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L J Martin

Publications and source records attributed to L J Martin.

At least 91 records · Page 5Linked to original sources
PubMed1998

Mammographic densities and breast cancer risk.

Variations between individuals in the radiographic appearance, or mammographic pattern, of the female breast arise because of differences in the relative amounts and X-ray attenuation characteristics of fat and connective and epithelial tissue. Studies using quantitative methods of assessment have consistently shown these variations to be strongly related to risk of breast cancer. Individuals with extensive areas of radiologically dense breast tissue on the mammogram have been found to have a risk of breast cancer that is four to six times higher than women with little or no density. In this paper, we propose a model for the relationship of mammographic densities to risk of breast cancer. We propose that the risk of breast cancer associated with mammographically dense breast tissue is due to the combined effects of two processes: cell proliferation (mitogenesis), induced by growth factors and sex hormones and influenced by reproductive risk factors for breast cancer; and damage to the DNA of dividing cells (mutagenesis) by mutagens generated by lipid peroxidation. We review the evidence that each of these processes is associated with mammographic densities and propose further work that we believe should be done to clarify these relationships.

Journal Article↗
PubMed1998

Serum leptin levels and energy expenditure in normal weight women.

To investigate whether circulating leptin levels are associated with energy expenditure in healthy humans, doubly labeled water energy measurements and food intake assessment were carried out in 27 women (mean age, 48.6 years; weight, 61.9 kg; body mass index, 23.2). Energy expenditure was determined over 13 days. Food intake was measured by 7-day food records. Leptin was measured by radioimmunoassay. Leptin level was strongly associated with percentage body fat (r = 0.59; p < 0.001), fat mass (r = 0.60; p < 0.001), and body mass index (r = 0.41; p = 0.03), but no correlation was observed with energy expenditure (r = 0.02; p = 0.93). After controlling for percentage body fat, a positive association of leptin level with energy expenditure of marginal significance (p = 0.06) was observed. There were no significant univariate associations of age, physical activity, lean body mass, height, or dietary variables with leptin level. When controlling for body fat, a significant positive correlation was observed for percent energy from carbohydrate and negative correlations with dietary fat and alcohol intake. These findings confirm previous associations between leptin and body fat content and suggest a relationship between serum leptin and energy expenditure level in healthy humans.

Body Weight↗
PubMed1998

Genetic and environmental components of thyroxine variation in Mennonites from Kansas and Nebraska.

Thyroxine is an endocrine hormone that regulates cellular and organismic metabolism. Current research on thyroxine has primarily examined its adaptive potential and genetic inheritance patterns. To date, no studies have attempted to investigate the interaction between the genetic and environmental components of thyroxine variation. This approach is useful because hormones are on feedback regulation; thus interaction occurs between the environment and gene expression. The purposes of this research are to characterize the genetic and environmental components of thyroxine variation using univariate statistics and to estimate the genetic and cultural heritabilities through path analysis. For univariate analyses, analyses of variance are used to determine whether or not age, sex, or community affiliation are covariates of thyroxine level. Significant differences existed in thyroxine level based on sex and community affiliation (p < 0.05). The genetic and environmental components of thyroxine variation were partitioned through path analysis. Heritability was estimated at 0.317 +/- 0.109 for the genetic component and at 0.060 +/- 0.029 for the environmental component. The environmental variables that contributed to the variation in thyroxine level were caffeine consumption, blood calcium level, and biceps skinfold thickness.

Adolescent↗
PubMed1997

Glutamate transporter protein subtypes are expressed differentially during rat CNS development.

