45Ca exchange in rat cortex slices in conditions of long-term potentiation

OBJECTIVE: An attempt was made to find out how many operations were performed in Europe in 1995 for congenital heart disease. METHODS: Representatives from the 20 most active European countries which could supply reliable information were contacted. They were asked to contact all surgeons performing significant numbers of operations for congenital heart disease in their country. The numbers of operations on children under and over 1 year operated on with and without cardiopulmonary bypass were collected. No attempt was made to collect more detailed information such as operative mortality as it was felt that many surgeons would be reluctant to give their results and the data would be incomplete. RESULTS: A total of 27,976 operations were recorded, of which 20,318 were performed with cardiopulmonary bypass and 7658 without. The total population of the 20 European countries was 448 million and the mean number of operations performed with cardiopulmonary bypass per million was 45.4. However, the rate varied from 9.1 to 70.1. The percentage of operations on cardiopulmonary bypass performed in the first year of life varied from 9.4% to 44.4%. CONCLUSIONS: The total of nearly 28,000 operations in 1995 is probably an underestimate, but it has been difficult to collect this data at all. Obviously many smaller countries have not been included, and some older patients undergoing operations such as atrial septal defect closure in adult units have been missed. The number of open heart operations per million vary in different countries and this presumably represents differing referral patterns. If their numbers are low in some countries, these results may be helpful in persuading their governments that more resources are needed for congenital heart surgery. It is also interesting to see the variation in the number of operations performed in the first year of life. Those countries with a lower rate may have a backlog of older patients who were previously palliated, or their surgeons may still prefer initial palliation and later correction in some conditions rather than early correction. It is hoped that with better prospective data collection, an assessment can be repeated in 2000.     

Metabotropic glutamate receptors are involved in calcium-induced LTP of AMPA and NMDA receptor-mediated responses in the rat hippocampus

INTRODUCTION: Previous studies have demonstrated a high prevalence of "white coat" hypertension (20%), but it is still controversial if it implies an increase in cardiovascular risk. PATIENTS: Between 1992 and 95 we prospectively studied 175 untreated hypertensive patients aged over 18 years (V Joint National Committee's stage I-II), and 91 controls. DESIGN AND METHODS: The subjects were submitted to clinical evaluation, ambulatory blood pressure monitoring, 24-hour Holter monitoring, signal-averaged ECG, echocardiography/Doppler and ergometry. "White coat" hypertension was defined as mean daytime (6.00-22.00 H) ambulatory blood pressure < 136/87 mm Hg (males) and < 131/86 mm Hg (females). RESULTS: "White coat" hypertension was present in 29 patients (18%). "White coat" hypertension patients had an identical prevalence of smoking, family history of cardiovascular disease, abnormal ECG and retinopathy (> Keith-Wagener II) as patients with daytime hypertension. Ambulatory blood pressure values (24 hour, 6.00-22.00 h, 22.00-6.00 h, sleep, blood pressure load, heart rate) were all significantly different from controls (p < 0.03 to 0.0007). In patients with daytime hypertension, only 24 hour and daytime diastolic ambulatory blood pressure (p < 0.005) were different from "white coat" hypertension patients. Exercise testing blood pressure values (6 min exercise, maximal, 3 min recovery) were significantly different between "white coat" hypertension patients and the control group (n = 70) (p varying from 0.05 to 0.005) but not between "white coat" hypertension and daytime hypertension (n = 33) patients. Diastolic function was studied only in 39 daytime hypertension patients, 10 individuals with "white coat" hypertension and 34 controls (for technical reasons and because we only analyzed individuals younger than 55 years). E velocity and E/A ratio were similar in "white coat" hypertension and daytime hypertension, but only in daytime hypertension patients they reached a significant difference from controls (p = 0.04; p = 0.01), probably due to the small number of patients. CONCLUSIONS: These data (clinical, ambulatory blood pressure, ergometric, diastolic function) suggest that "white coat" hypertension might not be a benign entity.     

