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J T Coyle

Publications and source records attributed to J T Coyle.

At least 145 records · Page 8Linked to original sources
PubMed1989

Specificity of the activation of [3H]hemicholinium-3 binding by phospholipase A2.

Phospholipase A2 (PLA2) treatment has been shown previously to stimulate the sodium-dependent high-affinity choline uptake system as assessed by both the specific binding of [3H]hemicholinium-3 ([ 3H]HCh-3) and the uptake of [3H]choline. In the present study, the specificity of PLA2-induced stimulation upon [3H]HCh-3 binding has been examined. PLA2, as well as phospholipase C (PLC), treatment of synaptic membranes produced a dose-dependent increase in the specific binding of [3H]HCh-3 whereas neither phospholipase B nor phospholipase D had any effect. PLC-induced stimulation of [3H]HCh-3 binding resulted from a significant decrease in the Kd without a change in the maximum binding of [3H]HCh-3 binding. PLC treatment of synaptosomes resulted in an inhibition of [3H]choline uptake accompanied by an inhibition of Na+, K+-adenosine triphosphatase activity. In contrast to the increase of [3H]HCh-3 binding, the specific binding of both [3H]desipramine and [3H]mazindol was decreased by PLA2 treatment. After PLA2 treatment, [3H]HCh-3 binding was increased about 2.5-fold over basal levels in different regions of the brain. Electrolytic lesions of the medial septal nucleus and kainic acid-induced lesions of the striatum resulted in a marked reduction of [3H]HCh-3 binding in the hippocampus and the striatum, respectively. Residual [3H]HCh-3 binding in the denervated hippocampus and lesioned striatum was increased by PLA2 treatment but remained lower than that in PLA2-treated controls. Finally, atropine-induced up-regulation of [3H]HCh-3 binding in vivo was not additive with PLA2-induced stimulation. These results support the hypothesis that PLA2 might be involved in the regulation of the sodium-dependent high-affinity choline uptake.

Animals↗
PubMed1989

Antioxidants protect against glutamate-induced cytotoxicity in a neuronal cell line.

The effects of reducing agents and antioxidants on L-Glutamate (Glu)-induced cytotoxicity were examined in the N18-RE-105 neuronal cell line. The cytotoxicity by Glu (1 and 10mM) was potentiated by exposure to growth medium containing a low concentration of cystine (5-100 microM), instead of the normal medium containing 200 microM cystine. In contrast, the toxicity was suppressed by increasing the cystine concentration to 500 to 1000 microM. Reducing agents, cysteine (30-1000 microM), dithiothreitol (10-250 microM) and glutathione (GSH, 10-1000 microM) also protected the cells against the cytotoxicity of 10 mM Glu in a concentration-dependent manner. The antioxidants vitamin E (10-100 microM), idebenone (0.1-3 microM) and vinpocetine (10-100 microM) also provided marked protection against the cytotoxicity of Glu (10 mM) or quisqualate (1 mM). Antioxidants also prevented the delayed cell death caused by lowering the concentration of cystine in the medium to 5 microM. Incubation of the cells with 10 mM Glu caused a marked decrease in cellular GSH levels. Although cysteine and dithiothreitol prevented the GSH reduction caused by Glu, antioxidants did not. The cellular levels of oxidants were assessed using 2,7-dichlorofluorescin, a probe that accumulates within cells and is converted to a fluorescent product by oxidation. Glu (10 mM) caused a marked increase in such fluorescence, whereas vitamin E and idebenone reduced markedly the number of fluorescent cells to control levels even added with 10 mM Glu. These results indicate that oxidative stress due to loss of cellular levels of GSH is one mechanism whereby Glu/quisqualate exert cytotoxicity and suggest that centrally active antioxidants may reduce neuronal damage in pathologic conditions associated with excessive Glu release.

Animals↗
PubMed1989

Effects of continuous infusion of cholinergic drugs on memory impairment in rats with basal forebrain lesions.

