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Biomedical subjects

E M Parker

Publications and source records attributed to E M Parker.

At least 19 recordsLinked to original sources
PubMed2005

Characterization of the nociceptin receptor (ORL-1) agonist, Ro64-6198, in tests of anxiety across multiple species.

RATIONALE: Previous studies have demonstrated behaviors indicative of anxiolysis in rats pretreated with the nociceptin receptor (opioid receptor like-1, ORL-1) agonist, Ro64-6198. OBJECTIVES: The aim of this study was to examine the effects of Ro64-6198 in anxiety models across three species: rat, guinea pig, and mouse. In addition, the receptor specificity of Ro64-6198 was studied, using the ORL-1 receptor antagonist, J-113397, and ORL-1 receptor knockout (KO) mice. Finally, neurological studies examined potential side effects of Ro64-6198 in the rat and mouse. RESULTS: Ro64-6198 (3-10 mg/kg) increased punished responding in a rat conditioned lick suppression test similarly to chlordiazepoxide (6 mg/kg). This effect of Ro64-6198 was attenuated by J-113397 (10 mg/kg), but not the mu opioid antagonist, naltrexone (3 mg/kg). In addition, Ro64-6198 (1-3 mg/kg) reduced isolation-induced vocalizations in rat and guinea pig pups. Ro64-6198 (3 mg/kg) increased the proportion of punished responding in a mouse Geller-Seifter test in wild-type (WT) but not ORL-1 KO mice, whereas diazepam (1-5.6 mg/kg) was effective in both genotypes. In rats, Ro64-6198 reduced locomotor activity (LMA) and body temperature and impaired rotarod, beam walking, and fixed-ratio (FR) performance at doses of 10-30 mg/kg, i.e., three to ten times higher than an anxiolytic dose. In WT mice, Ro64-6198 (3-10 mg/kg) reduced LMA and rotarod performance, body temperature, and FR responding, but these same measures were unaffected in ORL-1 KO mice. Haloperidol (0.3-3 mg/kg) reduced these measures to a similar extent in both genotypes. These studies confirm the potent, ORL-1 receptor-mediated, anxiolytic-like effects of Ro64-6198, extending the findings across three species. Ro64-6198 has target-based side effects, although the magnitude of these effects varies across species.

Animals↗
PubMed2001

Central melanocortin system modulates energy intake and expenditure of obese and lean Zucker rats.

Melanocortins play a critical role in appetite and body weight regulation, because manipulations of this pathway can lead to the development of obesity in several animal models. The purpose of this study was to use a melanocortin receptor agonist and antagonist to evaluate the involvement of melanocortins in feeding, energy metabolism, and body weight regulation in lean and obese Zucker rats. Central administration of a melanocortin receptor antagonist (SHU9119) elevated food intake and body weight of lean Zucker rats but had little effect in obese Zucker rats. In contrast, the melanocortin receptor agonist MTII reduced food intake in both lean and obese rats but was more potent in the obese Zucker rats. These data indicate the existence of functional melanocortin receptors in both lean and obese Zucker rats but suggest that obese Zucker rats have reduced endogenous melanocortin tone. In addition to its effects on food intake, MTII infusion elevated oxygen consumption and decreased respiratory quotient dose dependently during the light cycle. Our data suggest that a melanocortin receptor agonist can induce weight loss by increasing energy expenditure and promoting body fat utilization in addition to its inhibitory effects on food intake in both obese and lean Zucker rats.

Animals↗
PubMed2000

Rapamycin, but not FK506 and GPI-1046, increases neurite outgrowth in PC12 cells by inhibiting cell cycle progression.

Immunophilin ligands such as rapamycin, FK506 and GPI-1046 have been reported to increase neurite outgrowth in vitro and to have neuroprotective activity in vitro and in vivo. In this study, however, FK506 and GPI-1046 (0.1-1000 nM) had little effect on neurite outgrowth in PC12 cells in either the presence or absence of nerve growth factor. In contrast, rapamycin markedly increased neurite outgrowth in PC12 cells in the presence of a low concentration of nerve growth factor (EC(50)=10 nM). Unlike FK506 and GPI-1046, rapamycin is an inhibitor of cell cycle progression. Other cell cycle inhibitors such as ciclopirox and flavopiridol also increased neurite outgrowth in PC12 cells in the presence of a low concentration of nerve growth factor (EC(50)=250 nM and 100 nM, respectively). The neuroprotective effects of FK506, rapamycin and GPI-1046 were also tested in a rodent model of permanent focal cerebral ischemia. FK506 and rapamycin decreased infarct volume by 40% and 37%, respectively, whereas GPI-1046 was ineffective. These data do not support the previous suggestion that FK506 and GPI-1046 increase neurite outgrowth of PC12 cells in vitro. Rapamycin increases neurite outgrowth of PC12 cells, an effect that can be ascribed to its ability to inhibit cell cycle progression. The neuroprotective effect of FK506 and rapamycin against cerebral ischemia is probably not due to differentiation of neuronal precursors or stimulation of neuronal regeneration.

