Biomedical subjects

C Corti

Publications and source records attributed to C Corti.

At least 19 recordsLinked to original sources

PubMed2006

Prenatal diagnosis of a de novo complex chromosome rearrangement (CCR) mediated by six breakpoints, and a review of 20 prenatally ascertained CCRs.

OBJECTIVES: To describe the cytogenetic and FISH characterization of a prenatally diagnosed de novo complex chromosome rearrangement (CCR), showing the involvement of four chromosomes and six breakpoints, and review the literature concerning prenatally detected CCRs in order to obtain insights into addressing karyotype-phenotype correlations in prenatal genetic counseling. METHODS: Conventional protocols were used to set up cultures and chromosome preparations. Commercial and homemade probes were used for the FISH analyses. RESULTS: An apparently balanced de novo t(4;10;20) was prenatally identified by means of cytogenetic analysis. FISH revealed a rearrangement mediated by six breakpoints and the insertion of chromosome 8 material within the 4q region. The pregnancy was interrupted. The fetus showed malformations and anomalous cortical neuron migration. The assembled list of 20 prenatally detected CCRs points to the preferential involvement of chromosomes 4, 6 and 14. The involvement of chromosome 20 is described here for the first time. CONCLUSIONS: FISH analysis is essential for the accurate definition of a complex rearrangement. Phenotype description of fetuses carrying CCRs investigated by means of molecular cytogenetic techniques may contribute to improving and personalizing genetic counseling in prenatal diagnosis.

Abnormalities, Multiple↗

PubMed2003

Reduced nocturnal fall in blood pressure, assessed by two ambulatory blood pressure monitorings and cardiac alterations in early phases of untreated essential hypertension.

To investigate whether in recently diagnosed essential hypertensives a reduced nocturnal fall in blood pressure (BP), established on the basis of two 24-h ambulatory blood pressure monitorings (ABPM) is related to a greater cardiovascular damage. In all, 355 consecutive, recently diagnosed, never-treated essential hypertensives referred for the first time to our outpatient clinic were included in the study. Each patient underwent the following procedures: (1) two 24-h ABPMs performed within 3 weeks, (2) 24-h urinary collection for microalbuminuria, (3) nonmydriatic photography of ocular fundi, (4) echocardiography, (5) carotid ultrasonography. We defined nondipping profile as a night-day systolic and diastolic fall < or =10 % (mean of two ABPMs). A dipper BP profile was found in 238 patients, whereas in 117 patients a nondipper profile was present. The two groups were similar for age, gender, body mass index, smoking habit, clinic BP, 48-h BP and heart rate, while, by definition, night-time systolic and diastolic BP were significantly higher in nondippers than in dippers (130/81 vs 121/74 mmHg, P < 0.0001).The prevalence of left ventricular hypertrophy (LVH) defined by four different criteria: (a) LV mass index (LVMI) > or = 125 g/m(2) in both genders; (b) LVMI > or = 134 gm(2) in men and > or = 110 in women; (c) LVMI> or = 125 g/m(2) in men and > or = 110 g/m(2) in women; (d) LVMI > or = 51 g/m(2.7) in men and > or = 47 g/m(2.7) in women was significantly higher in nondippers than in dippers (a: 12 vs 7%, P < 0.05; b: 16 vs 7%, P < 0.01; c: 20 vs 11%, P < 0.01; d: 35 vs 23% P < 0.02) and this finding was associated with a significant increase in aortic root and left atrium dimensions. There were no differences between the two groups in the prevalence of carotid and retinal changes and microalbuminuria. In conclusion our findings suggest that never-treated hypertensives with a reduced BP fall in the night time, defined on the basis of two ABPMs, have a higher prevalence of TOD than dippers, in terms of echocardiographic LVH. In this population setting, cardiac structural alterations are a more sensitive marker of the impact of the nocturnal BP load on cardiovascular system than other extracardiac signs of TOD.

Adult↗

PubMed2002

Distribution and synaptic localisation of the metabotropic glutamate receptor 4 (mGluR4) in the rodent CNS.

