiments showed that there was no detectable rabbit IgG in caudate, cortex and hippocampus samples. These results suggest that beta-endorphin in the CSF coordinately regulates ET-1 levels and the ET-A receptor in rat caudate. These findings support the hypothesis that CSF neuropeptides have regulatory effects and further demonstrate a link between opioid and ET system.

Intracerebroventricular administration of anti-endothelin-1 IgG selectively upregulates endothelin-A and kappa opioid receptors

Endothelin (ET) type A receptor antagonists enhance morphine-induced antinociception and restore morphine analgesia in morphine tolerant rats [Peptides 23 (2002) 1837; Peptides 24 (2003) 553]. These studies suggest that the central ET and opioid systems functionally interact. To explore this idea further, we determined the effect of i.c.v. administration of anti-ET-1 IgG (rabbit) on brain opioid receptor and ET receptor expression. Three days after implanting cannula into the lateral ventricle, male Sprague-Dawley rats were administered 10 microl (i.c.v.) of either control rabbit IgG (2.5 microg/microl) or anti-ET IgG (2.5 microg/microl) on day 1, day 3, and day 5. On day 6, animals were killed and the caudate and hippocampus collected. Anti-ET IgG had no significant effect on expression, measured by Western blots, of mu, delta or ET-B receptors, but increased kappa opioid (59%) and ET-A (33%) receptor protein expression in the caudate. [35S]-GTP-gamma-S binding assays demonstrated that anti-ET IgG decreased [D-Ala2-MePhe4, Gly-ol5]enkephalin efficacy, but not potency in the caudate. Control experiments showed that there was no detectable rabbit IgG in caudate and hippocampal samples. These results suggest that ET in the CSF negatively regulates kappa opioid and ET-A receptors in certain brain regions. These findings support the hypothesis that CSF neuropeptides have regulatory effects and further demonstrate a link between ET and the opioid receptor system.

Endogenous CART peptide regulates mu opioid and serotonin 5-HT(2A) receptors

Previous experiments conducted in this laboratory showed that intracerebroventricular (i.c.v.) administration of IgG antibodies directed against selected neuropeptides changed the density of CNS receptors, suggesting that neuropeptides in the cerebrospinal fluid can perform a regulatory role. To further test this hypothesis, we administered anti-CART peptide (the peptide product of cocaine amphetamine related transcript) IgG to rats via the i.c.v. route, and measured the density of opioid mu and delta receptors, beta-adrenergic and alpha(2)-adrenergic receptors and serotonin 5-HT(2A) receptors using ligand binding methods. We also used Western blots to determine the expression level of the mu, delta and 5-HT(2A) receptors. The results demonstrated that anti-CART peptide IgG up-regulates mu and 5-HT(2A) receptor in the hippocampus and caudate We conclude that CART peptides in the cerebrospinal fluid may exert regulatory effects in the brain.

Opioid peptide receptor studies. 16. Chronic morphine alters G-protein function in cells expressing the cloned mu opioid receptor

Chronic morphine treatment results in functional uncoupling of the mu opioid receptor and its G protein in both cell culture and animal models. In the present study, Chinese hamster ovary (CHO) cells stably expressing the cloned human mu opioid receptor (hMOR-CHO cells) were incubated with 1 microM of morphine (or no drug) for 20 h. Subsequently, we assessed DAMGO- and morphine-stimulated [(35)S]-GTP-gamma-S binding and agonist-mediated inhibition of forskolin-stimulated cAMP accumulation. Using a single concentration of [(35)S]-GTP-gamma-S (0.05 nM), chronic morphine treatment did not significantly change basal [(35)S]-GTP-gamma-S binding, shifted the morphine EC(50) from 59 nM to 146 nM, and decreased the maximal stimulation (E(max)) from 201% to 177%. Similar results were observed with DAMGO. Binding surface analysis resolved two [(35)S]-GTP-gamma-S binding sites (high-affinity and low-affinity sites). In control cells, morphine stimulated [(35)S]-GTP-gamma-S binding by increasing the B(max) of the high-affinity site. In morphine-treated cells, morphine stimulated [(35)S]-GTP-gamma-S binding by decreasing the high-affinity K(d) without changing the B(max). Morphine treatment increased the EC(50) (5-11-fold) for agonist-mediated inhibition of forskolin-stimulated cAMP accumulation. These changes were not observed in cells expressing a mutant mu opioid receptor which does not develop morphine tolerance, suggesting that the changes in [(35)S]-GTP-gamma-S binding observed in hMOR-CHO cells result from the development of morphine tolerance.

Endogenous corticotropin releasing factor regulates adrenergic and opioid receptors

Previous work from this laboratory demonstrated that intracerebroventricular (i.c.v.) administration of IgG antibodies directed against selected neuropeptides changed the density of opioid receptors, suggesting that neuropeptides in the CNS can perform a regulatory role. To further test this hypothesis, we administered anticorticotropin (CRF) IgG to rats via the i.c.v. route and measured the density of opioid mu and delta receptors and also beta- and alpha(2)-adrenergic receptors. The results demonstrated that anti-CRF IgG upregulates mu and beta-adrenergic receptors. We conclude that CRF in the cerebrospinal fluid may exert regulatory effects throughout the brain.

Effects of intracerebroventricularly administered chimeric peptide of metenkephalin and FMRFa--[D-Ala2]YFa-on antinociception and its modulation in mice

An enzymatically stable analog of YGGFMKKKFMRFamide (YFa), a chimeric peptide of metenkephalin and FMRFa, was synthesised. The antinociceptive effects of intracerebroventricular injections of this analog-[D-Ala2)]YAGFMKKKFMRFamide ([D-Ala2]YFa)-was then investigated using the mouse radiant-heat tail-flick test. [D-Ala2]YFa produced modest to good antinociception at 1, 2, and 5 microg/mouse (0.64, 1.28, and 3.22 nmol, respectively). This antinociceptive effect was completely reversed by the opioid receptor antagonist naloxone (1.5 microg/mouse: 4.12 nmol, intracerebroventricular [i.c.v.]), administered 5 min prior. Pretreatment (5 min) with either neuropeptides FF (1 microg/mouse: 0.92 nmol, i.c.v.) or FMRFa (1 microg/mouse: 1.69 nmol, i.c.v.) significantly attenuated the antinociceptive effects induced by [D-Ala2]YFa (1 microg/mouse, i.c.v.). Intracerebroventricular administration of [D-Ala2]YFa at 1 microg/mouse dose with morphine (2 microg/mouse: 5.86 nmol, i.c.v.) produced an additive antinociceptive effect, suggesting that [D-Ala2]YFa may have a modulatory effect on opioid (morphine) analgesia. These results provide further support for a role of such amphiactive sequences in antinociception and its modulation.

Endogenous opiates: 1999

This paper is the twenty-second installment of the annual review of research concerning the opiate system. It summarizes papers published during 1999 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; learning, memory, and reward; eating and drinking; alcohol and other drugs of abuse; sexual activity, pregnancy, and development; mental illness and mood; seizures and other neurologic disorders; electrical-related activity; general activity and locomotion; gastrointestinal, renal, and hepatic function; cardiovascular responses; respiration and thermoregulation; and immunologic responses.