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

Sparing of the dopaminergic neurons containing calbindin-D28k and of the dopaminergic mesocortical projections in weaver mutant mice

In mice carrying the weaver mutation there is a spontaneous degeneration of dopaminergic neurons that is heterogeneous among cell groups: nigrostriatal neurons are more affected than mesolimbic neurons, while involvement of the mesocortical system is controversial. We questioned whether the pattern of cell loss in mesencephalon and fiber depletion in telencephalon could be related to the differential content of Calbindin-D28k in dopaminergic cells. The mesencephalon of seven-month-old mutants was serially sectioned and alternate series were immunostained with tyrosine hydroxylase and Calbindin-D28k. Cell counts indicated a 40% loss for the ensemble of dopamine mesencephalic neurons. However, double-immunostained preparations revealed that this cell loss was restricted to the neurons that lacked Calbindin-D28k, which were reduced by 72%, while the dopaminergic neurons containing Calbindin-D28k were completely spared. Calbindin-D28k was present in both the cytoplasm and nucleus of the dopaminergic cells. This nuclear localization was confirmed at the ultrastructural level. In the telencephalon of weaver mutants, areas receiving projections from the Calbindin-D28k-positive dopaminergic neurons, such as the cerebral cortex, contained normal densities of fibers, while areas harboring projections from the non-Calbindin-D28k dopaminergic neurons, such as the dorsal striatum, had reduced amounts of fibers. The vulnerability pattern in the mesencephalon of weaver mutants bears similarities to that described in idiopathic Parkinson's disease or in N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinsonism: Calbindin-D28k may thus delimit a group of dopaminergic neurons resistant to cell death in different conditions. On the other hand, the vulnerability pattern of dopaminergic fibers in weaver differs from that of Parkinson's disease, since there is a complete sparing of the dopaminergic mesocortical projection in weaver, contrasting with the damage of these projections in Parkinson's disease.

Interaction between 5-HT1A and nicotinic cholinergic receptors in the regulation of water maze navigation behavior

The interaction between serotonin (5-HT)1A and nicotinic cholinergic receptors in the regulation of spatial navigation behavior in the Morris water maze (WM) test was studied. Pretraining intraperitoneal (i.p.) injections of a combination of subthreshold doses of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (a 5-HT1A receptor agonist) at 30 micrograms/kg and mecamylamine (a nicotinic cholinergic receptor antagonist) a 2500 micrograms/kg greatly impaired WM navigation to a hidden platform and slightly, but not statistically significantly, impaired WM navigation to a visible platform. Post-training i.p. injections of this combination had no effect on WM navigation performance. Serotonin depletion induced by p-chlorophenylalanine (PCPA) increased the performance impairing action of pretraining injected combination of 8-OH-DPAT 30 micrograms/kg and mecamylamine 2500 micrograms/kg. In trained rats combined injections of 8-OH-DPAT 30 micrograms/kg and mecamylamine 2500 micrograms/kg given pretraining had no effect on the navigation to a hidden platform located in a familiar or in a novel position. Pretraining trial injected combination of hexamethonium 2000 micrograms/kg (a peripherally acting nicotinic antagonist) and 8-OH-DPAT 30 micrograms/kg had no effect on navigation. These data suggest that a combined treatment with a 5-HT1a receptor agonist and a nicotinic cholinergic receptor antagonist more severely impair non-mnemonic acquisition performance processes than consolidation and retrieval processes.

Vulnerability to excitotoxic stimuli of cultured rat hippocampal neurons containing the calcium-binding proteins calretinin and calbindin D28K

Rat embryonic hippocampal neurons cultured on astrocyte feeder-layers were sensitive to different excitotoxic stimuli after 10-12 DIV. Almost all neurons (approximately 95%) died within 20 h after a transient exposure for 10 min to 50 microM glutamate, a continuous exposure to either 25 microM NMDA or 250 microM kainate or after a 15-min deprivation of glucose and oxygen. Dizocilpine at 10 microM protected neurons against the glutamate- and NMDA-mediated toxicity as well as against 30 min glucose and oxygen deprivation. However, it failed to protect against kainate toxicity and prolonged glucose/oxygen deprivation (60 min). An additional treatment with CNQX (100 microM) protected neurons even under the latter two conditions. This indicates that the vast majority of neurons was sensitive to different excitotoxic stimuli acting through different types of glutamate receptors leading to calcium overload of the cells which might be the common denominator of triggering cell death under these conditions. Expression of calcium-binding proteins, such as calbindin D28K or calretinin, might increase the intracellular calcium buffer capacity of neurons, thus, rendering them more resistant to calcium overload. Therefore, we analysed whether neurons expressing these calcium-binding proteins would survive these toxic stimuli. Indeed, a small population of the neurons (3-5%) survived, including a subpopulation of calretinin-positive but not calbindin D28K-positive neurons. This implies that the expression of calcium-binding proteins per se does not render neurons more resistant towards these excitotoxic stimuli. Moreover, most of the surviving calretinin-positive neurons showed morphological damage as indicated by loss of neurites. When cytotoxicity due to calcium overload was induced by an exposure of the cells to the calcium ionophore 4-bromo-A23187 rather than by activation of glutamate receptors, calretinin-positive cells were found not to be significantly more resistant than the vast majority of neurons. This may indicate that the lower sensitivity of a subpopulation of calretinin-positive neurons to excitotoxic stimuli may be due to a lower expression of glutamate receptors.

Occurrence and localization of calbindin-D28K in kidney and cerebellum of the slider turtle, Trachemys scripta

BACKGROUND

Since its initial discovery in the avian intestine, calbindin-D28K has been reported to occur in various species and tissues. Although calbindin-D28K binds calcium ions in the physiologically relevant range of intracellular calcium, its functional role in the various cell types where it has been localized remains unknown.

METHODS

We examined the occurrence of calbindin-D28K in the brain and kidney of the testudine reptile, Trachemys scripta, by immunoblotting and immunocytochemistry using rabbit anti-sera directed against rat renal calbindin-D28K and chicken intestinal calbindin-D28K.

RESULTS

Immunoblotting revealed the presence of calbindin-D28K in the turtle tissues. A single immunoreactive band in the 28,000 relative molecular mass region was visualized in cerebellar and renal homogenates. Immunocytochemistry revealed reaction product for the presence of calbindin-D28K in the Purkinje cells of the cerebellum, and in the distal tubular cells of the nephron. Processes as well as the perikaryon of the Purkinje cell were immunoreactive.

CONCLUSION

This study describes the occurrence and cellular localization of calbindin-D28K in a reptilian cerebellum, and confirms the phylogenetic distribution of renal calbindin-D28K to the oldest major reptilian group.