Extracellular glutamate concentrations are regulated by glial and neuronal transporter proteins. Four glutamate transporter subtypes have been identified in rat brain; GLAST and GLT-1 are primarily astrocytic, whereas EAAC1 and EAAT4 are neuronal. Using immunoblotting and immunohistochemistry with subtype-specific antipeptide antibodies, we examined the protein expression and regional and cellular localization of each glutamate transporter subtype in embryonic and postnatal rat CNS. Each transporter had a specific pattern of expression. GLAST immunoreactivity was low prenatally but became enriched in cerebellar Bergmann glia early postnatally and then was also present in forebrain later postnatally. The post-translational modification of GLAST was unique among the subtypes; glycosylated GLAST increased with maturation, whereas nonglycosylated protein decreased in abundance postnatally. GLT-1 was present in fetal brain and spinal cord, with expression progressively increasing to adult levels throughout the neuraxis by postnatal day 26. Transient expression of GLT-1 immunoreactivity along axonal pathways was observed prenatally, in contrast to the exclusive localization of GLT-1 to astrocytes in the adult CNS. EAAC1, localized to neurons, was enriched in forebrain, diencephalon, and hindbrain during prenatal and postnatal development. EAAC1 expression was greater in newborn brain compared with adult brain. EAAT4 had a region-specific distribution; EAAT4 was mainly in cerebellum, localized to Purkinje cells, with much lower levels in forebrain. EAAT4 levels increased in cerebellum with age. We conclude that during CNS development the expression of glutamate transporter subtypes is differentially regulated, regionally segregated, and coordinated.

ATP-Binding Cassette Transporters↗
PubMed1997

Ontogeny of non-NMDA glutamate receptors in rat barrel field cortex: II. Alpha-AMPA and kainate receptors.

The ontogeny of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and kainate (KA) glutamate receptors in rat barrel field cortex was characterized by using receptor autoradiography and immunocytochemistry. A somatotopic pattern of AMPA receptors with fewer [3H]AMPA sites in barrel centers than in surrounding cortex did not emerge until postnatal day 10 (P10). After reaching a peak density at P14, the density of [3H]AMPA receptors declined in both barrel centers and surrounding cortex. Compared with AMPA receptors, the density of [3H]KA sites at all ages was low, a somatotopic expression of [3H]KA sites was missing, and the developmental curve for [3H]KA sites was more shallow than that for [3H]AMPA binding sites. A differential ontogeny of AMPA and KA receptors in barrel field cortex was also demonstrated in immunocytochemical studies with antibodies to the AMPA receptor subunits GluR1 and GluR2,3 and the KA receptor subunits GluR6,7. GluR1 and GluR2,3 staining was more dense in barrel septa than in barrel centers; this pattern persisted into adulthood. GluR1 and GluR2,3 receptors were localized to cell bodies and dendrites as well as the neuropil, but different populations of cortical neurons expressed these receptors. At P10, KA receptor subunits GluR6,7 exhibited a contrasting pattern to that of AMPA receptor subunits, with slightly more neuropil staining in barrel centers than in surrounding cortex. After that point, the somatotopic pattern of GluR6,7 subunit expression was lost. The contrasting developmental patterns of expression of the AMPA and KA receptors in the barrel field suggest that they may play different roles in the whisker-to-barrel pathway.

Aging↗
PubMed1997

Ontogeny of non-NMDA glutamate receptors in rat barrel field cortex: I. Metabotropic receptors.

The ontogeny of metabotropic excitatory amino acid receptors (mGluRs) in rat barrel field cortex was characterized by using receptor autoradiography and immunocytochemistry to test the hypothesis that changes in mGluR expression coincide with the emergence of somatotopic patterns in this region. On postnatal days 1 (P1) and 3, [3H]glutamate binding to mGluRs was not distributed in a somatotopic pattern. By P5, mGluRs exhibited a whisker-related pattern, with higher densities of mGluRs in barrel centers than in surrounding cortex. Between P5 and P14 and at P60, the overall binding density remained higher in barrels than in surrounding cortex. At P60, a somatotopic pattern of binding was not apparent. The majority of mGluR sites in the barrel field were blocked by the metabotropic agonist trans-1-aminocyclopentane-1,3-dicarboxylic acid but were not significantly displaced by quisqualate. Immunocytochemical studies of phosphoinositide-linked mGluRs, mGluR5 and mGluR1alpha, showed that the developmental expression of mGluR5 mirrored that of the pattern of autoradiographically labeled mGluRs. The immature barrel field (ages P5-P14) was enriched in mGluR5, with greater concentrations of mGluR5 immunoreactivity in barrels than in surrounding cortex. Within barrel centers, mGluR5 was localized within the neuropil, on the surfaces of cell bodies and dendrites in layer IV. A somatotopic pattern of mGluR5 immunoreactivity persisted into adulthood, although the pattern was less pronounced after P14. In contrast, mGluR1alpha was never localized in a somatotopic pattern in barrel field cortex. We conclude from the developmental localization of mGluRs that the spatiotemporal regulated expression of these receptors may influence barrel maturation and plasticity.