Animals↗
PubMed2000

Pharmacological characterization of the cloned neuropeptide Y y(6) receptor.

Neuropeptide Y has potent appetite stimulating effects which are mediated by hypothalamic receptors believed to be of the neuropeptide Y Y(1) and/or neuropeptide Y Y(5) subtype. In mice, the neuropeptide Y y(6) receptor is also expressed in the hypothalamus, suggesting that it too may function as a feeding receptor in this species. Several laboratories have studied the pharmacology of the neuropeptide Y y(6) receptor, but their results are not in agreement. Using neuropeptide Y and a variety of peptide analogs and small molecule antagonists, we have determined that the pharmacology of the cloned mouse neuropeptide Y y(6) receptor is distinct from that of the other known neuropeptide Y receptors. The rank order of binding affinity for the mouse neuropeptide Y y(6) receptor is [(Ile, Glu,Pro,Dpr,Tyr,Arg,Leu,Arg,Tyr-NH(2))(2)human peptide YY=human, rat neuropeptide Y=human, rat neuropeptide Y-(2-36)=human, rat [Leu(31), Pro(34)porcine (Cys(2))-neuropeptide Y-(1-4)-8-aminooctanoyl-(D-Cys(27)porcine [D-Trp(32)rat pancreatic polypeptide=human pancreatic polypeptide. A similar rank order of potency is seen for inhibition of forskolin-stimulated cyclic AMP. The neuropeptide Y Y(5) receptor antagonist trans-naphthalene-1-sulfonic acid ¿4-[4-amino-quinazolin-2-ylamino)-methyl]-cyclohexylmethy l¿-amide hydrochloride (CGP 71683A) and the neuropeptide Y Y(1) receptor antagonist ((R)-N(2)-diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-argininam ide) (BIBP3226) bind weakly to the neuropeptide Y y(6) receptor (K(i)10, 000 nM, respectively). Although the function of the neuropeptide Y y(6) receptor remains to be elucidated, its pharmacology is not consistent with a role in appetite regulation.

Animals↗
PubMed2000

[D-Trp(34)] neuropeptide Y is a potent and selective neuropeptide Y Y(5) receptor agonist with dramatic effects on food intake.

The neuropeptide Y (NPY) Y(5) receptor has been proposed to mediate several physiological effects of NPY, including the potent orexigenic activity of the peptide. However, the lack of selective NPY Y(5) receptor ligands limits the characterization of the physiological roles of this receptor. Screening of several analogs of NPY revealed that [D-Trp(34)]NPY is a potent and selective NPY Y(5) receptor agonist. Unlike the prototype selective NPY Y(5) receptor agonist [D-Trp(32)]NPY, [D-Trp(34)]NPY markedly increases food intake in rats, an effect that is blocked by the selective NPY Y(5) receptor antagonist CGP 71683A. These data demonstrate that [D-Trp(34)]NPY is a useful tool for studies aimed at determining the physiological roles of the NPY Y(5) receptor.

Animals↗
PubMed2000

GP2, a GPI-anchored protein in the apical plasma membrane of the pancreatic acinar cell, co-immunoprecipitates with src kinases and caveolin.

We previously showed that endocytosis at the apical plasma membrane (APM) of the pancreatic acinar cell is activated by the cleavage of GP2, a GPI-linked protein, from the apical cell surface. This endocytic process, as measured by horseradish peroxidase uptake into pancreatic acinar cells, is blocked by the tyrosine kinase inhibitors genistein and tyrphostin B42 as well as by disruption of actin filaments with cytochalasin. This suggests that the cleavage of GP2 from the cell membrane may activate endocytosis through a tyrosine kinase-regulated pathway. However, the mechanism by which GP2 and tyrosine kinases act together to activate endocytosis at the APM remains unknown. In this study, we demonstrate that pp60, p62yes, caveolin, and annexin, which have previously been implicated in endocytosis in other cell lines, were present in high abundance in GPI-enriched membranes by Western blot analysis. pp60, p62yes, and caveolin all co-immunoprecipitated with GP2 except annexin. An 85-kDa protein whose tyrosine-dependent phosphorylation is correlated with the activation of endocytosis in intact acinar cells also was present in these immunoprecipitates. This suggests that in pancreatic acini, GP2 may exist in a complex with src kinases, caveolin, and an 85-kDa phosphorylated substrate to regulate endocytosis at the APM.