The effects of continuous infusion of cholinergic drugs on behavior in normal rats and on impaired acquisition and retention of several behavioral tasks in rats with basal forebrain (BF) lesions were investigated. Physostigmine and oxotremorine were infused continuously with a miniosmotic pump for 3 weeks, and the performance on several different behavioral tasks was examined during the infusion. In normal rats high doses of physostigmine (4 and 8 mg/kg/day s.c.) produced significant changes in general behavior and impaired performance in the Morris water maze. Oxotremorine (0.25-2 mg/kg/day s.c.) had no significant effects on general behavior or cognitive performance in normal rats, although severe cataracts developed at the high dose (4 mg/kg/day). A deficit in motor habituation in rats with BF lesions produced by bilateral injections of ibotenic acid (30 nmol on each side) was improved markedly by the chronic administration of physostigmine (2 mg/kg/day) and oxotremorine (1 mg/kg/day). BF lesions produced severe impairments in acquisition and retention in a passive avoidance task, an active avoidance and the Morris water maze, which was characterized by a marked disruption of retention. The impairment was also ameliorated markedly by the cholinergic drugs, whereas other behavioral impairments were not affected by the drugs. These results indicate that the continuous administration of cholinergic drugs produces a marked improvement of acquisition and retention in rats with BF lesions, and suggest that the impairment in cognitive performance, especially with regard to retention, caused by BF lesions is due to the disruption of the BF-cortical cholinergic pathway.

Acetylcholinesterase↗
PubMed1988

Involvement of phospholipase A2 in the regulation of [3H]hemicholinium-3 binding.

We have examined the effects of exogenous phospholipase A2 (PLA2) on the sodium-dependent high-affinity choline uptake mechanism as assessed by the specific binding of [3H]hemicholinium-3 ([3H]HCh-3). Incubation of striatal synaptic membranes with bee venom PLA2 resulted in a concentration-dependent increase in the specific binding of [3H]HCh-3. The effect of PLA2 on [3H]HCh-3 binding was inhibited by quinacrine, a PLA2 inhibitor, and by removal of calcium. Scatchard analysis revealed that the observed changes in binding reflected a 2-fold increase in both the capacity and affinity of [3H]HCh-3 for its binding site. Choline and N-butylcholine inhibited the specific binding of [3H]HCh-3 in both control and PLA2-treated membranes with similar potency. When a low concentration of PLA2 was incubated with the striatal synaptosomes, a small but significant increase in high-affinity [3H]choline uptake was observed. However, higher concentrations of PLA2, which further increased the specific binding of [3H]HCh-3, caused a reduction of [3H]choline uptake, apparently due to disruption of synaptosomal integrity by PLA2. Finally, potassium depolarization- and PLA2-induced increases in specific [3H]HCh-3 binding were not additive. These results suggest a possible role for endogenous PLA2 in the calcium-dependent regulation of sodium-dependent high-affinity choline uptake.

Animals↗
PubMed1988

Glutamate cytotoxicity in a neuronal cell line is blocked by membrane depolarization.

To understand better the proximate mechanism involved in the excitotoxic response to L-glutamate (Glu), we have exploited the Glu receptor present in the N18-RE-105 neuroblastoma-embryonic retinal hybrid cell line. These cells undergo lysis dependent on extracellular Ca2+ when exposed to Glu. We now report that the depolarizing action of Glu is not responsible for its cytotoxic effects. Furthermore, depolarization of these cells with elevated K+, ouabain or veratridine does not cause cytotoxicity but rather protects against the cytotoxic effects of Glu. Our results may implicate a role for voltage-sensitive Ca2+ channels (VSCCs) in cytotoxicity, and depolarization-induced inactivation of VSCCs (Nature (Lond.), 316 (1985) 440-443) as a protection against Glu receptor agonists. Our findings demonstrate a clear dissociation between depolarization and the neuronal degeneration caused by Glu.

Animals↗
PubMed1988

Transient postnatal elevation of serotonin levels in mouse neocortex.

Serotonin (5-HT), norepinephrine (NE) and 5-hydroxyindoleacetic acid (HIAA) levels were measured during ontogeny of frontoparietal cortex in Balb/C mice by high-pressure liquid chromatography (HPLC) with electrochemical detection. Unlike NE, the concentration of 5-HT was transiently elevated to more than twice the adult level during the first postnatal week; this was accompanied by increased HIAA content comparable to the adult, indicating elevated levels of 5-HT release. Since a transient hyperplasia of 5-HT-immunoreactive fibers and uptake sites has been observed previously in the same cortical areas, the transient elevation of 5-HT levels may play an important role in shaping early postnatal morphogenetic events in neocortex.

Aging↗
PubMed1988

Neonatal lesions of the basal forebrain cholinergic neurons result in abnormal cortical development.