Aging↗
PubMed1997

Excitotoxic neuronal death in the immature brain is an apoptosis-necrosis morphological continuum.

Glutamate-induced excitotoxicity is a clinically relevant degenerative process that causes selective neuronal death by mechanisms that remain unclear. Cell death is usually classified as apoptotic or necrotic based on biochemical and morphological criteria. Excitotoxic lesions in the adult rat striatum result in neuronal death associated with apoptotic DNA laddering despite a necrotic appearance of neurons ultrastructurally. This suggests that apoptosis and necrosis may not be mutually exclusive modes of cell death. Here, we characterized normal developmental cell death in the newborn rat brain with respect to DNA fragmentation patterns and ultrastructural morphology to establish a standard for apoptosis in the nervous system, and we concluded that it is essentially indistinguishable from apoptosis described in other tissues. We then investigated whether brain maturity could influence the morphology of neuronal death in vivo in the excitotoxically lesioned newborn rat forebrain. Kainic acid induced DNA laddering and death of neurons exhibiting a variety of morphologies, ranging from necrosis to apoptosis. In neurons that were dying by apoptosis, morphologic changes were characterized by a highly ordered sequence of organelle abnormalities, with swelling of endoplasmic reticulum and Golgi vesiculation preceding most nuclear changes and mitochondrial disruption. We concluded that brain maturity influences the morphologic phenotype of neurodegeneration and that excitotoxic neuronal death in the immature brain is not a uniform event but, rather, a continuum of apoptotic, necrotic, and overlapping morphologies. This excitotoxic paradigm might prove useful for analyzing the mechanisms that govern cell death under physiological and pathological conditions.

Animals↗
PubMed1997

Non-NMDA and NMDA receptor-mediated excitotoxic neuronal deaths in adult brain are morphologically distinct: further evidence for an apoptosis-necrosis continuum.

Apoptosis and necrosis are generally recognized as two distinct pathways of cell death, based on biochemical and morphological characteristics. Despite rapid advances in elucidating molecular mechanisms of cell death, little is known about the morphological progression of death in neurons and the relationship between different mechanisms of neuronal death and the resulting subcellular alterations. With excitotoxicity, a clinically relevant model of neuronal death, apoptotic DNA laddering and morphologic evidence of necrosis can occur simultaneously in the same region of adult brain. Here, we tested the hypothesis that activation of N-methyl-D-aspartic acid (NMDA) and non-NMDA glutamate receptors (GluR) results in a spectrum of morphologically distinct phenotypes of neuronal death, with apoptosis and necrosis as its endpoints. The ultrastructural morphologies of newborn and adult neurons at different times following intrastriatal injections of non-NMDA and NMDA GluR agonists were compared to apoptosis, as established during naturally occurring neuronal death in the developing rat brain. Excitotoxic neuronal death in newborn striatum was morphologically indistinguishable from developmental apoptosis. In the adult, non-NMDA receptor agonist-induced neuronal death was characterized by extensive chromatin condensation that was reminiscent of, but not identical to, apoptosis during normal development. In contrast, quinolinate, an NMDA receptor agonist, produced only minor chromatin clumping and rapid cytoplasmic disintegration, which is suggestive of necrosis. These findings support the concept that degenerative phenotypes of excitotoxically injured neurons are influenced by the degree of brain maturity and GluR subtype stimulation, independent of the severity of excitotoxic insult, along a morphological continuum or gradient ranging from apoptosis to necrosis.