45Ca metabolism in slices of rat cerebral cortex during long-term potentiation

Ca45 kinetics was studied in 5, 15 and 30 min after potentiation. In the induction phase (1-5 min), the potentiation decreased the fraction of intracellular bound Ca. The 15-25 min potentiation the intra- and extracellular Ca levels was equal to the control ones. In 30 min, a considerable redistribution of Ca in the cells occurred.     

Correlates of membrane metabolism and long-term potentiation in slices of rat cerebral cortex

A group of interrelated parameters of the membrane metabolism was studied during stimulation of the lateral olfactory tract in the rat brain slices of olfactory cortex. All the parameters were studied in respect to electrical activity of the slices in three temporal points after the tetanisation: 3-5, 15, and 30 min. Regular phasic alterations of the metabolism parameters occurred in most of the cases. Their functional significance is discussed.     

Metabotropic glutamate receptors in the rat nucleus accumbens

The effects of glutamate metabotropic receptors (mGluRs) on excitatory transmission in the nucleus accumbens were investigated using electrophysiological techniques in rat nucleus accumbens slices. The broad-spectrum mGluR agonist (1S,3R)-1-aminocyclopentyl-1,3-dicarboxylate, the mGluR group 2 selective agonists (S)-4-carboxy-3-hydroxyphenylglycine, (1S,3S)-ACPD) and (2S,1'S,2'S)-2-(2'-carboxycyclopropyl)glycine (L-CCG1), and the mGluR group 3 specific agonist L-2-amino-4-phosphonobutyrate (L-AP4) all reversibly inhibited evoked excitatory synaptic responses. The specific group 1 mGluR agonist (R,S)-3,5-dihydroxyphenylglycine [(R,S)-DHPG] did not depress transmission. Dose-response curves showed that the rank order of agonist potencies was: L-CCG1 > L-AP4 > (1S,3S)-ACPD. Group 2 and 3 mGluRs inhibited transmission via a presynaptic mechanism, as they increased paired-pulse facilitation, decreased the frequency of miniature excitatory postsynaptic currents and had no effect on their amplitude. The mGluRs did not inhibit transmitter release by reducing voltage-dependent Ca2+ currents through N- or P-type Ca2+ channels, as inhibition persisted in the presence of omega-conotoxin-GVIA or omega-Aga-IVA. The depression induced by mGluRs was not affected by specific antagonists of dopamine D1, GABA-B or adenosine A1 receptors, indicating direct effects. Finally, (R,S)-DHPG specifically blocked the postsynaptic afterhyperpolarization current (I(AHP)). Our results represent the first direct demonstration of functional mGluRs in the nucleus accumbens of the rat.     

When are class I metabotropic glutamate receptors necessary for long-term potentiation?

The involvement of metabotropic glutamate receptors (mGluRs) in hippocampal long-term potentiation (LTP) is a matter of controversial debate. Using [Ca2+]i measurements by confocal laser scanning microscopy and field recordings of EPSPs (fEPSPs) in the hippocampal CA1-region, we found that the efficacy of the broad-spectrum mGluR-antagonist (S)-alpha-methyl-4-carboxyphenylglycine (MCPG) and of (S)-4-carboxy-phenylglycine (4-CPG), a selective antagonist at class I mGluRs, in LTP is contingent on the tetanization strength and the resulting [Ca2+]i response. As indicated by experiments in which we blocked voltage-dependent calcium channels (VDCCs) and intracellular Ca2+ stores (ICSs), the functional significance of class I mGluRs in LTP is confined to certain types of potentiation, which are induced by weak tetanization protocols and require the release of Ca2+ from ICSs for induction. During strong tetanic stimulation, this Ca2+ source is functionally bypassed by activating VDCCs.     

