Survival and growth of hippocampal neurons in defined medium at low density: advantages of a sandwich culture technique or low oxygen

Pyruvate protection against beta-amyloid-induced neuronal death: role of mitochondrial redox state

The mechanism by which beta-amyloid protein (A beta) causes degeneration in cultured neurons is not completely understood, but several lines of evidence suggest that A beta-mediated neuronal death is associated with an enhanced production of reactive oxygen species (ROS) and oxidative damage. In the present study, we address whether supplementation of glucose-containing culture media with energy substrates, pyruvate plus malate (P/M), protects rat primary neurons from A beta-induced degeneration and death. We found that P/M addition attenuated cell death evoked by beta-amyloid peptides (A beta(25-35) and A beta(1-40)) after 24 hr treatment and that this effect was blocked by alpha-ciano-3-hydroxycinnamate (CIN), suggesting that it requires mitochondrial pyruvate uptake. P/M supply to control and A beta-treated neuronal cultures increases cellular reducing power, as indicated by the ability to reduce the dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). The early increases in ROS levels, measured by dichlorofluorescein (DCF) fluorescence, and caspase-3 activity that follow exposure to A beta were notably reduced in the presence of P/M. These results place activation of caspase-3 most likely downstream of oxidative damage to the mitochondria and indicate that mitochondrial NAD(P) redox status plays a central role in the neuroprotective effect of pyruvate. Inhibition of respiratory chain complexes and mitochondrial uncoupling did not block the early increase in ROS levels, suggesting that A beta could initiate oxidative stress by activating a source of ROS that is not accesible to the antioxidant defenses fueled by mitochondrial substrates.

Lucifer Yellow slows voltage-gated Na+ current inactivation in a light-dependent manner in mice

Lucifer Yellow CH (LY), a membrane-impermeant fluorescent dye, has been used in electro-physiological studies to visualize cell morphology, with little concern about its pharmacological effects. We investigated its effects on TTX-sensitive voltage-gated Na+ channels in mouse taste bud cells and hippocampal neurons under voltage-damp conditions. LY applied inside cells irreversibly slowed the inactivation of Na+ currents upon exposure to light of usual intensities. The inactivation time constant of Na+ currents elicited by a depolarization to -15 mV was increased by fourfold after a 5 min exposure to halogen light of 3200 Ix at source (3200 Ix light), and sevenfold after a 1-min exposure to 12,000 Ix light. A fraction of the Na+ current became non-inactivating following the exposure. The non-inactivating current was approximately 20 % of the peak total Na+ current after a 5 min exposure to 3200 Ix light, and approximately 30 % after a 1 min exposure to 12,000 Ix light. Light-exposed LY shifted slightly the current-voltage relationship of the peak Na+ current and of the steady-state inactivation curve, in the depolarizing direction. A similar light-dependent decrease in kinetics occurred in whole-cell Na+ currents of cultured mouse hippocampal neurones. Single-channel recordings showed that exposure to 6500 Ix light for 3 min increased the mean open time of Na+channels from 1.4 ms to 2.4 ms without changing the elementary conductance. The pre-incubation of taste bud cells with 1 mM dithiothreitoL a scavenger of radical species, blocked these LY effects. These results suggest that light-exposed LY yields radical species that modify Na+ channels.

Developmental changes in the Ca2+-regulated mitochondrial aspartate-glutamate carrier aralar1 in brain and prominent expression in the spinal cord

Aralar1 and citrin are two isoforms of the mitochondrial carrier of aspartate-glutamate (AGC), a calcium regulated carrier, which is important in the malate-aspartate NADH shuttle. The expression and cell distribution of aralar1 and citrin in brain cells has been studied during development in vitro and in vivo. Aralar1 is the only isoform expressed in neurons and its levels undergo a marked increase during in vitro maturation, which is higher than the increase in mitochondrial DNA in the same time window. The enrichment in aralar1 per mitochondria during neuronal maturation is associated with a prominent rise in the function of the malate-aspartate NADH shuttle. Paradoxically, during in vivo development of rat or mouse brain there is very little postnatal increase in total aralar1 levels per mitochondria. This is explained by the fact that astrocytes develop postnatally, have aralar1 levels much lower than neurons, and their increase masks that of aralar1. Aralar1 mRNA and protein are widely expressed throughout neuron-rich areas in adult mouse CNS with clear enrichments in sets of neuronal nuclei in the brainstem and, particularly, in the ventral horn of the spinal cord. These aralar1-rich neurons represent a subset of the cytochrome oxidase-rich neurons in the same areas. The presence of aralar1 could reflect a tonic activity of these neurons, which is met by the combination of high malate-aspartate NADH shuttle and respiratory chain activities.

Functional inactivation of a fraction of excitatory synapses in mice deficient for the active zone protein bassoon

Mutant mice lacking the central region of the presynaptic active zone protein Bassoon were generated to establish the role of this protein in the assembly and function of active zones as sites of synaptic vesicle docking and fusion. Our data show that the loss of Bassoon causes a reduction in normal synaptic transmission, which can be attributed to the inactivation of a significant fraction of glutamatergic synapses. At these synapses, vesicles are clustered and docked in normal numbers but are unable to fuse. Phenotypically, the loss of Bassoon causes spontaneous epileptic seizures. These data show that Bassoon is not essential for synapse formation but plays an essential role in the regulated neurotransmitter release from a subset of glutamatergic synapses.

Antioxidants are necessary for myelination of dorsal root ganglion neurons, in vitro

We have demonstrated that myelination of dorsal root ganglion (DRG) axons occurs in a fully defined, serum-free medium (B27). This implies that there may be components in B27 medium that support myelination. To determine which of the components in B27 were essential for myelination, we systematically removed components from B27 until myelination was lost. We added these components to a fully defined minimal medium (N2) that supports neuron survival but not myelination. When antioxidants were removed from B27, myelination was lost. However, the individual antioxidants did not induce myelination when added to N2 medium. Addition of ascorbic acid along with the B27 antioxidants was sufficient to induce myelination in N2 medium, which was enhanced by retinyl acetate. Removal of vitamin E from B27 caused a partial loss of myelination, and addition of vitamin E to N2 medium containing ascorbic acid induced partial myelination. Addition of serum to the B27 myelinating medium inhibited myelination completely. These results indicate that antioxidants are important for myelination, in vitro. Vitamin E may play an important role. Use of a serum-free medium may be beneficial for in vitro myelination studies because serum has unknown inhibitory effects.

GABAergic terminals are required for postsynaptic clustering of dystrophin but not of GABA(A) receptors and gephyrin

In rat hippocampal cultures, we show by multilabeling immunocytochemistry that pyramidal cells, which receive little or no GABAergic input, mistarget alpha2-GABA(A) receptors and gephyrin to glutamatergic terminals. This mismatch does not occur in neurons innervated by numerous GABAergic terminals. A similar phenomenon has been reported for isolated autaptic hippocampal neurons (Rao et al., 2000). GABAergic synapses typically form multiple release sites apposed to GABA(A) receptor and gephyrin clusters. Remarkably, dystrophin, a protein highly abundant in skeletal muscle membranes, is extensively colocalized with alpha2-GABA(A) receptors exclusively opposite GABAergic terminals. In addition, selective apposition of syntrophin and beta-dystroglycan to GABAergic presynaptic terminals suggests that the entire dystrophin-associated protein complex (DPC) clusters at GABAergic synapses. In contrast to gephyrin and GABA(A) receptors, DPC proteins are not mistargeted to glutamatergic synapses, indicating independent clustering mechanisms. This was confirmed in hippocampal neurons cultured from GABA(A) receptor gamma2 subunit-deficient mice. Clustering of GABA(A) receptor and gephyrin in these neurons was strongly impaired, whereas clustering of dystrophin and associated proteins was unaffected by the absence of the gamma2 subunit. Our results indicate that accumulation of dystrophin and DPC proteins at GABAergic synapses occurs independently of postsynaptic GABA(A) receptors and gephyrin. We suggest that selective signaling from GABAergic terminals contributes to postsynaptic clustering of dystrophin.