Group III metabotropic glutamate receptors (mGluRs) are selectively activated by L-2-amino-4-phosphonobutyrate (L-AP4), which produces depression of synaptic transmission. The relative contribution of different group III mGluRs to the effects of L-AP4 remains to be clarified. Here, we assessed the distribution of mGluR4 in the rat and mouse brain using affinity-purified antibodies raised against its entire C-terminal domain. The antibodies reacted specifically with mGluR4 and not with other mGluRs in transfected COS 7 cells. No immunoreactivity was detected in brains of mice with gene-targeted deletion of mGluR4. Pre-embedding immunocytochemistry for light and electron microscopy showed the most intense labelling in the cerebellar cortex, basal ganglia, the sensory relay nuclei of the thalamus, and some hippocampal areas. Immunolabelling was most intense in presynaptic active zones. In the basal ganglia, both the direct and indirect striatal output pathways showed immunolabelled terminals forming mostly type II synapses on dendritic shafts. The localisation of mGluR4 on GABAergic terminals of striatal projection neurones suggests a role as a presynaptic heteroreceptor. In the cerebellar cortex and hippocampus, mGluR4 was also localised in terminals establishing type I synapses, where it probably operates as an autoreceptor. In the hippocampus, mGluR4 labelling was prominent in the dentate molecular layer and CA1-3 strata lacunosum moleculare and oriens. Somatodendritic profiles of some stratum oriens/alveus interneurones were richly decorated with mGluR4-labelled axon terminals making either type I or II synapses. This differential localisation suggests a regulation of synaptic transmission via a target cell-dependent synaptic segregation of mGluR4. Our results demonstrate that, like other group III mGluRs, presynaptic mGluR4 is highly enriched in the active zone of boutons innervating specific classes of neurones. In addition, the question of alternatively spliced mGluR4 isoforms is discussed.

Animals↗

PubMed2002

Left ventricular concentric remodelling and extracardiac target organ damage in essential hypertension.

Left ventricular (LV) concentric remodelling is an adaptive change in cardiac geometry frequently observed in arterial hypertension. This study was addressed to investigate the extent of extracardiac target organ damage (TOD) in patients with LV concentric remodelling. Two groups of never-treated essential hypertensives, 31 with normal LV geometry (group I, relative wall thickness: 0.39) and 31 with LV concentric remodelling (group II, relative wall thickness: 0.47) matched for age, sex, body mass index and mean 24-h systolic blood pressure (BP), were included in the study. They underwent clinical and laboratory examination, 24-h ambulatory BP monitoring (ABPM), 24-h urinary collection for microalbuminuria, non-mydriatic photography of ocular fundi, echocardiography and carotid ultrasonography. In both groups age (I: 51 +/- 11 years; II: 51 +/- 11 years), body mass index (I: 25 +/- 3 kg/m(2); II: 26 +/- 3 kg/m(2)), clinic and 24-h ABPM values (I: 149 +/- 11/95 +/- 8, 142 +/- 11/91 +/- 7 mm Hg; II: 150 +/- 11/98 +/- 9, 142 +/- 12/92 +/- 9 mm Hg) were similar by design. There were no differences between patients with normal LV geometry and with LV concentric remodelling in LVM index (97 +/- 16 vs 99 +/- 16), carotid intima-media thickness (0.7 +/- 0.02 vs 0.7 +/- 0.02) and carotid plaques prevalence (35% vs 35%). Furthermore, no significant differences among the two groups were found in the prevalence of retinal changes and microalbuminuria. These results suggest that in hypertensive patients with similar BP and LVMI levels, LV concentric remodelling is not associated with more prominent TOD.

Albuminuria↗

PubMed2002

Short-term reproducibility of nocturnal non-dipping pattern in recently diagnosed essential hypertensives.