Metabotropic glutamate receptors are associated with non-synaptic appendages of unipolar brush cells in rat cerebellar cortex and cochlear nuclear complex

Unipolar brush cells (UBCs) are a class of small neurons that are densely concentrated in the granular layers of the vestibulocerebellar cortex and dorsal cochlear nucleus. The UBCs form giant synapses with individual mossy fibre rosettes on the dendrioles which make up their brush formations and are provided with numerous, unusual non-synaptic appendages. In accord with the glutamatergic nature of mossy fibres, our previous post-embedding immunocytochemical studies indicated that various ionotropic glutamate receptor subunits are localized at the post-synaptic densities of the giant synapses, whereas the non-synaptic appendages are immunonegative. On the contrary, the metabotropic glutamate receptors mGluR1alpha and mGluR2/3 are situated at the non-synaptic appendages and are lacking at the post-synaptic densities. Other authors, however, have shown that antibodies to these metabotropic receptors stain both appendages and post-synaptic densities. In the present study, we have re-evaluated the distribution of metabotropic glutamate receptors in the UBCs of the cerebellum and the cochlear nuclear complex by light and electron microscopic pre-embedding immunocytochemistry with subtype-specific antibodies. We confirm that UBCs dendritic brushes are densely immunostained by antibody to mGluR1alpha particularly in the cerebellum and that antibody to mGluR2/3 labels at least a percentage of the UBC brushes in both the cerebellum and cochlear nuclei. At the ultrastructural level, it appears that mGluR1alpha and mGluR2/3 immunoreactivities are not associated with the post-synaptic densities of the giant mossy fibre-UBC synapses, but instead are concentrated on the non-synaptic appendages of the cerebellar UBCs. The non-synaptic appendages, therefore, may be an important avenue for regulating the excitability of UBCs and mediating glutamate effects on their still unknown intracellular signal transduction cascades. We also show that the pre-synaptic densities of UBC dendrodendritic junctions are mGluR2/3 positive. As previously demonstrated, antibodies to mGluR1alpha and mGluR2/3 label subsets of Golgi cells. Antibody to mGluR5 does not stain UBCs in the cerebellum and cochlear nucleus and reveals the somatodendritic compartment of Golgi cells situated in the core of the cerebellar granular layer, whilst cochlear nucleus Golgi cells are mGluR5 negative.     

Cholinergic agonist carbachol enables associative long-term potentiation in piriform cortex slices

Pyramidal cells in piriform (olfactory) cortex receive afferent input from the olfactory bulb as well as intrinsic association input from piriform cortex and other cortical areas. These two functionally distinct inputs terminate on adjacent apical dendritic segments of the pyramidal cells located in layer Ia and layer Ib of piriform cortex. Studies with bath-applied cholinergic agonists have shown suppression of the fast component of the inhibitory postsynaptic potentials (IPSPs) evoked by stimulation of the association fibers. It was previously demonstrated that an associative form of LTP can be induced by coactivation of the two fiber systems after blockade of the fast, gamma-aminobutyric acid-A-mediated IPSP. In this report, we demonstrate that an associative form of long-term potentiation can be induced by coactivation of afferent and intrinsic fibers in the presence of the cholinergic agonist carbachol.     

Possible regeneration of rat medial frontal cortex following neonatal frontal lesions

The experiments described here show that the cavity left by midline frontal cortex removals at 10 days of age (P10) fills in with neural tissue. Similar changes are not found at earlier and later ages. This neuronal filling is blocked by prior pretreatment by administration of Bromodeoxyuridine (BrdU) on embryonic day 13. Administration of BrdU following the P10 lesion does not interfere with regrowth. Subsequent immunohistochemical staining for BrdU demonstrates the regrown area to be composed of newly generated cells. which include pyramidal and nonpyramidal neurons. Injections of a retrograde tracer into the striatum or posterior parietal cortex shows that the new neurons have connections similar to those of undamaged brains. The regrowth of this tissue is correlated with recovery of function in a test of forelimb use. Thus, the mammalian brain, during some privileged postnatal stages of growth. is capable of extensive reorganization that includes regeneration of lost neurons. These results are discussed in relation to the proximity of the lesion to the stem cells in the lateral ventricle and their postnatal migrational activities.     

Regulatory phosphorylation of AMPA-type glutamate receptors by CaM-KII during long-term potentiation

Long-term potentiation (LTP), a cellular model of learning and memory, requires calcium-dependent protein kinases. Induction of LTP increased the phosphorus-32 labeling of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors (AMPA-Rs), which mediate rapid excitatory synaptic transmission. This AMPA-R phosphorylation appeared to be catalyzed by Ca2+- and calmodulin-dependent protein kinase II (CaM-KII): (i) it correlated with the activation and autophosphorylation of CaM-KII, (ii) it was blocked by the CaM-KII inhibitor KN-62, and (iii) its phosphorus-32 peptide map was the same as that of GluR1 coexpressed with activated CaM-KII in HEK-293 cells. This covalent modulation of AMPA-Rs in LTP provides a postsynaptic molecular mechanism for synaptic plasticity.     

