l-Homocysteate Preferentially Activates N-methyl-D-aspartate Receptors to CA1 Rat Hippocampal Neurons

Intracellular recordings and current and single-electrode voltage-clamp techniques were used to study the membrane responses of CA1 pyramidal neurons to bath application of l-homocysteic acid (l-HC) in the rat hippocampal slice preparation. In control artificial cerebrospinal fluid (ACSF), l-HC (25 - 250 microM) depolarized the membrane and induced a burst-like firing pattern. Both the membrane depolarization and the burst firing were blocked by the N-methyl-d-aspartic acid (NMDA) receptor antagonists d-(-)-2-amino-5-phosphonovaleric acid (AP-5, 50 microM), d-(-)-2-amino-7-phosphonoheptanoic acid (AP-7, 50 microM) and (+/-)-3-(2-carboxy-piperazin-4-yl)-propyl-1-phosphonic acid (CPP, 20 microM). In ACSF containing tetrodotoxin (1 microM), l-HC (100 - 300 microM) induced at resting membrane potential a depolarization which was associated with a small increase in input conductance. These effects were unaffected by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 - 20 microM) but were fully blocked by AP-5, AP-7 (50 microM) and CPP (10 - 20 microM). In voltage-clamp experiments, l-HC induced slow inward currents which were voltage-dependent between - 70 and - 30 mV and reversed polarity near 0 mV. The l-HC-induced inward current was unaffected by CNQX (10 - 20 microM) but was strongly reduced by AP-5 or AP-7 (50 microM). The l-HC-induced inward current was temperature-dependent. Between - 60 and - 70 mV, its amplitude increased by 320% when the temperature was lowered from 33 to 22 degrees C. The l-HC-induced current was also potentiated by the specific l-HC uptake blocker beta-p-chlorophenylglutamate (Chlorpheg, 0.5 - 2 mM). These data suggest that l-HC preferentially activates NMDA receptors in CA1 hippocampal neurons.

Serum deprivation-induced apoptosis in cultured hippocampi is prevented by kainate

Serum deprivation of hippocampal organotypic cultures induced cell death within 6 h in dentate gyrus granule cells and hilar interneurons whereas neurons from other hippocampal regions were spared. Dying neurons exhibited condensed chromatin in the nuclei, as revealed by cresyl violet, Hoescht staining, and electron microscopy. Cell death was abolished by cycloheximide. KA, an agonist of AMPA/KA receptors that induces depolarization, also prevented neuronal death. This effect was antagonized by the AMPA/KA receptor antagonist DNQX, but not by APV, an antagonist of NMDA receptors. PTX, a GABA(A) receptor antagonist, reduced neuronal death by 50% after serum withdrawal. These data indicate that protein synthesis-dependent programmed cell death (PCD) occurs in the dentate gyrus upon trophic support withdrawal and suggest that neuronal activity contributes to cellular homeostasis.

Model of spatio-temporal propagation of action potentials in the Schaffer collateral pathway of the CA1 area of the rat hippocampus

There is a sharp contrast between the profuse in vivo axonal arborization of CA3 pyramidal cells in the CA1 area and the low probability of finding pairs of connected CA3-CA1 pyramidal cells in vitro. These anatomical differences contribute to a connectivity argument for discrepancies between electrophysiological data recorded in vitro and in vivo. In order to investigate this issue, we have developed a realistic computer model of the Schaffer collateral pathway of the hippocampus and analyzed the spatio-temporal distribution of action potentials along this pathway following three different types of electrical test stimulus. Direct activation of mossy fibers, CA3 pyramidal cells and focal stimulation of CA1 stratum radiatum were investigated. The parameters of the model were selected from available biological data. Spikes in Schaffer collaterals were followed from their onset in the CA3 pyramidal cell initial segment to the last order branches of their axonal tree in two types of configuration: the whole hippocampus and the slice configuration. The anatomical and electropysiological characteristics of the mossy fibre and Schaffer collateral pathways were found to impose strong constraints on the spatio-temporal distribution of action potentials in the CA1 area. Specific projection zones are determined by the spatial localization of the emitting CA3 pyramidal cells. Their position also defines precise time windows during which some CA1 projection zones receive a large number of correlated signals. Moreover, the variability of the delay at the mossy fibre/CA3 pyramidal cell synapse seems to provide the CA1 projection zones with a background level of excitation. Finally, we show how the patterns of activation obtained in the whole hippocampus are different from those obtained in the slice.