Animals↗
PubMed1997

Primary sensory and forebrain motor systems in the newborn brain are preferentially damaged by hypoxia-ischemia.

Cerebral hypoxia-ischemia causes encephalopathy and neurologic disabilities in newborns by unclear mechanisms. We tested the hypothesis that hypoxia-ischemia causes brain damage in newborns that is system-preferential and related to regional oxidative metabolism. One-week-old piglets were subjected to 30 minutes of hypoxia and then seven minutes of airway occlusion, producing asphyxic cardiac arrest, followed by cardiopulmonary resuscitation and four-day recovery. Brain injury in hypoxic-ischemia piglets (n = 6) compared to controls (n = 5) was analyzed by hematoxylin-eosin, Nissl, and silver staining, relationships between regional vulnerability and oxidative metabolism were evaluated by cytochrome oxidase histochemistry. Profile counting-based estimates showed that 13% and 27% of neurons in layers II/III and layers of somatosensory cortex had ischemic cytopathology, respectively; CA1 neuronal perikarya appeared undamaged, and < 10% of CA3 and CA4 neurons were injured; and neuronal damage was 79% in putamen, 17% in caudate, but nucleus accumbens was undamaged. Injury was found preferentially in primary sensory neocortices (particularly somatosensory cortex), basal ganglia (predominantly putamen, subthalamic nucleus, and substantia nigra reticulata), ventral thalamus, geniculate nuclei, and tectal nuclei. In sham piglets, vulnerable region generally had higher cytochrome oxidase levels than less vulnerable areas. Postischemic alterations in cytochrome oxidase were regional and laminar, with reductions (31-66%) occurring in vulnerable regions and increases (20%) in less vulnerable areas. We conclude that neonatal hypoxia-ischemia causes highly organized, system-preferential and topographic encephalopathy, targeting regions that function in sensorimotor integration and movement control. This distribution of neonatal encephalopathy is dictated possibly by regional function, mitochondrial activity, and connectivity.

Animals↗
PubMed1997

Hypoxia-ischemia causes abnormalities in glutamate transporters and death of astroglia and neurons in newborn striatum.

The neonatal striatum degenerates after hypoxia-ischemia (H-I). We tested the hypothesis that damage to astrocytes and loss of glutamate transporters accompany striatal neurodegeneration after H-I. Newborn piglets were subjected to 30 minutes of hypoxia (arterial O2 saturation, 30%) and then 7 minutes of airway occlusion (O2 saturation, 5%), producing cardiac arrest, followed by cardiopulmonary resuscitation. Piglets recovered for 24, 48, or 96 hours. At 24 hours, 66% of putaminal neurons were injured, without differing significantly thereafter, but neuronal densities were reduced progressively (21-44%). By DNA nick-end labeling, the number of dying putaminal cells per square millimeter was increased maximally at 24 to 48 hours. Glial fibrillary acidic protein-positive cell body densities were reduced 48 to 55% at 24 to 48 hours but then recovered by 96 hours. Early postischemia, subsets of astrocytes had fragmented DNA; later postischemia, subsets of astrocytes proliferated. By immunocytochemistry, glutamate transporter 1 (GLT1) was lost after ischemia in the astroglial compartment but gained in cells appearing as neurons, whereas neuronal excitatory amino acid carrier 1 (EAAC1) dissipated. By immunoblotting, GLT1 and EAAC1 levels were 85% and 45% of control, respectively, at 24 hours of recovery. Thus, astroglial and neuronal injury occurs rapidly in H-I newborn striatum, with early gliodegeneration and glutamate transporter abnormalities possibly contributing to neurodegeneration.

ATP-Binding Cassette Transporters↗
PubMed1997

Assessment of a food frequency questionnaire as a screening tool for low fat intakes.