Human striatum: chemoarchitecture of the caudate nucleus, putamen and ventral striatum in health and Alzheimer's disease

The morphology and distribution of perikarya positive for choline acetyltransferase, somatostatin, calcium binding protein (calbindin D28K) and nicotinamide adenine dinucleotide phosphate diaphorase were surveyed in the human striatum. Choline acetyltransferase and somatostatin antibodies labeled separate populations of large striatal interneurons. Somatostatin immunoreactivity and nicotinamide adenine dinucleotide phosphate diaphorase (nitric oxide synthase) activity were completely co-localized. Calbindin antibody identified two distinct groups of striatal neurons: (1) numerous medium-sized, lightly stained neurons, probably analogous to striatopallidal projection neurons in the rat, and (2) much less numerous, large, darkly stained neurons. Half of the latter group, but none of the former, were also nicotinamide adenine dinucleotide phosphate diaphorase-positive. Somatostatin-positive and medium-sized, calbindin-positive neurons were more numerous in the caudate nucleus than in the putamen or ventral striatum. By contrast, large calbindin-immunoreactive neurons were more frequently encountered in the putamen. Choline acetyltransferase-positive neurons were evenly distributed across striatal components. In aged control subjects, the size of large, darkly stained calbindin-positive neurons was reduced relative to young subjects. Aging had no effect on somatostatin-, medium-sized calbindin-, or choline acetyltransferase-positive neurons. However, in histologically confirmed cases of Alzheimer's disease, there was a selective, 75% loss of choline acetyltransferase-immunoreactive perikarya from the ventral striatum, but not from the dorsal striatum, compared to aged controls. Furthermore, the remaining cholinergic neurons in the ventral striatum of Alzheimer's disease cases were significantly smaller than similar neurons in controls. These results indicate that various striatal components which have been shown to differ in their anatomical connectivity and functional specialization, also differ in their neurochemical signatures. The specific and marked loss of choline acetyltransferase-positive neurons from the ventral striatum in Alzheimer's disease is consistent with the characteristic cholinergic and 'limbic' pathology in this disease.

A comparative study of the calcium-binding proteins calbindin-D28K, calretinin, calmodulin and parvalbumin in the rat spinal cord

Comparison of the immunocytochemical localizations revealed distinct patterns of differential distribution and overlapping of calbindin-D28K (CB-D28K), calretinin (CR), calmodulin (CM) and parvalbumin (PV) in the rat spinal cord. In some areas, one of the four calcium-binding proteins (CBPs) appears to be predominant, for example, CB-D28K in lamina I and ependymal cells, PV at the inner part of laminae II, CR in laminae V and VI and CM in motoneurons of lamina IX. In other regions of the spinal cord, more than one CBPs was abundant. CB-D28K and CR were similarly distributed in lamina II and the lateral spinal and cervical nucleus; CM and PV were similarly abundant in the ventromedial dorsal horn, internal basilar and central cervical nucleus; CR and PV were similarly abundant in the ventromedial dorsal horn, internal basilar and central cervical nucleus; CR and PV were similarly heterogeneous in the gracile fasciculus from caudal to rostral spinal cord. In the sacral dorsal gray commissure, the distribution patterns of CR and PV were clearly complementary. The unilateral ganglionectomies resulted in a substantial reduction of CBP-like immunoreactivity (CBP-LI) in the dorsal columns and a reduction of CM- and PV-LI in the ventromedial dorsal horn. In the motor system, only CM labeled large motoneurons in lamina IX and CB-D28K lightly stained pyramidal tract. The apparent absence of CM-LI in the superficial dorsal horn is contradictory to the presence of a CM-dependent nitric oxide synthase in the region. These data indicate that most CBP-LI in the dorsal column pathway had primary afferent origin, while the superficial dorsal horn exhibited intrinsic CBP immunoreactivity. The differential and selective localizations of CBPs in the spinal cord suggest a role for these proteins in spinal nociceptive processing, visceral regulation and dorsal column sensory pathways.

Morphological and molecular characterization of the response of differentiated PC12 cells to calcium stress

The mechanisms that lead ultimately to neuronal death in pathological ageing of the brain remain mostly unknown as in the case of Parkinson's disease where there is a progressive and selective loss of dopaminergic neurons within the substantia nigra. Dopamine-expressing PC12 cells that were neuronally differentiated by nerve growth factor treatment were chosen as a culture model in which to study some of the changes that may occur during the course of the degenerative process. They were exposed to the calcium ionophore A23187 in order to produce a sustained rise in cytoplasmic calcium, a phenomenon related to various pathological conditions. The degenerative effects of the ionophore were dose- and time-dependent. They were characterized by early fragmentation of the neurites followed ultimately by a loss in cell viability. Biochemical changes, such as a decrease in [3H]dopamine uptake and modulations of the tyrosine hydroxylase gene, were detected before macroscopic evidence of cell suffering (e.g. neurite fragmentation) could be observed. Although an ongoing degenerative process was occurring in cell somata, PC12 cells were able to recover upon ionophore withdrawal. Characteristics of apoptosis such as chromatin condensation and DNA fragmentation were detectable in a small population of dying cells. DNA fragmentation could be prevented by the endonuclease inhibitor aurintricarboxylic acid. New protein synthesis was not required, as cycloheximide failed to prevent degeneration. Taken together, these results suggest that differentiated PC12 cells react to calcium stress through a sequence of regulatory processes which appears to be independent of the apoptotic pathway.

NT-3 and BDNF protect CNS neurons against metabolic/excitotoxic insults

Neurotrophin-3 (NT-3) and brain-derived neurotrophic factor (BDNF) were recently shown to have biological activity in central neurons. In the present study, NT-3 and BDNF attenuated glucose deprivation-induced neuronal damage dose-dependently in rat hippocampal, septal and cortical cultures. Direct measurements of intraneuronal free calcium levels ([Ca2+]i) and manipulations of calcium influx demonstrated that NT-3 and BDNF each prevented the elevation of [Ca2+]i that mediated glucose deprivation-induced injury. Studies in cultures depleted of glia indicated a direct action of NT-3 and BDNF on neurons. Neurons pretreated with NT-3 or BDNF for 24 hr were more resistant to glutamate neurotoxicity, and showed attenuated [Ca2+]i responses to glutamate. TrkB (BDNF receptor) and trkC (NT-3 receptor) proteins were present in hippocampal, cortical and septal cultures where they were localized to neuronal cell bodies and neurites. The data demonstrate that NT-3 and BDNF can protect neurons against metabolic and excitotoxic insults, and suggest that these neurotrophins may serve [Ca2+]i-stabilizing and neuroprotective functions in the brain.

