Low Doses of NMDA Receptor Antagonists Synergistically Increase the Anticonvulsant Effect of the AMPA Receptor Antagonist NBQX in the Kindling Model of Epilepsy

Excitatory amino acid transmitters are involved in the initiation of seizures and their propagation. Most attention has been directed to synapses using N -methyl-d-aspartate (NMDA) receptors, although more recent evidence indicates potential roles for the a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors as well. In the present experiments in amygdala-kindled rats, i.e. a model of partial epilepsy, competitive and uncompetitive NMDA antagonists exerted only weak anticonvulsant effects, whereas the AMPA antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)quinoxaline (NBQX) potently increased focal seizure threshold and inhibited seizure spread from the focus. These effects of NBQX were dramatically increased by pretreatment with low doses of NMDA antagonists, whereas adverse effects of NBQX were not potentiated. These data suggest that both non-NMDA and NMDA receptors are critically involved in the kindled state, and that combinations of AMPA and NMDA receptor antagonists provide a new strategy for treatment of epileptic seizures.     

Potent Analgesia Induced in Rats by Combined Action at PCP and Polyamine Recognition Sites of the NMDA Receptor Complex

The present study was performed to examine the analgesic effects of the intrathecal administration of agents acting at various sites in the N -methyl- d -aspartic acid (NMDA) receptor complex on the nociceptive responses to s.c. formalin injection in rats. Both the competitive NMDA receptor antagonist 2-amino-5-phosphonovaleric acid (APV) and the non-competitive NMDA antagonist dizocilpine maleate (MK-801) produced dose-dependent analgesic effects in the late, but not the early, phase of the formalin test. The polyamine antagonist ifenprodil, and the strychnine-insensitive glycine antagonists DCQX and 7-chlorokynurenic acid, failed to produce any analgesic effects in either the early or the late phase of the formalin test. The analgesic effects of APV were enhanced slightly by combined administration with a non-analgesic dose of glycine, and the analgesic effects of MK-801 were dramatically potentiated by combined adminstration of a non-analgesic dose of the polyamine spermine. The results indicate that much more potent analgesia can be produced in the formalin test by a combination of open channel blockers (such as MK-801) with agonists acting at the polyamine site, than by a single treatment with antagonists to either glycine allosteric or polyamine sites within the NMDA receptor complex.     

Excitatory Connections Between CA1 Pyramidal Cells Revealed by Spike Triggered Averaging in Slices of Rat Hippocampus are Partially NMDA Receptor Mediated

Spike triggered averaging was used to record local circuit connections between pairs of CA1 pyramidal neurons in isolated slices of rat hippocampus. Of 795 pairs of neurons tested, six were connected. These epsps were only partially blocked by 2-amino-5-phosphonovalerate (AP-5), which decreased the amplitude and half width of the epsp, but did not affect the early rising phase. In contrast, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) blocked all phases of the epsp and combinations of AP-5 and CNQX blocked the epsp almost entirely. These results indicate that these epsps were mediated by both N-methyl-d-aspartate (NMDA) and non-NMDA excitatory amino acid receptors. Moreover, they exhibited a voltage relation typical of neuronal responses to NMDA, increasing in amplitude and duration as the postsynaptic cell was depolarized. These epsps were brief (10 - 90% rise time < 5 ms, width at half amplitude < 20 ms), indicating a proximal location. Increasing presynaptic firing rate (1 - 4 spikes/s) reduced average epsp amplitude by almost 50%. When epsps were evoked by pairs of spikes (interval 3 - 25 ms), a large response to the first spike precluded a large response to the second. No evidence for selective enhancement of the NMDA receptor component by paired spike activation was found. It is concluded that a significant NMDA receptor mediated input to CA1 is provided by local circuit CA1 - CA1 connections and that these synapses can be demonstrated under control conditions.     

