Specific Opiate Binding Research Articles

Evidence for intrinsic expression of enkephalin-like immunoreactivity and opioid binding sites in cat superior colliculus

We have investigated the cellular localization of opioid peptides and binding sites in the cat's superior colliculus by testing the effects of retinal deafferentation and intracollicular excitotoxin lesions on patterns of enkephalin-like immunostaining and opiate receptor ligand binding. In normal cats, enkephalin-like immunoreactivity marks a thin tier in the most dorsal stratum griseum superficiale, small neurons of the stratum griseum superficiale, and patches of fibers in the intermediate and deeper gray layers. Eliminating crossed retinotectal afferents by contralateral eye enucleation had little immediate effect on this pattern, although chronic eye enucleation from birth did reduce immunoreactivity in the superficial layers. By contrast, fiber-sparing destruction of collicular neurons by the excitotoxins N-methyl- d-aspartate and ibotenic acid virtually eliminated enkephalin-like immunoreactivity in the neuropil of the upper stratum griseum superficiale, presumably by killing enkephalinergic cells of the superficial layers. Such lesions did not eliminate the patches of enkephalin-like immunoreactivity in the deeper layers. In normal cats, opiate receptor ligand binding is dense in the stratum griseum superficiale, particularly in its upper tier, and moderately dense in the intermediate gray layer. Contralateral eye removal had no detectable effect on the binding pattern, but excitotoxin lesions of the colliculus dramatically reduced binding in both superficial and deep layers. Some ligand binding, including part of that in the upper stratum griseum superficiale, apparently survived such lesions. Similar effects were observed in the lateral geniculate nucleus: enucleation produced no change in binding, whereas excitotoxin lesions greatly reduced specific opiate binding. We conclude that in the superficial collicular layers, both enkephalin-like opioid peptides and their membrane receptors are largely expressed by neurons of intrinsic collicular origin. The close correspondence between the location of these intrinsic opioid elements and the tier of retinal afferents terminating in the upper stratum griseum superficiale further suggests that opiatergic interneurons may modulate retinotectal transmission postsynaptically.

Reconstitution of solubilized delta-opiate receptor binding sites in lipid vesicles.

Delta-opiate receptors have been solubilized with the non-ionic bile salt detergent digitonin from NG108-15 cell membranes and reconstituted into lipid vesicles. Specific opiate binding was restored to soluble receptor preparations after supplementation with a brain lipid extract, and dilution below the effective detergent concentration. Saturable and specific opiate binding was measured for both membrane and vesicle preparations; dissociation constants (Kd) obtained from saturation isotherms of [3H]bremazocine binding were 1.3 and 4.2 nM, respectively. Relative affinity (IC50) values of ligand binding measured for subtype-selective agonists confirmed that a delta-opiate binding site interaction was recovered in vesicle preparations. Changes in agonist binding affinity noted for these experiments were explained by dissociation of the GTP-binding protein Gi from the receptor in detergent. The recovery of solubilized opiate receptors was nearly quantitative, and strictly dependent upon the total brain lipid preparation used in the reconstitution. Ligand binding was incompletely recovered after substituting pure, vesicle-forming phospholipid preparations. [3H]Bremazocine binding was also reconstituted after lectin affinity chromatography of solubilized receptor preparations, using conditions which likely effect the removal of endogenous lipid cofactors. A photoaffinity cross-linking methodology was employed to verify recovery of the delta-opiate receptor after its solubilization from membranes and reconstitution. Two membrane-associated proteins (50 and 70 kDa) were covalently tagged with an azido analog of beta-endorphin(Leu5) in cell membranes and subsequently identified by immunoblotting with antisera directed against this opioid. Labeling of the 50-kDa polypeptide was prevented by coincubating assay samples with a relative excess of (D-Pen2,5)enkephalin. This opioid binding polypeptide was also present in solubilized/reconstituted receptor preparations.

5′-Guanylylimidodiphosphate decreases affinity for agonists and apparent molecular size of a frog brain opioid receptor in digitonin solution.