Increased expression of mRNA encoding calbindin-D28K, the glucose-regulated proteins, or the 72 kDa heat-shock protein in three models of acute CNS injury

Changes at the level of gene expression are becoming an increasingly recognized component of the neuronal response to injury. We used Northern analysis and three in vivo models of central nervous system (CNS) injury in the rat to determine whether injury alters the expression of certain gene products related to cellular homeostasis. The three models included kainate (KA)-induced seizures, global ischemia, and lateral fluid percussion injury to the cerebral cortex. Animals were sacrificed at various times after injury, and total RNA was isolated from specific brain regions. Northern blots were hybridized with probes for calbindin-D28K, the 78 and 94 kDa glucose-regulated proteins (grp78, grp94), the inducible 72 kDa heat-shock protein (hsp72), and a control probe for the 18S ribosomal subunit. Results showed that mRNA for calbindin-D28K, grp78, and hsp72 increased in the hippocampus following seizures. Peak expression occurred 6-12 h after administration of KA, and returned towards baseline in most cases by 24 h. Changes in all four transcripts were seen in the hippocampus or cortex following global ischemia, although the return to baseline tended to exceed 24 h for the grps. In the trauma model, mRNA for hsp72 was increased in the cortex ipsilateral to the impact 12 h after injury. These results expand the repertoire of known changes in mRNA expression following CNS injury. The increases in hsp72 and grps indicate the occurrence of a generalized stress response. Furthermore, given the evidence that grp78 and grp94 are induced by calcium ionophores in vitro, and the potential role of calbindin-D28K in buffering cytoplasmic calcium, the changes observed in this study may represent a cellular response to perturbed calcium homeostasis that is known to occur in acute CNS injury.

Cellular distribution of calbindin D28K mRNAs in the adult mouse brain

We have determined the cellular distribution of calbindin D28K mRNAs throughout the mouse brain by in situ hybridization. While these studies identified neuronal populations similar to those previously identified in rat brain by immunohistochemistry, some discrepancies exist. These may derive from species differences or from the immunological cross-reactivity of calbindin D28K antiserum with other proteins. We note an intriguing association between the distribution of neurons containing calbindin D28K mRNA and those reported by others to contain the inositol 1,4,5-triphosphate (InsP3) receptor.

Immunohistochemical localization of calbindin-D28K and calretinin in the lamprey retina

Calbindin-D28K and calretinin are homologous cytosolic calcium binding proteins localized in many retinal neurons from different species. In this report, location of cells immunoreactive to both proteins was investigated in the retina of the lamprey, Lampetra fluviatilis. This organism constitutes one of the older representative vertebrates and possesses a peculiar organization, probably unique: two-thirds of the ganglion cells are in the classical amacrine cell layer and the nerve fiber layer is located in the scleral part of the inner plexiform layer. Calbindin-like immunoreactivity was demonstrated in large bipolar cells and in cell bodies located in the inner retina. Although the distinction between labelled ganglion cells and labelled amacrine cells was rendered difficult, we hypothesized that the majority of calbindin-immunoreactive cells observed in the inner retina are ganglion cells, because of the high number of labelled fibers in the nerve fiber layer. Calretinin-like immunoreactivity was detected in both large and small bipolar cells, and also in cells located in the inner retina. Since few calretinin-immunoreactive fibers were observed in the nerve fiber layer, we assume that the latter category of cells are amacrine cells. Horizontal cells were both negative for calbindin and calretin-like immunoreactivities. Calbindin and calretinin, which are present in cones from many species, could not be detected in the photoreceptor layer favouring the rod-dominated lamprey retina. Although their distribution differs from those observed in most vertebrates, the present results indicate the good conservation of both calcium binding proteins in the retina during the vertebrate evolution.

Endogenous neuroprotection factors and traumatic brain injury: mechanisms of action and implications for therapy

Throughout evolution the brain has acquired elegant strategies to protect itself against a variety of environmental insults. Prominent among these are signals released from injured cells that are capable of initiating a cascade of events in neurons and glia designed to prevent further damage. Recent research has identified a remarkably large number of neuroprotection factors (NPFs), whose expression is increased in response to brain injury. Examples include the neurotrophins (NGF, NT-3, NT-5, and BDNF), bFGF, IGFs, TGFs, TNFs and secreted forms of the beta-amyloid precursor protein. Animal and cell culture studies have shown that NPFs can attenuate neuronal injury initiated by insults believed to be relevant to the pathophysiology of traumatic brain injury (TBI) including excitotoxins, ischemia, and free radicals. Studies of the mechanism of action of these NPFs indicate that they enhance cellular systems involved in maintenance of Ca2+ homeostasis and free radical metabolism. Recent work has identified several low-molecular-weight lipophilic compounds that appear to mimic the action of NPFs by activating signal transduction cascades involving tyrosine phosphorylation. Such compounds, alone or in combination with antioxidants and calcium-stabilizing agents, have proved beneficial in animal studies of ischemic brain injury and provide opportunities for development of preventative/therapeutic approaches for TBI.

Tumor necrosis factors protect neurons against metabolic-excitotoxic insults and promote maintenance of calcium homeostasis

Emerging data indicate that neurotrophic factors and cytokines utilize similar signal transduction mechanisms. Although neurotrophic factors can protect CNS neurons against a variety of insults, the role of cytokines in the injury response is unclear. We now report that TNF beta and TNF alpha (1-100 ng/ml) can protect cultured embryonic rat hippocampal, septal, and cortical neurons against glucose deprivation-induced injury and excitatory amino acid toxicity. The elevation of intracellular calcium concentration ([Ca2+]i) induced by glucose deprivation, glutamate, NMDA, or AMPA was attenuated in neurons pretreated with TNF beta. The mechanism whereby TNFs stabilize [Ca2+]i may involve regulation of the expression of proteins involved in maintaining [Ca2+]i homeostasis, since both TNF beta and TNF alpha caused a 4- to 8-fold increase in the number of neurons expressing the calcium-binding protein calbindin-D28k. These data suggest a neuroprotective role for TNFs in the brain's response to injury.

Glutamate, beta-amyloid precursor proteins, and calcium mediated neurofibrillary degeneration

In this article we present evidence supporting the interaction between excitotoxicity, beta APP mismetabolism, metabolic compromise and intracellular calcium destabilization in the process of neurodegeneration associated with Alzheimer's disease (AD). AD is characterized by the presence of neurofibrillary tangles and amyloid-containing plaques in specific regions of the brain. There appear to be several processes which contribute to the neurodegeneration associated with AD. Although AD has been linked to genetic mutations on chromosomes 21, 19 and 14, there are sporadic forms of AD that have no known genetic mutation involved. Aging is the major risk factor for AD. During the course of normal aging several metabolic compromises may occur in the brain. Both decreased glucose transport and utilization, and increased glucocorticoid levels are known to occur with aging and may lead to decreased energy supplies, ATP depletion, failure of Ca2+ buffering systems, excess glutamate release and activation of glutamate receptors. In addition, a reduction in antioxidant enzymes and consequently an increase in free radicals has also been associated with aging. Each of the preceeding alterations would lead to an increase in neuronal [Ca2+]i. Elevated calcium could then activate calcium-dependent proteases which degrade particular cytoskeletal proteins, and lipases which generate free radicals resulting in membrane damage and possible cell death. In this article we provide evidence that amyloid beta-peptide (A beta), the substance which accumulates in AD plaques, exacerbates excitotoxic and metabolic compromises to neurons resulting in changes in the cytoskeleton which resemble those seen in the neurofibrillary tangles of AD. We also provide evidence that secreted forms of beta-amyloid precursor protein (beta APP) are neuroprotective against excitotoxic insults. Recent findings concerning the normal function of beta APP and the mechanism of A beta toxicity place beta APP at the center of changes leading to neuronal degeneration in AD.

