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Biomedical subjects

E J Simon

Publications and source records attributed to E J Simon.

At least 19 recordsLinked to original sources
PubMed1992

Lesioning of the nucleus basalis of Meynert has differential effects on mu, delta and kappa opioid receptor binding in rat brain: a quantitative autoradiographic study.

Opioid receptor binding was investigated in rat brain following lesioning of the nucleus basalis of Meynert (nbM). The nbM, which provides cholinergic input to the cortex, was lesioned unilaterally using ibotenic acid. The efficacy of lesioning was confirmed by the observation of a significant decrease in choline acetyltransferase (ChAT) activity in the ipsilateral prefrontal cortex. The specific laminar and regional distribution of mu, delta and kappa opioid receptor binding was quantitated in various cortical and limbic structures in the rat using autoradiography. Distinct medial to lateral gradients of mu and kappa opioid binding were observed in regions of the cerebral cortex. In the lesioned hemisphere the levels of mu, delta and kappa opioid binding were altered in localized areas of the cerebral cortex and the hippocampus. The direction of these binding changes varied with the opioid receptor type being assessed. Delta opioid binding was increased in the lateral portions of the frontal, occipital, perirhinal and retrosplenial granular cortices. Kappa opioid binding was increased in the lateral portion of the occipital cortex and in the CA3 region of the hippocampus. In contrast, mu opioid binding was decreased in the lateral portions of the frontal, entorhinal and forelimb cortices. These opioid receptor changes are discussed with respect to the interactions between the cholinergic and opioid systems, and relevance of the nbM lesion model to Alzheimer's disease.

Animals↗
PubMed1992

Immunoblots with rhodopsin antisera suggest that a purified mu opioid binding protein has structural characteristics of a G-protein-coupled receptor.

A mu opioid binding protein (OBP), previously purified to homogeneity from bovine striatal membranes, was examined by immunoblotting with six antisera against bovine rhodopsin. An antibody against the carboxyl-terminal tail of rhodopsin and one against membrane-associated rhodopsin gave strong signals at the appropriate molecular mass (65 kDa). An antibody directed against the first cytoplasmic loop of rhodopsin was weakly reactive. Three other antibodies did not recognize OBP. This pattern of crossreactivity was identical to that previously seen with beta-adrenergic receptors. The existence of domains in the OBP, which are antigenically similar to those in two other guanine nucleotide regulatory protein-coupled receptors, supports the hypothesis that mu opioid receptors have the structure characteristic of this receptor family.

Animals↗
PubMed1992

Effects of stress on opioid receptor binding in the rat central nervous system.

The endogenous opioid peptides are known to play a significant role in the modulation and/or mediation of numerous environmental or experimental stressors. However, the specific opioid peptide(s) and receptor type(s) involved, under what physiologic conditions they are engaged and within which regions of the CNS is not well understood. We therefore examined the effects of both a chronic and an acute stressor-90-h water deprivation and a single 20-min foot shock on opioid receptor binding in 17 specific rat brain nuclei. [3H]DSTLE (Tyr-D-Ser-Gly-Phe-Leu-Thr) and [3H]DAGO(Tyr-D-Gly-Phe-NMe-Phe-Gly-ol) were used to label delta and mu receptors, respectively. Foot shock induced profound antinociception as measured by tail-flick latency which outlasted the stressor by several minutes. However, only the septum responded with a decrease in [3H]DAGO binding to this type of stress-induced analgesia. No other alterations in either [3H]DAGO or [3H]DSTLE binding were seen in response to foot shock. In contrast, water deprivation induced increases in [3H-DAGO] binding in the septum as well as increases in [3H]DSTLE binding in the caudate and accumbens nuclei. Moreover, the presumptive mild stress of handling in the foot shock control group was sufficient to decrease mu or delta receptor binding in seven out of 17 brain regions investigated (including the frontal cortex and olfactory tubercle where both mu and delta binding were increased) when compared to unhandled deprivation control animals. These changes in opioid receptor binding may have been the result of alterations in treatment-induced peptide release, receptor regulation, or interactions with other released neurotransmitter ligand/receptor complexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1992

Age-related changes in kappa opioid receptors in the guinea-pig brain: a quantitative autoradiographic study.