Brain-derived neurotrophic factor enhances long-term potentiation in rat visual cortex

Brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), members of the nerve growth factor (NGF) gene family, have been suggested to play a role in experience-dependent modification of neural networks in the developing nervous system. In this study we addressed the question of whether these neurotrophins are involved in long-term potentiation (LTP) in developing visual cortex. We recorded layer II/III field potentials and whole-cell currents evoked by test stimulation of layer IV at 0.1 Hz in visual cortical slices prepared from young rats (postnatal day 15-25) and observed effects of BDNF, NT-3, and NGF on these responses. Then we analyzed the effects of these neurotrophins on LTP induced by tetanic (Theta-burst type) stimulation of layer IV. We found that BDNF at 200 ng/ml potentiated field potentials and EPSCs in most cases and that this potentiation lasted after cessation of the BDNF application. At the concentration of 20 ng/ml, BDNF did not show such an effect, but it enhanced the magnitude of expressed LTP. On the other hand, NT-3 and NGF had none of these effects. Immunohistochemical staining of slices with antibody against BDNF showed that exogenous BDNF penetrated into the whole slice within approximately 5 min of its application. The actions of BDNF were blocked by preincubation of slices with TrkB-IgG fusion protein, a BDNF scavenger, or coapplication of K252a, an inhibitor for receptor tyrosine kinases. TrkB-IgG or K252a itself completely blocked LTP, suggesting that endogenous BDNF or another TrkB ligand plays a role in LTP in the developing visual cortex.     

Metabotropic glutamate receptors in the ventrolateral medulla of rats

We investigated the hypothesis that stimulation of metabotropic excitatory amino acid receptors in the ventrolateral medulla evokes cardiovascular responses. Thus, (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid [(1S,3R)-ACPD], a selective agonist of metabotropic excitatory amino acid receptors, was microinjected into the rostral or caudal ventrolateral medulla of halothane-anesthetized Sprague-Dawley rats. Microinjections of (1S,3R)-ACPD (100 pmol-1 nmol) into the rostral ventrolateral medulla produced dose-dependent increases in mean arterial pressure (+20 +/- 4 mm Hg by 100 pmol and +35 +/- 2 mm Hg by 1 nmol, p < 0.01 versus artificial cerebrospinal fluid) and integrated splanchnic sympathetic nerve activity (+17 +/- 3% and +46 +/- 4%, respectively, p < 0.01), whereas (1S,3+)-ACPD microinjected into the caudal ventrolateral medulla decreased mean arterial pressure (-28 +/- 2 mm Hg by 100 pmol and -48 +/- 6 mm Hg by 1 nmol, p < 0.01 versus artificial cerebrospinal fluid) and splanchnic sympathetic nerve activity (-24 +/- 4% and -49 +/- 5%, p < 0.01). The blockade of ionotropic excitatory amino acid receptors by the combined injection of 2-amino-7-phosphonoheptanoic acid (200 pmol) and 6,7-dinitroquinoxaline-2,3-dione (200 pmol), which effectively blocked the responses elicited by either N-methyl-D-aspartate (20 pmol) or alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (5 pmol), failed to affect the responses evoked by either (1S,3R)-ACPD (100 pmol) or L-glutamate (2 nmol) microinjected in the rostral and caudal ventrolateral medulla. These results suggest that metabotropic receptors are present and mediate cardiovascular responses evoked by L-glutamate injections into the rostral and caudal ventrolateral medulla.     