Neuronal protective effects of calcium antagonists in cerebral ischemia

We investigated the effects of calcium antagonists against ischemic injury in vivo and against excitotoxic damage in vitro. In vivo nimodipine protected significantly the CA1 hippocampal neurons from neurodegeneration after transient global ischemia in rats without changing the local cerebral blood flow. Furnidipine reduced the area of ischemia after permanent MCA-occlusion in mice. The results in vitro using the Ca(2+)-sensitive dye fura-2 showed that nimodipine reduced in a dose-dependent manner the elevation of [Ca2+]i in hippocampal neurons induced by K(+)-stimulation. The present in vitro and in vivo data show that calcium antagonists are potent agents in protecting neurons against the deleterious consequences of an excitotoxic or ischemic insult.

Protective effect of nerve growth factor against glutamate-induced neurotoxicity in cultured cortical neurons

The effect of recombinant human nerve growth factor (hNGF) and mouse NGF on cultured rat cortical neurons was examined. The DNA fragment coding the human NGF gene was isolated and inserted downstream from the SV40 promoter in a plasmid containing the dihydrofolate reductase cDNA, and this plasmid was introduced into Chinese hamster ovary (CHO) cells to establish cells producing recombinant hNGF. The recombinant hNGF protein secreted by CHO cells was confirmed to be biologically active in an assay using PC12 cells. Brief exposure of cortical cells to glutamate followed by incubation with glutamate-free medium reduced cell viability by 60-70% when compared with the control culture. Simultaneous addition of recombinant hNGF or mouse NGF to rat cortical cultures with glutamate did not affect this reduction of cell viability. However, 24 h pretreatment of rat cortical cultures with recombinant hNGF or mouse NGF resulted in a significant reduction of glutamate-induced neuronal damage. Mouse NGF also protected cortical neurons against N-methyl-D-aspartate (NMDA)- and kainate-induced neuronal damage. These findings suggest that NGF can protect cortical neurons against glutamate-induced neurotoxicity.

Immunocytochemical localization of the plasma membrane calcium pump, calbindin-D28k, and parvalbumin in Purkinje cells of avian and mammalian cerebellum

A monoclonal antibody produced against the human erythrocyte plasma membrane calcium pump (PMCA) was shown to react immunohistochemically with an epitope of the PMCA in avian and mammalian cerebellum. Western blot analysis of purified synaptosomes and homogenates from avian cerebellum revealed major immunoreactive proteins with molecular masses (130 kDa and 138 kDa) similar to those of purified erythrocyte PMCA. Dual-imaging confocal immunofluorescence microscopy of avian cerebellum showed that the PMCA antibody stained the periphery of the soma whereas calbindin-D28k was located in the cytosol. PMCA heavily stained the more distal dendrites of the Purkinje cells and, within the resolution of the fluorescence procedure, colocalized with calbindin-D28k. By using alkaline phosphatase-conjugated second antibody, PMCA was again localized to the peripheral soma, to a segmental pattern in dendrites, and to presumed spiny elements. The soma periphery and dendrites of Purkinje cells of the rat cerebellum were also prominently stained with anti-PMCA antibody and compared to parvalbumin localization. Dendritic depolarization and dendritic spiking behavior are significant Ca(2+)-dependent events of Purkinje cells. The rapid decline of intracellular free Ca2+ after the rapid rise time of Ca2+ transients is considered to be due to sequestration by Ca2+ buffers, uptake by intracellular stores, and Ca2+ extrusion mechanisms, the latter a function of PMCA now shown immunohistochemically to be a prominent feature of Purkinje cell dendrites.

Calcium buffering properties of calbindin D28k and parvalbumin in rat sensory neurones

1. We have examined the ability of the Ca(2+)-binding proteins (CABP) calbindin D28k and paravalbumin to modulate increases in the intracellular free Ca2+ concentration ([Ca2+]i), produced by brief depolarizations, in rat dorsal root ganglion (DRG) neurones. 2. In order to obtain good voltage control, we replated DRG neurones prior to performing these experiments. Immunocytochemical staining of these cells revealed that approximately 10% stained for CABPs. 3. Using fluorescently labelled parvalbumin, we demonstrated that in the whole-cell voltage clamp mode the protein freely entered the cell soma with a mean half-life t0.5 of 6 min 22 s +/- 54 s. 4. Analysis of the effects of calbindin D28k (370 microM) and parvalbumin (1 mM) on Ca2+ currents in the whole-cell voltage clamp mode, revealed that neither protein changed the rate of inactivation of the Ca2+ current or its rate of run-down. 5. Introducing either calbindin D28k (370 microM) or parvalbumin (1 mM) into the cell soma did not significantly alter the basal [Ca2+]i when compared to control cells. 6. Compared to control cells, both CABPs significantly reduced the peak [Ca2+]i obtained for a Ca2+ influx of an equivalent charge density, whereas lysozyme (1 mM), a protein with low affinity for Ca2+, failed to do so. 7. Calbindin D28k caused an 8-fold decrease in the rate of rise in [Ca2+]i and altered the kinetics of decay of [Ca2+]i to a single slow component. Parvalbumin also slowed the rate of rise in [Ca2+]i. Parvalbumin selectively increased a fast component in the decay of the Ca2+ signal. 8. These data demonstrate that both calbindin D28k and paravalbumin effectively buffer Ca2+ in a cellular environment and may therefore regulate Ca(2+)-dependent aspects of neuronal function.

Repeated NMDA receptor activation induces distinct intracellular calcium changes in subpopulations of striatal neurons in vitro

The mechanisms underlying long-term calcium changes evoked by excitatory amino acids have not been previously examined in striatal neurons. Fura-2 fluorescence measurements were used to examine intracellular calcium concentration ([Ca2+]i) changes due to repeated N-methyl-D-aspartate (NMDA) receptor activation, in primary cultures of murine striatal neurons. Three applications of 200 microM NMDA (for 2 min, each application separated by 7 min), in 0 magnesium-containing artificial cerebral spinal fluid, elicited three distinct responses. In 50 +/- 8% of the NMDA-responsive neurons, no persistent increases in [Ca2+]i (final [Ca2+]i < or = 150% baseline) were observed, while in 33 +/- 7% and 17 +/- 3% of the cells, sustained (peak response > final [Ca2+]i > 150% baseline) and uncontrolled increases (final [Ca2+]i > or = peak response) were observed, respectively. NMDA-responsive neurons that were intensely immunoreactive for the calcium binding protein calbindin-D28k never exhibited uncontrolled increases in [Ca2+]i. Removal of extracellular Ca2+ significantly attenuated sustained, but not uncontrolled, increases in [Ca2+]i; sustained increases in some neurons were also attenuated by application of verapamil (100 microM) or MK-801 (1 microM). Pre-treatment of striatal neurons with the protein kinase C blocker sphingosine (20 microM), virtually eliminated the development of sustained or uncontrolled increases in [Ca2+]i. These findings suggest that specific intracellular mechanisms regulate the distinct [Ca2+]i responses of subpopulations of striatal neurons to repeated NMDA receptor activation.

