Synthesis and release of GABA in cerebral cortical neurons co-cultured with astrocytes from cerebral cortex or cerebellum

Cerebral cortical neurons were co-cultured for up to 7 days with astrocytes after plating on top of a confluent layer of astrocytes cultured from either cerebral cortex or cerebellum (sandwich co-cultures). Neurons co-cultured with either cortical or cerebellar astrocytes showed a high stimulus coupled release of gamma-aminobutyric acid (GABA), which is the neurotransmitter of these neurons. When the astrocyte selective GABA uptake inhibitor 4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol was added during the release experiments, an increase in the stimulus coupled GABA release was seen, indicating that the astrocytes take up a large fraction of GABA released from the neurons. The activity of the GABA synthesizing enzyme glutamate decarboxylase, which is a specific marker of GABAergic neurons, was markedly increased in sandwich co-cultures of cortical neurons and cerebellar astrocytes compared to neurons cultured in the absence of astrocytes whereas in co-cultures with cortical astrocytes this increase was less pronounced. Pure astrocyte cultures did not show any detectable glutamate decarboxylase activity. The astrocyte specific marker enzyme glutamine synthetase (GS) was present at high activity in a glucocorticoid-inducible form in pure astrocytes as well as in co-cultures regardless of the regional origin of the astrocytes. When neurons were cultured on top of the astrocytes, the specific activity of GS was lower compared to astrocytes cultured alone, a result compatible with the notion that neurons are devoid of this enzyme. The results show that cortical neurons develop and differentiate when seeded on top of both homotypic and heterotypic astrocytes. Moreover, it could be demonstrated that the two cell types in the culture system communicate with each other with regard to GABA homeostasis during transmitter release.     

Neuronal Soluble Factors Differentially Regulate the Expression of the GLT1 and GLAST Glutamate Transporters in Cultured Astroglia

Abstract: The glutamate transporters in the plasma membranes of neural cells secure termination of the glutamatergic synaptic transmission and keep the glutamate levels below toxic concentrations. Astrocytes express two types of glutamate transporters, GLAST (EAAT1) and GLT1 (EAAT2). GLT1 predominates quantitatively and is responsible for most of the glutamate uptake activity in the juvenile and adult brain. However, GLT1 is severely down-regulated in amyotrophic lateral sclerosis, a progressive neurodegenerative disease. Furthermore, selective loss of this transporter occurs in cultured astroglia. Expression of GLAST, but not of GLT1, seems to be regulated via the glutamate receptor signalling. The present study was undertaken to examine whether neuronal factors, other than glutamate, influence the expression of astroglial glutamate transporters. The expression of GLT1 and GLAST was examined in primary cultures of cerebellar granule neurons, cortical neurons, and astrocytes under different experimental conditions, including those that mimic neuron-astrocyte interactions. Pure astroglial cultures expressed only GLAST, whereas astrocytes grown in the presence of neurons expressed both GLAST (at increased levels) and GLT1. The induction of GLT1 protein and its mRNA was reproduced in pure cortical astroglial cultures supplemented with conditioned media from cortical neuronal cultures or from mixed neuron-glia cultures. This treatment did not change the levels of GLAST. These results suggest that soluble neuronal factors differentially regulate the expression of GLT1 and GLAST in cultured astroglia. Further elucidation of the molecular nature of the secreted neuronal factors and corresponding signalling pathways regulating the expression of the astroglial glutamate transporters in vitro may reveal mechanisms important for the understanding and treatment of neurological diseases.     

Selective reduction by serotonin, of neuronal excitation in the locus coeruleus evoked by glutamate

In the rat, iontophoretically applied serotonin substantially attenuated the excitation of locus coeruleus neurons evoked by iontophoretic glutamate but not that elicited by acetylcholine. These results occurred independently of serotonin's variable effects on spontaneous discharge, and indicate a neuromodulatory role of serotonin in locus coeruleus.     