This study tested the ability of a self-administered food frequency questionnaire (FFQ) to identify women with low fat intakes. FFQs were completed by 95 control participants of a dietary trial at a mean 2.9 +/- 0.8 years post-randomization. Subjects were selected in approximately equal numbers from women who were low-fat eaters (< or = 30% of energy from fat) and high-fat eaters (> 30% of energy from fat). Percentage energy from fat derived from food records and FFQ were similar in both the low- and high-fat eaters. Percentage of energy from carbohydrate and total grams of carbohydrate (low-fat eaters only) were slightly higher measured by FFQ than by food records, and percentage of energy from protein was slightly lower. The correlation between nutrient intake measured by FFQ and food records for the whole group was 0.74 for percentage of energy from fat, 0.50 for total fat, 0.59 for percentage of energy from carbohydrate, 0.43 for total carbohydrate, 0.53 for percentage of energy from protein, 0.27 for total protein, and 0.32 for energy intake. Correlations were slightly lower when the low- and high-fat eaters were examined separately. The area under the receiver operating characteristic (ROC) curve, 0.83, was significantly above 0.5 (p < < 0.001), indicating that the FFQ discriminated between low- and high-fat eaters significantly better than chance. The FFQ cutoff point of 30% of energy from fat had a true positive rate of 0.63 and false positive rate of 0.24. The use of this cutoff point for screening would result in the loss of 36% of potential subjects and an estimated increase in baseline percentage of energy from fat intake of 2.3 percentage points.

Adult↗
PubMed1997

Cellular and synaptic localization of the neuronal glutamate transporters excitatory amino acid transporter 3 and 4.

Glutamate transport is a primary mechanism for the synaptic inactivation of glutamate. Excitatory amino acid transporter 4 (EAAT4) is a novel glutamate transporter with properties of a ligand-gated chloride channel that was recently cloned from human brain. The present study was an investigation of the protein expression and cellular localization of EAAT4 in human and rat brain, and comparison with another neuronal glutamate transporter, EAAT3 (rabbit excitatory amino acid carrier 1; EAAC1). Regional immunoblot analysis of EAAT4, using a monospecific oligopeptide (carboxy-terminal) affinity-purified polyclonal antibody, revealed that the protein was restricted to the central nervous system. The EAAT4 protein was largely expressed in cerebellum, with a much lower expression in hippocampus, neocortex, striatum, brain stem and thalamus. Immunohistochemical studies showed intense EAAT4 immunoreactivity in the human and rat cerebellar Purkinje cells with a somatodendritic localization. Other brain regions including neocortex, hippocampus, striatum showed faint neuropil staining of EAAT4. Immunogold localization identified EAAT4 protein at plasma membranes of Purkinje cell dendrites and spines. In the hippocampus and neocortex, EAAT4 immunoreactivity was found mainly at small calibre dendrites. Rarely, EAAT4 immunoreactivity was found in astrocytic cell processes of forebrain. In the cerebellum, EAAT4 localization partly overlapped with the neuronal localization of EAAT3 (EAAC1). Immunoreactivity for EAAT3 was enriched in the somatodendritic compartment of the Purkinje cells like EAAT4, but EAAT3 was also found in Purkinje cell axons and in boutons in deep cerebellar nuclei, as well as in granular cells and stellate cells. Our results indicate that EAAT4 protein is largely localized to cerebellar cortex and lower levels of EAAT4 protein are present in forebrain by immunoblot and immunohistochemistry. Both neuronal glutamate transporter EAAT3 (EAAC1) and EAAT4 are located at somatodendritic compartment of Purkinje cells, and probably contribute to glutamate re-uptake mechanisms at Purkinje cell synapses.

Aged↗
PubMed1997

Feasibility of obtaining breast epithelial cells from healthy women for studies of cellular proliferation.