Acetaminophen protects hippocampal neurons and PC12 cultures from amyloid beta-peptides induced oxidative stress and reduces NF-kappaB activation

The present findings show that an atypical non-steroidal anti-inflammatory drug, such as acetaminophen, retains the ability to recover amyloid beta-peptides driven neuronal apoptosis through the impairment of oxidative stress. Moreover, this compound reduces the increased NF-kappaB binding activity, which occurs in these degenerative conditions. Therapeutic interventions aimed at reducing the inflammatory response in Alzheimer's disease (AD) recently suggested the application of non-steroidal anti-inflammatory drugs. Although the anti-inflammatory properties of acetaminophen are controversial, it emerged that in an amyloid-driven astrocytoma cell degeneration model acetaminophen proved to be effective. On these bases, we analyzed the role of acetaminophen against the toxicity exerted by different Abeta-peptides on rat primary hippocampal neurons and on a rat pheochromocytoma cell line. We found a consistent protection from amyloid beta-fragments 1-40 and 1-42-induced impairment of mitochondrial redox activity on both cell cultures, associated with a marked reduction of apoptotic nuclear fragmentation. An antioxidant component of the protective activity emerged from the analysis of the reduction of phospholipid peroxidation, and also from a significant reduction of cytoplasmic accumulation of peroxides in the pheochromocytoma cell line. Moreover, activation of NF-kappaB by amyloid-derived peptides was greatly impaired by acetaminophen pre-treatment in hippocampal cells. This evidence points out antioxidant and anti-transcriptional properties of acetaminophen besides the known capability to interfere with inflammation within the central nervous system, and suggests that it can be exploited as a possible therapeutic approach against AD.

Pulse-mode scanning ion conductance microscopy--a method to investigate cultured hippocampal cells

Scanning ion conductance microscopy (SICM) takes advantage of the increase in the resistance which occurs if a glass microelectrode is closely approached to a poorly conducting membrane (Science 243 (1989) 641) and has been shown to be a promising technique to study membranes of living cells (Biophys J 73 (1997a) 653; J Microsc 188 (1997b) 17). Based on a newly designed set-up on top of an inverted light microscope in combination with a speed optimized low noise intracellular amplifier, a novel mode for control of the distance between the probe and surface has been developed. By application of current pulses, the change in the resistance is monitored independently from electrode drift and parasitic DC currents. We demonstrate the applicability by showing first high-resolution images of neural cells produced with the pulse-mode operated SICM.

Evidence that toxicity of lipopolysaccharide upon cholinergic basal forebrain neurons requires the presence of glial cells in vitro

The cholinergic system of the basal forebrain is affected in brains of dementia patients and during neuroinflammation. The aim of this study was to establish a method to cultivate basal forebrain cholinergic neurons in dissociated, pure neuronal cultures and to apply this method to study the effect of acute and chronic experimentally-induced inflammation using lipopolysaccharide. Purity of the cultures, degrees of neuronal dissociation, connectivity and neuronal survival were investigated by immunocytochemistry for microtubule-associated protein-2 (neurons), glial fibrillary acidic protein (astroglia), complement receptor 3 (microglia), choline acetyltransferase and the neurotrophin receptor p75 (cholinergic neurons). Neuronal cultures only contained <7% astrocytes and <1% microglia when using a "sandwich-technique". Acute (1, 10 microg/ml) as well as chronic (0.1, 1 microg/ml) treatment with lipopolysaccharide did neither affect total number of neurons, nor number of p75-positive neurons or enhance expression of major histocompatibility complex I or II. Our results suggest that lipopolysaccharide-induced degeneration of both microtubule-associated protein-2-like immunoreactive as well as specific killing of cholinergic forebrain neurons in vitro are mediated by glial cells.

Immortalized chromaffin cells disimmortalized with Cre/lox site-directed recombination for use in cell therapy for pain after partial nerve injury

To prepare immortalized adrenal chromaffin cells for eventual clinical use, the immortalizing oncogene must be removed. We have utilized a Cre-mediated excision of a loxP-flanked Tag sequence to test whether immortalized chromaffin cells could be disimmortalized by this method. Cultures of embryonic rat adrenal cells were immortalized with the tsA-TN retroviral vector encoding the loxP-flanked temperature-sensitive allele of SV40 large T antigen (tsA-TN) and a positive/negative neo/HSV-TK sequence for selection with either G418 or gancyclovir, respectively. These cells were then infected with the 1710-CrePR1 bicistronic retroviral vector coding for a form of Cre modulatable by the synthetic steroid RU486. These immortalized loxTsTag/CrePR1/RAD cells expressed immunoreactivities (ir) for all the catecholamine enzymes: tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DbetaH), and phenylethanolamine-N-methyltransferase (PNMT). After initial incubation at 37 degrees C with RU486 for 3 days, followed by the addition of gancyclovir for 7 days, Tag-ir was not detectable in most of the surviving chromaffin cells, compared to 100% expression in immortalized loxTsTag/CreR1/RAD cells not treated with RU486 and gancyclovir. The expression of TH, DbetaH, and PNMT was increased after disimmortalization and the ability of disimmortalized cells to synthesize norepinephrine was also significantly increased compared to immortalized cells. When both types of chromaffin cells were transplanted in a model of neuropathic pain and partial nerve injury, both cell grafts were equally able to reverse the behavioral hypersensitivity induced by the injury. The use of Cre/lox site-directed disimmortalization of chromaffin cells that are able to deliver neuroactive molecules offers a novel approach to cell therapy.

Neurotrophin secretion from hippocampal neurons evoked by long-term-potentiation-inducing electrical stimulation patterns

The neurotrophin (NT) brain-derived neurotrophic factor (BDNF) plays an essential role in the formation of long-term potentiation (LTP). Here, we address whether this modulation by BDNF requires its continuous presence, or whether a local increase in BDNF is necessary during a specific time period of LTP initiation. Using electrical field stimulation of primary cultures of hippocampal neurons, we demonstrate that short high-frequency bursts of stimuli that induce LTP evoke also an instantaneous secretion of BDNF. In contrast, stimuli at low frequencies, inducing long-term depression, do not enhance BDNF secretion, suggesting that BDNF is specifically present, and thus required, at the time of LTP induction. The field-stimulation-mediated BDNF secretion depends on the formation of action potentials and is induced by IP(3)-mediated Ca(2+) release from intracellular stores. Experiments, aimed at determining the sites of NT secretion that use NT6, showed similar patterns of surface labeling by field stimulation to those shown previously by high potassium.

The protein kinase A inhibitor H89 acts on cell morphology by inhibiting Rho kinase

The small GTPase RhoA can retract cell extensions by acting on two Rho kinases (ROCKs). Activated protein kinase A (PKA) inhibits RhoA and induces extensions. The isoquinoline H89 inhibits PKA and thus should prevent the inactivation of RhoA. In kinase assays, H89 has been recently found to inactivate a ROCK-II also. Because H89 may be able to exert opposite effects on cell extensions, we have studied the effects of H89 on neurite formation in the neuroblastoma-glioma line NG 108-15, which expresses ROCK-I and ROCK-II. We found that H89 can indeed inhibit ROCKs and PKA. Because ROCKs act downstream of RhoA, the inhibitory effect of H89 on ROCKs is most prominent. The data indicate that H89 may not be used as an antagonist of PKA in systems in which ROCKs play a role.

Intact sorting, targeting, and clustering of gamma-aminobutyric acid A receptor subtypes in hippocampal neurons in vitro

The cellular and subcellular distribution of four GABA(A) receptor subtypes, identified by the presence of the alpha1, alpha2, alpha3, or alpha5 subunit, was investigated immunocytochemically in dissociated cultures of hippocampal neurons. We addressed the questions whether (1) cell-type specific expression, (2) axonal/somatodendritic targeting, and (3) synaptic/extrasynaptic clustering of GABA(A) receptor subtypes was retained in vitro. For comparison, the in vivo distribution pattern was assessed in sections from adult rat brain. The differential expression of GABA(A) receptor subunits allowed to identify five morphologically distinct cell types in culture: the alpha1 subunit was observed in glutamic acid decarboxylase-positive interneurons, the alpha2 and alpha5 subunits marked pyramidal-like cells, and the alpha3 subunit labeled three additional cell types, including presumptive hilar cells. All subunits were found in the somatodendritic compartment. In addition, appropriate axonal targeting was evidenced by the intense alpha2, and sometimes alpha3 subunit labeling of axon-initial segments (AIS) of pyramidal cells and hilar cells, respectively. Accordingly, both receptor subtypes were targeted to AIS in vivo, as well. Synaptic receptors were identified by colocalization with gephyrin, a postsynaptic clustering protein, and apposition to presynaptic terminals labeled with synapsin I. In vitro and in vivo, alpha1- and alpha2-receptor subtypes formed numerous synaptic clusters, alpha3-GABA(A) receptors were located either synaptically or extrasynaptically depending on the cell type, whereas alpha5-GABA(A) receptors were extrasynaptic. We conclude that receptor targeting to broad subcellular locations does not require specific GABAergic innervation patterns, which are disturbed in vitro, but depends on protein-protein interactions in the postsynaptic cell that are both subunit- and neuron-specific.