When assayed for specific opiate binding in the presence of 120 mM NaCl, digitonin extracts from frog (Rana ridibunda) brain membranes were found to contain about the same quantity (0.5 pmol/mg of protein) of high (Kdh = 0.4 nM) and of lower (Kdl = 15-20 nM) affinity sites for the opiate agonist [3H]etorphine. The two classes of [3H]etorphine binding sites displayed equally high (Kd = 0.3 nM) affinity for the opiate antagonist [3H]diprenorphine. 5'-Guanylylimidodiphosphate (GppNHp) selectively and potently (IC50 = 0.1 microM) inhibited high affinity binding of the tritiated agonist, and this inhibition resulted from the GppNHp-induced conversion of the high into the lower affinity sites for [3H]etorphine. Following centrifugation of the digitonin extract in sucrose gradients, opioid binding activity was found to be associated with two clearly separated macromolecular components of apparent sedimentation coefficients 11.5 and 9.7 S, respectively. The two components bound [3H]diprenorphine equally well, whereas the fast sedimented component bound [3H]etorphine better than did the slower sedimented one. In addition, labeling of the component of bigger apparent size with [3H]etorphine was considerably reduced in the presence of 50 microM GppNHp. Finally, in soluble extracts which had been (i) preincubated with and (ii) centrifuged in the presence of GppNHp, the fast sedimented component was no longer observed while there was about twice as much of the component of smaller apparent size as in control (no GppNHp) extracts. Together, these results demonstrated the existence of an opioid receptor-G protein complex which, in digitonin solution, was still amenable to regulation (dissociation) by guanine nucleotides.

NMB: A human neuroblastoma cell line with specific opiate binding sites

The human neuroblastoma cell line designated NMB (Brodeur et al., 1977, Cancer 40 : 2256) has been shown to have specific opiate binding sites. These sites are highly stereospecific. Two characteristic delta specific peptides, D-Ala 2-D-Leu 5 enkephalin and D-Thr 2-D-Thr 6 enkephalin, have high affinity for the binding sites. Morphine binds specifically but with a much lower affinity. Dextrorphan and the mu specific peptide morphiceptin (Tyr-Pro-Phe-Pro-CO-NH 2) do not bind to the site. The binding sites are heat and trypsin sensitive. Sodium ions specifically lower agonist binding to the sites. Approximately 14,000 binding sites per cell are found. The binding characteristics of these sites are very similar to those of the delta sites characterized on mouse neuroblastoma cell lines.

Pregnancy related changes of opiate receptors identified in rat uterine membranes by 3H-naloxone binding

3H-Naloxone was used to demonstrate the presence of specific opiate binding sites in uterine membrane preparations of rats. 3H-Naloxone binding (0.41–27 nM) was found to be rapid, saturable and reversible showing two populations of binding sites with the characteristic of high (K D 2.2 nM; B max 46.6 fmol/mg prot.) and low (K D 18.1 nM; B max 143.7 fmol/mg prot.) affinity. The number and affinity of the binding sites labelled by 3H-naloxone in the uterus were measured in the rat at mid (14 days), late (21 days) pregnancy and at parturition. The high and low affinity recognition sites labelled by 3H-naloxone showed a consistent reduction during pregnancy and at parturition without changes in the affinity constant. We concluded that pregnancy and parturition are associated with significant changes in the number of the opiate receptors bound in the uterus by 3H-naloxone. This phenomenon which seems to be linked with the several pregnancy-related changes in the levels of endogenous peptides and hormones could be relevant to further explain the pregnancy related changes in pain perception and maternal behavior.

Solubilization of two molecular forms of the frog brain opioid receptor

In equilibrium binding studies, using 3H-etorphine and 3H-diprenorphine, digitonin extracts of frog brain membranes are found to contain two classes of sites, one of which is seen only in the presence of Na + ions. Centrifugation of the extracts in sucrose gradients separates two macromolecular components (10S and 12S) which display specific opiate binding activity. The 12S component appears to carry the site that binds opiates in the absence of Na + ions while the 10S component would carry the other site, i.e. the one which is seen only in the presence of Na + ions in equilibrium binding studies. Preliminary evidence is also given that in extracts of frog brain membranes which have been pre-incubated with 120 mM NaCl, the balance of the two components is shifted in favor of the slower sedimenting (10S) one. These results are discussed in terms of the regulation of the state of equilibrium between an agonist (12S) and an antagonist (10S) form of the opioïd receptor.

Cell cycle-dependent expression of specific opiate binding with variable coupling to adenylate cyclase in a neurotumor hybrid cell line NG108-15.

Monolayer cultures of neuroblastoma X glioma hybrid (clonal) cell line NG108-15, synchronized by the isoleucine/glutamine deprivation method, showed maximal expression of opiate binding sites at the same point in the cell cycle at which prostaglandin E1 (PGE1) had a maximum stimulatory effect on cyclic AMP synthesis. However, the capacity of enkephalin [D-Ala2D-Leu5] to block the stimulation of cyclic AMP synthesis by PGE1 was not related to the number of opiate receptors expressed. The Ki for the inhibition of cyclic AMP synthesis by opioid peptides increased substantially during the period of the cell cycle at which maximal expression of opiate binding sites occurred, making the effective level of inhibition of adenylate cyclase activity by 0.1 microM enkephalin [D-Ala2D-Leu5] the same through the cell cycle. Data are presented to suggest that enkephalin receptor coupling to adenylate cyclase, via a GTP-binding protein, is maximal during G1 phase (which may approximate the state of the differentiated neuron) and minimal during S + G2 phase, just prior to cell division, when many receptors are uncoupled.