Characterization of lectin-mediated brain uptake of HIV-1 GP120

The viral coat of the HIV-1 virus, gp120, has been shown to cross the blood-brain barrier (BBB) in lectin-like fashion by inducing adsorptive endocytosis (AE), a vesicular mechanism that could provide pathways into and across brain endothelial cells for virus and infected immune cells. Here, we extended those findings to show that gp120 slowly crossed the BBB with about 0.15% of an intravenously injected dose entering the brain after about 2 hr. The plant lectin glycoprotein wheat germ agglutinin (WGA) greatly enhanced gp120 crossing without disrupting the BBB. WGA enhanced the uptake of gp120 into all peripheral tissues studied, but the greatest percent increase occurred for brain, whereas another barrier tissue, the testis, had the least increase. Five other plant lectins tested had little or no effect on gp120 uptake by brain, suggesting a key role for sialic acid and N-acetyl-β-d -glucosaminyl acid, the sugars to which WGA binds, in the uptake of gp120 by brain endothelial cells. WGA did not enhance the uptake of nonglycosylated gp120 and the uptake of gp120 was not self-inhibitable or altered by pretreatment of mice with aluminum. In conclusion, these studies show that gp120 crosses the BBB by a lectin-like mechanism resembling AE that is likely mediated by binding to specific sugar moieties and is rather selective for brain. J. Neurosci. Res. 54:522–529, 1998. © 1998 Wiley-Liss, Inc.     

HIV-1 Envelope Glycoprotein 120 Regulates Brain IL-1β System and TNF-α mRNAs In Vivo

Human immunodeficiency virus type I (HIV-1)-derived envelope glycoprotein 120 (gp120) is proposed to play an important role in HIV-1 neuropathology. Gp120 may act through mediators including proinflammatory cytokines. Here, we investigated the regulation of the IL-1β system [IL-1β, IL-1 receptor type I (IL-1RI), IL-1 receptor antagonist (IL-1Ra)], TNF-α and TGF-α mRNAs in the rat central nervous system (CNS) in response to the constant intracerebroventricular (ICV) microinfusion of HIV-1 gp120 for 72 h and 144 h. The results show that gp120: (1) increased IL-1β and IL-1Ra mRNAs levels in the same samples from the cerebellum, hypothalamus and midbrain, with the largest increase in the hypothalamus; (2) induced profiles of IL-1β mRNA and IL-1Ra mRNA that were highly intercorrelated; (3) increased the hypothalamic TNF-α mRNA levels; and (4) did not affect the IL-1RI mRNA and TGF-α mRNA levels in any brain region. A dysregulation in the IL-1β/IL-1Ra CNS balance and a mutual induction and synergistic activity of IL-1β and TNF-α could result in a deleterious amplification cycle of cellular activation and cytotoxicity with implications to HIV-1-associated encephalitis, encephalopathy, and neurological manifestations.     

Microinfusion of the Metabotropic Glutamate Receptor Agonist 1S, 3R–1-Aminocyclopentane-1, 3-dicarboxylic Acid Into the Nucleus Accumbens Induces Dopamine-dependent Locomotor Activation in the Rat

Although the striatum has one of the highest densities of metabotropic glutamate receptor (mGluR) binding sites in the brain, little is known about their physiological role. In this study we characterized the contribution of mGluRs located in the ventral part of the striatum (the nucleus accumbens) to the control of extrapyramidal motor function. Activation of mGluRs by local infusion of the selective agonist 1S, 3R–1-aminocyclopentane-1, 3-dicarboxylic acid (1 S, 3R-ACPD; 25, 50 and 100 nmol/0.5 μl) into the nucleus accumbens induced a dose-dependent increase in locomotor activity in rats. Intra-accumbens infusion of a selective antagonist of mGluRs, a-methyl-4-carboxyphenylglycine (MCPG) did not modify spontaneous locomotion but decreased the locomotor response to 1S, 3R-ACPD. This effect appeared to be mediated by dopamine, since blockade of dopamine receptors with haloperidol (0.05 and 0.1 mg/kg i.p.) dose-dependently reduced 1 S3R-ACPD-induced locomotor activation. Furthermore, D-amphetamine (0.5 mg/kg, i.p.) combined with intra-accumbens infusion of 1S, 3R-ACPD (100 nmol) potentiated the locomotor hyperactivity response to a higher level than that seen with a single treatment with either drug. In contrast, D-amphetamine-induced hypermotility was abolished by infusion of MCPG (100 nmol) into the nucleus accumbens. These results demonstrate that glutamate may control extrapyramidal motor function through metabotropic receptors. Furthermore, activation of metabotropic glutamate receptors appears to act in synergy with the dopamine system at the level of the nucleus accumbens to produce a motor stimulant response.     