OBJECTIVE: To investigate in a selected population of patients with a recently diagnosed essential hypertension the short-term intrasubject variability of diurnal changes in blood pressure (BP). METHODS: Two hundred and eight consecutive, recently diagnosed, never treated essential hypertensives (119 men, 89 women, 46 +/- 12 years) underwent 24-h ambulatory BP monitoring (ABPM) twice within 3 weeks. Dipping pattern was defined as a reduction in average systolic and diastolic BP at night greater than 10% compared to average daytime values. RESULTS: 177 subjects (85%) showed no change in their diurnal variations in BP. Of the 159 subjects who had a dipping pattern on first ABPM, 134 (90.6%) confirmed this type of profile on the second ABPM, while 15 (9.4%) showed a non-dipping pattern. Of the 59 subjects who had a non-dipping pattern on the first ABPM, 43 (72.2%) confirmed their initial profile on the second ABPM, while 16 (28.8%) did not. CONCLUSION: These findings indicate that short-term reproducibility of diurnal changes in BP in early phases of untreated essential hypertension, characterized by a large prevalence of dipping pattern, is overall satisfactory. However, our study underlines that also in this particularly selected population of hypertensives the definition of non-dipping status on the basis of a single ABPM remains unreliable in about one-third of patients.

Adult↗

PubMed2002

A comparison of blood pressure control in a hypertension hospital clinic between 1997 and 2000.

AIMS: (1) To evaluate the prevalence of clinic blood pressure (BP) control in a large sample of treated hypertensives followed in our hypertension clinic during the year 2000, and to compare it with our 1997 data. (2) To investigate the prevalence of left ventricular hypertrophy (LVH) according to different levels of BP control. METHODS AND RESULTS: One thousand consecutive hypertensive patients who attended our hypertension hospital clinic in a period of 7 months during the year 2000 and who had regularly been followed by the same medical team were included in the study. LVH was assessed using two different electrocardiographic criteria (Sokolow-Lyon and Cornell). This population had similar clinical characteristics of a cohort including 700 patients seen at our centre during 1997 in which BP control rate was 34% (Cuspidi et al., J Hypertens 1999; 17: 835-41). During follow-up, 441 of the treated patients had clinic BP < 140/90 mmHg, 283 < 150/95 mmHg and 276 > or = 150/95 mmHg, indicating that BP control was satisfactory in 44.1%, borderline in 28.3% and unsatisfactory in 27.6% of the cases. Thirty-five patients (3.6%) had LVH according to Cornell criteria and 25 (2.6%) according to Sokolow criteria. A significantly lower prevalence of LVH was detected in patients with optimal BP control (< 130/ 85 mmHg) compared to those with unsatisfactory BP (2.3% vs 9.4%, respectively, p < 0.01). CONCLUSION: The study demonstrates that: (1) hypertensive patients in a hypertension clinic have satisfactory BP control in 44.1% of cases, indicating a significant improvement of BP control in this clinical setting during the last 3 years; (2) prevalence of LVH is significantly related to BP control.

Aged↗

PubMed2001

Identification and characterization of the promoter region of the GRM3 gene.

We have recently described the genomic organisation of the human metabotropic glutamate receptor 3 (GRM3) gene. The putative promoter region is characterised by the presence of a CCAAT and Sp1 site and the absence of a TATA box. Using a reporter gene assay, now we describe the functional activity of GRM3 promoter by transient transfection in both human neuroblastoma and astroglioma cell lines. Deletion of the CCAAT box and Sp1 site resulted in a pronounced reduction of reporter gene expression in both cell types, which indicates that these elements to correspond to the core promoter region. Moreover, we found that the genomic sequence 140 bp upstream of the first transcription initiation site appears to contain regulatory promoter elements for a preferential transcription of the gene in neuroblastoma cells. We also provide evidence that the genomic sequence spanning exon I, corresponding to the GRM3 5'-untranslated region, contains a negative regulatory element that represses gene transcription.

5' Untranslated Regions↗

PubMed2001

Tolerance of human MSH2+/- lymphoblastoid cells to the methylating agent temozolomide.