Neurochemical compartmentation of monkey and human visual cortex: similarities and variations in calbindin immunoreactivity across species

The compartmental organization of visual cortical neurons was examined across species of primates by directly comparing the pattern of immunoreactivity for the 28-kD vitamin D-dependent calcium-binding protein (calbindin) in area 17 of squirrel monkeys, macaques, and neurologically normal adult humans. Area 17 of macaques and squirrel monkeys was similar in that somata and processes intensely immunoreactive for calbindin were present in the same layers (II-III, IVB, and V) and in both species formed a well-stained matrix that surrounded the CO-rich puffs in layer III. These intensely calbindin-immunoreactive neurons were identified as subpopulations of GABA-immunoreactive neurons. Among the most obvious differences in the two monkey species was the distribution of calbindin-positive elements outside of layer III: a dense immunostained matrix surrounded the puffs in layers II, IVB, V, and VI of squirrel monkeys but the immunostained neurons adopted no regular pattern outside layer III in macaques. In addition, although somata lightly immunoreactive for calbindin were present in both species, they were much more abundant in squirrel monkeys than macaques. The pattern of calbindin immunostaining in human area 17 resembled that of macaques in forming an intense matrix that surrounded puffs only in layer III, yet also resembled that of squirrel monkeys by including large numbers of light immunoreactive somata. These lightly immunostained somata included a very dense population forming a prominent band in layer IVA of human visual cortex. We conclude that for layer III of primary visual cortex, a similar pattern of neuronal chemistry exists across species of primates which is related to this layer's compartmental organization. Yet for other layers, the expression of calbindin immunoreactivity varies from one species to the next, perhaps reflecting variations in other neuronal properties.

Mice expressing a bovine basic fibroblast growth factor transgene in the brain show increased resistance to hypoxemic-ischemic cerebral damage

BACKGROUND AND PURPOSE

Cerebral intraventricular infusion of acidic or basic fibroblast growth factor has been shown to attenuate ischemic damage to hippocampal CA1 neurons in the gerbil. The purpose of the present study was to determine if the basic fibroblast growth factor transgenic mouse has an enhanced ability to resist the effects of severe cerebral hypoxemia-oligemia.

METHODS

Mice that were transgenic for bovine basic fibroblast growth factor were exposed to right carotid artery ligation, hyperglycemia, and 20 minutes of 1% carbon monoxide. After 5 days' recovery, brains were examined for histological damage.

RESULTS

Counts of CA1 neurons in the right hippocampus showed a significantly higher number of neurons per millimeter CA1 in hypoxic-ischemic transgenic mice compared with nontransgenic controls (transgenic, 260 +/- 33; nontransgenic, 151 +/- 37 neurons per millimeter CA1; P < .05).

CONCLUSIONS

The results indicate that basic fibroblast growth factor transgenic mice, as judged by CA1 hippocampal neuronal survival, have an enhanced ability to resist the effects of a complex hypoxic-ischemic cerebral insult.

Excitotoxicity and selective neuronal loss in epilepsy

The early stages of selective neuronal loss occurring in the hippocampus and other brain regions after prolonged epileptic activity have fine structural characteristics matching those induced by excitotoxic agents. NMDA receptor antagonists provide protection against such damage. The extracellular concentration of glutamate or aspartate may be transiently raised prior to or early in seizure activity but tends not to match the levels associated with hypothalamic damage in the original paradigm of excitotoxicity. Various aspects of the excitotoxic process are examined to see if they can account for particular details of the pattern of selective neuronal loss. A full explanation of selective vulnerability will take into account not only a range of characteristics of the vulnerable neuron but also its functional network during sustained activity.

Calcium-destabilizing and neurodegenerative effects of aggregated beta-amyloid peptide are attenuated by basic FGF

The mechanisms that contribute to neuronal degeneration in Alzheimer's disease (AD) are not understood. Abnormal accumulations of beta-amyloid peptide (beta AP) are thought to be involved in the neurodegenerative process, and recent studies have demonstrated neurotoxic actions of beta APs. We now report that the mechanism of beta AP-mediated neurotoxicity in hippocampal cell culture involves a destabilization of neuronal calcium homeostasis resulting in elevations in intracellular calcium levels ([Ca2+]i) that occur during exposure periods of 6 hr to several days. Both the elevations of [Ca2+]i and neurotoxicity were directly correlated with aggregation of the peptide as assessed by beta AP immunoreactivity and confocal laser scanning microscopy. Exposure of neurons to beta AP resulted in increased sensitivity to the [Ca2+]i-elevating and neurodegenerative effects of excitatory amino acids. Moreover, [Ca2+]i responses to membrane depolarization and calcium ionophore were greatly enhanced in beta AP-treated neurons. Neurons in low cell density cultures were more vulnerable to beta AP toxicity than were neurons in high cell density cultures. Basic fibroblast growth factor (bFGF), but not nerve growth factor (NGF), significantly reduced both the loss of calcium homeostasis and the neuronal damage otherwise caused by beta AP. In AD, beta AP may endanger neurons by destabilizing calcium homeostasis and bFGF may protect neurons by stabilizing intracellular calcium levels. Aggregation of beta AP seems to be a major determinant of its [Ca2+]i-destabilizing and neurotoxic potency.

Transient expression of calbindin-D28k immunoreactivity in layer V pyramidal neurons during postnatal development of kitten cortical areas

Calbindin-D28k is a 28 kDa calcium binding protein that has been shown to colocalize with a specific subpopulation of gamma-aminobutyric acid inhibitory interneurons in mammalian neocortex. We have examined the ontogeny of calbindin in neonatal kitten cortex in areas 17,18,19,7, medial and lateral suprasylvian visual areas, splenial visual area and cingulate cortex from the day of birth (P0) through maturation of the brain (P101). Transient staining of immature layer V pyramidal cells was seen in kittens six weeks old and younger. This transient staining of pyramidal cells was most intense and the stained neurons were most numerous in cingulate cortex. Apical dendrites of pyramidal cells in cingulate cortex were prominently stained and could be followed to layer I, where they were seen to branch extensively. There were very few calbindin immunoreactive pyramidal cells in primary cortical areas postnatally. Transient staining in extrastriate visual cortical areas disappeared first from the lateral suprasylvian areas, and persisted longest in area 7. Pyramidal neurons in the cingulate gyrus expressed calbindin longest, but calbindin expression by pyramidal neurons ceased by the sixth postnatal week in all areas of the brain.