The effect of electrolytic lesions of the neonatal forebrain on the morphogenesis of the mouse neocortex has been examined. Balb/C mice were lesioned unilaterally within 24 h of birth. The development of cortical cytoarchitecture was assessed in Nissl-stained sections, and the levels of presynaptic markers for cholinergic, noradrenergic and serotonergic afferents were measured in the fronto-parietal cortex ipsilateral and contralateral to the lesion at various postnatal ages and in adulthood. The basal forebrain (nBM) lesion resulted in a transient but severe reduction of cortical cholinergic markers and in abnormal cortical cytoarchitecture. Cytoarchitectural abnormalities were expressed as delay in the emergence of differentiated cell populations and affected sequentially more superficial layers with maturation following lesion. Furthermore, the location and extent of these morphologic abnormalities appeared to correlate with the degree of cholinergic denervation. Cortical monoamines were also temporarily reduced as a result of the lesion; however, pharmacologic lesions of the monoaminergic projections alone did not result in the abnormal cortical cytoarchitecture. Thus, the basal forebrain cholinergic projection appears to serve a role in regulating cortical differentiation.

5,7-Dihydroxytryptamine↗
PubMed1988

Development of beta 1 and beta 2 adrenergic receptors in baboon brain: an autoradiographic study using [125I]iodocyanopindolol.

[125I]iodocyanopindolol (ICYP) autoradiography was used to investigate the temporal development and distribution of beta 1 and beta 2 receptors in brains of baboons at ages embryonic day 100 (E100), full-term gestation (El80), and 3 years. In all brain regions examined, with the exception of the hippocampus, binding to beta 1 receptors exceeded that to beta 2 receptors. The highest densities of beta 1 receptors were found in the caudate nucleus, putamen, globus pallidus, substantia nigra, and cerebral cortex; intermediate receptor densities were observed in most nuclei of thalamus, and the lowest concentrations were in the hippocampus. At E100, beta receptors were identified in the striatum, globus pallidus, and thalamus. During maturation, the number of beta 1 receptors declined in cortical areas but increased in the head of the caudate and putamen. Significant differences in the developmental distribution of beta receptors during development were also detected: at E100 and E180 beta 1 receptors appeared as patches in the caudate and putamen, but by 3 years of age they were more homogeneously distributed in both regions; changes also occurred in the distribution of binding within cortical layers. Autoradiograms of [125I]ICYP and [3H]mazindol binding show overlapping patches of labeling in the E180 striatum, suggesting a possible developmental association between beta receptors and dopamine high-affinity uptake carrier sites. This study demonstrates that noradrenergic receptors in the primate forebrain undergo significant developmental reorganization with regional variations.

Aging↗
PubMed1988

A re-examination of the interaction of N-acetyl-L-aspartyl-L-glutamate with a subpopulation of rat brain membrane L-[3H]glutamate binding sites.

The neuropeptide, N-acetyl-L-aspartyl-L-glutamate (NAAG) has been reported to act at a subpopulation of putative quisqualate receptors on the basis of its competitive inhibition of specific binding of L-[3H]glutamate and on the basis of quisqualate-sensitive binding of [3H]NAAG radiolabeled on the glutamate moiety. Recently, a membrane-bound metallopeptidase, N-acetylated alpha-linked acidic dipeptidase (NAALADase), which cleaves NAAG to N-acetyl-aspartate (NAA) and glutamate, has been characterized and has been shown to exhibit optimal activity under incubation conditions used to measure NAAG binding sites. Accordingly, we have examined whether NAALADase mediated release of glutamate from NAAG might account for the receptor binding results. Insertion of empirically derived kinetic constants for NAALADase hydrolysis of NAAG into a theoretical model for peptide-derived glutamate inhibition of [3H]glutamate binding reveals that NAAG can appear to displace, with high affinity, a subpopulation of [3H]glutamate labeled sites, and yet have little or no intrinsic activity for these sites. Furthermore, empirical data relating time and protein concentration to NAAG displacement of [3H]glutamate binding are more consistent with a proteolytic mechanism rather than an equilibrium interaction of the peptide with membrane receptors. Coupled with recent findings attributing the Cl- -dependent glutamate binding to a sequestration phenomenon, these results demonstrate that the inferred action of NAAG at glutamate synaptic receptors through previous radioligand binding studies is probably incorrect. Furthermore, these studies offer a general caution regarding the conclusions about subpopulations of receptors drawn from receptor binding assays conducted with ligands, which may be structurally modified by enzymatic processes.