BMPs, FGF8 and Wnts regulate the differentiation of locus coeruleus noradrenergic neuronal precursors

In the present study, we investigated the involvement of rhombomere 1 patterning proteins in the regulation of the major noradrenergic centre of the brain, the locus coeruleus. Primary cultures of rat embryonic day 13.5 locus coeruleus were treated with fibroblast growth factor-8, noggin and members of the bone morphogenetic and Wnt protein families. We show that bone morphogenetic proteins 2, 5 and 7 increase and noggin decreases the number of tyrosine hydroxylase-positive locus coeruleus neurons. Interestingly, from all Wnts expressed in the first rhombomere by embryonic day 12.5 in the mice, we only found expression of wnt5a mRNA in the vicinity of the locus coeruleus. In agreement with this finding, from all Wnts studied in vitro, only Wnt5a increased the number of tyrosine hydroxylase-positive neurons in locus coeruleus cultures. Finally, we also found that fibroblast growth factor-8 increased the number of tyrosine hydroxylase-positive cells in locus coeruleus cultures. Neither of the identified factors affected the survival of tyrosine hydroxylase-positive locus coeruleus noradrenergic neurons or the proliferation of their progenitors or neurogenesis. Instead, our results suggest that these patterning signals of rhombomere 1 may work to promote the differentiation of noradrenergic progenitors at later stages of development.     

Vestibular mechanisms involved in idiopathic scoliosis

Patients affected by idiopathic scoliosis (IS) show not only a spinal deformity, but also postural and oculomotor deficits suggesting that such syndrome can be related to a vestibular disfunction. It appears, however, that, in children, a slight unbalance in the activity of vestibular complex of both sides escapes the neuronal mechanisms responsible for vestibular compensation and leads to the spinal curvature which characterises IS. Such process could be reinforced by a disrupted integration of vestibular and visual signals at cortical level, leading to an altered perception of the vertical and to abnormal motor commands. In addition to the classical ascending and descending pathways arising from the vestibular nuclei, which utilize glutamate or GABA as neurotransmitters, labyrinthine afferents may also affect spinal, cerebellar and cerebrocortical structures, through the noradrenergic and serotoninergic systems, which originate from the locus coeruleus and the raphe nuclei, respectively. Due to the role of these neuromodulators in brain plasticity, a disruption in the activity of monoaminergic neurons could favour the development of postural and oculomotor deficits. An impaired release of monoamine at cerebrocortical level could also explain the cognitive deficits which may occur in IS patients.     

MRS study of glutamate metabolism in cultured neurons/glia

[U-¹³C]Glutamate metabolism was studied in primary brain cell cultures. Cell extracts as well as redissolved lyophilized media were subjected to nuclear magnetic resonance spectroscopy in order to identify¹³C labeled metabolites. Both neurons and astrocytes metabolized glutamate extensively with¹³C label appearing in aspartate in all cultures. Additionally, GABA is synthesized in the GABAergic cortical neurons. Labeling of lactate and glutamine was prominent in medium from astrocytes, but not detectable in cerebral cortical neurons. Cerebellar granule neurons showed some labeling of lactate. Glutamate derived from the first turn of the tricarboxylic acid cycle (1,2,3-¹³C₃-isotopomer) is present in all cell types analyzed. However, glutamate derived from the second turn of the cycle was only detected in granule neurons. In astrocytes, the transaminase inhibitor aminooxyacetic acid not only abolished the appearance of aspartate, but also of the 1,2,3-¹³C₃-isotopomer of glutamate, thus showing that transmination is necessary for the conversion of 2-oxoglutarate to glutamate. The entry of glutamate into the tricarboxylic acid cycle was, however, not seriously impaired. 3-nitropropionic acid abolished the appearance of aspartate, the 1,2,3-¹³C₃-isotopomer of glutamate and lactate in cerebellar granule neurons. Special issue dedicated to Dr. Herman Bachelard.     

Ornithine-σ-Aminotransferase Exhibits Different Kinetic Properties in Astrocytes, Cerebral Cortex Interneurons, and Cerebellar Granule Cells in Primary Culture

To evaluate a possible role of ornithine-delta-aminotransferase (EC 2.6.1.13; Orn-T) as a rate-limiting enzyme for the synthesis of transmitter glutamate and gamma-aminobutyric acid (GABA), respectively, its activity and kinetic properties were analyzed in cultured astrocytes as well as in neuronal cultures consisting mainly of glutamatergic neurons (cerebellar granule cells) or GABAergic neurons (cerebral cortex interneurons). For comparison the activity and kinetics of Orn-T were also assayed in mouse brain homogenates. The highest activity of Orn-T was found in astrocytes and in cerebral cortical neurons (5.3 +/- 0.5 and 5.3 +/- 0.4 nmol X mg-1 X min-1, respectively) whereas the activities of Orn-T in cerebellar granule cell cultures and in mouse brain were found to be about half of these values (3.1 +/- 0.3 and 2.8 +/- 0.1 nmol X min-1 X mg-1, respectively). From a kinetic study of Orn-T in the different preparations only a relatively low affinity for the enzyme with respect to ornithine was found in cerebellar granule cells, astrocytes, and whole brain [apparent Km values (at 0.5 mM alpha-ketoglutarate): 4.7 +/- 0.9, 4.3 +/- 2.2, and 6.8 +/- 2.2 mM, respectively] whereas the corresponding Km value for Orn-T in cerebral cortex interneurons was found to be significantly lower (apparent Km: 0.8 +/- 0.3 mM). The enzyme was not found to be inhibited by GABA (range 0.1 - 10 mM) in any of the preparations.     