Intracellular compartmentation of pyruvate in primary cultures of cortical neurons as detected by (13)C NMR spectroscopy with multiple (13)C labels

The intracellular compartmentation of pyruvate in primary cultures of cortical neurons was investigated by high resolution (13)C NMR using mixtures of different pyruvate precursors conveniently labeled with (13)C or unlabeled. Cells were incubated with 1-5 mM (1-(13)C, 1,2-(13)C(2) or U-(13)C(6)) glucose only or with mixtures containing 1.5 mM (1-(13)C or U-(13)C(6)) glucose, 0.25-2.5 mM (2-(13)C or 3-(13)C) pyruvate and 1 mM malate. Extracts from cells and incubation media were analyzed by (13)C NMR to determine the relative contributions of the different precursors to the intracellular pyruvate pool. When ((13)C) glucose was used as the sole substrate fractional (13)C enrichments and (13)C isotopomer populations in lactate and glutamate carbons were compatible with a unique intracellular pool of pyruvate. When mixtures of ((13)C) glucose, ((13)C) pyruvate and malate were used, however, the fractional (13)C enrichments of the C2 and C3 carbons of lactate were higher than those of the C2 and C3 carbons of alanine and depicted a different (13)C isotopomer distribution. Moreover, neurons incubated with 1 mM (1,2-(13)C(2)) glucose and 0.25-5 mM (3-(13)C) pyruvate produced exclusively (3-(13)C) lactate, revealing that extracellular pyruvate is the unique precursor of lactate under these conditions. These results reveal the presence of two different pools of intracellular pyruvate; one derived from extracellular pyruvate, used mainly for lactate and alanine production and one derived from glucose used primarily for oxidation. A red-ox switch using the cytosolic NAD(+)/NADH ratio is proposed to modulate glycolytic flux, controlling which one of the two pyruvate pools is metabolized in the tricarboxylic acid cycle when substrates more oxidized or reduced than glucose are used.

Effect of forskolin and exogenously administered oxytocin mRNA on oxytocin release by dispersed hypothalamic cultures

Differential vasopressin (VP) gene expression and oxytocin (OT) gene expression were observed in hypothalamic cultures derived from 14-day-old rat fetuses, with VP but not OT being induced by treatment with forskolin and 3-isobutyl-1-methylxanthine. These cultures were used to demonstrate that exogenous VP mRNA could be taken up and translated into releasable VP. In the current studies a similar culture preparation was used to test the hypothesis that, due to the similarity in the mRNA and prohormone structures of VP and OT, the VP-expressing neurons in the cultures would be capable of utilizing exogenous OT mRNA for synthesis of releasable OT. Although OT release was increased by the administration of exogenous OT mRNA, endogenous OT gene expression was also observed. To determine what had induced OT gene expression in the current cultures, the undefined components of the culture preparation, e.g., the glial feeder layer and the serum component of the culture medium, were evaluated. Restraining growth of the glial carpet with cytosine-arabinoside did not alter OT gene expression. Use of a defined medium supplemented with B-27 induced optimal OT gene expression. From this, it is possible to conclude that the components included in B-27 are sufficient for OT gene expression.Factors included in earlier lots of sera may have been responsible for suppression of OT gene expression. Cultures maintained in serum-free, B-27-supplemented medium may provide a useful model system for studying OT gene regulation.

Simplified serum- and steroid-free culture conditions for high-throughput viability analysis of primary cultures of cerebellar granule neurons

A serum- and steroid-free primary culture system was developed for the maintenance and automated analysis of cerebellar granule cell viability. Conventional poly-lysine coated 96-well tissue culture plates serve as a platform for growth, experimental manipulation and subsequent automated analysis of these primary cultured neurons. Cerebellar granule neurons were seeded at densities ranging from 2 x 10(4) to 1.25 x 10(6) cells/cm(2) and maintained in serum- and steroid-free culture conditions for 7 days. Viability was subsequently determined by the reduction of [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS), and the degree of cell death occurring over that period was determined by the release of lactate dehydrogenase (LDH). At appropriate cell densities, the results of the MTS reduction and LDH release assays were directly proportional to the initial number of cerebellar granule cells plated. Those results indicate that an initial cell density of 0.5 - 1.0 x 10(5) cells per well (0.32 cm(2)) was appropriate for simultaneous analysis with the MTS reduction and LDH release assays. Both assays were then used to demonstrate the utility of this model system for analysis of tert-butyl-hydroperoxide and hydrogen peroxide induced oxidative stress. Additionally, the MTS reduction assay was used to demonstrate that the NMDA-receptor selective antagonist MK-801 was neuroprotective against glutamate-mediated excitotoxicity. This study defines a powerful and flexible primary culture system for cerebellar neurons that is useful for high-throughput analysis of factors that influence neuronal viability.

A new approach to neural cell culture for long-term studies

We have developed a new method for culturing cells that maintains their health and sterility for many months. Using conventional techniques, primary neuron cultures seldom survive more than 2 months. Increases in the osmotic strength of media due to evaporation are a large and underappreciated contributor to the gradual decline in the health of these cultures. Because of this and the ever-present likelihood of contamination by airborne pathogens, repeated or extended experiments on any given culture have until now been difficult, if not impossible. We surmounted survival problems by using culture dish lids that form a gas-tight seal, and incorporate a transparent hydrophobic membrane (fluorinated ethylene-propylene) that is selectively permeable to oxygen (O(2)) and carbon dioxide (CO(2)), and relatively impermeable to water vapor. This prevents contamination and greatly reduces evaporation, allowing the use of a non-humidified incubator. We have employed this technique to grow dissociated cortical cultures from rat embryos on multi-electrode arrays. After more than a year in culture, the neurons still exhibit robust spontaneous electrical activity. The combination of sealed culture dishes with extracellular multi-electrode recording and stimulation enables study of development, adaptation, and very long-term plasticity, across months, in cultured neuronal networks. Membrane-sealed dishes will also be useful for the culture of many other cell types susceptible to evaporation and contamination.

Effects of the novel cyclosporine derivative PSC833 on glucose metabolism in rat primary cultures of neuronal and glial cells

Cyclosporine A (CsA) and the cyclosporine degrees congener PSC833 are known to cause transient CNS symptoms at high dosages in animal and man. Since impaired glucose metabolism plays a fundamental role in many heriditary and drug-induced neurological disorders, it was the purpose of the present study to evaluate whether this mechanism of pathogenesis might apply to PSC833 and CsA, using neural cells from rats. PSC833 and CsA were investigated in primary cultures of rat neuronal and glial cells at the concentration of 0.1, 1, 10, and 20 microM for 24 and 48 hr. Lactate dehydrogenase was determined as a marker of cytotoxicity. Cell proliferation was determined in astrocytes. Cellular glucose metabolism was investigated by 13C-NMR using [1-13C]glucose as a substrate. Glucose and lactate concentrations in the cell culture supernatants were determined spectrophotometrically. PSC833 at 10 microM was not cytotoxic in neuronal or glial cells nor did it inhibit proliferation in astrocytes 24 hr after incubation. Under the same conditions, the determination of [1-13C]glucose and [3-13C]lactate revealed significantly increased glucose consumption and lactate production in both cell types, as well as decreased levels of Krebs cycle intermediates. In the cell culture medium of both cell types after treatment with 10 microM PSC833, the rates of glucose consumption and lactate formation increased in comparison to controls, between 60-83% and 54-78%, respectively. PSC833 (10 microM) and CsA (20 microM) resulted in nearly similar increased glucose consumption and lactate production. The major PSC833 metabolite in rats, M9, which was devoid of CNS effects, did not cause significant changes in glucose metabolism. The present data suggest that PSC833-impaired tricarboxylic acid cycle activity, resulting in decreased Krebs cycle metabolites, can cause energy depletion and acidosis, which might contribute to the transient neurological symptoms of PSC833 and CsA.