N-methyl-D-aspartate receptors are indispensable for the formation of long-term potentiation in the rat suprachiasmatic nucleus in vitro

Optic nerve (ON) stimulation caused a postsynaptic field potential in the suprachiasmatic nucleus (SCN) of rat hypothalamic slices. The postsynaptic field potential was suppressed by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA receptor antagonist, in a concentration-dependent manner, but not affected by D-amino-5-phosphonovaleric acid (APV), a competitive NMDA receptor antagonist. Tetanic stimulation to the ON induced long-term potentiation (LTP) in the SCN. Application of APV at 50 microM inhibited the induction of LTP by tetanic stimulation but CNQX at lower dose (5 microM) didn't inhibit it. These results suggest that NMDA receptors are indispensable for the induction of LTP after tetanic stimulation.     

Metabotropic glutamate receptor mediated long-term depression in developing hippocampus

The effects of bath application of the metabotropic glutamate receptor (mGluR) agonist 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD, 10 microM) were studied at the Schaffer collateral-CA1 synapse in hippocampal slices from rats of 8-33 days postnatal age. In immature animals (8-12 days) ACPD induced a biphasic response characterized by an acute decrease in field EPSP slope (approximately 50-60% of baseline) in the presence of the agonist, followed by long-term depression (LTD, approximately 75-80% of baseline) after washout. In animals older than 20 days, ACPD induced a slow onset potentiation or minimal change. Both the acute depression and LTD were blocked by the mGluR antagonist alpha-methyl-4-carboxyphenyl glycine (MCPG). ACPD-induced LTD was blocked by the N-methyl-D-aspartate receptor (NMDAR) antagonists D(-)-2-amino-5 phosphopentanoic acid (AP5) and dizocilpine maleate (MK-801), and by ethanol. Glutamic pyruvic transaminase, an enzyme that selectively metabolizes endogenous extracellular glutamate, also blocked LTD suggesting that the requisite NMDA currents were tonically activated by extracellular rather than synaptically released glutamate. ACPD-induced LTD was blocked by staurosporine, indicating a requirement for serinethreonine kinase activation, and was unaffected by the L-type voltage sensitive calcium channel blocker nitrendipine and the A1 adenosine receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine (CPT). Because mGluR-mediated LTD was observed only in immature CA1, mGluRs may play a role in hippocampal development, perhaps by contributing to synapse pruning in a temporally restricted fashion.     

Homo- and heterosynaptic long-term potentiation in the medial cortex of the turtle brain in vitro

Juvenile rheumatoid arthritis (JRA) is the most commonly diagnosed rheumatic disease in children and may represent not a single disease, but rather a syndrome of diverse aetiologies in which inflammation is an exceedingly complex process. Oxidative free radical production at inflammation sites contributes to tissue damage and could also play a significant role in the pathogenesis of JRA. The aim of this study was to evaluate the antioxidant status and lipid peroxidation parameters related to the clinical form of JRA. Plasma malondialdehyde and hydroperoxide concentrations in children with polyarticular and systemic JRA subtypes were significantly higher than in controls. Plasma vitamin E and beta-carotene levels of the JRA children were lower in the three forms compared with healthy children. Patients with JRA present an imbalance in the oxidant-antioxidant system that manifests clearly in the polyarticular and systemic forms through an increase in lipoperoxidation products and significant decrease in the lipid-soluble antioxidants vitamin E and beta-carotene.     

Role of platelet-activating factor in long-term potentiation of the rat medial vestibular nuclei