Cell-permeant Ca2+ chelators reduce early excitotoxic and ischemic neuronal injury in vitro and in vivo

We report the characterization of the first successful treatment of neuronal ischemic injury in vivo by cell-permeant Ca2+ chelators. The chelators attenuated glutamate-induced intracellular Ca2+ increases and neurotoxicity in neuronal explant cultures. When infused intravenously in rats, permeant fluorescent BAPTA analogs accumulated in neurons in several brain regions. BAPTA-AM, infused in vivo, reduced Ca(2+)-dependent spike frequency adaptation and post-spike train hyperpolarizations in CA1 neurons taken from treated animals. This effect was reproduced by direct injections of BAPTA into untreated neurons. The effects of three different chelators (BAPTA, 5,5'-difluoro BAPTA, and 4,4'-difluoro BAPTA) on Ca(2+)-dependent membrane excitability varied with their Ca2+ affinity. When the chelators' permeant forms were used to treat rats prior to the induction of focal cortical ischemia, they were highly neuroprotective, as gauged by significant reductions in cortical infarction volumes and neuronal sparing. The chelators' protective effects in vivo also reflected their affinity for Ca2+. This report provides the most direct evidence to date that intracellular Ca2+ excess triggers early neurodegeneration in vivo and contributes a novel therapeutic approach to neuronal ischemia of potential clinical utility.

Calretinin immunoreactivity in the monkey hippocampal formation--I. Light and electron microscopic characteristics and co-localization with other calcium-binding proteins

Calretinin-containing neurons were visualized by immunocytochemistry in the monkey hippocampal formation, subicular complex, and entorhinal cortex. Calretinin-immunoreactivity was present exclusively in non-granule cells of the dentate gyrus and in non-pyramidal cells of Ammon's horn, subiculum and entorhinal cortex. Most frequently, calretinin-positive neurons were found at the hilar border of the dentate granule cell layer and in the stratum radiatum of CA1-3 areas. In the subicular complex, immunoreactive neurons were evenly distributed in all layers, whereas in the entorhinal cortex, they were accumulated in external layers above the lamina dissecans. Distinct bands of calretinin-positive fibers occupied the supragranular zone of the molecular layer in dentate gyrus, the pyramidal cell layer of the CA2 area in Ammon's horn and the upper two layers of presubiculum. The majority of calretinin-immunoreactive neurons were small, bipolar or fusiform neurons with a dendritic tree oriented parallel to the dendrites of principal cells (granule cells in dentate gyrus and pyramidal neurons elsewhere). Dendrites were smooth or sparsely spiny, displaying small spines of conventional type. Co-existence studies showed that these neurons were completely devoid of other calcium-binding proteins, parvalbumin and calbindin. Electron microscopic analysis revealed somata of immunoreactive neurons which contained a large nucleus and a small cytoplasmic rim, which contained only few organelles. The nucleus displayed deep infoldings and intranuclear rods. Input synapses of immunoreactive neurons were rare both on somata and dendrites and large surface areas were frequently apposed by glial processes. This was very prominent in the dentate gyrus and Ammon's horn. Axons of calretinin-positive neurons were thin, arborized in all layers and had small varicosities. Their terminals formed symmetric synaptic contacts mainly with dendrites and less frequently with somata of principal cells. Axon terminals of calretinin-immunoreactive fiber bundles in the supragranular layer, as well as in the pyramidal layer of the CA2 area, formed asymmetric synaptic contacts with dendritic shafts. In addition, they established asymmetric axospinous and axosomatic synaptic contacts with granule cells of the dentate gyrus. In the presubiculum, the calretinin-positive axon bundle included a large number of immunoreactive myelinated axons, as well as axon terminals. The characteristic location and features of synapses suggests that these fibers derive from extra-hippocampal afferents (Nitsch, R. and Leranth C. (1993) Neuroscience 55, 797-812) and not from the calretinin-immunoreactive neurons of the hippocampal formation.

Calcium-binding proteins in the inner ear of Xenopus laevis (Daudin)

Parvalbumin, S-100, calbindin-D28K and calmodulin-immunoreactive sensory hair cells were located in the inner ear of tadpoles and mature frogs of Xenopus laevis (Daudin). The relative number of immunoreactive cells varied in different compartments of the inner ear, depending on the Ca-binding protein studied.

Corticosterone exacerbates kainate-induced alterations in hippocampal tau immunoreactivity and spectrin proteolysis in vivo

Aberrant elevations in intracellular calcium levels, promoted by the excitatory amino acid glutamate, may be a final common mediator of the neuronal damage that occurs in hypoxic-ischemic and seizure disorders. Glutamate and altered neuronal calcium homeostasis have also been proposed to play roles in more chronic neurodegenerative disorders, including Alzheimer's disease. Any extrinsic factors that may augment calcium levels during such disorders may significantly exacerbate the resulting damage. Glucocorticoids (GCs), the adrenal steroid hormones released during stress, may represent one such extrinsic factor. GCs can exacerbate hippocampal damage induced by excitotoxic seizures and hypoxia-ischemia, and we have observed recently that GCs elevate intracellular calcium levels in hippocampal neurons. We now report that the excitotoxin kainic acid (KA) can elicit antigenic changes in the microtubule-associated protein tau similar to those seen in the neurofibrillary tangles of Alzheimer's disease. KA induced a transient increase in the immunoreactivity of hippocampal CA3 neurons towards antibodies that recognize aberrant forms of tau (5E2 and Alz-50). The tau immunoreactivity appeared within 3 h of KA injection, preceded extensive neuronal damage, and subsequently disappeared as neurons degenerated. KA also caused spectrin breakdown, indicating the involvement of calcium-dependent proteases. Physiological concentrations of corticosterone (the species-typical GC of rats) enhanced the neuronal damage induced by KA and, critically, enhanced the intensity of tau immunoreactivity and spectrin breakdown. Moreover, the GC enhancement of spectrin proteolysis was prevented by energy supplementation, supporting the hypothesis that GC disruption of calcium homeostasis in the hippocampus is energetic in nature. Taken together, these findings demonstrate that neurofibrillary tangle-like alterations in tau, and spectrin breakdown, can be induced by excitatory amino acids and exacerbated by GCs in vivo.