Oxygen measurements in brain stem slices exposed to normobaric hyperoxia and hyperbaric oxygen

We previously reported (J Appl Physiol 89: 807-822, 2000) that < or =10 min of hyperbaric oxygen (HBO(2); < or = 2,468 Torr) stimulates solitary complex neurons. To better define the hyperoxic stimulus, we measured PO(2) in the solitary complex of 300-microm-thick rat medullary slices, using polarographic carbon fiber microelectrodes, during perfusion with media having PO(2) values ranging from 156 to 2,468 Torr. Under control conditions, slices equilibrated with 95% O(2) at barometric pressure of 1 atmospheres absolute had minimum PO(2) values at their centers (291 +/- 20 Torr) that were approximately 10-fold greater than PO(2) values measured in the intact central nervous system (10-34 Torr). During HBO(2), PO(2) increased at the center of the slice from 616 +/- 16 to 1,517 +/- 15 Torr. Tissue oxygen consumption tended to decrease at medium PO(2) or = 1,675 Torr to levels not different from values measured at PO(2) found in all media in metabolically poisoned slices (2-deoxy-D-glucose and antimycin A). We conclude that control medium used in most brain slice studies is hyperoxic at normobaric pressure. During HBO(2), slice PO(2) increases to levels that appear to reduce metabolism.

BDNF reduces miniature inhibitory postsynaptic currents by rapid downregulation of GABA(A) receptor surface expression

Changes in neurotransmitter receptor density at the synapse have been proposed as a mechanism underlying synaptic plasticity. Neurotrophic factors are known to influence synaptic strength rapidly. In the present study, we found that brain-derived neurotrophic factor (BDNF) acts postsynaptically to reduce gamma-aminobutyric acid (GABA)-ergic function. Using primary cultures of rat hippocampal neurons, we investigated the effects of BDNF on GABAergic miniature inhibitory postsynaptic currents (mIPSCs) and on the localization of GABAA receptors. Application of BDNF (100 ng/mL) led within minutes to a marked reduction (33.5%) of mIPSC amplitudes in 50% of neurons, recorded in the whole-cell patch-clamp mode, leaving frequency and decay kinetics unaffected. This effect was blocked by the protein kinase inhibitor K252a, which binds with high affinity to trkB receptors. Immunofluorescence staining with an antibody against trkB revealed that about 70% of cultured hippocampal pyramidal cells express trkB. In dual labelling experiments, use of neurobiotin injections to label the recorded cells revealed that all cells responsive to BDNF were immunopositive for trkB. Treatment of cultures with BDNF reduced the immunoreactivity for the GABAA receptor subunits-alpha2, -beta2,3 and -gamma2 in the majority of neurons. This effect was detectable after 15 min and lasted at least 12 h. Neurotrophin-4 (NT-4), but not neurotrophin-3 (NT-3), also reduced GABAA receptor immunoreactivity, supporting the proposal that this effect is mediated by trkB. Altogether the results suggest that exposure to BDNF induces a rapid reduction in postsynaptic GABAA receptor number that is responsible for the decline in GABAergic mIPSC amplitudes.

Developmental increase in asynchronous GABA release in cultured hippocampal neurons

Developmental changes in GABAergic synaptic transmission were examined in cultured hippocampal neurons using patch-clamp recordings and Ca(2+) imaging. In paired recordings, tetanization of the presynaptic GABAergic neuron with 80 pulses at either 40 or 80Hz was accompanied by tetanic depression of inhibitory postsynaptic responses. In neurons that had been cultured for more than two weeks, asynchronous inhibitory postsynaptic currents often appeared during the tetanus and continued for several seconds following stimulation. There was little asynchronous activity in neurons that had been cultured for shorter times. However, no age-related changes were observed in the amplitude of single synchronous inhibitory postsynaptic currents, paired-pulse depression or post-tetanic potentiation of inhibitory postsynaptic currents. Following equimolar replacement of extracellular Ca(2+) with strontium ions (Sr(2+)), single autaptic inhibitory postsynaptic currents were depressed in amplitude and asynchronous inhibitory postsynaptic currents were present on the decaying phase. Sr(2+)-induced asynchronous inhibitory postsynaptic currents showed no dependence on age in culture. Imaging of Ca(2+) in single GABAergic boutons was performed by including Fluo-3 in the patch pipette. During action potential firing induced by stimulating at 80Hz for 1s, intracellular calcium [Ca(2+)](i) increased rapidly in individual boutons. Following the stimulus, [Ca(2+)](i) decayed back to baseline within 10-15s. The half-time of decay increased from 1. 7+/-0.2s at 15days in vitro to 4.0+/-0.2s at 30days in vitro (P<0. 05), with a developmental profile that closely matched the increase in asynchronous inhibitory postsynaptic currents. We propose that the increase in tetanus-induced asynchronous GABA-release during the first month of synapse maturation in vitro is caused by a slowing of the Ca(2+)-clearing mechanisms in the GABAergic boutons. This results in larger and more prolonged elevations of [Ca(2+)](i) during tetanic stimulation, which leads to enhanced asynchronous transmitter release. We propose that the results of this study demonstrate a potentially important aspect of synapse maturation during development, and also imply that GABA release is up-regulated in conditions of decreased Ca(2+) buffering and clearing.

Method for serum-free culture of late fetal and early postnatal rat brainstem neurons

Primary culture of postnatal brainstem neurons in defined medium has not been described in the literature. Successful primary culture of brainstem neurons is typically restricted to embryonic ages E14-E18. This study describes a method for culture of late fetal and early postnatal brainstem neurons using a serum-free culture medium. The culture system is based on Neurobasal medium supplemented with antioxidant-rich B27 (Life Technologies). Neuron survival was optimized by replacing glutamine with GlutaMaxI, by matching osmolality with neuronal age, and by using Hibernate medium to increase neuron survival during tissue dissociation. This paper describes the first reliable method for culturing brainstem neurons from late fetal and early postnatal stages of the rat for up to 6 days postpartum.

Transgenic activation of Ras in neurons promotes hypertrophy and protects from lesion-induced degeneration

Ras is a universal eukaryotic intracellular protein integrating extracellular signals from multiple receptor types. To investigate its role in the adult central nervous system, constitutively activated V12-Ha-Ras was expressed selectively in neurons of transgenic mice via a synapsin promoter. Ras-transgene protein expression increased postnatally, reaching a four- to fivefold elevation at day 40 and persisting at this level, thereafter. Neuronal Ras was constitutively active and a corresponding activating phosphorylation of mitogen-activated kinase was observed, but there were no changes in the activity of phosphoinositide 3-kinase, the phosphorylation of its target kinase Akt/PKB, or expression of the anti-apoptotic proteins Bcl-2 or Bcl-X(L). Neuronal Ras activation did not alter the total number of neurons, but induced cell soma hypertrophy, which resulted in a 14.5% increase of total brain volume. Choline acetyltransferase and tyrosine hydroxylase activities were increased, as well as neuropeptide Y expression. Degeneration of motorneurons was completely prevented after facial nerve lesion in Ras-transgenic mice. Furthermore, neurotoxin-induced degeneration of dopaminergic substantia nigra neurons and their striatal projections was greatly attenuated. Thus, the Ras signaling pathway mimics neurotrophic effects and triggers neuroprotective mechanisms in adult mice. Neuronal Ras activation might become a tool to stabilize donor neurons for neural transplantation and to protect neuronal populations in neurodegenerative diseases.

Tauroursodeoxycholic acid partially prevents apoptosis induced by 3-nitropropionic acid: evidence for a mitochondrial pathway independent of the permeability transition

Ursodeoxycholic acid (UDCA) has been shown to be a strong modulator of the apoptotic threshold in both hepatic and nonhepatic cells. 3-Nitropropionic acid (3-NP), an irreversible inhibitor of succinate dehydrogenase, appears to cause apoptotic neuronal cell death in the striatum, reminiscent of the neurochemical and anatomical changes associated with Huntington's disease (HD). This study was undertaken (a) to characterize further the mechanism by which 3-NP induces apoptosis in rat neuronal RN33B cells and (b) to determine if and how the taurine-conjugated UDCA, tauroursodeoxycholic acid (TUDCA), inhibits apoptosis induced by 3-NP. Our results indicate that coincubation of cells with TUDCA and 3-NP was associated with an approximately 80% reduction in apoptosis (p < 0.001), whereas neither taurine nor cyclosporin A, a potent inhibitor of the mitochondrial permeability transition (MPT), inhibited cell death. Moreover, TUDCA, as well as UDCA and its glycine-conjugated form, glycoursodeoxycholic acid, prevented mitochondrial release of cytochrome c (p < 0.001), which probably accounts for the observed inhibition of DEVD-specific caspase activity and poly(ADP-ribose) polymerase cleavage. 3-NP decreased mitochondrial transmembrane potential (p < 0.001) and increased mitochondrial-associated Bax protein levels (p < 0.001). Coincubation with TUDCA was associated with significant inhibition of these mitochondrial membrane alterations (p < 0.01). The results suggest that TUDCA inhibits 3-NP-induced apoptosis via direct inhibition of mitochondrial depolarization and outer membrane disruption, together with modulation of Bax translocation from cytosol to mitochondria. In addition, cell death by 3-NP apparently occurs through pathways that are independent of the MPT.