Interaction of calcium with 3H-morphine binding to synaptosomes of the guinea-pig ileum.

Specific binding sites for 3H-morphine were assayed in subcellular fractions of a crude mitochondrial P2 pellet from the guinea-pig ileum longitudinal muscle-myenteric plexus, prepared by discontinuous sucrose-gradient fractionation. The highest specific binding (ca. 100 fmol/mg protein) was obtained in the fraction containing synaptosomes, as examined by electron microscopy. A synaptosomal fraction prepared from guinea-pig brain had comparable specific binding (ca 130 fmol/mg) to that of the ileal synaptosomal fraction. Addition of calcium (10 mM) to the binding assay medium resulted in a marked decrease in particular of the specific 3H-morphine binding. Detailed analysis of the specific 3H-morphine binding. Detailed analysis of the specific 3H-morphine binding in the synaptosomal fraction of the ileum revealed that 1) a saturable component of specific opiate binding was present between 0.34 and 21.74 nM of 3H-morphine; 2) in the presence of 3 and 10 nM of calcium similar decreases of specific 3H-morphine binding were obtained, indicating that this binding was maximally inhibited already by 3 mM of calcium; 3) both in the absence and presence of calcium the KD of specific 3H-morphine binding was about 38 nM, indicating a non-competitive nature of the calcium inhibition; 4) addition of magnesium exhibited a similar effect as that of calcium, although magnesium appeared to be less potent than calcium in this respect. The data are discussed in the context of previously observed calcium effects on opioid actions in the electrically stimulated guinea-pig ileum bioassay and may contribute to the evidence that the interaction of calcium and opioids on the stimulus-release coupling mechanism at the neuromuscular junction of the guinea-pig ileum is occurring beyond opioid receptor activation as well.

Further evidence for the existence of opiate binding sites on neurosecretory LHRH mediobasal hypothalamic terminals

Opiate binding sites as well as LHRH and SRIF content were evaluated in mediobasal hypothalamus (MBH) from normal male rats and animals subjected to anterolateral deafferentation of the hypothalamus. A 87 and 44% depletion of LHRH and SRIF content respectively and a 50% decrease in the number of specific opiate binding sites was observed in the deafferented MBH. Dopa-de-carboxylase activity remained unchanged. These data indicate that presynaptic opiate binding sites are present on LHRH and SRIF mediobasal hypothalamic nerve endings.

Opiate receptors in highly purified neuronal cell populations isolated in bulk from embryonic chick brain

A bulk isolation procedure was used to obtain neuronal and non-neuronal cell populations from embryonic chick brain. The procedure utilizes the differences in cell-substrate adhesiveness of the two populations and the ability of the former to form homotypic aggregates in the presence of intermittent mechanical agitation. [ 3H]-Thymidine incorporation, semi-quantification of S-100 protein, and recycling of radioactively labelled putative non-neuronal cells through the isolation procedure indicate that the neuronal fraction contained less than 1% of non-neuronal cells. The binding of [ 3H]-naloxone to the isolated neuronal cells was characterized. These cells were found to have opiate receptors which are very similar to those found in adult rat brain with respect to stereospecificity of [ 3H]-naloxone binding, the ability of several opiate agonists and antagonists of varying analgesic activity to displace bound [ 3H]-naloxone, and the differential response of these drugs to Na +. Isolated non-neuronal cells, in contrast, had no specific opiate binding activity. Total binding activity of both populations of cells was greatly increased after 24 hr in culture. However, while a major portion of the activity of the neuronal cells was of the specific type, all of the activity in the non-neuronal cells remained nonspecific.

Inhibition of specific opiate binding to synaptic membrane by cerebroside sulfatase

The role of cerebroside sulfate in the specific binding of opiates to the synaptic membrane was investigated by the use of the enzyme, sulfatase A (cerebroside sulfatase, cerebroside-3-sulfate-3-sulphohydrolyase, EC 3.1.6.8). It was observed that the hydrolysis of sulfatides in the synaptic membrane by this enzyme was dependent on the presence of a heat stable protein molecule. When [ 3H]naloxone binding to the enzyme-treated membrane was determined, specific binding was attenuated. This inhibition of specific binding was dependent on the concentration of the activator molecule and could not be prevented by the addition of bovine serum albumin in the binding assay mixtures. The enzymatic pH optimum for inhibiting the specific opiate binding was between pH 4.7 and 5.0. This correlated well with the pH optimum for the sulfatase A to hydrolyze free cerebroside sulfate molecules. Scatchard analysis indicated a significant decrease in the number of binding sites with no statistically significant alteration in binding affinity of the remaining sites.