Evidence for calcium-reducing and excito-protective roles for the calcium-binding protein calbindin-D28k in cultured hippocampal neurons

GDNF induces the calretinin phenotype in cultures of embryonic striatal neurons

Glial cell line-derived neurotrophic factor (GDNF), a member of the transforming growth factor-beta (TGF-beta) superfamily, is a potent neurotrophic factor for several neuron populations in the central and peripheral nervous system. Members of the neurotrophin, neurokine, and TGF-beta families of growth factors can affect neurons beyond their capacity to promote survival. They can play instructive roles including the determination of a particular transmitter phenotype. Here, we show that GDNF enhances the number of calretinin (CaR)-positive neurons in serum-free cultures of striatal cells isolated from embryonic rats. The effect is dose-dependent, can be elicited with concentrations as low as 0.1 ng/ml, and is not accompanied by increased incorporation of 5-bromo-2'-desoxyuridine and appearance of glial fibrillary acidic protein-positive cells. Similar, but weaker effects can be elicited by brain-derived neurotrophic factor, neurotrophin-3 and -4, fibroblast growth factor-2. Ciliary neurotrophic factor, nerve growth factor, and TGF-beta 1 do not affect striatal CaR expression. GDNF can augment CaR-positive cells at any time point and with a minimal exposure of 18 hr, suggesting induction of the phenotype rather than increased survival. By reverse transcription polymerase chain reaction (RT-PCR), we show that GDNF is expressed in the E16 striatum and in cultures derived from this tissue. GDNF also protected striatal CaR-positive neurons against glutamate toxicity. We conclude that striatal GDNF, in addition to its retrograde trophic role for nigrostriatal dopaminergic neurons, may also act locally within the striatum (e.g., by inducing the CaR phenotype and protecting these cells against toxic insult).

Androgen mitigates axotomy-induced decreases in calbindin expression in motor neurons

Androgens can rescue axotomized motor neurons from cell death. Here we examine a possible mechanism for this trophic action in juvenile Xenopus laevis: regulation of a calcium-binding protein, calbindin, after axotomy. Western analysis revealed that a monoclonal antibody to calbindin D specifically recognizes a single approximately 28 kDa band in X. laevis CNS and rat cerebellum. Retrograde transport of peroxidase combined with immunohistochemistry demonstrated that somata, axons, and synaptic terminals of laryngeal motor neurons in nucleus (N.) IX-X of X. laevis are calbindin-positive. The number of calbindin-positive cells was compared in the intact and axotomized sides of N.IX-X of gonadectomized males that were either hormonally untreated or DHT-treated for 1 month. Although axotomy decreased the number of calbindin-positive cells by 86% in hormonally untreated males, the decrease was only 56% in DHT-treated animals. Compared with hormonally untreated animals, the number of calbindin-labeled cells in N.IX-X of DHT-treated males was increased in both the intact (14%) and axotomized sides (75%). We conclude that axotomy decreases and that DHT enhances calbindin immunoreactivity in N.IX-X. Axotomy-induced decrease in calbindin immunoreactivity precedes cell loss in N.IX-X and may impair the capacity of motor neurons to regulate cytoplasmic calcium. Androgen-mediated maintenance of calbindin expression is thus a candidate cellular mechanism for trophic maintenance of hormone target neurons.

Impaired long-term potentiation induction in dentate gyrus of calretinin-deficient mice

Calretinin (Cr) is a Ca2+ binding protein present in various populations of neurons distributed in the central and peripheral nervous systems. We have generated Cr-deficient (Cr-/-) mice by gene targeting and have investigated the associated phenotype. Cr-/- mice were viable, and a large number of morphological, biochemical, and behavioral parameters were found unaffected. In the normal mouse hippocampus, Cr is expressed in a widely distributed subset of GABAergic interneurons and in hilar mossy cells of the dentate gyrus. Because both types of cells are part of local pathways innervating dentate granule cells and/or pyramidal neurons, we have explored in Cr-/- mice the synaptic transmission between the perforant pathway and granule cells and at the Schaffer commissural input to CA1 pyramidal neurons. Cr-/- mice showed no alteration in basal synaptic transmission, but long-term potentiation (LTP) was impaired in the dentate gyrus. Normal LTP could be restored in the presence of the GABAA receptor antagonist bicuculline, suggesting that in Cr-/- dentate gyrus an excess of gamma-aminobutyric acid (GABA) release interferes with LTP induction. Synaptic transmission and LTP were normal in CA1 area, which contains only few Cr-positive GABAergic interneurons. Cr-/- mice performed normally in spatial memory task. These results suggest that expression of Cr contributes to the control of synaptic plasticity in mouse dentate gyrus by indirectly regulating the activity of GABAergic interneurons, and that Cr-/- mice represent a useful tool to understand the role of dentate LTP in learning and memory.

Activation of NF-kappaB protects hippocampal neurons against oxidative stress-induced apoptosis: evidence for induction of manganese superoxide dismutase and suppression of peroxynitrite production and protein tyrosine nitration

The transcription factor NF-kappaB is expressed in neurons wherein it is activated in response to a variety of stress- and injury-related stimuli including exposure to cytokines such as tumor necrosis factor-alpha (TNFalpha), and excitotoxic and oxidative insults. NF-kappaB may play a role in the anti-death actions of TNFalpha in cultured hippocampal neurons exposed to metabolic and oxidative insults. We now report that pretreatment of hippocampal cell cultures with agents that activate NF-kappaB (TNFalpha and C2-ceramide) confers resistance of neurons to apoptosis induced by the oxidative insults FeSO4 and amyloid beta-peptide (Abeta25-35). The neuroprotective actions of TNFalpha and ceramide were abolished in cultures cotreated with kappaB decoy DNA demonstrating a requirement for NF-kappaB activation for prevention of cell death. Levels of manganese superoxide dismutase (Mn-SOD) in neurons were increased following exposure of cultures to TNFalpha and ceramide in control cultures, but not in cultures cotreated with kappaB decoy DNA. FeSO4 and Abeta25-35 induced accumulation of mitochondrial peroxynitrite, and membrane lipid peroxidation, in neurons. Peroxynitrite accumulation and lipid peroxidation were largely prevented in neurons pretreated with TNFalpha and ceramide prior to exposure to FeSO4 and Abeta25-35, an effect blocked by kappaB decoy DNA. Immunoreactivity of neurons with an anti-nitrotyrosine antibody was increased following exposure to FeSO4 and Abeta25-35; TNFalpha and C2-ceramide suppressed protein tyrosine nitration, and kappaB decoy DNA blocked the effects of TNFalpha and C2-ceramide. Finally, the peroxynitrite scavenger uric acid protected neurons against apoptosis induced by FeSO4 and Abeta, and suppressed peroxynitrite accumulation. We conclude that, by inducing production of Mn-SOD and suppressing peroxynitrite formation and membrane lipid peroxidation, NF-kappaB plays an anti-apoptotic role in neurodegenerative conditions that involve oxidative stress. The data further suggest important roles for peroxynitrite and NF-kappaB in the pathogenesis of neuronal degeneration in Alzheimer's disease.