Alpha-brain spectrin mRNA belongs to the population of intradendritically transported mRNAs

Brain spectrin is a cytoskeletal protein involved in neuronal polarization and differentiation. We have studied the intraneuronal expression of non-erythroid (NE) alpha-spectrin mRNA in the rat brain during the development of the CA3 pyramidal cells, and compared it with alpha-tubulin mRNA expression. In contrast to alpha-tubulin expression, which remains located in the neuronal somata, NE alpha-spectrin mRNA was present in the dendritic compartment during the first 2 weeks of life. NE alpha-Brain spectrin mRNA transport into the dendrites coincides with critical development events, including dendritic arborization, growth and synaptogenesis, and could be dependent on the appearance of synaptic activity at the mossy fibre/CA3 synapse.

N-Methyl-D-aspartate receptor subunits NR1 and NR2C are overexpressed in the inferior colliculus of audiogenic mice

Some non-DBA2 Albino Swiss mice exhibit noise induced epileptic seizures during a short period of postnatal development. Because N-methyl-D-aspartate (NMDA) glutamate ionotropic receptors are involved in the occurrence of audiogenic seizures, we investigated by in situ hybridization methods, the expression of the different subunits (NR1, NR2A, NR2B, NR2C) of this receptor in the central nucleus of the inferior colliculus (IC), a main relay of the auditory pathways. At postnatal day 20, the NR2C subunit is highly expressed in the IC of convulsive mice, while in non-convulsive mice a slight signal is only found for NR1, NR2A, and NR2B. In adult mice, the NR1 and NR2A signals are observed while the NR2B signal is almost undetectable. The audiogenic susceptibility may be related to the transient expression of the NR2C subunit during a brief neonatal period during which synaptic reorganization happens.

Persistent current oscillations produced by activation of metabotropic glutamate receptors in immature rat CA3 hippocampal neurons

1. The single-electrode voltage-clamp technique was used to study the effects of the metabotropic glutamate receptors (mGluRs) agonist 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD, ACPD, 3-10 microM) on CA3 hippocampal neurons during the 1st 10 days of postnatal (P) life and in adulthood. 2. Repeated applications of 1S,3R-ACPD, in the presence of tetrodotoxin (TTX, 1 microM), tetraethylammonium chloride (TEACl 10 mM), and CsCl (2 mM), induced in immature but not in adult neurons periodic inward currents (PICs) that persisted for several hours after the last application of the agonist. 3. PICs, which were generated by nonspecific cationic currents, reversed polarity at 2.8 +/- 3 (SD) mV. They were reversibly blocked by kynurenic acid (1 mM), suggesting that they were mediated by glutamate acting on ionotropic receptors. They were also abolished in a nominally Ca(2+)-free medium. 4. PICs were irreversibly abolished by thapsigargin (10 microM) but were unaffected by ryanodine (10-40 microM). Caffeine (2 mM) also reversibly blocked PICs; this effect was independent from adenosine 3',5'-cyclic monophosphate (cAMP) accumulation, inhibition of voltage-dependent Ca2+ current, or blockade of adenosine receptors. 5. We suggest that, in neonatal slices, mGluRs-induced PICs are triggered by elevation of [Ca2+]i, after mobilization of Ca2+ from inositol 1,4,5-trisphosphate (InsP3)-sensitive stores. This will lead to a persistent, pulsatile release of glutamate from presynaptic nerve terminals, a phenomenon that is probably maintained via a calcium-induced-calcium release process.