In rat brain stem slices, we investigated the role of platelet activating factor (PAF) in long-term potentiation (LTP) induced in the ventral part of the medial vestibular nuclei (MVN) by high-frequency stimulation (HFS) of the primary vestibular afferent. The synaptosomal PAF receptor antagonist, BN-52021 was administered before and after HFS. BN-52021 did not modify the vestibular potentials under basal conditions, but it reduced the magnitude of potentiation induced by HFS, which completely developed after the drug wash-out. The same effect was obtained by using CV-62091, a more potent PAF antagonist at microsomal binding sites, but with concentrations higher than those of BN-52021. By contrast both BN-52021 and CV-6209 had no effect on the potentiation once induced. This demonstrates that PAF is involved in the induction but not in the maintenance of vestibular long-term effect through activation of synaptosomal PAF receptors. In addition, we analyzed the effect of the PAF analogue, 1-O-hexadecyl-2-O- (methylcarbamyl)-sn-glycero-3-phosphocoline (MC-PAF) and the inactive PAF metabolite, 1-O-hexadecyl-sn-glycero-3-phosphocoline (Lyso-PAF) on vestibular responses. Our results show that MC-PAF, but not Lyso-PAF induced potentiation. This potentiation was prevented by D,L-2-amino 5-phosphonopentanoic acid, suggesting an involvement of N-methyl-D-aspartate receptors. Furthermore, under BN-52021 and CV-6209, the MC-PAF potentiation was reduced or abolished. The dose-effect curve of MC-PAF showed a shift to the right greater under BN-52021 than under CV-6209, confirming the main dependence of MC-PAF potentiation on the activation of synaptosomal PAF receptors. Our results suggest that PAF can be released in the MVN after the activation of postsynaptic mechanisms triggering LTP, and it may act as a retrograde messenger which activates the presynaptic mechanisms facilitating synaptic plasticity.     

Metabotropic glutamate receptors mediate activation of NPY-Y2 receptor expression in the rat dentate gyrus

Neuropeptide Y-Y2 receptor mRNA and binding were investigated after local injection of excitatory amino acid receptor agonists into the rat hippocampus. The general metabotropic glutamate receptor (mGluR) agonist (1S,3R)ACPD (200 and 400 nmol) and the group I mGluR agonist DHPG (50 nmol) enhanced Y2 receptor mRNA levels in granule cells (by up to 470%) and [125I]PYY(3-36) binding in mossy fibers. The group I mGluR antagonist 4-CPG (200 nmol) inhibited the action of (1S,3R)ACPD. On the other hand, AMPA and NMDA enhanced Y2 receptor expression only at neurodegenerative doses (> 0.3 and 3 nmol, respectively). It is suggested that seizure-induced Y2 receptor expression in granule cells may be mediated by group I mGluRs.     

Serotonin inhibits the induction of long-term potentiation in rat primary visual cortex

1. The effect of serotonin (5-hydroxytryptamine; 5-HT) on the induction of long-term potentiation (LTP) in rat visual cortex was investigated by using slice preparations in vitro. 2. Bath application of 5-HT (0.1-10 microM) did not affect the baseline synaptic potentials evoked by single-pulse test stimulation, but inhibited the induction of LTP in a concentration-dependent manner. 3. The effect of 5-HT was blocked by the 5-HT1 receptor antagonist pindolol or the 5-HT2,7 receptor antagonist ritanserin, but not by the 5-HT3,4 receptor antagonist MDL72222. 4. These results suggest that 5-HT plays a role in suppressing the induction of LTP in the rat visual cortex.     

Metabotropic glutamate receptors: electrophysiological properties and role in plasticity

Electrophysiological research on mGluRs is now very extensive, and it is clear that activation of mGluRs results in a large number of diverse cellular actions. Studies of mGluRs and on ionic channels has clearly demonstrated that mGluR activation has a widespread and potent inhibitory action on both voltage-gated Ca2+ channels and K+ channels. Inhibition of N-type Ca2+ channels, and inhibition of Ca(++)-dependent K+ current, IAHP, and IM being particularly prominent. Potentiation of activation of both Ca2+ and K+ channels has also been observed, although less prominently than inhibition, but mGluR-mediated activation of non-selective cationic channels is widespread. In a small number of studies, generation of an mGluR-mediated slow excitatory postsynaptic potential has been demonstrated as a consequence of the effect of mGluR activation on ion channels, such as activation of a non-selective cationic channels. Although certain mGluR-modulation of channels is a consequence of direct G-protein-linked action, for example, inhibition of Ca2+ channels, many other effects occur as a result of activation of intracellular messenger pathways, but at present, little progress has been made on the identification of the messengers. The field of study of the involvement of mGluRs in synaptic plasticity is very large. Evidence for the involvement of mGluRs in one form of LTD induction in the cerebellum and hippocampus is now particularly impressive. However, the role of mGluRs in LTP induction continues to be a source of dispute, and resolution of the question of the exact involvement of mGluRs in the induction of LTP will have to await the production of more selective ligands and of selective gene knockouts.