Maturation of vulnerability to excitotoxicity: intracellular mechanisms in cultured postnatal hippocampal neurons

Neuronal vulnerability to excitotoxicity changes dramatically during postnatal maturation. To study the intracellular mechanisms by which maturation alters vulnerability in single neurons, we developed techniques to maintain hippocampal neurons from postnatal rats in vitro. After establishing their neuronal phenotype with immunohistochemistry and electrophysiology, we determined that these neurons exhibit developmentally regulated vulnerability to excitotoxicity. At 5 days in vitro, NMDA-induced cell death at 24 h increased from 3.6% in 3-day-old rats to >90% in rats older than 21 days. Time-lapse imaging of neuronal morphology following NMDA demonstrated increasingly prevalent and severe injury as a function of postnatal age. Neither high- nor low-affinity calcium dyes demonstrated differences in peak NMDA-induced [Ca(2+)](i) increases between neurons from younger and older animals. However, neurons from older animals were uniformly distinguished from those from younger animals by their subsequent loss of [Ca(2+)](i) homeostasis. Because of the role of mitochondrial Ca(2+) buffering in [Ca(2+)](i) homeostasis, we measured NMDA-induced changes in mitochondrial membrane potential (DeltaPsi) as a function of postnatal age. NMDA markedly dissipated DeltaPsi in neurons from mature rats, but minimally in those from younger rats. These data demonstrate that, in cultures of postnatal hippocampal neurons, (a) vulnerability to excitotoxicity increases as a function of the postnatal age of the animal from which they were harvested, and (b) developmental regulation of vulnerability to NMDA occurs at the level of the mitochondrion.

Role played by sodium in activity-dependent secretion of neurotrophins - revisited

In previous experiments, a causal relationship between sodium influx and secretion of nerve growth factor (NGF) was deduced from the observation that the sodium substitute N-methyl-D-glucamine (NMDG) abolished any activity-mediated NGF secretion that depends on intact internal calcium stores. However, all available experimental evidence speaks against sodium-mediated calcium mobilization from these stores under physiological conditions. We now report that rapid sodium influx initiated by monensin or ouabain did not induce brain-derived neurotrophic factor (BDNF) secretion from either native hippocampal slices or BDNF-transduced hippocampal neuronal cultures. Additionally, we found marked differences between the replacement of sodium by NMDG and sucrose on the one hand, and choline and lithium on the other. Replacement of 100% (and as little as 10%) sodium by NMDG or sucrose not only blocked the activity-mediated neurotrophin secretion, but itself led to a rapid and substantial increase of neurotrophin secretion. In contrast, the replacement of sodium (10% and 100%) by lithium and choline did not result in a release of neurotrophins, and only 100% replacement blocked the activity-mediated neurotrophin secretion. We conclude that the blocking effects of NMDG and sucrose on neurotrophin secretion do not reflect the sodium replacement, but instead represent an independent blocking effect. These differences were also reflected in part by electrophysiological investigations in individually patched hippocampal neurons. The importance of the present observations lies not only in the reevaluation of the involvement of sodium in activity-dependent neurotrophin secretion, but also in the demonstration that sodium replacement may initiate 'side effects' that are unrelated to sodium replacement.

Adenosine A(1) receptor in cultured neurons from rat cerebral cortex: colocalization with adenosine deaminase

Adenosine A(1) receptors (A(1)Rs) have been characterized in primary cultures of neurons from cerebral cortex. The specific adenosine A(1) antagonist 8-cyclopentyl-1,3-[(3)H]dipropylxanthine bound to both membranes and intact cells. When saturation experiments were performed in membranes, a K(D) value of 0.76 nM and a B(max) of 57 fmol/mg of protein were obtained. Competition assays revealed a pharmacological profile characteristic of A(1)Rs. The presence of this receptor was further confirmed by RT-PCR analysis. The expression of the receptor showed no significant changes during the period of culture studied, up to 12 days in vitro. A(1)R agonist inhibited forskolin-stimulated adenylyl cyclase, showing the functional coupling of these receptors with the effector. alphaG(i1, 2) protein level, detected by immunoblot, presented an increase during the period of culture. This increase correlated with an increase in the mRNA level of alphaG(i1) but not alphaG(i2). By immunochemical assays, it is shown that these receptors are expressed in both the neuronal cell body and the proximal dendrites. Colocalization of A(1)Rs with microtubule-associated protein 2 and cell surface adenosine deaminase was shown by confocal microscopy. The high degree of colocalization observed between A(1)Rs and ectoadenosine deaminase in neurons could suggest an important role of the enzyme in adenosine-mediated neuromodulation.

Expansion of adult Schwann cells from mouse predegenerated peripheral nerves

We present an effective technique for culture and expansion of Schwann cells (SC) from adult peripheral nerves. Cultures from adult mouse sciatic nerves (one to six nerves per culture) in defined medium showed markedly higher purity and density of SC when the nerve was predegenerated in vivo for 7 days than when it was harvested fresh. SC from degenerated nerves were then cultured in defined media conditioned by primary cultures of adult SC. The best results were obtained with a conditioned medium supplemented with 1% fetal calf serum. In these conditions the purity of SC was about 90% and the density about 190 cell/mm(2) by 7-10 days in vitro. These findings indicate that adult SC can be expanded from small preinjured nerve fragments in a short time period to provide a source of SC for autologous cellular transplants.

Lumbar transplant of neurons genetically modified to secrete brain-derived neurotrophic factor attenuates allodynia and hyperalgesia after sciatic nerve constriction

Chronic delivery of anti-nociceptive molecules by means of cell grafts near the pain processing centers of the spinal cord is a newly developing technique for the treatment of neuropathic pain. The rat neuronal cell line, RN33B, derived from E13 rat brainstem raphe and immortalized with the SV40 temperature-sensitive allele of large T antigen (tsTag), was transfected with rat brain-derived neurotrophic factor cDNA (BDNF), and the BDNF-synthesizing cell line, 33BDNF.4, was isolated. The 33BDNF.4 cells synthesized mature BDNF protein at permissive temperature (33 degrees C), when the cells were proliferating, and during differentiation at non-permissive temperature (39 degrees C) in vitro. The bio-active BDNF protein was also secreted by the cells during both growth conditions, as measured by ELISA analysis of BDNF content and secretion. The bio-activity of the BDNF in 33BDNF.4 cell conditioned media was assessed by neurite outgrowth from E15 dorsal root ganglion (DRG) cultures. A control cell line, 33V1, transfected with the vector alone, did not synthesize or secrete any significant BDNF at either growth condition. Both cell lines were used as grafts in a model of chronic neuropathic pain induced by unilateral chronic constriction injury (CCI) of the sciatic nerve. Pain-related behaviors, including cold and tactile allodynia and thermal and tactile hyperalgesia, were evaluated after CCI in the affected hindpaw. When 33BDNF.4 and 33V1 cells were transplanted in the lumbar subarachnoid space of the spinal cord 1 week after CCI, they survived greater than 7 weeks on the pia mater around the spinal cord and the 33BDNF.4 cells continued to synthesize BDNF in vivo. Furthermore, the tactile and cold allodynia and tactile and thermal hyperalgesia induced by CCI was significantly reduced during the 2-7 week period after grafts of 33BDNF.4 cells. The maximal effect on chronic pain behaviors with the BDNF grafts occurred 2-3 weeks after transplant and the anti-nociceptive effects of the BDNF cell grafts was permanent. Transplants of the control 33V1 cells had no effect on the allodynia and hyperalgesia induced by CCI and these cells did not synthesize BDNF in vivo. These data suggest that a chronically applied, low local dose of BDNF supplied by transplanted cells near the spinal dorsal horn was able to reverse the development of chronic neuropathic pain following CCI. The use of neural cell lines that are able to deliver anti-nociceptive molecules, such as BDNF, in a model of chronic pain offers a novel approach to pain management and such 'biologic minipumps' can be developed for safe use in humans.