A long-term depression of AMPA currents in cultured cerebellar Purkinje neurons.

Cerebellar long-term depression (LTD) is a model of synaptic plasticity in which conjunctive stimulation of parallel fiber and climbing fiber inputs to a Purkinje neuron induces a persistent depression of the parallel fiber-Purkinje neuron synapse. We report that an analogous phenomenon may be elicited in the cultured mouse Purkinje neuron when iontophoretic glutamate application and depolarization of the Purkinje neurons are substituted for parallel fiber and climbing fiber stimulation, respectively. The induction of LTD in these cerebellar cultures requires activation of both ionotropic (AMPA) and metabotropic quisqualate receptors, together with depolarization in the presence of external Ca2+. This postsynaptic alteration is manifest as a depression of glutamate or AMPA currents, but not aspartate or NMDA currents. These results strengthen the contention that the expression of cerebellar LTD is at least in part postsynaptic and provide evidence that activation of both ionotropic and metabotropic quisqualate receptors are necessary for LTD induction.     

Energy metabolism in glutamatergic neurons,GABAergic neurons and astrocytes in primary cultures

Several aspects of energy metabolism (glucose utilization, lactate production,¹⁴CO₂ production from labeled glucose, glutamate or pyruvate, oxygen consumption and contents of ATP and phosphocreatine) were measured in cerebellar granule cells (glutamatergic) in primary cultures and compared with corresponding data for cerebral cortical neurons (mainly GABA-ergic) and astrocytes. Cerebellar granule cells and astrocytes were metabolically more active than cerebral cortical neurons. Glutamate which is utilized as a major metabolic fuel as astrocytes and, to a lesser extent, in cerebral cortical neurons, was virtually not oxidized in cerebellar granule cells.Special Issue dedicated to Prof. Holger Hydén.     

Induction of Ornithine Decarboxylase by N-Methyl-D-Aspartate Receptor Activation Is Unrelated to Potentiation of Glutamate Excitotoxicity by Polyamines in Cerebellar Granule Neurons

Abstract: Polyamines positively modulate the activity of the N -methyl- d -aspartate (NMDA)-sensitive glutamate receptors. The concentration of polyamines in the brain increases in certain pathological conditions, such as ischemia and brain trauma, and these compounds have been postulated to play a role in excitotoxic neuronal death. In primary cultures of rat cerebellar granule neurons, exogenous application of the polyamines spermidine and spermine (but not putrescine) potentiated the delayed neurotoxicity elicited by NMDA receptor stimulation with glutamate. Furthermore, both toxic and nontoxic concentrations of glutamate stimulated the activity of ornithine decarboxylase (ODC)—the key regulatory enzyme in polyamine synthesis—and increased the concentration of ODC mRNA in cerebellar granule neurons but not in glial cells. Glutamate-induced ODC activation but not neurotoxicity was blocked by the ODC inhibitor difluoromethylornithine. Thus, high extracellular polyamine concentrations potentiate glutamate-triggered neuronal death, but the glutamate-induced increase in neuronal ODC activity may not play a determinant role in the cascade of intracellular events responsible for delayed excitotoxicity.     

Glutaminase in neurons and astrocytes cultured from mouse brain: Kinetic properties and effects of phosphate,glutamate, and ammonia

Phosphate activated glutaminase comprises two kinetically distinguishable enzyme forms in cultures of cerebellar granule cells, of cortical neurons and of astrocytes. Specific activity of glutaminase is higher in cultured neurons compared with astrocytes. Glutaminase is activated by phosphate in all cell types investigated, however, glutaminase in astrocytes reguires a much higher concentration of phosphate for half maximal activation. One of the products, glutamate, inhibits the enzyme strongly, whereas the other product ammonia has only a slight inhibitory action on the enzyme.     