Peptide growth factors but not ganglioside protect against excitotoxicity in rat retinal neurons in vitro

Glutamate is the major excitatory neurotransmitter in the retina, but excessive stimulation of its receptors leads to widespread neuronal stress and death. Both growth factors and gangliosides display important influences on responses to neuronal injury and degeneration. In this study, we have investigated the potential protective effects of two well characterized growth factors, epidermal and basic fibroblast growth factor (EGF and bFGF respectively), and the monosialoganglioside GM1, on cultured rat retinal neurons submitted to toxic levels of excitatory amino acids. Application of 1 mM glutamic acid reduced global neuronal viability by 80% when compared to control untreated cultures, whereas treatment with the glutamic acid agonist kainic acid (1 mM) led to specific, large decreases (75% reduction) in amacrine cell numbers. 24 h pretreatment with either EGF or bFGF (500 pM each) prevented the majority of excitatory amino acid-induced neuronal death, whereas similar treatment with 10(-5) M GM1 did not block neuronal degeneration. These findings demonstrate that EGF and bFGF act as neuroprotective agents against retinal excitotoxicity in vitro, whereas ganglioside GM1 is not effective in this particular paradigm.

A calcium responsive element that regulates expression of two calcium binding proteins in Purkinje cells

Calbindin D28 encodes a calcium binding protein that is expressed in the cerebellum exclusively in Purkinje cells. We have used biolistic transfection of organotypic slices of P12 cerebellum to identify a 40-bp element from the calbindin promoter that is necessary and sufficient for Purkinje cell specific expression in this transient in situ assay. This element (PCE1) is also present in the calmodulin II promoter, which regulates expression of a second Purkinje cell Ca2+ binding protein. Expression of high levels of exogenous calbindin or calretinin decreased transcription mediated by PCE1 in Purkinje cells 2.5- to 3-fold, whereas the presence of 1 microM ionomycin in the extracellular medium increased expression. These results demonstrate that PCE1 is a component of a cell-specific and Ca2+-sensitive transcriptional regulatory mechanism that may play a key role in setting the Ca2+ buffering capacity of Purkinje cells.

Developmental expression of calretinin in the medial basal hypothalamus and amygdala from male and female rats

Developmental expression of calretinin in the medial basal hypothalamic (MBH) and amygdala region was examined by Western analysis. Males displayed significantly higher calretinin levels compared to females in the MBH (but not the amygdala) on gestational day 19 and 20. These data imply that hormonal factors may regulate developmental MBH calretinin expression. In turn, sexually dimorphic brain structures might be influenced by calretinin levels that can alter sexually dimorphic patterns of steroidogenesis, cellular migration or programmed cell loss mechanism(s) during neuronal development by modulating intracellular calcium concentrations.

Early induction of mRNA for calbindin-D28k and BDNF but not NT-3 in rat hippocampus after kainic acid treatment

The influence of kainic acid (KA), which induces acute seizures, on expression of mRNA for the calcium-binding protein, calbindin-D28k, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and early-response genes [c-fos, zif268 (NGFI-A), nur77 (NGFI-B)] was examined in rat hippocampus by Northern blot analysis. A significant increase (3.2-fold) in BDNF mRNA was observed 1 h after KA injection (12 mg/kg i.p.) and peak expression (9.4-fold) occurred 3 h after KA. The induction of BDNF mRNA was preceded by the induction of c-fos, mRNA (30 min after KA) and was followed by the induction of calbindin-D28k mRNA (3.5-fold 3 h after KA; a maximal response was at 3-6 h after KA). Region-specific changes, analyzed by immunocytochemistry and in situ hybridization, indicated that the most dramatic increases in calbindin protein and mRNA after KA treatment were in the dentate gyrus. Although calbindin-D28k and BDNF mRNAs were induced, a 3.4-3.8-fold decrease in NT-3 mRNA was observed by Northern analysis 3-24 h after KA treatment. Calbindin-D28k gene expression was also examined in rats with a chronic epileptic state characterized by recurrent seizures established with an episode of electrical stimulation-induced status epilepticus (SE). When these animals were examined 30 days post-SE, no changes in hippocampal calbindin-D28k mRNA were observed. Our findings suggest that the induction of calbindin-D28k mRNA (which may be interrelated to the induction of BDNF mRNA) is an early response which may not be related to enhanced neuronal activity or seizures per se, but rather to maintaining neuronal viability.

Mechanisms and effects of intracellular calcium buffering on neuronal survival in organotypic hippocampal cultures exposed to anoxia/aglycemia or to excitotoxins

Neuronal calcium loading attributable to hypoxic/ischemic injury is believed to trigger neurotoxicity. We examined in organotypic hippocampal slice cultures whether artificially and reversibly enhancing the Ca2+ buffering capacity of neurons reduces the neurotoxic sequelae of oxygen-glucose deprivation (OGD), whether such manipulation has neurotoxic potential, and whether the mechanism underlying these effects is pre- or postsynaptic. Neurodegeneration caused over 24 hr by 60 min of OGD was triggered largely by NMDA receptor activation and was attenuated temporarily by pretreating the slices with cell-permeant Ca2+ buffers such as 1, 2 bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid acetoxymethyl ester (BAPTA-AM). This pretreatment produced a transient, reversible increase in intracellular buffer content as demonstrated autoradiographically using slices loaded with 14C-BAPTA-AM and by confocal imaging of slices loaded with the BAPTA-AM analog calcium green-acetoxymethyl ester (AM). The time courses of 14C-BAPTA retention and of neuronal survival after OGD were identical, indicating that increased buffer content is necessary for the observed protective effect. Protection by Ca2+ buffering originated presynaptically because BAPTA-AM was ineffective when endogenous transmitter release was bypassed by directly applying NMDA to the cultures, and because pretreatment with the low Ca2+ affinity buffer 2-aminophenol-N,N,O-triacetic acid acetoxymethyl ester, which attenuates excitatory transmitter release, attenuated neurodegeneration. Thus, in cultured hippocampal slices, enhancing neuronal Ca2+ buffering unequivocally attenuates or delays the onset of anoxic neurodegeneration, likely by attenuating the synaptic release of endogenous excitatory neurotransmitters (excitotoxicity).

Time window of infarct reduction by intravenous basic fibroblast growth factor in focal cerebral ischemia

Basic fibroblast growth factor (bFGF) is a heparin-binding polypeptide with potent trophic and protective effects on brain neurons, glia and endothelia. In previous studies, we showed that intravenously administered bFGF reduced the volume of cerebral infarcts following permanent occlusion of the middle cerebral artery in rats. In the current study, we examined the time dependence of bFGF infusion on infarct reduction, and the effect of co-infusion of bFGF with heparin. We found a significant reduction in infarct volume when the bFGF infusion (50 microg/kg per h for 3 h) was begun up to 3 h, but not 4 h after the onset of ischemia. The infarct reducing effects of bFGF were not altered by co-infusion of heparin. These results are potentially important in light of the ongoing clinical trials of intravenous bFGF in acute stroke.

Basic FGF attenuates amyloid beta-peptide-induced oxidative stress, mitochondrial dysfunction, and impairment of Na+/K+-ATPase activity in hippocampal neurons

Basic fibroblast growth factor (bFGF) exhibits trophic activity for many populations of neurons in the brain, and can protect those neurons against excitotoxic, metabolic and oxidative insults. In Alzheimer's disease (AD), amyloid beta-peptide (A beta) fibrils accumulate in plaques which are associated with degenerating neurons. A beta can be neurotoxic by a mechanism that appears to involve induction of oxidative stress and disruption of calcium homeostasis. Plaques in AD brain contain high levels of bFGF suggesting a possible modulatory role for bFGF in the neurodegenerative process. We now report that bFGF can protect cultured hippocampal neurons against A beta25-35 toxicity by a mechanism that involves suppression of reactive oxygen species (ROS) accumulation and maintenance of Na+/K+-ATPase activity. A beta25-35 induced lipid peroxidation, accumulation of H2O2, mitochondrial ROS accumulation, and a decrease in mitochondrial transmembrane potential; each of these effects of A beta25-35 was abrogated in cultures pre-treated with bFGF. Na+/K+-ATPase activity was significantly reduced following exposure to A beta25-35 in control cultures, but not in cultures pre-treated with bFGF. bFGF did not protect neurons from death induced by ouabain (a specific inhibitor of the Na+/K+-ATPase) or 4-hydroxynonenal (an aldehydic product of lipid peroxidation) consistent with a site of action of bFGF prior to induction of oxidative stress and impairment of ion-motive ATPases. By suppressing accumulation of oxyradicals, bFGF may slow A beta-induced neurodegenerative cascades.