Investigation into the effect of aging on kappa opioid receptors in the brains of guinea-pigs was carried out in animals aged one, six, 24 and 36 months. Quantitative autoradiography was used to monitor the concentration of kappa receptors in various anatomic regions at five rostrocaudal levels in each age-group. Areas of high binding were found in the deep layers (laminae V, VI) of the neocortex and in the internal band of the periallocortical, dorsal agranular insular cortex. Among non-cortical areas examined, the nucleus accumbens and the substantia nigra possessed kappa binding levels equal to those seen in the deep neocortical layers. In all cases where an age-related change in the level of kappa receptors was detected, the direction of the change was one of decreased binding with advancing age. Statistical analysis of the binding data revealed that the one-month-old animal possessed the highest levels of kappa binding among all age groups examined. The vast majority of age-related changes in kappa binding levels occurred in laminae V and VI of neocortical regions. The per cent decreases (18-42%), as well as their age of onset (six to 36 months) varied in different anatomical regions. Possible mechanisms to explain the age-related decreases in kappa opioid binding are presented. The majority of the age-related decreases in kappa opioid binding are found in areas of the neocortex which are characterized by their motor, sensory and associative functions. It is within these three areas of function that diminutions in performance are most apparent in senescence.

Aging↗
PubMed1992

Characterization of solubilized opioid receptors: reconstitution and uncoupling of guanine nucleotide-sensitive agonist binding.

Opioid receptors were solubilized from bovine striatal membranes with the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate-(CHAPS). High concentrations of NaCl (0.5-1.0 M) were necessary to ensure optimal yields, which ranged from 40 to 50% of membrane-bound receptors. This requirement was found to be specific for sodium, with only lithium able to substitute partially, as previously reported for solubilization with digitonin. Opioid antagonists, but not agonists, were able to bind to soluble receptors with high affinity. High-affinity binding of mu, delta, and kappa agonists was reconstituted following polyethylene glycol precipitation and resuspension of CHAPS extract. Evidence is presented suggesting that this is the result of inclusion of receptors in liposomes. Competition and saturation studies indicate that the three opioid receptor types retain their selectivity and that they exist in the reconstituted CHAPS extract in a ratio (50:15:35) identical to that in the membranes. In reconstituted CHAPS extract, as in membranes, mu-agonist binding was found to be coupled to a guanine nucleotide binding protein (G protein), as demonstrated by the sensitivity of [3H][D-Ala2,N-methyl-Phe4,Gly5-ol]-enkephalin ([3H]DAGO) binding to guanosine 5'-O-(thiotriphosphate) (GTP gamma S). In the reconstituted CHAPS extract, complete and irreversible uncoupling by GTP gamma S was observed, whereas membrane-bound receptors were uncoupled only partially. Treatment with GTP gamma S, at concentrations that uncoupled the mu receptors almost completely, resulted in a fourfold decrease in the Bmax of [3H]DAGO binding with a relatively small change in the KD. Competition experiments showed that the Ki of DAGO against [3H]bremazocine was increased 200-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Lumbar subarachnoid ethylenediaminetetraacetate induces hindlimb tetanic contractions in rats: prevention by CaCl2 pretreatment; observation of spinal nerve root degeneration.

Disodium ethylenediaminetetraacetate (Na2EDTA) has replaced sodium bisulfite as the antioxidant in 2-chloroprocaine, Nesacaine CE. This study was undertaken to determine whether this new formulation has neurotoxic effects when administered in the subarachnoid space. Sprague-Dawley rats receiving subarachnoid injections of 1.5 mM or higher concentrations of Na2EDTA immediately initiated a circling behavior that was followed by the development of tetanic contractions of the hindlimbs lasting for 15-20 min. The tetanic contractions were followed by a brief period of hindlimb paralysis. Pretreatment of rats by subarachnoid injections of 1 mM CaCl2 prevented the development of tetanic contractions and paralysis of the hindlimb. Histologic examination of animals receiving Na2EDTA revealed moderate to severe focal degenerative changes in spinal nerve roots. Control rats receiving subarachnoid injections of normal saline solution did not develop tetanic contraction nor pathological changes on light microscopy. These results suggest that the preservative used in Nesacaine-MPF may be neurotoxic.

Animals↗
PubMed1992

Sulfhydryl groups on opioid receptors revisited. Evidence for two sulfhydryl groups at or near the active site of the mu opioid receptor.