Members of hereditary nonpolyposis colon cancer (HNPCC) families harboring heterozygous germline mutations in the DNA mismatch repair genes hMSH2 or hMLH1 present with tumors generally two to three decades earlier than individuals with nonfamilial sporadic colon cancer. We searched for phenotypic features that might predispose heterozygous cells from HNPCC kindreds to malignant transformation. hMSH2(+/-) lymphoblastoid cell lines were found to be on average about 4-fold more tolerant than wild-type cells to killing by the methylating agent temozolomide, a phenotype that is invariably linked with impairment of the mismatch repair system. This finding was associated with an average 2-fold decrease of the steady-state level of hMSH2 protein in hMSH2(+/-) cell lines. In contrast, hMLH1(+/-) heterozygous cells were indistinguishable from normal controls in these assays. Thus, despite the fact that HNPCC families harboring mutations in hMSH2 or hMLH1 cannot be distinguished clinically, the early stages of the carcinogenic process in hMSH2 and hMLH1 mutation carriers may be different. Should hMSH2(+/-) colonocytes and lymphoblasts harbor a similar phenotype, the increased tolerance of the former to DNA-damaging agents present in the human colon may play a key role in the initiation of the carcinogenic process.

Adaptor Proteins, Signal Transducing↗

PubMed2001

Bidirectional regulation of neurite elaboration by alternatively spliced metabotropic glutamate receptor 5 (mGluR5) isoforms.

Alternative splicing in the mGluR5 gene generates two different receptor isoforms, of which expression is developmentally regulated. However, little is known about the functional significance of mGluR5 splice variants. We have examined the functional coupling, subcellular targeting, and effect on neuronal differentiation of epitope-tagged mGluR5 isoforms by expression in neuroblastoma NG108-15 cells. We found that both mGluR5 splice variants give rise to comparable [Ca2+]i transients and have similar pharmacological profile. Tagged receptors were shown by immunofluorescence to be inserted in the plasma membrane. In undifferentiated cells the subcellular localization of the two mGluR5 isoforms was partially segregated, whereas in differentiated cells the labeling largely redistributed to the newly formed neurites. Interestingly, we demonstrate that mGluR5 splice variants dramatically influence the formation and maturation of neurites; mGluR5a hinders the acquisition of mature neuronal traits and mGluR5b fosters the elaboration and extension of neurites. These effects are partly inhibited by MPEP.

Alternative Splicing↗

PubMed2001

Activated astrocytes in areas of kainate-induced neuronal injury upregulate the expression of the metabotropic glutamate receptors 2/3 and 5.

All forms of brain injury induce activation of astrocytes, although different types of injury induce different astrocytic responses. Activated astrocytes are characterised by hypertrophy, proliferation and increased expression of glial fibrillary acidic protein (GFAP). However, neither the process by which astrocytes become reactive nor the consequences are well understood. Recently, the application of specific growth factors to primary astrocytic cultures was shown to regulate dramatically the level of expression of the metabotropic glutamate receptors (mGluR) 5 and 3. In the present study, we have used an intracerebroventricular injection of a subconvulsive dose of kainic acid to produce a lesion of CA3a pyramidal neurones in the mouse hippocampus and to investigate whether mGluR expression was altered in reactive astrocytes in vivo. Immunohistochemical analysis showed strong mGluR5 and mGluR2/3 immunoreactivity in glial cells within the area of neuronal loss possessing the morphological feature of activated astrocytes. Double labelling with GFAP confirmed the expression of mGluRs by reactive astrocytes. The mechanical injury produced by the needle insertion in the cerebral cortex also produced enhanced expression of mGluR5 and mGluR2/3 in activated astrocytes proximal to the area of neuronal injury. Our finding of an increased mGluR expression in reactive astrocytes in vivo suggests that transcriptional regulation by specific growth factors on mGluRs is a phenomenon extendible to specific circumstances in vivo and not limited to in vitro models. Identification of the mechanisms of this adaptive plasticity will be central in the understanding of the events leading to neuronal survival and/or death.

Adaptation, Physiological↗

PubMed2001

Influence of different echocardiographic criteria for detection of left ventricular hypertrophy on cardiovascular risk stratification in recently diagnosed essential hypertensives.