Animals↗
PubMed1999

A membrane lipid imbalance plays a role in the phenotypic expression of cystic fibrosis in cftr(-/-) mice.

A deficiency in essential fatty acid metabolism has been reported in plasma from patients with cystic fibrosis (CF). However, its etiology and role in the expression of disease is unknown. The objective of this study was to determine whether alterations in fatty acid metabolism are specific to CF-regulated organs and whether they play a role in the expression of disease. A membrane lipid imbalance was found in ileum, pancreas, and lung from cftr(-/-) mice characterized by an increase in phospholipid-bound arachidonic acid and a decrease in phospholipid-bound docosahexaenoic acid (DHA). This lipid imbalance was observed in organs pathologically affected by CF including lung, pancreas, and ileum and was not secondary to impaired intestinal absorption or hepatic biosynthesis of DHA. As proof of concept, oral administration of DHA to cftr(-/-) mice corrected this lipid imbalance and reversed the observed pathological manifestations. These results strongly suggest that certain phenotypic manifestations of CF may result from remediable alterations in phospholipid-bound arachidonic acid and DHA levels.

Administration, Oral↗
PubMed1999

Calpain inhibitor I increases beta-amyloid peptide production by inhibiting the degradation of the substrate of gamma-secretase. Evidence that substrate availability limits beta-amyloid peptide production.

The calpain inhibitor N-acetyl-leucyl-leucyl-norleucinal (ALLN) has been reported to have complex effects on the production of the beta-amyloid peptide (Abeta). In this study, the effects of ALLN on the processing of the amyloid precursor protein (APP) to Abeta were examined in 293 cells expressing APP or the C-terminal 100 amino acids of APP (C100). In cells expressing APP or low levels of C100, ALLN increased Abeta40 and Abeta42 secretion at low concentrations, decreased Abeta40 and Abeta42 secretion at high concentrations, and increased cellular levels of C100 in a concentration-dependent manner by inhibiting C100 degradation. Low concentrations of ALLN increased Abeta42 secretion more dramatically than Abeta40 secretion. ALLN treatment of cells expressing high levels of C100 did not alter cellular C100 levels and inhibited Abeta40 and Abeta42 secretion with similar IC50 values. These results suggest that C100 can be processed both by gamma-secretase and by a degradation pathway that is inhibited by low concentrations of ALLN. The data are consistent with inhibition of gamma-secretase by high concentrations of ALLN but do not support previous assertions that ALLN is a selective inhibitor of the gamma-secretase producing Abeta40. Rather, Abeta42 secretion may be more dependent on C100 substrate concentration than Abeta40 secretion.

Alzheimer Disease↗
PubMed1999

Extensive alternative splicing in the 5'-untranslated region of the rat and human neuropeptide Y Y5 receptor genes regulates receptor expression.

Neuropeptide Y (NPY) elicits a plethora of physiological effects by interacting with several distinct G protein-coupled receptors. Activation of one of these receptors, the NPY Y5 receptor, is thought to result in increased food intake, anticonvulsant effects, attenuation of opiate withdrawal, inhibition of neuronal activity, and alteration of renal function. Several alternatively spliced human and rat NPY Y5 receptor cDNAs have been isolated that use different combinations of exons in the 5'-untranslated region. The various human NPY Y5 receptor cDNAs appear to be differentially expressed in different brain regions. The level of human NPY Y5 receptor expressed transiently in COS1 cells was significantly influenced by the sequence of the 5'-untranslated region. These results indicate that alternative splicing in the 5'-untranslated region of the human and rat NPY Y5 receptor genes occurs in a tissue-specific manner and is one mechanism by which cells control the level of NPY Y5 receptor expression.

5' Untranslated Regions↗
PubMed1999

Endocytosis at the apical plasma membrane of pancreatic acinar cells is regulated by tyrosine kinases.