The HIV-1 coat protein gp120 and some of its fragments potently activate native cerebral NMDA receptors mediating neuropeptide release

The objective of this study was to investigate the effects of the HIV-1 envelope protein gp120 and its peptide fragments on the function of N-methyl-D-aspartate (NMDA) receptors mediating release of cholecystokinin (CCK) and somatostatin (SRIF). These are nonconventional NMDA receptors recently found to be activated by glycine or D-serine 'only'. The release of cholecystokinin-like immunoreactivity (CCK-LI) and of somatostatin-like immunoreactivity (SRIF-LI) elicited by 12 mM K+ from superfused rat neocortex synaptosomes was potently increased by gp120, its cyclic V3 loop and the linear V3 sequence BRU-C-34-A, but not by RP-135 (a central portion of BRU-C-34-A). The EC50 values of gp120 were 0.02 nM (CCK-LI release) and 0.01 nM (SRIF-LI release). The releasing effect of gp120 was prevented by blocking the glycine site or the ion channel of NMDA receptors, but not the glutamate recognition site; in addition, the gp120 effect was strongly inhibited by nanomolar concentrations of Zn2+ ions and by low micromolar concentrations of ifenprodil. It is concluded that gp120 acts as a very potent agonist at the glycine site of NMDA receptors sited on CCK- and SRIF-releasing nerve endings; the protein is able to activate the receptor channel in the absence of glutamate. Gp120 activates the receptors through its V3 loop as peptide fragments related to V3 retain near-maximal activity. The sensitivity of the gp120 effect to both Zn2+ and ifenprodil would not be incompatible with the idea that these NMDA receptors contain the triple subunit combination NR1/NR2A/NR2B.     

Exposure to gp120 of HIV-1 Induces an Increased Release of Arachidonic Acid in Rat Primary Neuronal Cell Culture Followed by NMDA Receptor-mediated Neurotoxicity

After incubation of highly enriched neurons from rat cerebral cortex with the HIV-1 coat protein gp120 for 18 h, cells showed fragmentation of DNA at internucleosomal linkers followed by NMDA receptor-mediated neurotoxicity. We report that in response to exposure to gp120 cells react with an increased release of arachidonic acid (AA) via activation of phospholipase A₂. This process was not inhibited by NMDA receptor antagonists. To investigate the role of AA on the sensitivity of the NMDA receptor towards its agonist, low concentrations of NMDA were co-administered with AA. This condition enhanced the NMDA-mediated cytotoxicity. Administration of mepacrine reduced cytotoxicity caused by gp120. We conclude that gp120 causes an activation of phospholipase A₂, resulting in the increased release of AA, which may in turn sensitize the NMDA receptor.     

Blockade of NMDA receptors increases cell death and birth in the developing rat dentate gyrus