BACKGROUND: Hypertensive patients with left ventricular hypertrophy (LVH) need a prompter and more intensive pharmacological treatment than subjects without evidence of cardiac involvement. So the detection of LVH plays an important role for decision-making in hypertensives. OBJECTIVE: To evaluate the impact of different echocardiographic criteria to define LVH in a more precise stratification of absolute cardiovascular risk in hypertensives without target organ damage (TOD) as assessed by routine investigations. METHODS: A total of 100 never treated patients with grade 1 and 2 essential hypertension (53 men, 47 women, age 44 +/- 12 years) referred for the first time to our outpatient clinic were included in the study. They underwent the following procedures: (1) family and personal medical history, (2) clinic blood pressure (BP) measurement, (3) routine blood chemistry and urine analysis, (4) electrocardiogram, (5) echocardiogram. Risk was stratified according to the criteria suggested by the 1999 WHO-ISH guidelines. TOD was initially evaluated by routine procedures only, and subsequently reassessed by using six different echocardiographic criteria to recognise LVH: (a) left ventricular mass index (LVMI) >120 g/m(2) in men and 100 g/m(2) in women; (b) 125 g/m(2) in men and 110 g/m(2) in women; (c) 134 g/m(2) in men and 110 g/m(2) in women; (d) 125 g/m(2) in men and 125 g/m(2) in women; (e) 51 g/m(2.7) in men and 47 g/m(2.7) in women; (f) 126 g/m in men and 105 g/m in women. RESULTS: According to the first classification based on routine investigations, 46% were low risk and 54% were medium risk patients. Significant changes in risk stratification were obtained when LVH was assessed by echocardiography. A percentage of patients, ranging from 9 (f) to 25% (d), were found to having LVH according to different criteria, and consequently moved from low and medium risk strata to high risk stratum. CONCLUSIONS: The detection of LVH by echocardiography allowed a much more accurate identification of high risk patients. In particular our results suggest that: (1) cardiovascular risk stratification only based on a simple routine work-up can often underestimate overall risk; (2) a better standardisation in defining LVH is needed, considering that the impact of cardiac hypertrophy on risk stratification is markedly dependent on the echocardiographic criteria used to diagnose it.

Adult↗

PubMed2001

Evaluation of target organ damage in arterial hypertension: which role for qualitative funduscopic examination?

BACKGROUND: The objective of this study was to compare the prevalence of quantitative markers of target organ damage, such as echocardiographically documented left ventricular hypertrophy (LVH), carotid structural changes and microalbuminuria with that of retinal abnormalities detected by qualitative funduscopic examination in a large selected population of patients with essential hypertension. METHODS: Eight hundred consecutive untreated (n = 232) and treated (n = 568) hypertensive patients (386 men, 414 women, mean age 52.7 +/- 11.8 years) referred for the first time to our out-patient clinic were included in the study. In order to search for target organ damage, they were submitted to the following procedures: 1) amydriatic retinography, 2) 24-hour urine collection for microalbuminuria, 3) echocardiography, and 4) carotid ultrasonography. Retinal changes were evaluated according to the Keith, Wagener and Barker (KWB) classification by two physicians, who had no knowledge of the patients' characteristics. Microalbuminuria was defined as a urinary albumin excretion > 30 and < 300 mg/24 hours, LVH as a left ventricular mass index > or = 134 g/m2 in men and > or = 110 g/m2 in women; finally carotid plaque was defined as a focal thickening > 1.3 mm. RESULTS: Hypertensive retinopathy was the most frequent (KWB grade I 46%, II 32%, III-IV < 2%) marker of target organ damage, followed by carotid plaques (43%), LVH (22 %, eccentric LVH was the prevalent type and was 1.8 times as frequent as the concentric one) and microalbuminuria (14%). CONCLUSIONS: At variance with the markers of cardiac, macrovascular and renal damage, an extremely high prevalence of retinal abnormalities (narrowings and initial arterio-venous crossings) were found in our population. If, as suggested by the WHO/ISH guidelines, these retinal abnormalities were considered as a reliable marker of target organ damage, then almost all patients would be affected by hypertensive vascular disease. Based on this evidence it is suggested that retinal abnormalities included in funduscopic grades I and II of the KWB classification should not be considered among the criteria for the quantitative detection of target organ damage.

Adult↗

PubMed2000

Decreased UV sensitivity, mismatch repair activity and abnormal cell cycle checkpoints in skin cancer cell lines derived from UVB-irradiated XPA-deficient mice.