A subpopulation of large calbindin-like immunopositive neurones is present in the hippocampal formation in food-storing but not in non-storing species of bird

The avian hippocampal formation (HP) is thought to play a role in the processing of spatial memory related to food-storing behaviour. The HP of two food-storing species (marsh tit (Parus palustris) and magpie (Pica pica)) and two non-storing species (great tit (Parus major) and jackdaw (Corvus monedula)) were compared following calbindin-like immunostaining. In the dorsal hippocampal region, both species of food-storing birds had larger calbindin-immunoreactive cells than did the two non-storing species. The fact that this association between storing behaviour and cell morphology is seen in two unrelated families of birds, the Paridae (marsh tit versus great tit) and Corvidae (magpie versus jackdaw) suggests that there may be a direct link between food-storing behaviour and the dorsal hippocampal calbindin-immunoreactive cell population.

Transient expression of calretinin during development of chick cerebellum. Comparison with calbindin-D28k

Calcium ions play a critical role in neural development. Insights into the ontogeny of Ca2+ homeostasis were gained by investigating the developmental expression of two E-F hand calcium-binding proteins. Calretinin and calbindin were monitored through their immunoreactivity in the developing chick cerebellum (from E6 to E20). Calbindin was detected from E13 and in Purkinje cells only. Intensity of labelling increased with Purkinje cell development. Calretinin presented a transitory immunoreactivity between E11 and E20 in the internal granular cell layer. This cell layer contains cells which will differentiate into Golgi and granular cells which are calretinin-negative in adult chick cerebellum. Calretinin immunoreactivity presented a peak (both in number of cells and in intensity) at E15 and fell dramatically after E20 while calbindin immunoreactivity was restricted to the Purkinje cells and increased with the development of these cells.

Altered calcium signaling and neuronal injury: stroke and Alzheimer's disease as examples

Several cellular signaling systems have been implicated in the neuronal death that occurs both in development ("natural" cell death) or in pathological conditions such as stroke and Alzheimer's disease (AD). Here we consider the possibility that neuronal degeneration in an array of disorders including stroke and AD arises from one or more alterations in calcium-regulating systems that result in a loss of cellular calcium homeostasis. A long-standing hypothesis of neuronal injury, the excitatory amino acid (EAA) hypothesis, is revisited in light of new supportive data concerning the roles of EAAs in stroke and the neurofibrillary degeneration in AD. Two quite new concepts concerning mechanisms of neuronal injury and death are presented, namely: 1) growth factors normally "stabilize" intracellular free calcium levels ([Ca2+]i) and protect neurons against ischemic/excitotoxic injury, and 2) aberrant processing of beta-amyloid precursor protein (APP) can cause neurodegeneration by impairing a neuroprotective function of secreted forms of APP (APPs) which normally regulate [Ca2+]i. Altered APP processing also results in the accumulation of beta-amyloid peptide which contributes to neuronal damage by destabilizing calcium homeostasis; in AD beta-amyloid peptide may render neurons vulnerable to excitotoxic conditions that accrue with increasing age (e.g., altered glucose metabolism, ischemia). Growth factors may normally protect neurons against the potentially damaging effects of calcium influx resulting from energy deprivation and overexcitation. For example, bFGF, NGF and IGFs can protect neurons from several brain regions against excitotoxic/ischemic insults. Growth factors apparently stabilize [Ca2+]i by several means including: a reduction in calcium influx; enhanced calcium extrusion or buffering; and maintenance or improvement of mitochondrial function. For example, bFGF can suppress the expression of a N-methyl-D-aspartate (NMDA) receptor protein that mediates excitotoxic damage in hippocampal neurons. Growth factors may also prevent the loss of neuronal calcium homeostasis and the increased vulnerability to neuronal injury caused by beta-amyloid peptide. Since elevated [Ca2+]i can elicit cytoskeletal alterations similar to those seen in AD neurofibrillary tangles, we propose that neuronal damage in AD results from a loss of calcium homeostasis. The data indicate that a variety of alterations in [Ca2+]i regulation may contribute to the neuronal damage in stroke and AD, and suggest possible means of preventing neuronal damage in these disorders.

Spatial calcium buffering in saccular hair cells

The potential importance of intracellular calcium-binding proteins in rapid and highly localized Ca2+ signalling is poorly understood. During fast synaptic transmission, which occurs at specialized active zones where Ca2+ diffuses only a few tens of nanometers from channels to neurotransmitter release sites, a cytoplasmic Ca2+ buffer would have to be extremely fast or present in millimolar concentrations to intercept a significant fraction of the calcium ions en route to their targets. Therefore, Ca2+ buffers have been presumed to be unimportant in fast exocytosis and another fast calcium-mediated process, electrical resonance in hair cells. Here I present evidence to the contrary by showing that hair cells in the frog sacculus contain millimolar concentrations of a mobile cytoplasmic calcium buffer that captures Ca2+ within a few microseconds after it enters through presynaptic Ca2+ channels and carries it away from the point of entry. This spatial buffering reduces the presynaptic free Ca2+ by up to 60 per cent and probably restricts the region in which the internal calcium ion concentration exceeds 1 microM to within < 250 nm of each synaptic site. The buffer can thus influence both electrical resonance and synaptic transmission. Calbindin-D28K or a related protein may serve as the mobile calcium buffer, an action similar to its function in transporting Ca2+ across intestinal epithelial cells.

Differential localization of NADPH-diaphorase and calbindin-D28k within the cholinergic neurons of the basal forebrain, striatum and brainstem in the rat, monkey, baboon and human

The localization of Calbindin-D28k and NADPH-diaphorase in the cholinergic neurons of the basal forebrain, striatum and brainstem was investigated in the rat, monkey, baboon and human using calbindin and choline acetyltransferase immunohistochemistry and NADPH-diaphorase histochemistry. Considerable regional and species-specific variations were observed. Double-stained sections demonstrated that NADPH-diaphorase activity occurred in as much as 20-30% of basal forebrain cholinergic neurons in the rat but in virtually none of those neurons in the monkey, baboon or human. In all of the species studied, virtually every cholinergic neuron within the pedunculopontine and laterodorsal tegmental nuclei contained NADPH-diaphorase activity, while none of the cholinergic neurons of the striatum did so. In the rat brain, calbindin immunoreactivity was not present in any of the cholinergic neurons of the basal forebrain, while in the primate brain virtually all of the basal forebrain cholinergic neurons were also calbindin-positive. None of the cholinergic neurons of the striatum, pedunculopontine nucleus or laterodorsal tegmental nucleus were found to be calbindin-positive in any of the species examined. These results demonstrate major species-specific differences in the cytochemical signatures of the basal forebrain cholinergic neurons, in contrast to the cholinergic neurons of the striatum and brainstem, which displayed little interspecies variation with respect to the markers that were used in this study. Our findings also suggest that caution must be exercised in using results from studies of rodent basal forebrain cholinergic systems to infer the role of this system in the primate brain.