Sulfhydryl groups were studied in opioid receptors solubilized from bovine striatal membranes and reconstituted into liposomes. This system has the advantage of permitting the complete uncoupling of tightly coupled opioid binding sites from guanine nucleotide binding proteins. Sensitivity of opioid receptors to N-ethylmaleimide (NEM) inactivation, as measured by [3H]bremazocine binding, was similar whether coupled or uncoupled from the G protein. Moreover, the binding of uncoupled receptors could be protected from NEM inactivation by preincubation with a ligand, as previously observed in coupled, membrane-bound receptors. These findings provide strong support of earlier results suggesting the presence of sulfhydryl groups on opioid binding sites. An examination of the major receptor types provided the following decreasing order of sensitivity to NEM: mu > delta > kappa. Mu agonist binding was found to be much more sensitive to NEM than antagonist binding, especially in the presence of NaCl, which affects the binding of the two types of ligands in opposite directions, as previously reported for membrane-bound receptors. At 100 microM NEM in the presence of 100 mM NaCl, [3H] (D-Ala2,N-methyl-Phe4,Gly-ol)-enkephalin (DAGO) binding is essentially eliminated, whereas [3H]bremazocine or [3H]naloxone binding is virtually unaffected. These results are most readily explained by the hypothesis that there are two sulfhydryl groups at or near the mu binding site; one essential for agonist (but not antagonist) binding, the other essential for antagonist and perhaps, also agonist binding. The sodium effect on NEM inactivation of antagonist binding was maintained in the uncoupled state indicating that this effect occurs at the level of the receptor protein.

Animals↗
PubMed1991

Effects of parabrachial opioid antagonism on stimulation-induced feeding.

The pontine parabrachial nucleus (PBN) contains gustatory relay neurons and a high concentration of opioid receptors. To investigate the involvement of PBN opioid activity in feeding behavior, antagonists were infused into the PBN bilaterally and effects on stimulation-induced feeding were determined. Naloxone, a mu-preferring antagonist, increased the lateral hypothalamic stimulation threshold for eliciting feeding behavior while nor-binaltorphimine, a kappa-selective antagonist, did not. Neither antagonist increased threshold when infused into dorsal pontine sites outside of the PBN or the fourth ventricle. In as much as PBN contains mu and kappa but no detectable delta receptors, the present results suggest that mu opioid activity within the PBN is involved in the mediation of feeding behavior.

Animals↗
PubMed1990

Brain stimulation-induced feeding alters regional opioid receptor binding in the rat: an in vivo autoradiographic study.

Although opioid antagonists block feeding behavior in a variety of animal models, the number and identity of CNS regions in which the inferred endogenous opioid activity mediates feeding have yet to be established. Furthermore, it is not yet clear whether the opioid activity that sustains feeding is a concomitant of the appetitive motivational state or the consummatory response. In an effort to address these issues, an in vivo autoradiographic method was used to visualize CNS regional changes in opioid release during appetitively motivating electrical stimulation in the lateral hypothalamus (ESLH) and during consummatory behavior elicited by such stimulation. Regional decreases in [3H]diprenorphine [(3H]Dpr) binding, suggesting increased release of an endogenous opioid peptide, were observed in the medial prefrontal cortex, medial septum, gustatory cortex, zona incerta, mediodorsal thalamus, and hippocampus of rats receiving ESLH. Decreased binding in the latter 4 structures did not appear when animals were allowed to eat during ESLH, suggesting that the inferred opioid release is associated with appetitive behaviors elicited by ESLH which are suppressed when food is available and consummatory behavior predominates. When animals were allowed to eat during ESLH, [3H]Dpr binding in anterior cingulate cortex decreased substantially, suggesting that feeding behavior specifically triggers opioid release in this region. ESLH and feeding were found to increase [3H]Dpr binding in a number of CNS regions. Alternative explanations for increased binding, including inhibition of tonic opioid release, changes in cerebral blood flow, and opioid receptor up-regulation are discussed.

Animals↗
PubMed1990

Differential effects of cyanogen bromide on ligand binding by mu, delta and kappa opioid receptors.

Guinea pig brain membranes treated with cyanogen bromide (CNBr) demonstrate a loss in the number of mu opioid receptors and a lower binding affinity of delta opioid receptors. These receptor changes are irreversible. Results from ligand protection experiments support the hypothesis that the location of the methionine groups, the sites at which CNBr cleaves peptides, differs between these two types of opioid receptors. Kappa receptors are significantly less sensitive to the action of CNBr than mu or delta receptors.