Crucial role of TrkB ligands in the survival and phenotypic differentiation of developing locus coeruleus noradrenergic neurons

The role of glial cell-line derived neurotrophic factor (GDNF) and neurotrophins in the development of locus coeruleus noradrenergic neurons was evaluated. We found that two neurotrophic factors previously reported to prevent the degeneration of lesioned adult central noradrenergic neurons, GDNF and neurotrophin 3 (NT3), do not play significant roles in the prenatal development of locus coeruleus noradrenergic neurons, as demonstrated by: (1) the lack of alterations in double Gdnf/Nt3 null mutant mice; and (2) the lack of survival-promoting effects of GDNF and/or NT3 in rat E13.5 primary cultures. In contrast, null mutant mice for TrkB, the tyrosine kinase receptor for brain-derived neurotrophic factor and neurotrophin 4, displayed a clear loss of locus coeruleus noradrenergic neurons. In accordance with this, treatment of rat E13.5 primary cultures with TrkB ligands prevented the early loss of noradrenergic neurons and maintained their survival for up to 6 days in vitro. Moreover, an additional 5-10-fold increase in the number of tyrosine hydroxylase positive noradrenergic neurons was detected after 12 hours in culture. This second effect of TrkB ligands involved neither proliferation nor survival, because the number of BrdU- or TUNEL-positive noradrenergic neurons did not change and the effect was elicited by delayed administration of either factor. Because TrkB ligands increased the number of tyrosine hydroxylase-positive cells expressing Phox2a, a paired homeodomain protein required for the development of locus coeruleus noradrenergic neurons, but did not affect the number of Phox2a-positive tyrosine hydroxylase-negative cells, our results suggest that the second effect of TrkB ligands may involve promoting or inducing a noradrenergic phenotype. In summary, our findings suggest that, unlike NT3 and GDNF, TrkB ligands are required and sufficient to promote the development of central noradrenergic neurons.     

Synaptic Chemistry Associated with Aberrant Neuronal Development in the Reeler Mouse

Abstract: Pre- and postsynaptic neurochemical markers for several afferent and intrinsic neuronal systems were measured in the mouse mutant, reeler. In the neocortex of the reeler, the relative positions of the polymorphic and pyramidal cells were inverted but this was not associated with alterations in the content/mg protein of synaptic markers for noradrenergic [tyrosine hydroxylase (TH), norepinephrine (NE), NE uptake], cholinergic [choline acetyltransferase (ChAT), quinuclidinyl benzilate (QNB) binding], γ-aminobutyric acid (GABA)ergic (glutamate decarboxylase, GABA uptake, GABA receptors, GABA) or glutamatergic (glutamate uptake, receptors, glutamate) neurons. The laminar distributions of the hippocampal neurons were disrupted and associated with mild hypoplasia; consistent with this alteration, the content/mg protein of some GABAergic (GABA uptake) and glutamatergic (glutamate receptors) markers were slightly increased. The reeler cerebellum was characterized not only by misalignment of neurons but also by a marked loss of granule cells. Commensurate with the degree of cerebellar hypoplasia, the total amount of glutamate content, [³H]l-glutamate uptake activity, [³H]muscimol, and [³H]QNB ligand binding were reduced in the reeler cerebellum. In contrast, presynaptic markers for the noradrenergic (TH, NE) climbing fibers and the cholinergic (ChAT) mossy fibers were significantly increased/mg protein but their total content/cerebellum was near normal. Our data support suggestions that cerebellar granule cells use glutamate as their neurotransmitter and contain GABA and cholinergic receptors. The findings also suggest that misplaced cortical and cerebellar neurons retain normal neurochemical characteristics and that the morphologic alterations do not markedly affect the quantitative development of aminergic afferent systems.     

Monoamine Metabolism in the Locus Coeruleus Measured Concurrently with Behavior During Opiate Withdrawal: An In Vivo Microdialysis Study in Freely Moving Rats

Abstract: Using microdialysis, changes in monoamine metabolism were monitored in the locus coeruleus of freely moving rats during opiate withdrawal concomitantly with behavioral symptoms. Rats were infused with morphine (2 mg/kg/h, s.c.) or saline for 5 days and challenged with naltrexone (100 mg/kg, s.c.) on day 6. Following naltrexone challenge, the classic behavioral symptoms of morphine withdrawal were observed in rats treated with morphine but not in saline-infused rats. In morphine-dependent rats, naltrexone induced a marked increase (280%) in dialysate concentrations of 3,4-dihydroxyphenylacetic acid, an index of the functional activity of the noradrenergic neurons in the locus coeruleus. The local concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid were also increased (70%) during morphine withdrawal. Taken together, these results (a) confirm in unanesthetized rats the hypothesis of an activation by opiate withdrawal of noradrenergic neurons in the locus coeruleus and (b) suggest an increase in serotonergic transmission in the same nucleus during morphine withdrawal.     