Calcium-binding protein phenotype defines metabolically distinct groups of neurons in barrel cortex of behaving hamsters

Physiological/anatomical studies of rat frontal cortex in vitro have distinguished subpopulations of gamma-aminobutyric acid (GABA)-expressing inhibitory interneurons defined by expression of the calcium-binding proteins, parvalbumin (PV) and calbindin (CA). Using a novel 2DG/immunostaining technique to double-label hamster barrel cortex for metabolism and phenotype, we have recently shown that while many GABAergic neurons are heavily 2DG labeled during normal exploratory behavior, a subset of GABAergic cells shows relatively sparse 2DG labeling. For this study we used the 2DG/immunostaining technique to test whether, in awake behaving animals, calcium-binding protein expression in a given cell in barrel cortex (as indicated by immunohistochemistry for PV or CA) was related to the degree of 2DG labeling. We found that most PV+ cells were moderately to heavily 2DG labeled, while most CA+ cells were lightly 2DG labeled. Our data indicate that the PV+ and CA+ cells represent metabolically distinct subpopulations of GABAergic neurons in barrel cortex. This distinction corresponds well with the in vitro physiological and anatomical data from frontal cortex and suggests functional implications for the expression of PV and CA, or other colocalized factors, in normally functioning cortical circuitry.

Protective effects of neurotrophin-4/5 and transforming growth factor-alpha on striatal neuronal phenotypic degeneration after excitotoxic lesioning with quinolinic acid

Lesioning of the mammalian striatum with the excitotoxin quinolinic acid results in a pattern of neuropathology that resembles that of post mortem Huntington's disease brain. Certain neurotrophic factors can rescue degenerating cells in a variety of lesion types, including those produced by neurotoxins. Several neurotrophic factors promote the survival of striatal neurons and/or are localized within the striatum. Of these factors, neurotrophin-4/5 and transforming growth factor-alpha were chosen for administration to rats lesioned with quinolinic acid. Adult rats received a single unilateral intrastriatal injection of quinolinic acid (120 nmol) and either trophic factors or the control protein cytochrome c for seven days thereafter. The pattern of phenotypic degeneration was assessed by immunocytochemical labeling of various striatal neuronal populations at five rostrocaudal levels. Quinolinic acid produced a preferential loss in the number of cells immunoreactive for glutamate decarboxylase, with a relative sparing of the number of choline acetyltransferase-immunoreactive cells and, to a lesser degree, calretinin-immunoreactive cells. None of these phenotypic populations was protected by either neurotrophin-4/5 or transforming growth factor-alpha. In contrast, when glutamate decarboxylase cells were alternatively identified by calbindin immunolabeling, both factors were found to have partially reversed the loss in the number of calbindin-positive cells induced by excitolesioning. In addition, the loss in the number of parvalbumin-immunopositive cells due to quinolinic acid was partially reversed by neurotrophin-4/5, while the loss in the number of NADPH-diaphorase-stained cells was partially reversed by transforming growth factor-alpha. These findings reveal a new population of striatal cells, calretinin neurons, that are relatively resistant to quinolinic acid toxicity and that neurotrophin-4/5 and transforming growth factor-alpha partially protect against the phenotypic degeneration of striatal cell populations in an in vivo animal model of Huntington's disease.

Genistein inhibits Na+/Ca2+ exchange activity in primary rat cortical neuron culture

We have examined the possible regulatory effect of tyrosine kinase activity on Ca2+ transport observed in the cultured rat cortical neurons. Na+/Ca2+ exchange was studied using cells cultured for various time periods. A nearly two fold increase in Ca2+ uptake was seen when comparing 3 day and 9 day cultures. Western blot analysis also showed a two fold increase in Na+/Ca2+ exchanger (NCX1) protein levels as cells matured in culture. To study the effect of genistein (a specific tyrosine kinase inhibitor) cells were incubated with 100 microM genistein (in 1% DMSO) for 1 hour before the assay of Na+/Ca2+ exchange activity. There was a significant decrease of Ca2+ uptake in genistein treated neurons (control: 4.596+/-0.205 nmol/mg protein/15 min, n=12; genistein: 1.420+/-0.131 nmol/mg protein/15 min, n=12, mean+/-S.E. P<0.001). Daidzein, an inactive analog of genistein and phorbol myristate acetate (PMA), a PKC activator were without effect. The results suggest that as cells mature in culture, Na+/Ca2+ exchange capacity increases, as a result of greater protein expression. Exposure to genistein inhibited Ca2+ uptake suggesting that the exchanger may be modulated by tyrosine phosphorylation.

Combinations of AMPA receptor subunit expression in individual cortical neurons correlate with expression of specific calcium-binding proteins

The functional properties of AMPA-type glutamate receptors are determined by their subunit composition. We detected the expression of the AMPA receptor subunits (GluR1-GluR4) in neurons in the somatosensory cortex of adult rats by combining nonradioactive in situ hybridization using digoxigenin-labeled RNA probes of GluR1 and GluR2 with immunocytochemistry using specific antibodies against GluR1, GluR2/3, and GluR4. On the basis of differential expression of the GluR1 and GluR2 subunits, we classified the cortical neurons into four categories. To correlate the differential expression of AMPA receptor subunits in each neuron with that of two calcium-binding proteins, parvalbumin and calbindin-D28k, we used a triple-labeling method. The majority of cortical neurons ( approximately 2/3) showed expression of GluR2 and undetectable expression of GluR1. GluR1-/GluR2-expressing neurons and GluR1-expressing/GluR2-undetectable neurons comprised approximately 1/10 each. Regarding the morphology, most GluR1-undetectable/GluR2-expressing neurons were pyramidal cells in layers II/III, V, and VI, whereas most GluR1-expressing/GluR2-undetectable neurons were nonpyramidal cells in layers II-VI. The GluR1-/GluR2-expressing neurons were either pyramidal or nonpyramidal. The majority of GluR1-/GluR2-expressing nonpyramidal cells was intensely stained with monoclonal antibody against calbindin-D28k, and one-half of the GluR1-undetectable/GluR2-expressing pyramidal neurons in layer II/III were lightly stained with this antibody. Most of GluR1-expressing/GluR2-undetectable neurons possessed parvalbumin immunoreactivity. These results indicate that neurons in the rat somatosensory cortex express differential combinations of GluR subunits, which correlate with the specific expression of the calcium-binding proteins.