Excitatory input regulates cell birth and survival in many systems. The granule cell population of the rat dentate gyrus is formed primarily during the postnatal period. Excitatory afferents enter the dentate gyrus and begin to form synapses with granule cells during the first postnatal week, the time of maximal cell birth and death. In order to determine whether excitatory input plays a role in the regulation of cell birth and survival in the developing granule cell layers and their germinal regions, the subependymal layer and hilus, we treated rat pups with the N-methyl D-aspartate (NMDA) receptor antagonists MK-801, CGP 37849, or CGP 43487 during the first postnatal week and examined the numbers of ³H-thymidine-labeled cells, pyknotic cells, and healthy cells in these regions. In order to determine the cell type that was affected, sections from brains of MK-801-treated rats were processed for ³H-thymidine autoradiography combined with immunohistochemistry for the marker of radial glia, vimentin, and the marker of mature astrocytes, glial fibrillary acidic protein (GFAP). Within the dentate gyrus, NMDA receptor blockade resulted in the following changes: (1) the density of ³H-thymidine-labeled cells was increased, (2) the density of pyknotic cells was increased, (3) the density of ³H-thymidine-labeled pyknotic cells was increased, and (4) the density of healthy cells was decreased. The infrapyramidal blade/hilus showed changes throughout its extent, whereas the suprapyramidal blade showed changes only at the rostral level. No change in the numbers of ³H-thymidine-labeled vimentin-immunoreactive or GFAP-immunoreactive cells was observed in the dentate gyrus with MK-801 treatment, indicating that glia are not primarily affected by NMDA receptor blockade. Blockade of NMDA receptors resulted in gross morphologic changes in the dentate gyrus; in most cases, the infrapyramidal blade was indistinguishable from the hilus. Moreover, in several brains of animals treated with CGP 37849 or CGP 43487 on postnatal day (P)5, an abnormal aggregation of cells was observed ventral to the normal location of the infrapyramidal blade. This cellular cluster contained many pyknotic and ³H-thymidine-labeled cells and may represent cells that normally comprise the infrapyramidal blade. Dramatic changes to the subependymal layer were also seen following NMDA receptor blockade. The cross-sectional area of this region was significantly increased with MK-801, CGP 37849, or CGP 43487 treatment and contained a high density of ³H-thymidine-labeled cells and ³H-thymidine-labeled pyknotic cells. These results indicate that NMDA receptor activation is critical for the normal development of the rat dentate gyrus. The finding that blockade of NMDA receptors resulted in increased levels of cell death and birth supports the hypothesis that NMDA receptor activation is a natural signal for the inhibition of these processes in the developing dentate gyrus. © Wiley-Liss, Inc.     

Age-related behavioural deficits in transgenic mice expressing the HIV-1 coat protein gp120

Transgenic mice expressing HIV-1 coat glycoprotein gp120 in brain glial cells were previously shown to display AIDS dementia-like neuropathological changes and reduced hippocampal long-term potentiation. In this report, neuromotor and cognitive performance in 3- and 12-month-old gp120-expressing mice was compared with wildtype controls. Rotarod and cage activity measures showed no significant differences between transgenic animals and controls of either age. Open field activity was slightly altered in 12-month-old gp120 animals (reduced corner crossings and dwell in centre), but not in the 3-month-olds. Cognitive assessment using the Morris water maze showed unimpaired performance in 3-month-old mice during acquisition and (no-platform) probe trials. In 12-month-old gp120 animals, escape latency and swimming velocity during the acquisition trials were significantly reduced, but performance improved at roughly the same rate as in control animals. However, the probe trials revealed a highly significant reduction in spatial retention in transgenic mice of this age. This demonstration of age-dependent impairments in open field activity and spatial reference memory may relate to cognitive and neuromotor deficits seen in a proportion of HIV-1-infected individuals.     

Differential long-term neurotoxicity of HIV-1 proteins in the rat hippocampal formation: a design-based stereological study

The human immunodeficiency virus type 1 (HIV-1) proteins, gp120 and Tat, are believed to play a role in mediating central nervous system (CNS) pathology in HIV-1 infected patients. Using design-based stereology, we examined the role of neonatal intrahippocampal injections of gp120 and Tat on the adult hippocampus ( approximately 7(1/2) month). Postnatal day (P)1-treated Sprague-Dawley rats were bilaterally injected with vehicle (VEH, 0.5 microl sterile buffer), gp120 (100 ng), Tat (25 microg) or combined gp120 + Tat (100 ng + 25 microg). Using Nissl-stained tissue sections, we quantified total neurons in five subregions of the rat hippocampus [granual layer (GL), hilus of the dentate gyrus (DGH), cornu ammonis fields (CA)2/3, CA1, and subiculum (SUB)], and total glial cells (astrocytes and oligodendrocytes) in two subregions (DGH and SUB). Estimates of cell area and cell volume were taken in the DGH. There was a significant reduction of neuron number in the CA2/3 subfield by Tat and gp120, and a significant reduction in the DGH by Tat only. For glial cells, numbers of astrocytes in the DGH and SUB were increased by the Tat protein, whereas no effects were noted for gp120. Finally, for oligodendrocytes Tat increased cell number in the DGH but not in any other region; gp120 had no detectable effect in any brain region. Estimates of cell area and cell volume of the three different cell types revealed no significant differences between treatments. Collectively, these results suggest differential effects of gp120 and Tat on the estimated total number of neurons, as well as on the number of glial cells.     