Increased dietary fat intake and rate of breast epithelial cell proliferation have each been associated with the development of breast cancer. The goal of this study was to measure the effect of a low fat, high carbohydrate diet on the rate of breast epithelial cell proliferation in women at high risk for breast cancer. Women were recruited from the intervention and control groups of a randomized low fat dietary intervention trial, breast epithelial cells were obtained by fine needle aspiration, and cell proliferation was assessed in these samples using immunofluorescent detection of Ki-67 and PCNA. The effects of needle size and study group on cell yield and cytologic features of the cells were also examined. Fifty three women (20 in the intervention group and 33 in the control group) underwent the biopsy procedure. Slides from 38 subjects were stained for Ki-67 and from 14 subjects for PCNA. No cell proliferation (fluorescence) was detected for either Ki-67 or PCNA in any of the slides. Epithelial cell yield and number of stromal fragments were greater with a larger needle size. Numbers of stromal fragments and bipolar naked nuclei were greater in the low fat as compared to the control group but no differences in epithelial cell yield were observed between the two groups. This study confirms that fine needle aspiration biopsy is a feasible method of obtaining epithelial cells from women without discrete breast masses, but suggests that cell proliferation cannot be assessed using Ki-67 and PCNA in such samples.

Biomarkers↗
PubMed1997

Effects of a low-fat high-carbohydrate diet on plasma sex hormones in premenopausal women: results from a randomized controlled trial. Canadian Diet and Breast Cancer Prevention Study Group.

We are conducting a long-term randomized controlled trial to determine if intervention with a low-fat high-carbohydrate diet reduces breast cancer risk. The present study examines the effects of 2 years of dietary intervention on serum sex hormone levels in premenopausal women. Subjects with extensive mammographic densities were enrolled in a dietary intervention trial. The intervention involved intensive individual counselling aimed at reducing total dietary fat to 15% of calories. Control subjects received general advice about diet but were not counselled to change their fat intake. Serum sex hormone levels were measured in 220 premenopausal subjects at entry and 2 years after randomization. Two years after randomization oestradiol levels were 20% (70 pmol l(-1)) lower (P = 0.04) and progesterone levels were 35% (1.0 nmol l(-1)) lower (P = 0.004) and follicle-stimulating hormone (FSH) levels were 7% (1 IU) higher (P = 0.38) in the intervention group than in the control group. The FSH-oestradiol ratio was 13% higher in the intervention group (P = 0.18). Samples analysed accounting for the timing of the blood sample in relation to the menstrual cycle showed that, in the intervention group, oestradiol and progesterone levels were lower and FSH levels higher in subjects with blood samples taken more than 30 days after the last menstrual period. Because of the strong evidence linking ovarian hormonal activity to breast cancer risk, these results suggest that a low-fat high-carbohydrate diet may reduce risk of breast cancer by reducing exposure to ovarian hormones that are a stimulus to cell division in the breast.

Adult↗
PubMed1997

A deletion in the bovine myostatin gene causes the double-muscled phenotype in cattle.

An exceptional muscle development commonly referred to as 'double-muscled' (Fig. 1) has been seen in several cattle breeds and has attracted considerable attention from beef producers. Double-muscled animals are characterized by an increase in muscle mass of about 20%, due to general skeletal-muscle hyperplasia-that is, an increase in the number of muscle fibers rather than in their individual diameter. Although the hereditary nature of the double-muscled condition was recognized early on, the precise mode of inheritance has remained controversial; monogenic (domainant and recessive), oligogenic and polygenic models have been proposed. In the Belgian Blue cattle breed (BBCB), segregation analysis performed both in experimental crosses and in the outbred population suggested an autosomal recessive inheritance. This was confirmed when the muscular hypertrophy (mh) locus was mapped 3.1 cM from microsatellite TGLA44 on the centromeric end of bovine chromosome 2 (ref. 5). We used a positional candidate approach to demonstrate that a mutation in bovine MSTN, which encodes myostatin, a member of the TGF beta superfamily, is responsible for the double-muscled phenotype. We report an 11-bp deletion in the coding sequence for the bioactive carboxy-terminal domain of the protein causing the muscular hypertrophy observed in Belgian Blue cattle.