Postnatal developmental changes of neurons expressing calcium-binding proteins and GAD mRNA in the pretectal nuclear complex of the cat

The postnatal development of the cat pretectum has been analysed with in situ hybridization and immunohistochemistry with the aim to establish the time course of morphological and neurochemical maturation of parvalbumin (PARV), calbindin-D28k (CALB), and glutamic acid decarboxylase (GAD) expressing neuronal populations. At birth, PARV-ir retinal afferents to the pretectum have already formed distinct termination zones which appear as 3 clusters separated by intercluster regions in coronal sections. The clusters contain two sets of large neurons expressing either PARV or CALB. The two sets of neurons differ in the time at which they grow rapidly. Both sets reach the adult size at P38. PARV-ir retinal fibers contact dendrites of large PARV-negative, and thus presumably CALB-ir neurons. A population of smaller CALB-ir neurons appears within the clusters during the second postnatal week. In intercluster regions, small PARV-ir and CALB-ir neurons are present at birth, but increase in number during development. Only PARV-ir intercluster neurons increase in size between P4 and P38. GAD neurons are present dorsal to the clusters and in intercluster regions from P0 onwards. However, within the clusters GAD neurons do not appear until the second postnatal week. The different onset of marker expression and cellular growth patterns suggest the existence of several populations of CaBP-ir excitatory and inhibitory neurons in the pretectum. The final complement of inhibitory neurons is not present until the second postnatal week. These developmental processes may correlate with the slow maturation of the pretectal motion processing system and the cortico-pretectal projection.

Transfection and overexpression of the calcium binding protein calbindin-D28k results in a stimulatory effect on insulin synthesis in a rat beta cell line (RIN 1046-38)

Calbindin-D28k, a calcium binding protein that is thought to act as a facilitator of calcium diffusion in intestine and kidney, is known to be regulated by vitamin D in these tissues. Calbindin-D28k is also present in pancreatic beta cells, but its function in these cells is not known. To determine a role for calbindin-D28k in the beta cell, rat calbindin-D28k was overexpressed in the pancreatic beta cell line RIN 1046-38 by transfection of calbindin in expression vector, and changes in insulin mRNA were examined. Five transfected RIN cell clones were found to overexpress calbindin 6- to 35-fold as determined by radioimmunoassay. Northern blot analysis revealed increases in abundance in calbindin mRNA (>20-fold for most clones). Overexpressed calbindin was functional because it was capable of buffering calcium in response to a rapid calcium influx induced by 1 and 5 microM calcium ionophore. In cells transfected with calbindin, there was a marked increase in the expression of insulin mRNA (>20-fold for most clones compared with vector transfected cells). Besides an increase in insulin mRNA, calbindin overexpression was also associated with an increase in insulin content and release (a 5.8-fold increase in insulin release was noted for clone C10, and a 54-fold increase was noted for clone C2). To begin to address the mechanism whereby overexpression of calbindin results in increased insulin gene expression, calbindin-overexpressing clones were transiently transfected with plasmids incorporating various regions of the rat insulin I (rInsI) promoter linked to the chloramphenicol acetyltransferase coding sequence. Transient transfection with reporter plasmids bearing the regulatory sequences of the rInsI promoter (-345/+1) or five copies of the Far-FLAT minienhancer (-247/-198) from the rInsI promoter suggests that increased insulin mRNA in calbindin transfected cells is due, at least in part, to enhanced insulin gene transcription. These studies provide the first direct evidence (to our knowledge) for a role for calbindin in beta cell function.

Low mobility of the Ca2+ buffers in axons of cultured Aplysia neurons

Cellular Ca2+ buffers determine amplitude and diffusional spread of neuronal Ca2+ signals. Fixed Ca2+ buffers tend to retard the signal and to lower the apparent diffusion coefficient (D(app)) of Ca2+, whereas mobile buffers contribute to Ca2+ redistribution. To estimate the impact of the expression of specific Ca2+-binding proteins or the errors in Ca2+ measurement introduced by indicator dyes, the diffusion coefficient De and the Ca2+-binding ratio kappa(e) of endogenous Ca2+ buffers must be known. In this study, we obtain upper bounds to these quantities (De < 16 microm2/s; kappa(e) < 60) for axoplasm of metacerebral cells of Aplysia california. Due to these very low values, even minute concentrations of indicator dyes will interfere with the spatiotemporal pattern of Ca2+ signals and will conceal changes in the expression of specific Ca2+-binding proteins, which in the native neuron are expected to have significant effects on Ca2+ signals.

Projection status of calbindin- and parvalbumin-immunoreactive neurons in the superficial layers of the rat's superior colliculus

Immunocytochemistry and retrograde labeling were used to define the thalamic projections of calbindin- and parvalbumin-containing cells in superficial layers of the rat's superior colliculus (SC). Quantitative analysis revealed that 90.8 +/- 2.2% (mean +/- standard deviation) of the calbindin-immunoreactive neurons in the stratum griseum superficiale (SGS) projected to the dorsal lateral geniculate nucleus (LGNd) and that 91.3 +/- 4.3% of calbindin-immunoreactive neurons in the stratum opticum (SO) projected to the lateral posterior nucleus (LP). In contrast, only 17.3 +/- 2.5% of parvalbumin-immunoreactive neurons in the SGS were found to project to the LGNd and 16.5 +/- 3.1% of the parvalbumin-immunoreactive SO cells were retrogradely labeled after LP injections. Few of the parvalbumin-immunoreactive neurons in either the SGS (7.2 +/- 2.5%) or the SO (9.2 +/- 2.5%) were GABA positive. The retrograde-labeling results suggest that parvalbumin-immunoreactive neurons in the rat's SO and SGS may either be primarily interneurons or have descending projections, while calbindin-containing cells are primarily thalamic projection neurons. These results are consistent with data from other rodents, but almost exactly the opposite of data that have been reported for the cat for these same populations of SC projection neurons. Such interspecies differences raise questions regarding the functional importance of expressing one calcium-binding protein versus another in a specific neuronal population.

Progressive decline in avoidance learning paralleled by inflammatory neurodegeneration in transgenic mice expressing interleukin 6 in the brain

Inflammation with expression of interleukin 6 (IL-6) in the brain occurs in many neurodegenerative disorders. To better understand the role of IL-6 in such disorders, we examined performance in a learning task in conjunction with molecular and cellular neuropathology in transgenic mice that express IL-6 chronically from astrocytes in the brain. Transgenic mice exhibited dose- and age-related deficits in avoidance learning that closely corresponded with specific progressive neuropathological changes. These results establish a link between the central nervous system expression of IL-6, inflammatory neurodegeneration, and a learning impairment in transgenic mice. They suggest a critical role for a proinflammatory cytokine in the cognitive deficits and associated neuroinflammatory changes that have been documented in neurodegenerative diseases such as Alzheimer disease and AIDS.

Progressive loss of glutamic acid decarboxylase, parvalbumin, and calbindin D28K immunoreactive neurons in the cerebral cortex and hippocampus of adult rat with experimental hydrocephalus

The authors investigated functional neuronal changes in experimental hydrocephalus using immunohistochemical techniques for glutamic acid decarboxylase (GAD) and two neuronal calcium-binding proteins: parvalbumin (PV) and calbindin D28K (CaBP). Hydrocephalus was induced in 16 adult Wistar rats by intracisternal injection of a kaolin solution, which was confirmed microscopically via atlantooccipital dural puncture. Four control rats received the same volume of sterile saline. Immunohistochemical staining for GAD, PV, and CaBP, and Nissl staining were performed at 1, 2, 3, and 4 weeks after the injection. Hydrocephalus occurred in 90% of kaolin-injected animals with various degrees of ventricular dilation. In the cerebral cortex, GAD-, PV-, and CaBP-immunoreactive (IR) interneurons initially lost their stained processes together with a concomitant loss of homogeneous neuropil staining, followed by the reduction of their total number. With progressive ventricular dilation, GAD- and PV-IR axon terminals on the cortical pyramidal cells disappeared, whereas the number of CaBP-IR pyramidal cells decreased, and ultimately in the most severe cases of hydrocephalus, GAD, PV, and CaBP immunoreactivity were almost entirely diminished. In the hippocampus, GAD-, PV-, and CaBP-IR interneurons demonstrated a reduction of their processes and terminals surrounding the pyramidal cells, with secondary reduction of CaBP-IR pyramidal and granular cells. On the other hand, Nissl staining revealed almost no morphological changes induced by ischemia or neuronal degeneration even in the most severe cases of hydrocephalus. Hydrocephalus results in the progressive functional impairment of GAD-, PV-, and CaBP-IR neuronal systems in the cerebral cortex and hippocampus, often before there is evidence of morphological injury. The initial injury of cortical and hippocampal interneurons suggests that the functional deafferentation from intrinsic projection fibers may be the initial neuronal event in hydrocephalic brain injury. Although the mechanism of this impairment is still speculative, these findings emphasize the importance of investigating the neuronal pathophysiology in hydrocephalus.