Glutamate Neurotoxicity Is Independent of Calpain I Inhibition in Primary Cultures of Cerebellar Granule Cells

Glutamate-induced neurotoxicity and calpain activity were studied in primary cultures of rat cerebellar granule neurons and glial cells. Calpain activation, as monitored by quantitative immunoblotting of spectrin, required micromolar concentrations of Ca2+ in neuronal homogenates (calpain I) and millimolar Ca2+ concentrations in glial homogenates (calpain II). Glutamate-induced toxicity and calpain activation were observed in neuronal, but not in glial, cultures. In neurons, calpain I activation by glutamate was dose-dependent and persisted after withdrawal of neurotoxic doses of glutamate. Natural (GM1) and semisynthetic (LIGA4) gangliosides or the glutamate receptor blocker MK-801 prevented calpain I activation and delayed neuronal death elicited by glutamate. GM1 and LIGA4 had no effect on calpain I activity in neuronal homogenates, however. Furthermore, two calpain I inhibitors (leupeptin and N-acetyl-Leu-Leu-norleucinal) prevented glutamate-induced spectrin degradation, but failed to affect glutamate neurotoxicity. These results thus suggest that glutamate-induced neurotoxicity is independent of calpain I activation.     

Characterization of a developmentally transient adrenergic depolarizing response in cultured locus coeruleus neurons

The effects of iontophoretically applied noradrenaline have been tested on intracellularly recorded locus coeruleus neurons grown in explant cultures from neonatal mice. In addition to hyperpolarizing responses mediated by alpha 2-adrenergic receptors, as observed in locus coeruleus neurons in vivo and in brain slices from adult animals, alpha 1-mediated depolarizations were observed to succeed the initial hyperpolarizations in some cultures. It was shown that the depolarizing responses were only present in younger cultures, i.e., less than 26 days in vitro. In cultures less than 20 days old, all cells displayed the biphasic hyperpolarizing-depolarizing responses. Both components of the response appear to be direct, since they were present when synaptic transmission was blocked by including tetrodotoxin or by altering divalent cations in the perfusate. The depolarizing responses were frequently reduced in solutions with altered divalent cation content, and this might reflect a calcium dependency of this response. The hyperpolarizing and depolarizing components of the responses to noradrenaline were progressively blocked by increasing concentrations of the selective antagonists yohimbine and prazosin, respectively, in the dose ranges of 100 mM - 1 microM (yohimbine) and 20-200 nM (prazosin). Recent results from electrophysiological studies of locus coeruleus neurons in brain slices suggest that similar changes occur in the animal as well as in culture. It is possible that the transient depolarizing responses reflect a developmentally important enhanced responsiveness of locus coeruleus neurons during the early postnatal period.     

Pharmacological characterization of threo-3-methylglutamic acid with excitatory amino acid transporters in native and recombinant systems

The glutamate analog (+/-) threo-3-methylglutamate (T3MG) has recently been reported to inhibit the EAAT2 but not EAAT1 subtype of high-affinity, Na(+)-dependent excitatory amino acid transporter (EAAT). We have examined the effects of T3MG on glutamate-elicited currents mediated by EAATs 1-4 expressed in Xenopus oocytes and on the transport of radiolabeled substrate in mammalian cell lines expressing EAATs 1-3. T3MG was found to be an inhibitor of EAAT2 and EAAT4 but a weak inhibitor of EAAT1 and EAAT3. T3MG competitively inhibited uptake of D-[(3)H]-aspartate into both cortical and cerebellar synaptosomes with a similar potency, consistent with its inhibitory activity on the cloned EAAT2 and EAAT4 subtypes. In addition, T3MG produced substrate-like currents in oocytes expressing EAAT4 but not EAAT2. However, T3MG was unable to elicit heteroexchange of preloaded D-[(3)H]-aspartate in cerebellar synaptosomes, inconsistent with the behavior of a substrate inhibitor. Finally, T3MG acts as a poor ionotropic glutamate receptor agonist in cultured hippocampal neurons: concentrations greater than 100 microM T3MG were required to elicit significant NMDA receptor-mediated currents. Thus, T3MG represents a pharmacological tool for the study of not only the predominant EAAT2 subtype but also the EAAT4 subtype highly expressed in cerebellum.     