Developmental change of alpha-spectrin mRNA in the rat brain

Spectrin is a cytoskeletal protein considered to be a major component of intracellular cohesion. Using an in situ hybridization approach, we have investigated the developmental expression of the mRNA encoding the alpha-subunit of rat brain spectrins, from birth to adulthood. alpha-Subunit mRNA is detectable at birth, in brain areas with perinatal neurogenesis, such as the cerebral cortex, hippocampus, thalamus, and olfactory bulb. alpha-Brain-spectrin mRNA increases gradually during the first postnatal days to reach a plateau between the second and the third week of life. In the young adult brain, the level of alpha-brain spectrin mRNA decreased globally. This spacio-temporal distribution argues for the involvement of the mRNA in the synthesis of both the erythroid and non-erythroid brain spectrin isoforms. We have focused our attention on the hippocampal formation and the cerebellum. In both regions, in situ hybridization signal variations are superimposable with neuronal maturation gradients. This pattern of variation, coupled with the known interaction of brain spectrins with other cytoskeletal proteins, agrees with the notion that brain spectrins may be involved in neuronal differentiation by way of the cytoskeletal lattice organization.

Use of hippocampal slices to study mRNA changes in relation to synaptic plasticity

We have developed a method allowing suitable morphological conservation combined with in situ hybridization, on hippocampal slices used in conventional electrophysiological studies. After a bath application of kainate (KA, 750 nM, 2 min 15 s), electrical stimulation of the mossy fibre zone evoked epileptiform activity for up to 2 h. In situ hybridization performed on these slices showed a marked increased in expression of the transcription factor Zif/268 over the pyramidal and the granule cells and the surrounding neuropils. Bath application of tetraethylammonium (TEA, 25 mM, 10 min) elicited long-term potentiation in CA1 lasting up to 4 h. This was associated with enhanced expression of Zif/268 which returned to control values after 2 h 30 min. These observations suggest that slice preparations are suitable for the study of the role of neuronal activity in the regulation of gene expression.

Apoptosis associated DNA fragmentation in epileptic brain damage

We have examined the epileptic brain damage generated by intra-amygdaloid administration of kainic acid (KA). In the vulnerable CA3 region of the rat hippocampus, neurones developed apoptotic properties since, (i) their nuclei were positively stained with a selective in situ DNA fragmentation staining method; (ii) DNA cleavage into internucleosome-sized fragments was observed on agarose gels. Our results suggest that epileptic seizures generated in the amygdala by KA trigger apoptotic cell damage in pyramidal CA3 neurones.

Aplastic anemia in neonatal lupus erythematosus

OBJECTIVE

To describe an infant with neonatal lupus erythematosus associated with aplastic anemia.

SETTING

The pediatric department in a tertiary-care hospital.

INTERVENTIONS

Packed red blood cell transfusions and a 3-week course of high-dose steroid therapy.

MEASUREMENTS/MAIN RESULTS

The patient presented with severe anemia and a circumscribed, reticular, macular rash on the face and neck at 5 months of age. Skin lesion biopsy revealed epidermic hyperkeratosis, hydropic degeneration of the basal layer, and deposition of immunoglobulins and granular C1q at the dermoepidermal junction. Ro/SS-A antibodies were present in the infant. BFU-E (erythroid progenitor burst-forming unit) colonies in bone marrow increased by about tenfold when suppressor CD8+ T lymphocytes were removed, indicating immune suppression of hematopoiesis. High-dose steroid therapy failed. The infant subsequently developed gram-negative sepsis, severe metabolic acidosis, and consumptive coagulopathy and died.

CONCLUSIONS

Neonatal lupus erythematosus may present as part of a spectrum. The disease may range from mild and transient to a severe, life-threatening condition requiring immediate intervention, as in the case reported here. This is the first report of neonatal lupus associated with aplastic anemia due to immune-mediated suppression of hematopoiesis.