Expressions of a calcium-binding protein (spot35/calbindin-D28K) in mouse olfactory cells: possible relationship to neuronal differentiation

We used immunohistochemistry to investigate the expression of spot35/calbindin-D28k (calbindin) in mouse olfactory epithelium during development. Cell stages of immunopositive olfactory cells were determined by comparing the levels of proliferating cell nuclear antigen (PCNA). Calbindin-positive cells were abundant in the middle layer of the epithelium of animals before 2 weeks of age and gradually diminished during development. Only low levels were detectable near the basement membrane in the adult. Changes of calbindin-positive cells in terms of number and distribution were apparently compatible with localization changes of premature olfactory cells. PCNA overlapped calbindin in the nasal mucosa at lower magnifications on stained serial sections and immunohistochemical double staining revealed that calbindin-immunoreactive cells were located mainly just above PCNA-immunoreactive cells in the basal layer of the epithelium. This indicated that calbindin is expressed postmitotically in immature olfactory cells and is lost by mature cells. These findings suggest that calbindin might support the maturation of the olfactory cells, such as the projection of the neuronal processes, by stabilizing intracellular calcium ions in immature cells.

Vulnerability of midbrain dopaminergic neurons in calbindin-D28k-deficient mice: lack of evidence for a neuroprotective role of endogenous calbindin in MPTP-treated and weaver mice

Calbindin-D28k (calbindin) is an intracellular calcium binding protein of unknown in vivo function. It is abundantly expressed in many populations of neurons, and it can, presumably by buffering calcium overload, protect cells against excitotoxic damage. In the midbrain, calbindin is preferentially expressed in those dopamine neurons which are spared from degeneration in Parkinson's disease and its animal models. Whether calbindin itself determines neuronal vulnerability is questioned in other lesion models where calbindin expression is not positively correlated with neuronal resistance. To study the possible neuroprotective role of calbindin in vivo, we generated calbindin-deficient mice by gene targeting and assessed the viability of midbrain dopamine neurons in both a chemical and a genetic lesion paradigm. Tyrosine hydroxylase-immunoreactive neurons were counted in calbindin null-mutant mice treated with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and in a calbindin-deficient weaver strain (homozygous for weaver and the calbindin null mutation). The extent and pattern of neuron loss observed in MPTP-treated wild-type and homozygous weaver mice were as previously described. Surprisingly, no significant differences were observed between MPTP-treated calbindin null mutants and their wild-type littermates, or between calbindin-weaver double mutant mice and weaver mice. Thus, in all four groups the same subpopulation of tyrosine hydroxylase-positive midbrain neurons (i.e. those normally containing calbindin) were preferentially spared. Calretinin, a closely related calcium-binding protein, which is also expressed in some midbrain dopamine neurons, was not up-regulated in these surviving neurons. These findings indicate that the resistance of calbindin-containing neurons in the MPTP and weaver models is not causally related to the expression of calbindin, and that endogenous calbindin is not required for protection of these neurons.

Delayed decrease of calbindin immunoreactivity in the granule cell-mossy fibers after kainic acid-induced seizures

Kainic acid (KA) administration induces an abnormal excitation and spontaneous recurrent seizures. Alterations of granule cell properties may be potential mechanisms. In this study, dynamic alterations of calbindin, a calcium binding protein particularly abundant in the granule cells, have been investigated immunocytochemically in the rat hippocampus after the KA-induced seizures. The calbindin immunoreactivity decreased slightly in the CA1/CA2 fields already after 1 and 3 days, and was lost partly or completely in the pyramidal layer after 10 days. From day 21, the calbindin immunoreactivity decreased in dendrites and soma of the granule cells and mossy fibers. The alterations remained at least to day 90, while no evident neuronal loss occurred in the granule cells. This may reflect a disturbance of calcium homostasis in the granule cells after seizures. The delayed decrease of calbindin has a time course similar to the occurrence of spontaneous recurrent seizures, suggesting a possible correlation between the two events.

Dopamine-glutamate interactions in the striatum: behaviourally relevant modification of excitotoxicity by dopamine receptor-mediated mechanisms

The two most important afferent projections to the striatum contain glutamate and dopamine, respectively. Excitotoxic damage resulting from excessive stimulation of the N-methyl-D-aspartate subtype of glutamate receptor has been implicated in pathophysiology of ischaemic stroke, hypoglycaemic brain damage and Huntington's disease. We studied the ability of the dopamine system to modify the anatomical, neurochemical and behavioural consequences of glutamatergic toxicity in the striatum. In a first set of experiments, the specific N-methyl-D-aspartate receptor agonist quinolinate was injected unilaterally into the striatum of rats pretreated with one of (i) intraperitoneal (i.p.) saline (controls); (ii) i.p. haloperidol, a D2 dopamine receptor agonist; or (iii) 6-hydroxydopamine lesion of the ipsilateral nigrostriatal tract. Quinolinate-induced striatal damage, as assessed by morphometric and neurochemical criteria, was significantly attenuated in the animals with 6-hydroxydopamine lesions and in those pretreated with haloperidol, compared with saline-pretreated controls. There were no significant differences between the 6-OHDA and haloperidol groups. In a second set of experiments, animals received (i) bilateral intrastriatal quinolinate plus perioperative i.p. saline; (ii) bilateral intrastriatal quinolinate plus i.p. haloperidol; or (iii) bilateral intrastriatal saline. Again, the quinolinate-lesioned animals treated with perioperative haloperidol had significantly less striatal damage than the bilateral quinolinate rats. Behavioural assessment in the Morris Water Maze showed the bilateral quinolinate+haloperidol group to be significantly less impaired on a spatial acquisition task than the bilateral quinolinate animals. Measures of spontaneous daytime motor activity showed significant differences in average speed and rest time between the bilateral quinolinate+haloperidol rats and the bilateral quinolinate group. The performance of the bilateral quinolinate+haloperidol group was not significantly different from that of controls on any of the behavioural tasks. These results indicate an important role for D2 dopamine receptor-mediated mechanisms in striatal excitotoxicity. Since the excitotoxic process involves the same fundamental signalling mechanism that is involved in normal glutamatergic transmission, these findings imply an ability of D2 receptor blockade to modify glutamate signalling in the striatum. These results may have implications for treatment strategies in ischaemic stroke, hypoglycaemic brain damage and schizophrenia.