Animals↗
PubMed1988

Neonatal enucleations reduce specific activity of acetylcholinesterase but not choline acetyltransferase in developing rat visual cortex.

Infant rats were subjected to unilateral or bilateral enucleation or sham lesions on the day of birth. On postnatal day 13 or 14, tissue blocks from cortex were assayed for acetylcholinesterase (AChE) and choline acetyltransferase (ChAT). Bilateral enucleation resulted in a decrease in specific activity of AChE in occipital cortex, as compared with control animals. Unilateral enucleation resulted in a decrease of AChE activity in the hemisphere contralateral to the enucleated orbit. However, neither type of enucleation resulted in significant changes of ChAT specific activity. These data suggest that reductions in AChE activity resulting from neonatal enucleations are not due to a direct involvement of cholinergic afferents to visual cortex.

Acetylcholinesterase↗
PubMed1988

Calcium-dependent glutamate cytotoxicity in a neuronal cell line.

Membranes from the neuroblastoma x embryonic retina cell hybrid cell line, N18-RE-105, bind L-[3H]glutamate with a pharmacologic profile consistent with a 'quisqualate-type' brain L-glutamate receptor. We describe here the cytotoxic effect of L-glutamate receptor agonists on intact N18-RE-105 cells. Cytotoxicity was quantitated by measurement of the release of the cytosolic enzyme, lactate dehydrogenase, into the culture medium after addition of L-glutamate and its analogs to the cell culture medium. L-Glutamate (10 mM) and its confirmationally restricted analogs, quisqualate (1 mM) and ibotenate (10 mM), caused cell lysis. In contrast, similar analogs which do not bind to N18-RE-105 cell membranes (kainic acid, N-methyl-D,L-aspartic acid and gamma-aminobutyric acid) were not cytotoxic. L-Glutamate-induced cytotoxicity was eliminated when calcium-free medium was used. Addition of inorganic or organic calcium channel antagonists also reduced the cytotoxicity of L-glutamate, even when 1.8 mM calcium was present in the medium. Cadmium chloride (10 microM) completely blocked L-glutamate toxicity, whereas manganese chloride (150 microM) and lanthanum chloride (25 microM) reduced toxicity by greater than 50%. Dihydropyridine voltage-sensitive calcium channel agonists or antagonists, had little or no significant effect on L-glutamate-induced toxicity. In contrast, the verapamil derivatives, D600 and D888, and the diltiazem derivative, MDL 12,330A reduced L-glutamate toxicity by greater than 50%. These results suggest that a subtype of voltage-sensitive calcium channels is involved in the mechanism of L-glutamate receptor mediated cytotoxicity in this cell line.

Calcium↗
PubMed1988

The role of calcium in the regulation of [3H]hemicholinium-3 binding sites in rat brain.

The role of calcium in the regulation of sodium-dependent high-affinity uptake of choline was assessed in vitro in slices of the rat brain, by measuring the specific binding of [3H]hemicholinium-3 ([3H]HCh-3) and the uptake of [3H]choline. Depolarization with potassium of slices of hippocampus, cortex, or striatum significantly increased the specific binding of [3H]HCh-3 when compared to control slices. However, the observed potentiation of specific binding of [3H]HCh-3 was markedly inhibited by the removal of calcium from the incubation medium in cortex or hippocampus, but not in slices of striatum. Alterations in the uptake of [3H]choline directly paralleled the observed changes in the specific binding of [3H]HCh-3 in striatum of the rat and were unaffected by the reduction of calcium in the incubation medium. The inorganic calcium channel antagonists, cadmium and cobalt, but not magnesium, zinc, manganese or lanthanum, significantly inhibited the 40 mM potassium chloride-induced stimulation of the binding of [3H]HCh-3 in the striatum. Finally, the calcium ionophore A23187 significantly increased the binding of [3H]HCh-3 in slices of striatum, either in the presence or absence of calcium in the bathing medium. This study demonstrates regional differences in the role of extracellular calcium in the regulation of the uptake of choline and suggests the involvement of intracellular release of calcium in the in vitro regulation of the sodium-dependent high-affinity uptake of choline in the striatum.