Transient expression of the NR2C subunit of the NMDA receptor in developing rat brain

Pharmacologically distinct NMDA-glutamate receptor subtypes have been reported in brain. We have studied the developmental expression of the mRNA encoding the NMDA receptor NR2C subunit in the rat brain by in situ hybridization. In contrast with the adult where no hybridization signal was detected in the hippocampus, a significant signal was seen in this formation during a restricted developmental period (P7-P14). The labelling covered large parts of the hippocampus including in particular the stratum radiatum, pyramidal and oriens layers of the CA1 area. The role of the NR2C subunit in neonatal NMDA receptor properties is discussed.

A contribution to the structure-activity relationship in glutamate receptor ligands: 2. Characterization of 2-amino-4-oxo-5-pentanoic acid as NMDA receptor antagonist

Pharmacological properties of 2-amino-4-oxo-5-phosphonopentanoic acid (AOPA) on excitatory amino acids mediated responses have been tested in CA1 rat hippocampal neurones, using intracellular recordings and current and voltage clamp techniques. These properties were compared with those of the well-known NMDA antagonist, D(-)2-amino-5-phosphonopentanoic acid (AP-5). AOPA completely abolished the response to NMDA but had no effects on the responses to AMPA, quisqualate and kainate. In voltage clamp experiments AOPA antagonized NMDA-induced currents and produced a parallel shift of the NMDA concentration-response curve. Schild analysis gave a Kd value of 26 microM. AP-5 also produced a similar shift in this curve with a Kd of 6.9 mu.

A contribution to the structure-activity relationship in glutamate receptor ligands: 1. omega-Aminophosphonic acids do not antagonize NMDA receptors

Pharmacological properties of a series of alpha, omega-diamino-omega-phosphonocarboxylic acids and alpha, omega-diamino-alpha, omega-bis(phosphonic acids) on different excitatory amino acids mediated responses have been tested in CA1 rat hippocampal neurones, using intracellular recordings and current and voltage clamp techniques. In contrast with known antagonists as D(-)2-amino-5-phosphonopentanoic acid (AP-5) and 2-amino-4-oxo-5-phosphonopentanoic acid, which completely abolished the NMDA-response, no antagonistic activity was found. We conclude that the introduction of an omega-amino function abolishes the NMDA-antagonistic activity of alpha-amino-omega-phosphonocarboxylic acids.

Mast Cell Degranulating Peptide Increases the Frequency of Spontaneous Miniature Postsynaptic Currents in CA3 Rat Hippocampal Neurons

Mast cell degranulating peptide (MCDP) is a neurotoxic agent isolated from bee venom. It produces a long-term potentiation in the hippocampus. We now report that MCDP, at nanomolar concentrations, induces a reduction of a transient voltage-dependent potassium current (ID) in CA3 rat pyramidal neurons and a persistent (>30 min) enhancement of the frequency of spontaneous miniature excitatory and inhibitory postsynaptic currents (m.e.p.s.c.s. and m.i.p.s.c.s.). M.e.p.s.c.s. and m.i.p.s.c.s. were recorded in the presence of bicuculline (30 microM) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM), respectively. The increased frequency of m.e.p.s.c.s. (408 +/- 60%) and m.i.p.s.c.s. (583 +/- 553%) was independent of the reduction of ID because 4-aminopyridine (4-AP, 30 microM - 2 mM) blocked ID but had no effects on m.e.p.s.c.s. and m.i.p.s.c.s. In the presence of the calcium channel blocker manganese (3 mM), MCDP still enhanced the frequency of m.e.p.s.c.s. (326 +/- 162%). It is concluded that MCDP augments the release of excitatory and inhibitory transmitter by an action, which is independent of calcium influx, through voltage-dependent channels.