Calretinin mRNA and immunoreactivity in the medullary reticular formation of the rat: colocalization with glutamate receptors

Calretinin-positive cells were identified in the medullary reticular formation of the rat by both immunohistochemistry and in situ hybridization histochemistry. In addition, double immunocytochemical labeling was used to examine the degree of colocalization of calretinin with GluR2/R3, GluR4 and GluR5-7 glutamate receptor subtypes. Results indicated regional variation in calretinin expression across reticular formation regions with the exception of the largest cells which were mostly calretinin-positive. Calretinin mRNA was particularly abundant in the parvocellular reticular nucleus. Most calretinin-immunoreactive cells also expressed at least one of the glutamate receptor subtypes examined with the exception of the smallest calretinin-positive cells of the parvocellular reticular formation which were generally not immunoreactive for any of the glutamate receptors examined. Calretinin immunoreactivity was colocalized with immunoreactivity for all three glutamate receptor subtypes examined in most of the large cells of the reticular formation. Immunoreactivity for the GluR4 antibody was least abundant in the reticular formation and GluR4 immunoreactive cells were least likely to co-express calretinin. These results suggest that calretinin and glutamate receptor antibodies may be used to identify specific subsets of reticular formation neurons.

Modulation of hippocampal synaptic transmission by low concentrations of cell-permeant Ca2+ chelators: effects of Ca2+ affinity, chelator structure and binding kinetics

Calcium chelators are commonly used for fluorescence and electrophysiological studies of neuronal Ca2+ signalling. Recently, they have also been used as neuroprotectants. Since they buffer calcium ions, these agents also modify the same signals which are being studied. These properties may be used to modulate Ca2+ signals such as those involved in synaptic transmission, and may explain their neuroprotective mechanism. To define factors which govern the modulation of synaptic transmission by Ca2+ chelators, we examined their actions on synaptic responses evoked in CA1 neurons of rat hippocampal slices. We used a spectrum of cell-permeant Ca2+ chelators having different structures, Ca(2+)-binding kinetics and Ca2+ affinities, as well as an impermeant, intracellularly perfused chelator salt. Application of the cell-permeant 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetate acetoxymethyl ester (50 microM) markedly attenuated evoked synaptic responses. This application produced an intracellular chelator accumulation of 79-125 microM, as estimated using 14C-labelled chelator. The actions of a Ca2+ chelator on synaptic responses were dependent on the chelator's Ca2+ affinity, Ca(2+)-binding rate and Ca2+ selectivity, because 1,2-bis(2-amino-5-nitrophenoxy)ethane-N,N,N',N'-tetra-acetate acetoxymethyl ester (a low Ca2+ affinity analogue), ethyleneglycolbis(beta-aminoethyl ether)-N,N,N',N'-tetra-acetate acetoxymethyl ester (a slow buffer with similar Ca2+ affinity to 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetate) and the selective Zn2+ chelator, tetrakis(2-pyridylmethyl)ethylenediamine, were ineffective. The intrinsic cell membrane properties, including the post-spike train afterhyperpolarization, were not significantly affected by any of the Ca2+ chelators used in this study. Intracellular perfusion of 100-200 microM 1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetate salt through patch pipettes into postsynaptic cells did not affect synaptic potentials, suggesting a presynaptic action of cell-permeant Ca2+ chelators on transmitter release. Other cell-permeant, fast Ca(2+)-binding chelators reduced synaptic responses according to their Ca2+ affinities, and not their chemical structure: those chelators with Kd values < or = 25 microM attenuated synaptic responses, whereas chelators of lesser affinity did not. These data support the ideas that [Ca2+]i rises to high (micromolar) levels during transmitter release, and that Ca2+ chelators may be used to attenuate excitotoxicity by attenuating excitatory neurotransmission without affecting Ca2+ signalling in the submicromolar [Ca2+]i range.

A chronological study of the expression of glial fibrillary acidic protein and calbindin-D28 k by reactive astrocytes in the electrically lesioned rat brain

Immunoreactivity of neuronal and glial marker proteins of reactive astrocytes around the electrically damaged pyramidal layer and stratum radiatum of the hippocampal CA1 region and corpus callosum was chronologically studied in electrically lesioned rat brains. A monoclonal antibody against calbindin-D28 k (CD28-Ab) and a polyclonal antibody against glial fibrillary acidic protein (GFAP-Ab) were used for immunostaining. Immunoreactivity of CD28 and GFAP in the reactive astrocytes was detected in brains 1-6 weeks post-lesion but not in non-lesioned brains. The number of immunohistochemically stained reactive astrocytes around the electrically damaged areas were counted and then compared with the number of those in the same areas of non-lesioned brains. The number of CD28- and GFAP-immunoreactive astrocytes began to increase around the lesion from 1-3 weeks following lesion in the pyramidal layer of the hippocampal CA1 region and from 1-4 weeks following lesion in the stratum radiatum of the hippocampal CA1 region and corpus callosum. These immunoreactive astrocytes could be observed for 6 weeks (the maximum survival time studies) in all areas of the lesioned brains studied. The increase in the number of reactive astrocytes might have been induced by the stimulatory effects of neurotrophic factors, or growth factors, produced around the lesioned site. The constancy in the number of reactive astrocytes after 3 and 4 weeks in the lesioned areas may have been due to the termination of the initial phase of the repair process, i.e. space-filling. Reactive astrocytes which were stained by GFAP-Ab were separated into two groups, based on the presence of CD28, i.e. CD28-positive and CD28-negative reactive astrocytes. The presence of CD28 might confer certain functions via calcium-mediated mechanisms on CD28-positive astrocytes in addition to the constructive role mediated by GFAP.

Distribution of glutamate receptor subunit GluR1 and GABA in human cerebral neocortex: a double immunolabelling and electron microscopic study

Specimens of human cerebral neocortex were obtained during neurosurgical operations and studied by immunocytochemistry and electron microscopy, using antibodies to the glutamate receptor subunit GluR1 and gamma-aminobutyric acid (GABA). Many GluR1-positive pyramidal neurons and fewer GluR1-positive non-pyramidal neurons were present in the cortex. Non-pyramidal neurons were more heavily labelled for GluR1 than pyramidal neurons. Most GABAergic neurons were labelled for GluR1. The white matter was unstained, except for occasional labelled neurons. This pattern of GluR1 immunostaining is similar to that in rat cerebral cortex, but is different from that in the hippocampus and amygdala, where large numbers of pyramidal or projection neurons, but few non-pyramidal or GABAergic neurons, were labelled for GluR1.

The expression of calretinin in transfected PC12 cells provides no protection against Ca(2+)-overload or trophic factor deprivation

To address the question whether calretinin (CR) may protect cells against Ca2+ overload or trophic factor deprivation, PC12 cells were transfected with plasmids containing a CR coding region under control of a cytomegalovirus promoter. Nerve growth factor (NGF) treatment induced differentiation, increased transfection efficiency (at least 10-fold) and activated the CR gene (as found by RNase protection method and immunohistochemistry). Exogenous CR expression was identified either in living cells by fluorescence of green fluorescent protein (when the CR coding region was fused to this protein) or in fixed cells by CR immunoreactivity. Undifferentiated and NGF-differentiated populations of transfected cells were incubated in the presence of a Ca(2+)-ionophore or in media deprived of serum or NGF. Expression of exogenous CR in undifferentiated or NGF-treated cells (due to transfection) or endogenous CR (due to gene activation by NGF) did not render PC12 cells more resistant to insults such as Ca(2+)-overload and trophic factor deprivation.