Simultaneous blockade of non-NMDA ionotropic receptors and NMDA receptor-associated ionophore partially protects hippocampal slices from protein synthesis impairment due to simulated ischemia

A large body of evidence exists to demonstrate that excitatory amino acids (EAA) and their receptors are involved in the pathophysiological mechanisms linking several acute brain insults, such as cerebral ischemia, to neuronal degeneration and death. Accordingly, the use of EAA receptor antagonists can be beneficial in attenuating or preventing the neuronal irreversible damage subsequent to various neuropathological syndromes. We have investigated the effect of 15 min of simulated ischemic conditions, i. e., oxygen/glucose deprivation, on hippocampal slices preparation measuring, as neurotoxicity indexes, both the amino acids efflux in the incubation medium, detected by HPLC, and the inhibition of protein synthesis, evaluated as ³H-Leucine incorporation into proteins. Accumulation of neurotransmitter amino acids was measured in the medium during the “ischemic” period. Glutamate increased 30-fold over the basal level while aspartate was sevenfold and GABA 12-fold higher than in normal conditions. After a reoxygenation period of 30 min, the rate of protein synthesis of hippocampal slices subjected to “ischemia” was reduced to 35–50% of controls. The non-competitive NMDA antagonist MK-801 (100 μM) and the competitive NMDA antagonist CGP 39551 (100–250 μM) as well as the non-NMDA receptor antagonist NBQX (100 μM) and AP3 (300 μM) were unable to counteract the metabolic impairment when they were present alone in the incubation fluid during simulated “ischemia.” An incomplete, but highly significant (p < 0.001), protection from protein synthesis impairment was achieved in the presence of an equimolar concentration (100 μM) of MK-801 and NBQX. A similar protective effect could be reproduced using 100 μM NBQX in concomitance with a high Mg⁺⁺ (20 μM) voltage-dependent block of the NMDA receptor-associated channel but not exposing the slices to a NBQX (100 μM) and CGP 39551 (100–250 μM) mixture. The recovery of protein synthesis in the presence of the MK-801/NBQX effective combination was not paralleled by a detectable decrease in the amount of amino acids released in the incubation medium during the “ischemic” period. Taken together, the present data allow new insights into neurotoxicity-mediating mechanisms, suggesting that multiple additive processes are involved and that antagonists acting at different sites on excitatory amino acid receptor subtype can show different neuroprotective potency. © 1995 Wiley-Liss, Inc.     

Characteristics of HIV-1 gp120 glycoprotein binding to glycolipids

We examined the binding of the gp120 envelope glycoprotein (gp120) of the human immunodeficiency virus (HIV-1) to sulfatide (GalS), galactocerebroside (GalC), and GMI-ganglioside (GMI). The gp120 glycoprotein bound to GalS but not to GalC or GMI by enzyme-linked immunosorbent assay (ELISA) and by an immunospot assay on nitrocellulose paper. However, it bound to all three glycolipids by an immunospot assay on thin layer chromotography (TLC) plates. In studies to determine whether GalS could be a receptor for gp120 on the surface of cells, gp120 bound to GalS incorporated into the plasma membrane of lymphoid cells as determined by cytofluorometric analysis and immunofluorescence microscopy. These studies indicate that GalS may function as a receptor for gp120 and HIV-1. © 1994 Wiley-Liss, Inc.     