A minimal promoter for the GABA(A) receptor alpha6-subunit gene controls tissue specificity

The ability of nerve cells to regulate the expression of specific neurotransmitter receptors is of central importance to nervous system function, but little is known about the DNA elements that mediate neuron specific gene expression. The type A gamma-aminobutyric acid (GABA(A)) receptor alpha6-subunit gene, which is expressed exclusively in cerebellar granule cells, presents a unique opportunity to study the cis elements involved in restricting gene expression to a distinct neuronal population. In an effort to identify the regulatory elements that govern cerebellar granule cell-specific gene expression, the proximal 5' flanking regions for the human, rat, and mouse alpha6 genes were cloned and sequenced, and a major transcriptional initiation site was identified in the rodent genes. Functional analysis of rat alpha6 gene-reporter constructs in primary neuronal cultures reveals that a 155-bp TATA-less promoter region (-130 to +25 bp) constitutes a minimal promoter that can drive cerebellar granule cell-specific expression. Internal deletion and decoy competition studies demonstrate that the minimal promoter contains a 60-bp region (-130 to -70 bp) that is critical for enhanced promoter activity in cerebellar granule cells. Activity of the compromised promoter containing the deletion cannot be rescued by placing the 60-bp region downstream of the reporter gene, demonstrating that it is not a classical enhancer but rather a positionally dependent regulator. An additional cerebellar-specific activating sequence is located between -324 and -130 bp, and a downstream negative regulatory region (+158 to +294) has been shown to be active in fibroblasts but inactive in cerebellar granule cells. Taken together, the results suggest a possible mechanism for the control of cerebellar granule cell-specific expression of the GABA(A) receptor alpha6 subunit gene.

Survival of hippocampal and cortical neurons in a mixture of MEM+ and B27-supplemented neurobasal medium

Serum-free B-27 supplemented neurobasal (NB) and a 10% fetal bovine serum-supplemented Eagle's minimum essential medium (MEM+) are used to culture rat embryonic hippocampal neurons for different purposes. Although NB medium leads to enhanced cell survival, it contains biological antioxidants and is not suitable for the study of free radical damage and oxidation in cultured neurons. MEM+ without additional antioxidants has been used widely in the study of free radical damage and oxidation, although it does not support optimum neuronal survival in culture. Serum in MEM+ leads to enhanced cell survival but also promotes glial cell proliferation. In this study, we used a new combination medium (NM-2) that consists of both NB and MEM+ for growing primary hippocampal and cortical neuronal cultures. NM-2 enhanced neuronal survival 78.9% for dissociated neurons at a density of 50 cells/mm(2) and 83.1% for 100 cells/mm(2), while decreasing glial cell proliferation to 2-3% and completely inhibiting oligodendrocytes. The NM-2 minimized the effectiveness of antioxidants in the medium to the neurotoxin 4-hydroxynonenal. It also decreased neuronal clumping and provided a more even distribution of neurons. Neurons survived for 4 weeks in NM-2 without changing the original medium. NM-2 provides a good environment for studies of free radical damage and oxidation of neurons. The combination incorporates the best of both NB and MEM+ that results in high neuron survival rate, low glial cell proliferation, reduced antioxidant level, and provides relatively pure cultures of hippocampal and cortical neurons.

Schwann-like macroglia in adult rat brain

Olfactory ensheathing cells (OECs) share properties with astrocytes and Schwann cells. This study was designed to test the hypothesis that glia with properties similar to those exhibited by OECs might be present in brain areas other than the olfactory bulb. We found tanycytes and pituicytes to express a distinctive set of immunological markers in common with OECs and nonmyelinating Schwann cells, namely low-affinity neurotrophin receptor (p75NTR), O4 antigen, estrogen receptor-alpha type, and insulin-like growth factor 1 (IGF-1). The two glial types could be cultured from adult hypothalamus and neurohypophysis, respectively, using the methods developed for olfactory OECs. Both glial types displayed morphologies reminiscent of Schwann cells, in primary culture. Schwann-like central glia presented a preferred growth substrate for dorsal root ganglion neurites and, when making intimate contacts with them, manifested a myelinating phenotype. These combined properties define a type of CNS macroglia that would not fit within conventional central glia types.

Okadaic acid induces cycloheximide and caspase sensitive apoptosis in immature neurons

Previous studies have shown that okadaic acid (OA) evokes tau phosphorylation and neurofibrillary changes in vivo, and in cultured neurons, that resemble Alzheimer's disease pathogenesis. In order to investigate the mechanism of OA-neurotoxicity, we treated cultured rat neurons with OA and examined nuclear morphology, phosphatidylserine (PS) externalization, alpha-fodrin cleavage, and the effects of cell death inhibitors. Our results demonstrated that cycloheximide (CHX) and the broad-spectrum caspase inhibitor, ZVAD, significantly reduced cell death in a dose-dependent manner. Nuclear fragmentation, a hallmark of apoptosis, occurred after OA treatment and was inhibited by CHX or ZVAD. PS externalization was apparent in 6-12 h in neurites and in cell bodies, and peaked at 24 h after OA treatment. Cleavage of alpha-fodrin as visualized by the appearance of 150- and 120-kDa bands appeared with a time course similar to PS externalization. These results suggest that OA induce CHX and caspase sensitive neuronal apoptosis.

Microtubule binding by CRIPT and its potential role in the synaptic clustering of PSD-95

CRIPT is a postsynaptic protein that binds selectively to the third PDZ domain (PDZ3) of PSD-95. Here we show that CRIPT also binds directly to microtubules, thereby linking PSD-95 to the microtubule cytoskeleton. Disrupting the CRIPT-PSD-95 interaction in cultured hippocampal neurons with a PDZ3-specific peptide prevented the association of PSD-95 with microtubules and inhibited the synaptic clustering of PSD-95, chapsyn-110/PSD-93 and GKAP (a PSD-95-binding protein). However, the number of synapses and the synaptic clustering of NMDA receptors were unaffected, suggesting that PSD-95-family proteins are not essential for the maintenance of synapses and the synaptic localization of NMDA receptors.

Sphingosine-1-phosphate induces apoptosis of cultured hippocampal neurons that requires protein phosphatases and activator protein-1 complexes

In this study, we report that mobilization of internal Ca2+ by sphingosine-1-phosphate, a metabolite of ceramide, induces apoptosis in cultured hippocampal neurons. This sphingosine-1-phosphate-induced apoptosis is dependent upon the activation of protein phosphatases, possibly calcineurin and phosphatase 2A (or a related phosphatase). In addition, pretreatment of neurons with double-stranded oligonucleotides containing the metallothionein phorbol-12-myristate-13-acetate response element sequence as transcription factor decoys suppressed apoptosis. In contrast, double-stranded oligonucleotides containing either the c-jun or SV40 phorbol-12-myristate-13-acetate response element sequences were ineffective. Electrophoretic mobility shift assays and supershift assays revealed that c-Fos-containing activator protein- complexes preferentially bound the metallothionein phorbol-12-myristate-13-acetate response element sequence-containing oligonucleotides. Furthermore, antisense oligonucleotides to c-fos and c-jun were also protective. The apoptotic death of hippocampal neurons has been hypothesized to contribute to the cognitive impairments observed following insults to the brain. While increases in intracellular calcium are thought to be key mediators of neuronal apoptosis, the biochemical cascade(s) activated as a result of increased Ca2+ which mediates apoptosis of hippocampal neurons is (are) not well understood. The findings presented in this study suggest that mobilization of internal calcium via prolonged exposure of sphingosine-1-phosphate induces apoptosis of hippocampal neurons in culture. Sustained increases in intracellular calcium activate a phosphatase cascade that includes calcineurin and a phosphatase 2A-like phosphatase, and leads to the expression of genes containing metallothionein phorbol-12-myristate-13-acetate response element (TGAGTCA)-type enhancer sequences. The expression of genes containing TGAGTCA-type enhancer sequences appears to be essential for sphingosine-1-phosphate-induced apoptosis of hippocampal neurons.