Amino Acid Sequence↗
PubMed1997

Hyperaccumulation of FAD-linked presenilin 1 variants in vivo.

Mutations in the presenilin 1 (PS1) and presenilin 2 (PS2) genes can cause Alzheimer's disease in affected members of the majority of early-onset familial Alzheimer's disease (FAD) pedigrees. PS1 encodes an ubiquitously expressed, eight transmembrane protein. PS1 is endoproteolytically processed to an amino-terminal derivative (approximately 27-28 kDa) and a carboxy-terminal derivative (approximately 17-18 kDa). These polypeptides accumulate to saturable levels in the brains of transgenic mice, independent of the expression of PS1 holoprotein. We now document that, in the brains of transgenic mice, the absolute amounts of accumulated N- and C-terminal derivatives generated from the FAD-linked PS1 variants in which Glu replaces Ala at codon 246 (A246E) or Leu replaces Met at codon 146 (M146L) accumulate to a significantly higher degree (approximately 40-50%) than the fragments derived from wild-type PS1. Moreover, the FAD-linked deltaE9 PS1 variant, a polypeptide that is not subject to endoproteolytic cleavage in vivo, also accumulates in greater amounts than the fragments generated from wild-type human PS1. Thus, the metabolism of PS1 variants linked to FAD is fundamentally different from that of wild-type PS1 in vivo.

Actins↗
PubMed1997

Characterization of metabotropic glutamate receptor-mediated nitric oxide production in vivo.

We tested the hypothesis that stimulation of metabotropic glutamate receptors (mGluRs) increases nitric oxide (NO) production in the hippocampus in vivo. Microdialysis probes were placed bilaterally into the CA3 region of the hippocampus of adult Sprague-Dawley rats under pentobarbital anesthesia. Probes were perfused for 5 h with artificial cerebrospinal fluid (CSF) containing 3 microM [14C]-L-arginine. Recovery of [14C]-L-citrulline in the effluent was used as a marker of NO production. In nine groups of rats, increases in [14C]-L-citrulline recovery were compared between right- and left-sided probes perfused with various combinations of the selective mGluR agonist, trans-(1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid (ACPD); the mGluR antagonist, (+/-)-alpha-methyl-4-carboxyphenylglycine (MCPG); the NO synthase inhibitor, N-nitro-L-arginine (LNNA); the ryanodine sensitive calcium-release channel inhibitor dantrolene, the non-N-methyl-D-aspartate (NMDA); receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX); the NMDA receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine (MK-801); and the Na+ channel blocker, tetrodotoxin. Recovery of [14C]-L-citrulline during perfusion with artificial CSF progressively increased to 90 +/- 21 fmol/min (+/-SD) over 5 h. Perfusion in the contralateral hippocampus with 1 mM ACPD augmented [14C]-L-citrulline recovery to 250 +/- 81 fmol/min. Perfusion of 1 mM nitroarginine + ACPD inhibited [14C]-L-citrulline recovery compared to that with ACPD alone. Perfusion with 1 mM MCPG + ACPD attenuated ACPD enhanced [14C]-L-citrulline recovery. Perfusion of 1 mM dantrolene + ACPD inhibited the ACPD-evoked increase in [14C]-L-citrulline recovery. Perfusion of 1 mM MCPG or dantrolene without ACPD did not decrease [14C]-L-citrulline recovery as compared to CSF alone. ACPD-enhanced [14C]-L-citrulline recovery was not attenuated by CNQX, MK-801, or tetrodotoxin (TTX). Using an indirect method of assessing NO production in vivo, these data demonstrate that mGluR stimulation enhances NO production in rat hippocampus. Inhibition with dantrolene suggests that calcium-induced calcium release amplifies the inositol triphosphate-mediated calcium signal associated with mGluR stimulation, thereby resulting in augmented calcium-dependent NO production.

6-Cyano-7-nitroquinoxaline-2,3-dione↗