Xeroderma pigmentosum group A gene (XPA)-deficient mice are defective in nucleotide excision repair (NER) and are therefore highly sensitive to ultraviolet (UV)-induced skin carcinogenesis. We established cell lines from skin cancers of UVB-irradiated XPA-deficient mice to investigate the phenotypic changes occurring during skin carcinogenesis. As anticipated, the skin cancer cell lines were devoid of NER activity but were less sensitive to killing by UV-irradiation than the XPA(-/-) fibroblast cell line. The lines were also more resistant to 6-thioguanine (6-TG) than XPA(-/-) and XPA(+/+) fibroblasts, which was suggestive of a mismatch repair (MMR) defect. Indeed, in vitro mismatch binding and MMR activity were impaired in several of these cell lines. Moreover, these cell lines displayed cell cycle checkpoint derangements following UV-irradiation and 6-TG exposure. The above findings suggest that MMR downregulation may help cells escape killing by UVB, as was seen previously for methylating agents and cisplatin, and thus that MMR deficient clones are selected for during the tumorigenic transformation of XPA(-/-) cells.

Animals↗

PubMed2000

Genomic organization of the human metabotropic glutamate receptor subtype 3.

In this study, the genomic organization of the human metabotropic glutamate receptor subtype 3 (mGluR3) gene has been determined. We have identified two transcription initiation sites and the polyadenylation signal by using 5'-rapid amplification of cDNA ends (RACE) and 3'-RACE, respectively. The exon/intron organization of the human mGluR3 gene revealed the presence of 6 exons separated by 5 introns. The size of introns varied from 10.4 to 120 kbp that contained consensus sequences for repetitive elements such as Alu and long interspersed elements. A putative promoter region flanking the 5' sequence of exon 1 was identified by computer-aided analysis. The putative promoter region was characterized by the presence of a CAAT and GC box, and the absence of a TATA box or CpG islands. Several putative binding sites for transcription factors were also identified. In addition, we have isolated, from a mouse genomic library, part of the mouse mGluR3 gene and found it to correspond to exon 2 in the human mGluR3 gene. The mouse mGluR3 gene was then mapped by fluorescent in situ hybridization analysis to chromosome 5qA2.

Animals↗

PubMed1999

Serine/threonine phosphorylation of calmodulin modulates its interaction with the binding domains of target enzymes.

The interaction of serine/threonine-phosphorylated calmodulin with synthetic peptides corresponding to the calmodulin-binding domains of six enzymes has been studied by fluorescence spectroscopy. For five peptides, the dissociation constant of the calmodulin-peptide complex (K(d)) increased when calmodulin was phosphorylated. An increase of more than one order of magnitude was observed with peptides derived from smooth-muscle myosin light-chain kinase and cAMP phosphodiesterase. In contrast, only a slight increase in K(d) was noted with two peptides derived from the plasma membrane Ca(2+)-ATPase and for the peptide derived from nitric oxide synthase. No significant change in affinity was detected with the peptide derived from calcineurin. In contrast, a decrease in the dissociation constant was observed with the peptide derived from the Ca(2+)-calmodulin dependent kinase II. Phosphorylation also affected the peptide-calmodulin binding stoichiometry: a decrease from two to one binding sites was observed with the peptides derived from myosin light-chain kinase and phosphodiesterase.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1999

Tyrosine phosphorylation modulates the interaction of calmodulin with its target proteins.

The activation of six target enzymes by calmodulin phosphorylated on Tyr99 (PCaM) and the binding affinities of their respective calmodulin binding domains were tested. The six enzymes were: myosin light chain kinase (MLCK), 3'-5'-cyclic nucleotide phosphodiesterase (PDE), plasma membrane (PM) Ca2+-ATPase, Ca2+-CaM dependent protein phosphatase 2B (calcineurin), neuronal nitric oxide synthase (NOS) and type II Ca2+-calmodulin dependent protein kinase (CaM kinase II). In general, tyrosine phosphorylation led to an increase in the activatory properties of calmodulin (CaM). For plasma membrane (PM) Ca2+-ATPase, PDE and CaM kinase II, the primary effect was a decrease in the concentration at which half maximal velocity was attained (Kact). In contrast, for calcineurin and NOS phosphorylation of CaM significantly increased the Vmax. For MLCK, however, neither Vmax nor Kact were affected by tyrosine phosphorylation. Direct determination by fluorescence techniques of the dissociation constants with synthetic peptides corresponding to the CaM-binding domain of the six analysed enzymes revealed that phosphorylation of Tyr99 on CaM generally increased its affinity for the peptides.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1999