Animals↗
PubMed1988

A long-acting cholinesterase inhibitor reverses spatial memory deficits in mice.

The effects of the long-acting acetylcholinesterase (AChE) inhibitor, galanthamine, on spatial memory were investigated in mice. Mice received ibotenic acid or sham lesions to the nucleus basalis magnocellularis (nBM). Groups of nBM-lesioned and control mice were then trained on a modified Morris swim maze task. Each mouse was first placed on a platform and then into quadrants of the swim tank in a random order. Time required to find the hidden platform was measured. In different phases of testing, the animal had to find a platform that either remained in the same quadrant (reference memory component) or was moved daily (working memory component). The nBM-lesioned mice took significantly longer to find the platform as compared to controls on the working, but not on the reference, memory component of the task. Galanthamine (5.0 mg/kg, IP), given 3.5 hours before testing, improved performance on the working memory task in nBM-lesioned mice by 70% and strikingly impaired performance in controls. Galanthamine's ability to reverse cognitive deficits induced by nBM lesions and its comparatively long half-life suggest that it may be effective in treating the central cholinergic deficits in Alzheimer's disease patients.

Animals↗
PubMed1988

Genetic mapping and analysis of somatostatin expression in Snell dwarf mice.

Mice homozygous for the gene dwarf (dw) have elevated levels of somatostatin (SS) in extra-hypothalamic brain regions. By in situ hybridization, increased levels of SS mRNA were observed in regions shown previously to contain higher levels of the SS peptide. Thus, the rate of transcription and/or the stability of SS mRNA are affected by the dw mutation. Since both dw and the gene encoding SS, Smst, are located on mouse chromosome 16, two backcrosses segregating dw and Smst were used to determine whether dw is an allele of Smst. In one backcross, an inbred strain derived from the subspecies Mus musculus molossinus was used to provide a high degree of DNA sequence polymorphism. The gene order and map distances determined on this backcross were: (centromere) - Prm-1 - 7 - Igl-1 - 3 - Smst - 29 - dw - 15 - Sod-1 - 4 - Ets-2, demonstrating clearly that Smst and dw are distinct genes. Additional evidence against a primary role for SS excess in the pathogenesis of dw/dw mice was obtained by injecting normal newborn mice with a potent SS analog (cyclo II). In contrast to the pattern of cell loss observed in the dwarf anterior pituitary, the pituitaries of injected mice were indistinguishable from normal controls, further suggesting that the Smst locus is not the primary site of dw gene action.

Alleles↗
PubMed1988

Quantitation of N-acetyl-aspartyl-glutamate in microdissected rat brain nuclei and peripheral tissues: findings with a novel liquid phase radioimmunoassay.

Antibodies were raised in rabbits against the neuropeptide N-acetyl-L-aspartyl-L-glutamate (NAAG) coupled to bovine serum albumin via a carbodiimide linkage. One of these rabbit antisera, which preferentially recognizes coupled NAAG-like immunoreactivity (LIR), has been previously used to immunocytochemically localize NAAG-LIR. We have now employed a second of these antisera, which preferentially recognizes free NAAG, to develop a competitive liquid phase radioimmunoassay (RIA). Using this assay, we were able to detect picomole amounts of NAAG in rat tissue extracts. The specificity of the assay revealed a 60-fold greater affinity of the antibody for NAAG over N-acetyl-aspartate (NAA) and greater than one million-fold specificity for NAAG over both aspartate and glutamate. High-pressure liquid chromatographic (HPLC) separation of tissue extracts yielded only two detectable peaks of NAAG-LIR in collected fractions and these co-chromatographed with NAAG and NAA. NAAG levels determined by this liquid phase RIA and by HPLC were essentially identical after correction for the presence of NAA crossreactivity. The antibody that preferentially recognizes coupled NAAG was used to immunocytochemically localize NAAG-LIR to the red nucleus, the facial nucleus, the dorsal raphe, and the locus coeruleus. To further confirm this localization of NAAG, these and other nuclei were microdissected and levels of NAAG were determined by liquid phase RIA. Nuclei which stained intensely were found to contain high levels of NAAG by RIA and between 60 and 100% of this NAAG-LIR co-chromatographed with NAAG. These results support our previous conclusion that NAAG is co-localized in noradrenergic, serotonergic and cholinergic neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