We have shown that endocytosis at the apical plasma membrane of pancreatic acinar cells is regulated by the pH of the acinar lumen and is associated with cleavage of GP2, a glycosyl phosphatidylinositol-anchored protein. The aim of this study was to determine the transduction pathway by which endocytosis is activated. Apical endocytosis was studied in rat pancreatic acini by prestimulation with cholecystokinin followed by measurement of horseradish peroxidase (HRP) uptake. Lanthanum, staurosporine, and forskolin had no effect on HRP uptake. Cytochalasin D significantly inhibited endocytosis, indicating a dependence on actin filament integrity. Genistein and the specific tyrphostin inhibitor B42 also inhibited HRP uptake, implicating tyrosine kinases in the regulation of HRP uptake. With the use of an Src kinase-specific substrate, Src kinase activity was temporally related to activation of endocytosis. The tyrosine-dependent phosphorylation of an 85-kDa substrate in both rat and mouse pancreatic acini correlated with Src kinase activation and pH-dependent regulation of HRP uptake. These results indicate that apical endocytosis in acinar cells is associated with tyrosine kinase activation and is dependent on the actin cytoskeleton.

Animals↗
PubMed1999

Activation of the NPY Y5 receptor regulates both feeding and energy expenditure.

Intracerebroventricular (ICV) administration of neuropeptide Y (NPY) has been shown to decrease energy expenditure, induce hypothermia, and stimulate food intake. Recent evidence has suggested that the Y5 receptor may be a significant mediator of NPY-stimulated feeding. The present study attempts to further characterize the role of NPY Y5-receptor subtypes in feeding and energy expenditure regulation. Satiated Long-Evans rats with temperature transponders implanted in the interscapular brown adipose tissue (BAT) displayed a dose-dependent decrease in BAT temperature and an increase in food intake after ICV infusion of NPY. Similar effects were induced by ICV administration of peptide analogs of NPY that activate the Y5 receptor, but not by analogs that activate Y1, Y2, or Y4 receptors. Furthermore, ICV infusion of the Y5 selective agonist D-[Trp(32)]-NPY significantly reduced oxygen consumption and energy expenditure of rats as measured by indirect calorimetry. These data suggest that the NPY Y5-receptor subtype not only mediates the feeding response of NPY but also contributes to brown fat temperature and energy expenditure regulation.

Adipose Tissue, Brown↗
PubMed1998

GR231118 (1229U91) and other analogues of the C-terminus of neuropeptide Y are potent neuropeptide Y Y1 receptor antagonists and neuropeptide Y Y4 receptor agonists.

GR231118, BW1911U90, Bis(31/31')[[Cys31, Trp32, Nva34] neuropeptide Y(31-36)] (T-190) and [Trp-Arg-Nva-Arg-Tyr]2-NH2 (T-241) are peptide analogs of the C-terminus of neuropeptide Y that have recently been shown to be antagonists of the neuropeptide Y Y1 receptor. In this study, the activity of these peptides at each of the cloned neuropeptide Y receptor subtypes is determined in radioligand binding assays and in functional assays (inhibition of forskolin-stimulated cAMP formation). GR231118 is a potent antagonist at the human and rat neuropeptide Y Y1 receptors (pA2 = 10.5 and 10.0, respectively; pKi = 10.2 and 10.4, respectively), a potent agonist at the human neuropeptide Y Y4 receptor (pEC50 = 8.6; pKi = 9.6) and a weak agonist at the human and rat neuropeptide Y Y2 and Y5 receptors. GR231118 also has high affinity for the mouse neuropeptide Y Y6 receptor (pKi = 8.8). Therefore, GR231118 is a relatively selective neuropeptide Y Y1 receptor antagonist, but has appreciable activity at the neuropeptide Y Y4 and Y6 receptors as well. BW1911U90, T-190 and T-241 are moderately potent neuropeptide Y Y1 receptor antagonists (pA2 = 7.1, 5.8 and 6.5, respectively; pKi = 8.3, 6.5 and 6.8, respectively) and neuropeptide Y Y4 receptor agonists (pEC50 = 6.8, 6.3 and 6.6, respectively; pKi; 8.3, 7.7 and 8.3, respectively). These data suggest that the C-terminus of neuropeptide Y and related peptides is sufficient for activation of the neuropeptide Y Y4 receptor, but is not sufficient for activation of the neuropeptide Y Y1 receptor. Because BW1911U90, T-190 and T-241 are significantly less potent at the cloned human neuropeptide Y Y1 receptor than at the neuropeptide Y receptor in human erythroleukemia cells, these cells may express a novel neuropeptide Y receptor with high affinity for these peptides.