Animals↗
PubMed1990

No-carrier-added (NCA) N-(3-[18F]fluoropropyl)-N-norbuprenorphine and N-(3-[18F]fluoropropyl)-N-nordiprenorphine--synthesis, anatomical distribution in mice and rats, and tomographic studies in a baboon.

N-(3-Fluoropropyl)-N-norbuprenorphine (3a) and N-(3-fluoropropyl)-N-nordiprenorphine (4a) were synthesized by N-alkylation of norbuprenorphine (1) and nordiprenorphine (2) with 1-bromo-3-fluoropropane. The corresponding no-carrier-added (NCA) N-(3-[18F]fluoropropyl)-N-norbuprenorphine (3b) and N-(3-[18F]fluoropropyl)-N-nordiprenorphine (4b) were synthesized by N-alkylation of 1 and 2 with NCA 1-[18F]fluoro-3-iodopropane in a synthesis time of approximately 100 min from end of bombardment (EOB) with an overall radiochemical yield of approximately 15% (EOB) and a mass of 2-3 nmol. In vitro studies indicate that in the absence of sodium chloride, compounds 3a, 4a, N-propyl-N-norbuprenorphine (5), buprenorphine and diprenorphine are reasonably comparable in binding affinity for opioid receptors. In the presence of 100 mM sodium chloride, however, compounds 3a, 4a and 5, are clearly less potent than buprenorphine and diprenorphine. The anatomical distribution study of compound 3b in mice shows radioactivity accumulating in bone, indicating that in vivo defluorination may have occurred. Rat studies of both compounds 3b and 4b indicate the specific distribution of these two radioligands within certain cortical and subcortical regions of rat brain. However, the absolute uptake of compound 4b in rat brain was only half that of compound 3b. PET studies of 3b in a baboon revealed specific binding of compound 3b in striatum and cerebellum. At 1 h after injection, ratios of specific/non-specific binding of 3b in striatum and cerebellum of a baboon were 1.9 and 1.7 respectively.

Animals↗
PubMed1990

Conjugate addition ligands of opioid antagonists. Methacrylate esters and ethers of 6 alpha- and 6 beta-naltrexol.

Alpha- and beta-naltrexol derived esters 9 and 10 and ethers 11 and 12, each containing the alpha, beta-unsaturated ester functionality, were prepared as conformationally more flexible analogues of spiro-alpha-methylene-gamma-lactones 5 and 6. All were active in the opioid radioreceptor binding assay against [3H]bremazocine and more active against [3H]DAGO, indicating mu-subtype selectivity, but only ether 12 showed significant irreversible activity. We conclude that small structural changes, made in very closely related electrophilic opioids, lead to changes in receptor binding. All four compounds were long-acting antagonists to morphine in mice, with ester 10 being approximately equipotent with naltrexone.

Animals↗
PubMed1990

Electrophilic alpha-methylene-gamma-lactone and isothiocyanate opioid ligands related to etorphine.

Isothiocyanate and alpha-methylene-gamma-lactone analogues of 6,14-endo-ethenotetrahydrothebaine and -oripavine were prepared with the electrophilic groups being located at C-19 in the C-7 alpha-side chain. Isothiocyanates were prepared in the N-Me and N-CPM (N-cyclopropylmethyl) series, both as the phenols and 3-O-methyl ethers from the diastereomeric amines formed from reductive amination of thevinone (2) and N-(cyclopropylmethyl)northevinone (13). Although addition of the organozinc reagent from methyl alpha-bromomethacrylate to 25 failed, addition to 3-O-protected aldehydes 27 and 35 produced, after subsequent deprotection, alpha-methylene-gamma-lactones 29 and 37, respectively. In the opioid receptor displacement assays against [3H]bremazocine as the radiolabeled ligand, the phenolic compounds were most potent with N-CPM isothiocyanates 20 and 21 showing IC50s of 0.32 and 0.76 nM, respectively, and N-CPM alpha-methylene-gamma-lactone 37 having an IC50 = 1.0 nM. Compound 37 showed irreversible effects in the binding assay which were mu-selective, as demonstrated by analogous experiments using [3H]DAGO, and naloxone was found to protect against the irreversible effects. This observation suggests that a receptor-bound nucleophile is located at a position where it can readily reach the alpha-methylene group of lactone 37.

Chemical Phenomena↗