BDNF gene transfer to the mammalian brain using CNS-derived neural precursors

Neural stem cell lines represent a homogeneous source of cells for genetic, developmental, and gene transfer and repair studies in the nervous system. Since both gene transfer of neurotrophic factors and cell replacement strategies are of immediate interest for therapeutical purposes, we have generated BDNF-secreting neural stem cell lines and investigated to what extent different endogenous levels of BDNF expression affect in vitro survival, proliferation and differentiation of these cells. Also, we have investigated the in vivo effects of such BDNF gene transfer procedure in the rat neostriatum. Hippocampus- and cerebellum-derived cell lines reacted differently to manipulations aimed at varying their levels of BDNF production. Over-expression of BDNF enhanced survival of both cell types, in a serum-deprivation assay. Conversely, and ruling out unspecific effects, expression of an antisense version of BDNF resulted in compromised survival of cerebellum-derived cells, and in a lethal phenotype in hippocampal progenitors. These data indicate that endogenous BDNF level strongly influences the in vitro survival of these cells. These effects are more pronounced for hippocampus- than for cerebellum-derived progenitors. Hippocampus-derived BDNF overproducers showed no major change in their capacity to differentiate towards a neuronal phenotype in vitro. In contrast, cerebellar progenitors overproducing BDNF did not differentiate into neurons, whereas cells expressing the antisense BDNF construct generated cells with morphological features of neurons and expressing immunological neuronal markers. Taken together, these results provide evidence that BDNF controls both the in vitro survival and differentiation of neural stem cells. After in vivo transplantation of BDNF-overproducing cells to the rat neostriatum, these survived better than the control ones, and induced the expected neurotrophic effects on cholinergic neurons. However, long-term (3 months) administration of BDNF resulted in detrimental effects, at this location. These findings may be of importance for the understanding of brain development, for the design of therapeutic neuro-regenerative strategies, and for cell replacement and gene therapy studies.

Reorganization and movement of microtubules in axonal growth cones and developing interstitial branches

Local changes in microtubule organization and distribution are required for the axon to grow and navigate appropriately; however, little is known about how microtubules (MTs) reorganize during directed axon outgrowth. We have used time-lapse digital imaging of developing cortical neurons microinjected with fluorescently labeled tubulin to follow the movements of individual MTs in two regions of the axon where directed growth occurs: the terminal growth cone and the developing interstitial branch. In both regions, transitions from quiescent to growth states were accompanied by reorganization of MTs from looped or bundled arrays to dispersed arrays and fragmentation of long MTs into short MTs. We also found that long-term redistribution of MTs accompanied the withdrawal of some axonal processes and the growth and stabilization of others. Individual MTs moved independently in both anterograde and retrograde directions to explore developing processes. Their velocities were inversely proportional to their lengths. Our results demonstrate directly that MTs move within axonal growth cones and developing interstitial branches. Our findings also provide the first direct evidence that similar reorganization and movement of individual MTs occur in the two regions of the axon where directed outgrowth occurs. These results suggest a model whereby short exploratory MTs could direct axonal growth cones and interstitial branches toward appropriate locations.

Post-tetanic potentiation of GABAergic IPSCs in cultured rat hippocampal neurones

1. Dual whole-cell patch-clamp recording was used to investigate post-tetanic potentiation (PTP) of GABAergic IPSCs evoked between pairs of cultured rat hippocampal neurones. Tetanization of the presynaptic neurone at frequencies (f) ranging from 5 to 100 Hz resulted in PTP of the IPSCs. Maximum PTP had a magnitude of 51.6 % just after the stimulus train, and lasted up to 1 min. PTP was shown to be dependent on the number of stimuli in the train, but independent of f at frequencies > or =5 Hz. 2. Blocking postsynaptic GABAA receptors with bicuculline during the tetanus did not affect the expression of PTP, showing that it is a presynaptic phenomenon. PTP was strongly affected by changing [Ca2+]o during the tetanus: PTP was reduced by lowering [Ca2+]o, and increased by high [Ca2+]o. 3. PTP was still present after presynaptic injection of BAPTA or EGTA, or following perfusion of the membrane-permeable ester EGTA-tetraacetoxymethyl ester (EGTA AM, 50 microM). On the other hand, EGTA AM blocked spontaneous, asynchronous IPSCs (asIPSCs), which were often associated with tetanic stimulation. 4. Tetanic stimulation in the presence of 4-aminopyridine (4-AP), which promotes presynaptic Ca2+ influx, evoked sustained PTP of IPSCs in half of the neurones tested. 5. The results indicate that PTP at inhibitory GABAergic synapses is related to the magnitude of presynaptic Ca2+ influx during the tetanic stimulation, leading to an enhanced probability of vesicle release in the post-tetanic period. The increase in [Ca2+]i occurs despite the presence of high-affinity exogenous and endogenous intracellular Ca2+ buffers. That PTP of IPSCs depends on the number, and not the frequency, of spikes in the GABAergic neurone is in accordance with a slow clearing of intracellular Ca2+ from the presynaptic terminals.

Lithium protects cultured neurons against beta-amyloid-induced neurodegeneration

The deposition of beta-amyloid peptide (A beta), the hyperphosphorylation of tau protein and the death of neurons in certain brain regions are characteristic features of Alzheimer's disease. It has been proposed that the accumulation of aggregates of A beta is the trigger of neurodegeneration in this disease. In support of this view, several studies have demonstrated that the treatment of cultured neurons with A beta leads to the hyperphosphorylation of tau protein and neuronal cell death. Here we report that lithium prevents the enhanced phosphorylation of tau protein at the sites recognized by antibodies Tau-1 and PHF-1 which occurs when cultured rat cortical neurons are incubated with A beta. Interestingly, lithium also significantly protects cultured neurons from A beta-induced cell death. These results raise the possibility of using chronic lithium treatment for the therapy of Alzheimer's disease.

Differential expression of bcl-w and bcl-x messenger RNA in the developing and adult rat nervous system

The bcl-2 family of proteins comprises both anti-apoptotic and pro-apoptotic members, which play a pivotal role in regulating cell death. Bcl-w is a recently identified member of this family, which was shown to inhibit apoptosis in haemopoietic cell lines. However, the function and expression patterns of bcl-w in the nervous system have so far not been described. We have cloned complementary DNA corresponding to rat bcl-w and analysed the expression of bcl-w messenger RNA during rat brain development, using RNA blotting and in situ hybridization techniques. We also compared the expression patterns of bcl-w with those of bcl-xL. During brain development, the levels of bcl-w messenger RNA were found to increase, with highest expression located to specific regions of the mature brain, such as hippocampus, cerebellum, piriform cortex and locus coeruleus. Bcl-w messenger RNA was expressed by neurons, as shown with double labeling with neuronal markers. In contrast to bcl-w, bcl-xL messenger RNA expression levels were highest during early development, particularly in cortex, hippocampus, thalamus, spinal cord and dorsal root ganglia. During postnatal development the expression of bcl-xL messenger RNA decreased and were only detected at low levels in the adult nervous system. As shown earlier for bcl-2, the expression of bcl-w and bcl-x messenger RNA in cultured cerebellar granule cells was not altered by the deprivation of neurotrophic factors. The present results suggest that bcl-w may play an important role in the mature nervous system.

Liposome-mediated NGF gene transfection following neuronal injury: potential therapeutic applications

We have systematically investigated the therapeutic potential of cationic liposome-mediated neurotrophic gene transfer for treatment of CNS injury. Following determination of optimal transfection conditions, we examined the effects of dimethylaminoethane-carbamoyl-cholesterol (DC-Chol) liposome-mediated NGF cDNA transfection in injured and uninjured primary septo-hippocampal cell cultures and rat brains. In in vitro studies, we detected an increase of NGF mRNA in cultures 1 day after transfection. Subsequent ELISA and PC12 cell biological assays confirmed that cultured cells secreted soluble active NGF into the media from day 2 after gene transfection. Further experiments showed that such NGF gene transfection reduced the loss of chol- ine acetyltransferase (ChAT) activity in cultures following calcium-dependent depolarization injury. In in vivo studies, following intraventricular injections of NGF cDNA complexed with DC-Chol liposomes, ELISA detected nine- to 12-fold increases of NGF in rat CSF. Further studies showed that liposome/NGF cDNA complexes could attenuate the loss of cholinergic neuronal immunostaining in the rat septum after traumatic brain injury (TBI). Since deficits in cholinergic neurotransmission are a major consequence of TBI, our studies demonstrate for the first time that DC-Chol liposome-mediated NGF gene transfection may have therapeutic potential for treatment of brain injury.