A new method for the measurement of endogenous transmitter release in localized regions of hippocampal slices

We describe here a method that allows measurement of the release of endogenous amino acids from localized regions of brain slices combined with conventional electrophysiological experiments. Hippocampal slices were placed in fully submerged chambers and a cannula was positioned just above the dendritic layers of CA1. The cannula was connected to a peristaltic pump and the content of amino acids in the perfusate was measured by HPLC. Extracellular field potentials were concomitantly recorded. Stable levels of aspartate and glutamate were found above the stratum radiatum of CA1. No detectable release was found when the cannula was located above the alveus, the fimbria or in the effluent of the slice. A pulse of K+ (50 mM) produced a brief 3-fold increase in glutamate, aspartate and a detectable release of GABA in CA1. Brief high frequency trains (10 Hz) also increased significantly the release. This method will be useful in determining alterations in transmitter release in the slice in relation to anoxia, epilepsy and long term potentiation.

GABA mediated excitation in immature rat CA3 hippocampal neurons

Intracellular recordings from rat hippocampal neurons in vitro during the first postnatal week revealed the presence of spontaneous giant depolarizing potentials (GDPs). These were generated by the synchronous discharge of a population of neurons. GDPs reversed polarity at -27 and -51 mV when recorded with KCl or K-methylsulphate filled electrodes, respectively. GDPs were blocked by the GABAA receptor antagonist bicuculline (10 microM). Iontophoretic or bath applications of GABA (10-300 microM) in the presence of tetrodotoxin (1 microM), induced a membrane depolarization or in voltage clamp experiments an inward current which reversed polarity at the same potential as GDPs. The response to GABA was blocked in a non-competitive manner by bicuculline (10 microM) and did not desensitize. GABA mediated GDPs were presynaptically modulated by N-methyl-D-aspartate (NMDA) and non-NMDA receptors. Their frequency was reduced or blocked by NMDA receptor antagonists and by the rather specific non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). The frequency of GDPs was enhanced by glycine and D-serine (10-30 microM) in a strychnine insensitive manner. This effect was blocked by AP-5, suggesting that it was mediated by the allosteric modulatory site of the NMDA receptor. These observations suggest that most of the 'excitatory' drive in immature neurons is mediated by GABA acting on GABAA receptors; furthermore excitatory amino acids modulate the release of GABA by a presynaptic action on GABAergic interneurons.

Mechanism of induction of long term potentiation by the mast cell degranulating peptide

The properties of Long Term Potentiation (LTP), which is a sustained enhancement of the synaptic response produced by a brief train of electrical stimulation, and its mechanisms are briefly reviewed. Bath application of the mast cell degranulating peptide (MCD) - a peptide isolated from bee venom- also produces in hippocampal slices LTP which is indistinguishable from that produced by a train of electrical stimulation (no change in postsynaptic cell properties, APV sensitive). In vivo push-pull experiments indicate that this LTP is not associated with a sustained enhancement of release of glutamate and aspartate, the two principle transmitters of the hippocampus, but there is a delayed enhanced release of proteins in the extracellular space which may contribute to the maintenance of the potentiation.

Transient increase in the number of cholinergic neurons in the developing rat dentate gyrus

Using a monoclonal antibody against choline acetyltransferase (ChAT), we have examined the distribution of cholinergic neurons in the rat dentate gyrus during development. ChAT-positive neurons were occasionally detected in the hilus on postnatal day 2 (P2). There was a transient abrupt increase in the number and density of ChAT-positive neurons between P15 and P20 and then a decline to the adult level with few ChAT-immunoreactive neurons. A few ChAT-positive varicose fibers and punctae were first seen at P5. They increased in number and density until P20 when they reached the adult level and distribution. These observations suggest the occurrence of a transient expression of cholinergic markers in the hippocampus.

Antidiabetic sulfonylureas: localization of binding sites in the brain and effects on the hyperpolarization induced by anoxia in hippocampal slices

The distribution of antidiabetic sulfonylurea [( 3H]glibenclamide) binding sites is heterogeneous in rat brain. Pyramidal and extrapyramidal motor system contain the highest densities of sites, particularly in the substantia nigra and in the globus pallidus. Only low levels are present in the hypothalamic nuclei and the main medulla oblongata regions. In hippocampal formation the stratum lucidum and the stratum lacunosum moleculare of CA3 show an important density of glibenclamide binding sites. Electrophysiological studies with hippocampal slices show that glibenclamide blocks hyperpolarization induced by anoxia, suggesting the involvement of adenosine triphosphate-sensitive K+ channel in this early hyperpolarization event.