Tonic Activation of NMDA Receptors Causes Spontaneous Burst Discharge of Rat Midbrain Dopamine Neurons In Vivo

Midbrain dopamine neurons in vivo discharge in a single-spike firing pattern or in a burst-firing pattern. Such activity in vivo strikingly contrasts with the pacemaker activity of the same dopamine neurons recorded in vitro. We have recently shown that burst activity in vivo of midbrain dopamine neurons is due to the local activation of excitatory amino acid receptors, as microapplication of the broad-spectrum antagonist of excitatory amino acids, kynurenic acid, strongly regularized the spontaneous firing pattern of these dopamine neurons. In the present study, we investigated which subtypes of excitatory amino acid receptors are involved in the burst-firing of midbrain dopamine neurons in chloral hydrate-anaesthetized rats, Iontophoretic or pressure microejections of 6-cyano,7-nitroquinoxaline-2,3-dione (CNQX), a non- N -methyl- d -aspartate (NMDA) receptor antagonist, did not alter the spontaneous burst firing of dopamine neurons ( n = 36). In contrast, similar ejections of (±)2-amino,5-phos-phonopentanoic acid (AP-5), a specific antagonist at NMDA receptors, markedly regularized the firing pattern by reducing the occurrence of bursts ( n = 52). In addition, iontophoretic ejections of NMDA, but not kainate or quisqualate, elicited a discharge of these dopamine neurons in bursts ( n = 20, 12 and 14, respectively). These data suggest that burst-firing of midbrain dopamine neurons in vivo results from the tonic activation of NMDA receptors by endogenous excitatory amino acids. In view of the critical dependency of catecholamine release on the discharge pattern of source neurons, excitatory amino acid inputs to midbrain dopamine neurons may constitute a major physiological substrate in the control of the dopamine level in target areas.     

Synaptic coexistence of AMPA and NMDA receptors in the rat hippocampus: A postembedding immunogold study

Synaptic distributions of N-methyl-d -aspartate (NMDA) and α-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) receptor subunits, NMDAR1 and GluR2, respectively, were examined by electron microscopy with the high spatial resolution of postembedding immunogold localization. We provide direct evidence for colocalization at individual axodendritic asymmetric synapses within the CA1 subfield of rat hippocampus. AMPA/ NMDA receptor colocalization was found both in γ-aminobutyric acid (GABA)ergic dendrites and non-GABAergic dendritic shafts, as well as dendritic spines. Some asymmetric synapses were found to contain only NMDAR1 or GluR2; however, most immunopositive synapses contained both subunits. Many NMDAR1 and/ or GluR2 immunopositive profiles received GABAergic innervation at an adjacent synapse, providing a substrate for GABAergic modulation of both GluR classes. These data suggest that excitatory neuronal transmission in CA1 neurons may generally involve activation of both NMDA and AMPA receptor subunits at a single synapse, however, they also offer ultrastructural evidence for NMDAR1-only synapses that might represent silent synapses. J. Neurosci. Res. 54:444–449, 1998. © 1998 Wiley-Liss, Inc.     

Blood-brain barrier changes during invasion of the central nervous system by HIV-1

The mechanism underlying the early invasion of the central nervous system by HIV-1 is unclear. Here, we summarize old and new findings supporting blood-brain barrier changes during HIV and experimental simian immunodeficiency virus (SIV) infection. The effect of inflammatory and toxic molecules secreted by monocytes and microglia on the functional integrity of tight junctions of brain endothelium is highlighted. Furthermore, recent findings on a possible direct role of the envelope and regulatory HIV-1 proteins (gp120, Tat, Nef) in causing the blood-brain barrier changes are reviewed. The possibility that these proteins, as circulating molecules, may bind to microvessel endothelial cells and cause blood-brain changes with no direct participation of the virus is raised. Several issues deserve further investigation and answers to these questions may provide keys for new therapeutic strategies in HIV-1 infection of the central nervous system.     