Sulfated and unsulfated steroids modulate gamma-aminobutyric acidA receptor function through distinct sites

Sulfated and unsulfated neurosteroids such as pregnenolone sulfate, dehydroepiandrosterone sulfate (DHEAS), pregnanolone, and allopregnanolone, modulate ionotropic amino acid neurotransmitter receptors, and may function as endogenous neuromodulators. The gamma-aminobutyric acid type A (GABAA) receptor exhibits both negative and positive modulation by neurosteroids, but the interaction between negative and positive modulators is not well-understood. For a number of neuroactive steroids, sulfation at C-3 reverses the direction of modulation from positive to negative, suggesting that sulfation could be an important control point for the activity of endogenous neurosteroids. Modulation by endogenous and synthetic steroids of the response to exogenous or synaptically released GABA was examined in primary chick spinal cord and rat hippocampal neurons, and in Xenopus laevis oocytes expressing alpha1beta2gamma2S GABAA receptors. Inhibitory activity is retained when hemisuccinate is substituted for sulfate at C-3, suggesting that it is the negative charge, rather than the sulfate group, that confers inhibitory efficacy. The interaction between steroid negative and positive modulators is not competitive, indicating that steroid negative and positive modulators act through distinct sites. Some steroids, such as 11-ketopregnenolone sulfate, appear to act at both negative and positive modulatory sites, as indicated by an 'off-response' upon washout. A similar off-response is also observed after co-application of the negative modulator DHEAS and the positive modulator allopregnanolone. The observation that simultaneous application of sulfated and unsulfated steroids, such as DHEAS and allopregnanolone, act at distinct sites implies that steroid negative and positive modulators can act independently or coordinately to regulate GABA-mediated inhibition in the central nervous system.

Trophic effects of selegiline on cultured dopaminergic neurons

Trophic effects of the neuroprotective agent selegiline on cultured dopaminergic neurons were investigated and compared with the effects produced by brain derived neurotrophic factor (BDNF). Both treatments increased the total length of TH-positive neurites, but selegiline increased the average length of neuritic branches, whereas BDNF increased the formation of new branches. This trophic effect of selegiline may contribute to its action in neurodegenerative disease treatment.

Are there differences between the secretion characteristics of NGF and BDNF? Implications for the modulatory role of neurotrophins in activity-dependent neuronal plasticity

In previous experiments the activity-dependent secretion of nerve growth factor (NGF) from native hippocampal slices and from NGF-cDNA transfected hippocampal neurons showed unusual characteristics [Blochl and Thoenen (1995) Eur J Neurosci 7:1220-1228; (1996) Mol Cell Neurosci 7:173-190]. In both hippocampal slices and cultured hippocampal neurons the activity-dependent secretion proved to be independent of extracellular calcium, but dependent on the release of calcium from intracellular stores. Under different experimental conditions, Goodman et al. [(1996) Mol Cell Neurosci 7:222-238] reported that the high potassium-mediated secretion of brain-derived neurotrophic factor (BDNF) from hippocampal cultures was dependent on extracellular calcium. Mowla et al. [(1997) Proc 27th Annu Meet Soc Neurosci New Orleans 875.10] reported on even further-reaching differences between NGF and BDNF secretion, namely, that in hippocampal neurons and in pituitary cell lines NGF was secreted exclusively according to the constitutive pathway, whereas BDNF was exclusively sorted according to the activity-dependent regulated pathway. In view of the crucial importance of such potential differences between the processing, sorting, and secretory mechanisms of different neurotrophins for their modulatory roles in activity-dependent neuronal plasticity, a thorough analysis under comparable experimental conditions was mandatory. We demonstrate that in native hippocampal slices and adenoviral-transduced hippocampal neurons there are no differences between NGF and BDNF with respect to the subcellular distribution and mechanism of secretion; that the activity-dependent secretion of both NGF and BDNF is dependent on intact intracellular calcium stores; and that the differences between our own observations and those of Goodman et al. (ibid.) regarding the dependence on extracellular calcium do not reflect differences between NGF and BDNF sorting and secretion, but reflect the differing experimental conditions used.

Ca2+-permeable P2X receptor channels in cultured rat retinal ganglion cells

ATP has been identified as an excitatory neurotransmitter in both the CNS and peripheral nervous system; however, little is known about the functional properties of ATP-gated channels in central neurons. Here we used a culture preparation of the postnatal rat retina to test the responsiveness of identified retinal ganglion cells (RGCs) and putative amacrines to exogenous ATP and other purinoceptor agonists. Rapidly activating ATP-induced currents (IATP) were exclusively generated in a subpopulation (approximately 65%) of RGCs. The latter were identified by Thy1.1 immunostaining, repetitive firing patterns, and activation of glutamatergic autaptic currents. None of the putative amacrine cells was ATP-sensitive. IATP could be induced with ATP, ADP, and alpha,beta-mATP but not with adenosine. It was antagonized by suramin. The current-voltage relationship of IATP showed marked inward rectification. Dose-response analysis yielded an EC50 of 14.5 microM, with a Hill coefficient of 0.9. Noise analysis of IATP suggested a mean single channel conductance of 2.3 pS. Retinal P2X purinoceptor channels exhibited a high permeability for Ca2+. PCa/PCs obtained from reversal potentials of IATP under bi-ionic conditions amounted to 2. 2 +/- 0.7. In the majority of cells, the decay of IATP was biphasic. The degree of current inactivation during the first 2 sec of agonist application was highly variable. Heterogeneity was also found with respect to the sensitivity to ADP and alpha,beta-mATP and the blocking action of suramin, suggesting expression of multiple P2X receptor subtypes. Our results indicate that activation of P2X receptor channels represents an important pathway for Ca2+ influx in postnatal RGCs.

Protein kinase C and cAMP-dependent protein kinase regulate the neuronal differentiation of immortalized raphe neurons

These studies examined the extent to which protein kinase C (PKC) and cAMP-dependent protein kinase (PKA) regulate the neuronal differentiation of the raphe-derived neuronal cell line, RN33B. A differentiation-specific 2.25-fold increase in soluble PKA activity was observed. Neither membrane-associated-PKA, -PKC, or soluble PKC activities changed concomitant with differentiation. The PKC activity was derived from PKC alpha, gamma, epsilon, and theta isoenzymes. Activation of PKC inhibited the immunocytochemical expression of low and medium molecular weight neurofilament proteins, an effect due at least in part to decreased steady-state levels of protein. PKC activation also decreased glutamate immunoreactivity and increased cell number, protein synthesis, and bromodeoxyuridine uptake by 2.4-fold, 25%, and 32%, respectively. Coupled with the decrease in mature neuronal antigen expression, these data suggest that PKC activation inhibits neuronal differentiation by inducing proliferation. Inhibition of PKC markedly upregulated glutamate immunoreactivity. PKA activation potentiated the glutamatergic phenotype of RN33B cells, but inhibition of PKA was without effect on the expression of all neuronal antigens examined. Thus, both PKC and PKA regulate the differentiation of RN33B cells, although neither is absolutely necessary for expression of the differentiated neuronal phenotype. These results suggest the existence of parallel pathways regulating raphe neuronal differentiation.

Dehydroepiandrosterone antagonizes the neurotoxic effects of corticosterone and translocation of stress-activated protein kinase 3 in hippocampal primary cultures

Glucocorticoids are toxic to hippocampal neurons. We report here that the steroid dehydroepiandrosterone protects neurons of primary hippocampal cultures against the toxic effects of corticosterone. Corticosterone (20-500 nM) added for 24h to primary cultures of embryonic day 18 rat hippocampus resulted in significant neurotoxicity. Dissociated cells were grown for at least 10 days, initially in serum-containing medium, but serum was removed before adding steroids for 24 h. Neurotoxicity was measured by counting the number of cells stained either for beta-tubulin III or glial fibrillary acidic protein. Corticosterone-induced toxicity was prevented by co-treatment of the cultures with dehydroepiandrosterone (20-500 nM). Dehydroepiandrosterone on its own had little effect, though the highest concentration used (500 nM) was mildly toxic. Immunohistochemical studies on the nuclear translocation of a range of stress-activated protein kinases showed that stress-activated protein kinases 1, 2, 3 and 4 were all translocated by 10 min exposure to corticosterone (100 nM). Dehydroepiandrosterone (100 nM) attenuated the translocation of stress-activated protein kinase 3, but not the others. These experiments show that dehydroepiandrosterone has potent anti-glucocorticoid actions on the brain, and can protect hippocampal neurons from glucocorticoid-induced neurotoxicity. This protective action may involve stress-activated protein kinase 3-related intracellular pathways, though direct evidence for this has still to be obtained.