Epileptogenic properties of the mast cell degranulating peptide in CA3 hippocampal neurones

The epileptogenic properties of the mast cell degranulating peptide (MCD) have been investigated in the CA3 region of the hippocampal slice preparation. Brief (3-5 min) bath application of MCD (0.5-2 microM) to CA3 hippocampal neurones produced an enhancement of the spontaneous synaptic activity and the appearance of spontaneous bursts that persisted for several hours. These bursts were network driven and the underlying paroxysmal depolarizing shift met the criteria for a giant excitatory postsynaptic potential (EPSP), with a reversal potential close to 0 mV. Furthermore following the application of MCD, stimulation of the mossy fibres, commissural or temporo-ammonic pathway evoked an EPSP followed by an evoked network burst. The bursts which could be elicited for several hours were reversibly blocked by a brief application of tetrodotoxin (TTX; 1 microM) or cobalt (2 mM). In contrast, prior and concomitant treatment with TTX or cobalt prevented the occurrence of the bursts induced by MCD. The effects of MCD were not due to a blockade of GABAergic inhibition since the toxin did not reduce the fast and slow IPSP. Furthermore, the N-methyl-D-aspartate (NMDA) antagonists D-2-amino-phosphonovalerate (D-APV; 30 microM) or DL-amino-phosphoheptanoic acid (AP-7, 30 microM) did not block the action of MCD, suggesting that the activation of NMDA receptors are neither necessary nor sufficient for MCD-induced bursts. It is concluded that MCD induces in the CA3 region long-lasting changes in the synaptic responses which may be mediated through a presynaptic mechanism.

Long-term potentiation of synaptic transmission in the hippocampus induced by a bee venom peptide

Several neurotoxins have been isolated from bee venom. One of these, the mast cell degranulating peptide (MCD), releases histamine from mast cells and on central administration produces arousal at low concentrations and convulsions at higher doses. These effects are mediated through specific high-affinity binding sites which are concentrated in cortical structures, notably the hippocampus. This structure appears to be the source of changes in the electrocorticogram that follow injections of MCD into the cerebral ventricle, and which induce a quasi-permanent hippocampal theta rhythm in the motionless rat alternating with epileptiform spike waves. We report here that brief application of MCD to the CA1 region of hippocampal slices induces long-term potentiation, that is, a long-lasting increase in the efficacy of synaptic transmission. This potentiation seems to be indistinguishable from the classical LTP produced by trains of high-frequency electrical stimulation and considered to be related in some way to memory. Using binding to synaptosomal membranes and radioimmunoassay techniques, we have also found an endogenous peptide equivalent of MCD in brain extracts. This raises the possibility that a MCD-like peptide may be important in long-term potentiation.

Acquired factor X and antithrombin III deficiency in a patient with primary amyloidosis and nephrotic syndrome

A 45-year-old man with primary amyloidosis was initially seen with nephrotic syndrome. Factor X was found to be 5% and antithrombin III (AT III) 45% of normal plasma values. During an 11-month period, despite severe factor X deficiency, the patient did not have any bleeding complications. He developed progressive renal failure and AT III levels increased to normal, at which time he developed severe bleeding complications. These findings suggest a protective role of AT III deficiency against bleeding in a patient with severe factor X deficiency.

The management of obstructive hydrocephalus by the use of external continuous ventricular drainage

External continuous ventricular drainage (CVD) in patients suffering from obstructive hydrocephalus is being used in many neurosurgical centers as a routine procedure for the temporary relief of intracranial pressure. The results of this treatment have been insufficiently evaluated. In the present study two groups of patients were investigated. In one, CVD was never used. In the other one it was used in all cases. It was found that the use of CVD decreased mortality rate most significantly. It is recommended that CVD should be used as a temporary measure for the treatment of the increased intracranial pressure in patients suffering from obstructive hydrocephalus.