Amino Acid Sequence↗
PubMed1997

Human 5-HT1 receptor subtypes exhibit distinct G protein coupling behaviors in membranes from Sf9 cells.

The G protein coupling behavior of four human 5-hydroxytryptamine receptor subtypes (5-HT1A, 5-HT1B, 5-HT1D, and 5-HT1E) has been studied in membranes from Sf9 cells expressing the individual receptors. The 5-HT1A and 5-HT1B receptors exhibited both high- and low-affinity states for agonist, with the majority of the receptors in a low-affinity state. Addition of purified G protein subunits to membranes expressing either 5-HT1A or 5-HT1B receptors shifted the majority of the receptors to a high-affinity state in the absence, but not in the presence, of guanine nucleotides. The alphai1, alphai2, alphai3, and alphao subunits were able to shift the receptors to a high-affinity state with either betagammabrain or betagammaretina while alphat subunits were inactive regardless of which betagamma preparation was used. A significantly higher affinity for agonist was observed with both receptors in the presence of alphai3 subunits compared with either alphai2 or alphao subunits, while a significantly lower concentration of alpha subunits was required for a maximal affinity shift of 5-HT1A receptors compared with 5-HT1B receptors (EC50 values of 6.4 and 12. 0 nM, respectively). The 5-HT1D and 5-HT1E receptors exhibited only a single affinity state for agonist. Addition of purified G protein subunits to membranes containing 5-HT1D receptors caused a small increase in affinity for agonist that was only partially reversed by guanine nucleotides while the addition of purified G protein subunits to membranes containing 5-HT1E receptors had no affect on agonist binding. Thus when expressed in an identical membrane environment these four closely related 5-HT1 receptor subtypes exhibit different G protein coupling behaviors.

Animals↗
PubMed1997

Genomic organization and functional characterization of the mouse GalR1 galanin receptor.

Galanin mediates diverse physiological functions in digestive, endocrine, and central nervous systems through G-protein-coupled receptors. Two galanin receptors have been cloned but the gene structures are unknown. We report genomic and cDNA cloning of the mouse GalR1 galanin receptor and demonstrate that the coding sequence is uniquely divided into three exons encoding the N-terminal portion through the fifth transmebrane domain, the third intracellular loop, and the sixth transmembrane domain through the C-terminus. Functional analysis of the encoded cDNA revealed active ligand binding and intracellular signaling. The expression is detected in brain, spinal cord, heart and skeletal muscle.

Amino Acid Sequence↗
PubMed1997

Molecular approaches to the discovery of new treatments for obesity.

The treatment of obesity requires modulation of both energy intake and energy expenditure, and pharmaceutical treatments are being developed to complement the traditional means of dietary restriction and exercise. The recent discovery of the protein leptin, which modulates both food intake and energy expenditure, has provided a new tool with which to define and analyze potential pathways for pharmacological intervention. Neurotransmitters, such as neuropeptide Y (NPY) and norepinephrine, act downstream of leptin to modulate energy homeostasis. Specific subtypes of the receptors for these neurotransmitters represent promising molecular targets for the discovery of new drugs for the treatment of obesity.

Anti-Obesity Agents↗
PubMed1996

Two amino acid differences in the sixth transmembrane domain are partially responsible for the pharmacological differences between the 5-HT1D beta and 5-HT1E 5-hydroxytryptamine receptors.

5-Hydroxytryptamine elicits its physiological effects by interacting with a diverse group of receptors. Two of these receptors, the 5-HT1D beta and the 5-HT1E receptors, are approximately 60% identical in the transmembrane domains that presumably form the ligand binding site yet have very different pharmacological properties. Analysis of the pharmacological properties of a series of chimeric 5-HT1D beta/5-HT1E receptors indicates that sequences in the sixth and seventh transmembrane domains are responsible for the differential affinity of 5-carboxamidotryptamine for these two receptors. More detailed analysis shows that two amino acid differences in the sixth transmembrane domain (Ile333 and Ser334 in the 5-HT1D beta receptor, corresponding to Lys310 and Glu311 in the 5-HT1E receptor) are largely responsible for the differential affinities of some, but not all, ligands for the 5-HT1D beta and 5-HT1E receptors. It is likely that these two amino acids subtly determine the overall three-dimensional structure of the receptor rather than interact directly with individual ligands.

Amino Acid Sequence↗