Activation of the extracellular signal-regulated kinase 2 by metabotropic glutamate receptors.

Activation of metabotropic glutamate receptors (mGluRs) leads to modulation of a variety of second messenger pathways probably including the mitogen-activated protein kinase (MAPK) extracellular signal-regulated protein kinases (ERK). MAPK play a key role in the control of cellular responses to changes in the external environment by regulating transcriptional activity and the phosphorylation state of several cytoplasmic targets. In this study, Chinese hamster ovary (CHO) cells permanently transfected with rat mGluR1a, mGluR2 and mGluR4 were employed as a model to examine the activation of MAPK by glutamate through mGluRs. All three mGluR subtypes rapidly stimulated ERK activation. In particular, mGluR1a and mGluR2 preferentially mediated phosphorylation and activation of ERK2 in a pertussis toxin (PTX)-sensitive and concentration-dependent manner. The activation was blocked completely by pretreatment with the antagonist (rs)-alpha-methyl-4-carboxyphenylglycine (MCPG) or with the MEK inhibitor PD098059. Furthermore, mGluR1a-mediated ERK activation was suppressed by the depletion of endogenous protein kinase C (PKC) activity and by the PKC inhibitors staurosporine and calphostin C, but not chelerythrine. When cAMP was elevated in mGluR2-expressing cells, by forskolin or dibutyryl-cAMP, slight elevation of ERK activity was observed. However, glutamate-stimulated ERK activation remained unaffected. In these cells, the phosphatidylinositol 3 kinase (PI3K) inhibitor wortmannin produced a significant, albeit only partial, inhibition of mGluR2-mediated ERK activation. These findings raise the possibility of a MAPK cascade involvement in glutamate-dependent neuronal plasticity mediated through stimulation of mGluRs.

Animals↗

PubMed1998

Immunohistochemical localization of the mGluR1beta metabotropic glutamate receptor in the adult rodent forebrain: evidence for a differential distribution of mGluR1 splice variants.

Alternative splicing has been shown to occur at the metabotropic glutamate receptor 1 (mGluR1) gene. Three main isoforms that differ in their carboxy-termini have been described so far and named mGluR1alpha, mGluR1beta and mGluR1c. These variants when expressed in recombinant systems all activate phospholipase C, although the [Ca2+] signals generated have different kinetics. Tissue distribution studies of specific mGluR1 splice variants are limited to the mGluR1alpha isoform. In the present work, we examined the localization of mGluR1beta in the adult rat and mouse forebrain by using a specific antipeptide antibody. Furthermore, the mGluR1beta immunostaining was compared with that obtained with antibodies specific for mGluR1alpha or with a pan-mGluR1 antibody which recognizes all isoforms. mGluR1beta-like immunoreactivity (LI) was found confined to the neuropil and neuronal perikarya and appeared discretely distributed in the rodent forebrain. Differential cellular distribution between mGluR1alpha and mGluR1beta was observed. In the hippocampus, mGluR1alpha-LI was restricted to non-principal neurons in all fields, whereas mGluR1beta-LI was strongest in principal cells of the CA3 field and dentate granule cells but absent in CA1. We have also shown that the vast majority of neurons in the striatum express mGluR1. The predominant form appeared to be mGluR1beta, with a distribution pattern reflecting the patch-matrix organization of the striatum. The specificity of the immunoreactivity described for mGluR1 splice variants was confirmed in mGluR1-deficient mice. The observation of a different cellular and regional distribution of mGluR1 splice variants, in particular in the hippocampus, suggests that they may mediate different roles in synaptic transmission.

Animals↗