Plasticity of Astroglial Glutamate and γ-Aminobutyric Acid Uptake in Cell Cultures Derived from Postnatal Mouse Cerebellum

Abstract: The plasticity of astroglial glutamate and γ-aminobutyric acid (GABA) uptakes was investigated using mouse cerebellar cell cultures. The influence of external factors, such as different sera and/or the presence of neurons, was examined. Control autoradiography experiments showed that after short-term exposure to radioactive amino acids, granule cells took up neither glutamate nor GABA, and β-alanine predominantly inhibited astroglial GABA uptake. Astroglial uptake was quantified by measuring the radioactivity taken up by the cells in the culture and relating this measurement to the number of glial fibrillary acidic protein-positive cells present. Glutamate uptake was investigated in astroglial cultures and subcultures and in neuro-nal-astroglial cultures derived from postnatal day 4 mouse cerebella. In the absence of neurons, glutamate uptake increased during the first 9 days after plating and then leveled off. At 14 days in vitro in horse serum, which favors the differentiation of fibrous-like astrocytes, glutamate uptake related to astrocyte number was twice as high as in fetal calf serum. In the presence of cerebellar neurons, this rate was even higher. The specificity of the responsiveness of astrocytes to neurons with respect to glutamate uptake was investigated by comparing GABA uptake in the different culture conditions. Neurons also increased the rate of GABA uptake by astrocytes. Another component of the astroglial plasma membrane, the density of β-adrenergic receptors, was, however, not markedly affected by the presence of neurons. Hence, these results showed that in astrocytes plated from postnatal day 4 mouse cerebella, the level of neuro-transmitter uptake can be regulated in vitro by factors present in sera and by cerebellar neurons in the culture. However, this plasticity declined during development because astrocytes plated from postnatal day 8 cerebella and cultured under identical conditions were less active in glutamate uptake and were insensitive to the presence of horse serum. The latter observation suggested that the metabolic plasticity of astrocytes is restricted to a period defined early in cerebellar development and is no longer evident by postnatal day 8.     

Membrane cholesterol depletion in cortical neurons highlights altered NMDA receptor functionality in a mouse model of amyotrophic lateral sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a chronic neurodegenerative disease affecting upper and lower motor neurons, with unknown aetiology. Lipid rafts, cholesterol enriched microdomains of the plasma membrane, have been linked to neurodegenerative disorders like ALS. The NMDA-receptor subcellular localization in lipid rafts is known to play many roles, from modulating memory strength to neurotoxicity. In this study, performed on the widely used G93A mouse model of ALS, we have shown an equal content of total membrane cholesterol in Control and G93A cortical cultures. Moreover, by electrophysiological studies, we have recorded NMDA- and AMPA-evoked currents which were not significantly different between the two neuronal populations. To study the role of membrane cholesterol on glutamate receptor functionality, we have analysed NMDA and AMPA receptors following cholesterol membrane depletion by methyl-β-cyclodextrin (MβCD). Interestingly, MβCD chronic treatment has provoked a significant reduction of NMDA-evoked currents in both cellular populations which was dose- and time-dependent but significantly higher in ALS neurons compared to Control. The different MβCD effect on NMDA-evoked currents was not due to a different membrane receptor subunit composition but seemed to cause in both neuronal populations a NMDA receptor membrane redistribution. MβCD treatment effect was receptor-specific since no alterations in the two neuronal populations were detected on AMPA receptors.These results lead us to speculate for an altered proteomic composition of lipid rafts in cortical mutated neurons and suggest the need for further studies on the lipid rafts composition and on their interaction with membrane receptors in ALS cortices.     

蓝斑对迷走─心血管反射的影响

实验用家兔３６只,采用低频（５－８Ｈｚ）和高频（５０－１００Ｈｚ）电流刺激颈部迷走神经中枢端（ＶＡＳ）,建立迷走－减压和迷走－升压反射,两种频率电刺激均导致肾交感神经传出活动（ＲＳＡ）减少。以迷走－血压反射和迷走－交感反射为指标,连续电流刺激蓝斑（ＬＣ）或ＬＣ微量注射谷氨酸钠均抑制迷走－血压反射和迷走－交感反射。而连续电流刺激ＬＣ或ＬＣ微量注射谷氨酸钠本身均引起平均动脉血压升高和ＲＳＡ增加。本文对新近提出的对ＬＣ整体功能认识的理论,结合本文的结果进行了讨论