Phosphoproteins of Cultured Cerebellar Granule Cells and Response to the Differentiation-promoting Stimuli NMDA, High K+ and Ionomycin

In order to investigate signalling pathways involved in the control of granule cell differentiation, survival and other functions by depolarization or activation of NMDA receptors we have characterized protein phosphorylation in cerebellar granule cells. Cultures of cerebellar granule cells were incubated with ³²P orthophosphate and then challenged with NMDA, K⁺ or the Ca²⁺ ionophore ionomycin, agents which raise [Ca²⁺]_i and stimulate differentiation and survival. Upon separation of labelled phosphoproteins by two-dimensional gel electrophoresis three differences were found in response to all of these agents. These were an increase in acidity of two phosphoproteins of 87 and 48 kDa (p87 and p48) and increased ³²P-incorporation into a phosphoprotein of 120 kDa (p120). Treatment with PMA which stimulates neurite outgrowth but not survival affected p87 (increased its acidity) but not p48. The acidic shift of p87, therefore, is not sufficient to stimulate granule cell survival. The identification of p87 as the actin-binding MARCKS protein and the demonstration of its presence in neurites and growth cones of granule cells suggests that it may be involved in NMDA-stimulated neurite outgrowth. The phosphoproteins p120 and p48 may potentially be involved in events linking the rise in [Ca²⁺]_i to increased granule cell survival or other aspects of granule cell differentiation.     

NMDA Receptor Activation Triggers Voltage Oscillations, Plateau Potentials and Burstinq in Neonatal Rat Lumbar Motoneurons ln Vitro

Whole-cell recordings of lumbar motoneurons in the intact neonatal rat spinal cord in vitro were undertaken to examine the effects of Kmethyl-D-aspartate (NMDA) receptor activation on membrane behaviour. Bath application of NMDA induced rhythmic voltage oscillations of 5.9 ± 2.1 mV (SD) at a frequency of 4.4 ± 1.5 Hz. Amplitude, but not frequency, of the voltage oscillations was membrane potential-dependent. Voltage oscillations could recruit action potentials and/or plateau potentials with or without superimposed bursting. Blockade of synaptic transmission with tetrodotoxin (TTX) sometimes resulted in a loss of oscillatory activity which could then be restored by increasing the NMDA concentration. After application of TTX, the trajectory of NMDA-induced oscillations was similar to the trajectory induced in the presence of intact synaptic networks, although the mean oscillation duration was longer and the oscillation frequency was slower (1.8 ± 1.1 Hz). Current ramps delivered after bath application of NMDA demonstrated bistable membrane properties which may underlie the plateau potentials. Injection of intracellular current pulses could initiate, entrain and terminate individual plateau potentials. The results suggest that membrane depolarization produced by oscillations may activate other intrinsic conductances which generate plateau potentials, thereby providing the neuron with enhanced voltage sensitivity, compared to that produced by NMDA receptor activation alone. These oscillatory events may have a role in the regulation of motor output in a variety of rhythmic behaviours including locomotion.     

Morphology and distribution of HIV-1 gp41-positive microglia in subacute AIDS encephalitis

Summary Among 100 brains from patients with acquired immunodeficiency syndrome (AIDS), 33 brains (21 adults and 12 children) with histological evidence of subacute AIDS encephalitis were immunostained with one of the most sensitive antibodies to HIV-1 antigen, anti-gp41. Twenty-six (20/21 adults, 6/12 children) of the 33 brains showed pg41 positivity. Brains from children had fewer gp41-positive cells than brains from adults. The distribution of gp41-positive cells was characteristic. They were frequently detected and most numerous in the globus pallidus (medial > lateral). Although gp41-positive cells were prevalent, fewer were detected in the corpus striatum and thalamus. Of infratentorial areas involved, the ventral midbrain, especially the substantia nigra, and the dentate nucleus contained many positive cells. Lower levels of infections, often patchy, were noted in the cerebral and cerebellar white matter and pontine base. Gp41-positive cells were rarely seen in the cerebral cortex, medulla, spinal cord, leptomeninges, choroid plexus, ependyma, subependymal areas and endothelia. Besides immunoreactive macrophages and multinucleated cells, gp41-positive microglia with various morphological alterations were abundant in the deep cerebral gray matter, ventral midbrain and dentate nucleus. Most of these microglia were undetectable with conventional histological methods. We discuss the significance of the distribution of HIV-1-infected cells, especially microglia, with respect to cellular tropism and involvement of deep gray matter nuclei in a pattern reminiscent of a multisystem atrophy.Supported by NIA 06803, DA 045583, DA 055583, and NS 11920