Calbindin localization in African giant rat kidney (Cricetomys gambianus)

Cricetomys gambianus are rodents living in savanna and follow area. They can live with restricted drinking water eating fresh food. Therefore their kidney may have some adaptive mechanisms for ion/water homeostasis compared to usual laboratory rats. In this study we have looked for calbindin, an intracellular calcium binding protein previously found in distal convoluted tubules from all mammalian species that have been studied and able to increase, in vitro, Ca2+ reabsorption. We have shown by using in situ hybridization, immunoblotting and immunohistochemistry that calbindin was expressed in three different portions of the distal nephron of the African giant rat. Calbindin was found in distal convoluted tubules, in cortical collecting tubules and in outer medullary collecting ducts. By contrast, in laboratory rat, calbindin was only found in distal convoluted tubules and undetectable in medullary collecting ducts. Thick ascending limb of Henle's loop were calbindin negative as shown by double immunolabelling using anti-uromucoid (Tamm-Horsfall protein). As previously shown in laboratory rat and rabbit, transcellular Ca2+ movement seems to be facilitated by calbindin in renal tubules segments predominantly actively transporting Ca2+, it may be suggested that in African giant rat, outer medullary collecting ducts may also actively transport Ca2+. As calretinin, another intracellular calcium binding protein highly homologous to calbindin but whose function is still conjectural has been suspected to be expressed in kidney, we have looked and not found any calretinin in both adult rat species.

Coexistence of calbindin D-28k and NADPH-diaphorase in vagal and glossopharyngeal sensory neurons of the rat

The presence and coexistence of calbindin D-28k-immunoreactivity (ir) and nicotinamide adenosine dinucleotide phosphate (NADPH)-diaphorase activity (a marker of neurons that are presumed to convert L-arginine to L-citrulline and nitric oxide) were examined in the glossopharyngeal and vagal sensory ganglia (jugular, petrosal and nodose ganglia) of the rat. Calbindin D-28k-ir nerve cells were found in moderate and large numbers in the petrosal and nodose ganglia, respectively. Some calbindin D-28k-ir nerve cells were also observed in the jugular ganglion. NADPH-diaphorase positive nerve cells were localized to the jugular and nodose ganglia and were rare in the petrosal ganglion. A considerable portion (33-51%) of the NADPH-diaphorase positive neurons in these ganglia colocalized calbindin D-28k-ir. The presence and colocalization of calbindin D-28k-ir and NADPH-diaphorase activity in neurotransmitter-identified subpopulations of visceral sensory neurons were also studied. In all three ganglia, calcitonin gene-related peptide (CGRP)-ir was present in many NADPH-diaphorase positive neurons, a subset of which also contained calbindin D-28k-ir. In the nodose ganglion, many (42%) of tyrosine hydroxylase (TH)-ir neurons also contained NADPH diaphorase activity but did not contain calbindin D-28k-ir. These data are consistent with a potential co-operative role for calbindin D-28k and NADPH-diaphorase in the functions of a subpopulation of vagal and glossopharyngeal sensory neurons.

Quantitative immunocytochemical analysis of the spinal cord in G86R superoxide dismutase transgenic mice: neurochemical correlates of selective vulnerability

Transgenic mice with a G86R mutation in the mouse superoxide dismutase (SOD-1) gene, which corresponds to a mutation that has been observed in familial amyotrophic lateral sclerosis (ALS), display progressive loss of motor function and provide a valuable model of ALS. The pathology in the spinal cords of these mice was evaluated to determine whether there are chemically identified populations of neurons that are either highly vulnerable or resistant to degeneration. Qualitatively, there were phosphorylated neurofilament protein (NFP)-immunoreactive inclusions and a pronounced loss of motoneurons in the ventral horn of the spinal cord without the presence of vacuoles that has been reported in other SOD-1 transgenic mice. Neuron counts from SOD-1 and control spinal cords revealed that the percentage loss of NFP-, choline acetyltransferase (ChAT)-, and calretinin (CR)-immunoreactive neurons was greater than the percentage loss of total neurons, suggesting that these neuronal groups are particularly vulnerable in SOD-1 transgenic mice. In contrast, calbindin-containing neurons did not degenerate significantly and represent a protected population of neurons. Quantitative double-labeling experiments suggested that the vulnerability of ChAT- and CR-immunoreactive neurons was due primarily to the presence of NFP within a subset of these neurons, which degenerated preferentially to ChAT- and CR-immunoreactive neurons that did not colocalize with NFP. Our findings suggest that NFP, which has been demonstrated previously to be involved mechanistically in motoneuron degeneration, may also be important in the mechanism of degeneration that is initiated by the SOD-1 mutation.

Progressive loss of glutamic acid decarboxylase, parvalbumin, and calbindin D28K immunoreactive neurons in the cerebral cortex and hippocampus of adult rat with experimental hydrocephalus

The authors investigated functional neuronal changes in experimental hydrocephalus using immunohistochemical techniques for glutamic acid decarboxylase (GAD) and two neuronal calcium-binding proteins: parvalbumin (PV) and calbindin D28K (CaBP).

Hydrocephalus was induced in 16 adult Wistar rats by intracisternal injection of a kaolin solution, which was confirmed microscopically via atlantooccipital dural puncture. Four control rats received the same volume of sterile saline. Immunohistochemical staining for GAD, PV, and CaBP and Nissl staining were performed at 1, 2, 3, and 4 weeks after the injection. Hydrocephalus occurred in 90% of kaolin-injected animals with various degrees of ventricular dilation. In the cerebral cortex, GAD-, PV-, and CaBP-immunoreactive (IR) interneurons initially lost their stained processes together with a concomitant loss of homogeneous neuropil staining, followed by the reduction of their total number. With progressive ventricular dilation, GAD- and PV-IR axon terminals on the cortical pyramidal cells disappeared, whereas the number of CaBP-IR pyramidal cells decreased, and ultimately in the most severe cases of hydrocephalus, GAD, PV, and CaBP immunoreactivity was almost entirely diminished. In the hippocampus, GAD-, PV-, and CaBP-IR interneurons demonstrated a reduction of their processes and terminals surrounding the pyramidal cells, with secondary reduction of CaBP-IR pyramidal and granular cells. On the other hand, Nissl staining revealed almost no morphological changes induced by ischemia or neuronal degeneration even in the most severe cases of hydrocephalus.

Hydrocephalus results in the progressive functional impairment of GAD-, PV-, and CaBP-IR neuronal systems in the cerebral cortex and hippocampus, often before there is evidence of morphological injury. The initial injury of cortical and hippocampal interneurons suggests that the functional deafferentation from intrinsic projection fibers may be the initial neuronal event in hydrocephalic brain injury. Although the mechanism of this impairment is still speculative, these findings emphasize the importance of investigating the neuronal pathophysiology in hydrocephalus.

Expression of the calcium-binding protein, parvalbumin, in cultured cortical neurons using a HSV-1 vector system enhances NMDA neurotoxicity

Calcium-binding proteins (CaBPs) are a family of proteins having a unique distribution in the brain and are thought to be important in buffering intracellular calcium. Glutamate neurotoxicity is a process by which the over-activation of glutamate receptors can cause the influx of excessive extracellular calcium and neuronal cell death. It has been proposed that neurons containing CaBP may be more resistant to glutamate neurotoxicity due to their increased ability to buffer calcium. Using a herpes simplex virus-1 (HSV-1) vector system we packaged the CaBP gene, parvalbumin, or the marker gene, beta-galactosidase (beta-gal), correctly in viron particles, which were found upon infection to express mRNA specific to these vectors. PC12 and neocortical cultures showed strong immunohistochemical staining for either beta-gal or parv. The cortical cultures stained positively for endogenous glutamate decarboxylase, a marker for GABAergic neurons, but not for endogenous parvalbumin, indicating that parvalbumin was being expressed ectopically from the HSV-1 vector. Interestingly, the expression of parvalbumin increased cortical culture's susceptibility to N-methyl-D-aspartate-induced neurotoxicity. This increase in neurotoxicity was not due to the wild-type virus or the helper virus which accompanies the packaging of these vectors. We speculate that the ectopic expression of parvalbumin in cortical cultures may be increasing glutamate release which in turn increases cell death.

Increased M-calpain expression in the mesencephalon of patients with Parkinson's disease but not in other neurodegenerative disorders involving the mesencephalon: a role in nerve cell death?

Parkinson's disease is characterized by the loss of dopaminergic neurons in the substantia nigra and, to a lesser extent, the ventral tegmental area and catecholaminergic cell group A8. However, among these dopaminergic neurons, those expressing the calcium buffering protein calbindin are selectively preserved, suggesting that a rise in intracellular calcium concentrations may be involved in the cascade of events leading to nerve cell death in Parkinson's disease. We therefore analysed immunohistochemically the expression of the calcium-dependent protease calpain II (m-calpain) in the mesencephalon of patients with Parkinson's disease, progressive supranuclear palsy or striatonigral degeneration, where nigral dopaminergic neurons degenerate, and matched controls without nigral involvement. Calpain immunoreactivity was found in fibers and neuronal perikarya in the substantia nigra, the ventral tegmental area, catecholaminergic cell group A8 and the locus coeruleus. In patients with Parkinson's disease but not with the other neurodegenerative disorders, m-calpain immunoreactivity was detected in fibers with an abnormal morphology and in Lewy bodies. Sequential double staining revealed that most of these m-calpain-positive fibers and neuronal perikarya co-expressed tyrosine hydroxylase, indicating that most m-calpain neurons are catecholaminergic. Quantitative analysis of m-calpain staining in the substantia nigra and locus coeruleus revealed an increased density of fibers and neuronal perikarya in parkinsonian patients in both structures. These data suggest that increased calcium concentrations may be associated with nerve cell death in Parkinson's disease.

Cytosolic Ca2+ buffering, a cell property that in some neurons markedly decreases during aging, has a protective effect against NMDA/nitric oxide-induced excitotoxicity

In order to clarify the role of cytosolic Ca2+ buffering, a property that in living cells is sustained primarily by high affinity binding proteins, in NMDA receptor-sustained neuron excitotoxicity, cultures of the neuroblastoma line CHP 100 (which is known to express the receptor) were loaded with the chelator BAPTA by incubation with various concentrations (0.03-1 microM) of its acetoxymethylester derivative. The effectiveness of the loading in terms of cytosolic buffering was confirmed by fura-2 measurement experiments in which the [Ca2+]i transients induced by cell exposure to ATP were blunted in the initial peak (up to -75%) and also in the following plateau. When the BAPTA-loaded neuroblastoma cells were exposed to NMDA (1 mM), excitotoxicity was reduced dose-dependently up to almost 70%, while the generation of cGMP was inhibited up to completion. The latter result suggested the possible involvement of nitric oxide in the NMDA-induced excitoxicity, a mechanism confirmed by the dose-dependent inhibitory effect induced by the nitric oxide synthase blocker, L-N-(1-iminoethyl)-ornithine, which protected the cells completely when administered at 300 microM. Flow cytometry analysis of DNA revealed that the mechanism of excitotoxicity in CHP100 cells does not involve apoptosis. We conclude that cytosolic Ca2+ buffering, a property known to vary considerably among neuronal cells and to change in some neurons also during ageing, has a general protective effect. Such a protection appears to take place via the blunting of the glutamate-induced [Ca2+]i responses mediated by the NMDA receptor, with prevention of the ensuing overactivation of nitric oxide synthase and of the irreversible derangement of the ionic homeostasis of the cell.

Expression of calbindin-D28K in motoneuron hybrid cells after retroviral infection with calbindin-D28K cDNA prevents amyotrophic lateral sclerosis IgG-mediated cytotoxicity

Calbindin-D28K and/or parvalbumin appear to influence the selective vulnerability of motoneurons in amyotrophic lateral sclerosis (ALS). Their immunoreactivity is undetectable in motoneurons readily damaged in human ALS, and in differentiated motoneuron hybrid cells [ventral spinal cord (VSC 4.1 cells)] that undergo calcium-dependent apoptotic cell death in the presence of ALS immunoglobulins. To provide additional evidence for the role of calcium-binding proteins in motoneuron vulnerability, VSC 4.1 cells were infected with a retrovirus carrying calbindin-D28K cDNA under the control of the promoter of the phosphoglycerate kinase gene. Differentiated calbindin-D28K cDNA-infected cells expressed high calbindin-D28K and demonstrated increased resistance to ALS IgG-mediated toxicity. Treatment with calbindin-D28K antisense oligodeoxynucleotides, which significantly decreased calbindin-D28K expression, rendered these cells vulnerable again to ALS IgG toxicity.

Normal and abnormal calcium homeostasis in neurons: a basis for the pathophysiology of traumatic and ischemic central nervous system injury

Clinical recovery after central nervous system (CNS) trauma or ischemia may be limited by a neural injury process that is triggered and perpetuated at the cellular level, rather than by a lesion amenable to surgical repair. It is widely thought that one such process, a fundamental pathological mechanism initiated by CNS injury, is a disruption of cellular Ca2+ homeostasis. Because of the critical role of Ca2+ ions in regulating innumerable cellular functions, this major homeostatic disturbance is thought to trigger neuronal and axonal degeneration and produce clinical disability. We review those aspects of normal and pathological Ca2+ homeostasis in neurons that relate to neurodegeneration and to the application of neuroprotective strategies for the treatment of CNS injury. In particular, we examine the contribution of Ca(2+)-permeable ionic channels, Ca2+ pumps, intracellular Ca2+ stores, intracellular Ca2+ buffering systems, and the roles of secondary, Ca(2+)-dependent processes in neurodegeneration. A number of hypotheses linking Ca2+ ions and Ca2+ permeable channels to neurotoxicity are discussed with an emphasis on strategies for lessening Ca(2+)-related damage. A number of these strategies may have a future role in the treatment of traumatic and ischemic CNS injury.

Neuronal lesions and behavioral modifications in rat following cerebral ischemia and reperfusion

Neurons of the mammalian CNS differ in their vulnerability to various disease processes and other insults, particularly in their response to total anoxia/ischemia. In this study we have tested the histological and behavioral modifications induced by experimental conditions of partial cerebral ischemia in the rats. The specific morphological and histological alterations, observed in our experimental conditions of reversible partial cerebral ischemia, confirm the selective vulnerability of certain neuronal populations to ischemic injury and are also evidenced by behavioral modifications which may mirror the functional impairment observed in humans after a transitory ischemic attack.

The human homologue of the weaver mouse gene in familial and sporadic Parkinson's disease

The pathological hallmark of Parkinson's disease is cell death of dopaminergic neurons in the substantia nigra, resulting in striatal dopaminergic deficit and a clinical syndrome dominated by disorders of movement. The cause for this cell loss is unknown, but the possibility of a contributing genetic factor is increasingly recognized. Homozygous weaver mice, a mutant mouse strain, display progressive postnatal depletion of dopaminergic cells in the mesencephalon and have thus been proposed as an animal model for Parkinson's disease. Recently, mGIRK2, a putative G-protein inward rectifier K+ channel, has been identified as the causative gene in the weaver mouse and a homozygous mutation has been described in the H5 pore region of this channel. The human homologue of mGIRK2, KCNJ7 or hiGIRK2, has previously been isolated on chromosome 21q22.1. A possible involvement of this gene in the pathogenesis of Parkinson's disease has been discussed. To evaluate the possibility of a shared genetic defect in weaver mouse and Parkinson's disease, we analysed the H5 pore region of hiGIRK2 in familial and sporadic cases of Parkinson's disease. The sequence was normal in all cases examined, suggesting a differing aetiology of nigral cell loss in Parkinson's disease and weaver mice.