Neuronal localization in the rat brain of the messenger RNA encoding calcyphosine, a new calcium-binding protein

The cDNA encoding calcyphosine, a new calcium-binding protein of the calmodulin superfamily which is regulated by cAMP, has been cloned in the dog thyroid (EMBO J., 8 (1989) 111-116). By in situ hybridization with synthetic oligonucleotides, we here demonstrate for the first time its neuronal localization in the rat brain. Hybridization signal was detected in all the olfactory areas; in pyramidal and non pyramidal-shaped neurons in the different layers of the cerebral cortex, especially the superficial ones; in the pyramidal cells of the different sectors of the Ammon's horn and in the granule cells of the dentate gyrus of the hippocampus; in the subiculum; in the medium-sized and large neurons of the different quadrants of the caudate-putamen and accumbens and in the cerebellar Purkinje cells. Hybridization was also observed to a lesser extent in the majority of the neurons in the basal areas of the forebrain, including septum, nucleus of the diagonal band and amygdala; in the globus pallidus, entopeduncular nucleus, substantia nigra pars reticulata and compacta, ventral tegmental area; in the subthalamic nucleus; in the thalamus; in the hypothalamus; in the brainstem and in the upper cervical spinal cord. In addition to its neuronal localization, calcyphosine mRNA was also found in ependymal cells. The non-detection of positive cells in the white matter was not in favor of prominent glial localization, although it does not exclude it.

Distribution of calcium binding protein mRNAs in rat cerebellar cortex

The distribution of three calcium binding protein mRNAs in the rat cerebellar cortex was investigated using alkaline phosphatase labelled specific antisense oligodeoxynucleotide probes. Calbindin D28k mRNA was detected in the Purkinje cells, parvalbumin mRNA was located in the Purkinje cells and also in basket/stellate cells of the molecular layer. Calretinin in contrast was found only in the granule cell layer. Use of multiple alkaline phosphatase (AP)-labelled oligodeoxynucleotides resulted in an increase in signal strength and reduced detection time with no increase in background staining indicating the utility of these enzyme labelled probes for non-isotopic in situ.

Calretinin-immunoreactive neocortical interneurons are unaffected in Alzheimer's disease

Recent studies have revealed that select neuronal populations may display a differential sensitivity to degeneration in Alzheimer's disease. For example, large pyramidal neurons have been shown to be vulnerable, whereas small, local circuit neurons appear to be resistant to the pathologic process. More significantly, interneurons that contain the calcium-binding proteins parvalbumin and calbindin are particularly resistant to degeneration in Alzheimer's disease. Using a polyclonal antibody to the calcium-binding protein calretinin, we analyzed the possible changes in the subset of interneurons containing this protein in two neocortical areas that are generally devastated in Alzheimer's disease. In the prefrontal cortex as well as in the inferior temporal cortex, we observed no difference in the density of calretinin-immunoreactive neurons in Alzheimer's disease brains as compared to control cases. Moreover, the cellular morphology of these neurons was well preserved in the Alzheimer's disease cases. These data suggest that calretinin-immunoreactive neurons, like other calcium-binding protein-containing interneurons, are resistant to degeneration in Alzheimer's disease. The results support the notion that the pathological process in Alzheimer's disease involves specific cellular populations sharing particular morphological and neurochemical characteristics. In addition, it is possible that the presence of calcium-binding proteins confers a certain degree of resistance to degeneration in specific neuronal subsets.

Modulation of calcium current, intracellular calcium levels and cell survival by glucose deprivation and growth factors in hippocampal neurons

Basic fibroblast growth factor (bFGF) and nerve growth factor (NGF) can protect CNS neurons against ischemic/excitotoxic insults, but the mechanism of action is unknown. Imaging of the calcium indicator dye fura-2 and whole-cell patch clamp recordings of calcium currents were used to examine the mechanisms whereby hypoglycemia damages and growth factors protect cultured rat hippocampal neurons. When cultures were deprived of glucose, massive neuronal death occurred 16-24 h following the onset of hypoglycemia. Early hypoglycemia-induced changes included calcium current inhibition and a reduction in intracellular free calcium levels ([Ca2+]i) without morphological signs of neuronal damage. Later changes included a large elevation of [Ca2+]i which was causally involved in neuronal damage. NGF and bFGF prevented or reduced both the early and later responses to hypoglycemia. The growth factors increased calcium (barium) current and [Ca2+]i to normal limits during the early stages of hypoglycemia and prevented the later elevation in [Ca2+]i and neuronal damage. Nifedipine, but not omega-conotoxin, blocked calcium currents. The increased calcium current caused by the growth factors was apparently not sufficient to protect neurons against hypoglycemic damage since K+ depolarization during the early stages of hypoglycemia did not prevent and, in fact exacerbated, the subsequent neuronal damage. In addition, exposure of neurons to K+, NGF or bFGF only during the first 1 h of hypoglycemia did not protect against hypoglycemic damage. Taken together, the data suggest that neurons initially respond to hypoglycemia with a reduction in calcium currents which may provide a means to maintain [Ca2+]i within a concentration range conducive to cell survival. Prolonged energy deprivation eventually results in a failure of calcium extrusion systems, glutamate receptor activation and a loss of neuronal calcium homeostasis. Taken together, the data indicate that the mechanism of growth factor protection against energy deprivation involves prevention of the late rise in [Ca2+]i.

Reduction of calbindin-28k mRNA levels in Alzheimer as compared to Huntington hippocampus

Disturbances in calcium homeostasis have been observed to be associated with Alzheimer's and other neurodegenerative diseases. Increased total calcium levels and decreased levels of calcium binding proteins have been found in Alzheimer brain tissue. However, the mechanism behind these disturbances remain unknown. In situ hybridization with tritiated antisense RNA probes for the calcium binding proteins, calbindin-28k and calmodulin, was used to examine the expression of genes coding for these proteins in Alzheimer and Huntington brain tissues matched for age, agonal process and autopsy interval. mRNA levels for calbindin-28k were reduced by 35% in CA1 and CA2 regions of Alzheimer hippocampus, as compared to Huntington control. In contrast, calmodulin expression was unchanged in CA1 but reduced by 30% in CA2. mRNA expression of calbindin-28k and calmodulin in Alzheimer temporal cortex did not differ from control. There were no significant differences in calcium binding protein message levels in cerebellar Purkinje cells between Alzheimer and Huntington control. There was no correlation between calcium binding protein message levels and brain weight, autopsy interval, patient age or the extent of neurofibrillary degeneration. Instead, decreased calbindin-28k expression in Alzheimer-affected hippocampus was due to an increase in the percentage of neurons expressing lower message levels for these proteins.

Calbindin-D28k immunoreactivity and selective vulnerability to ischemia in the dentate gyrus of the developing rat

Hippocampal dentate granule cells normally express the calcium-binding protein calbindin-D28k and, in the adult, are the hippocampal neurons least vulnerable to an ischemic insult. We evaluated hippocampal structure 2-3 days after hypoxic/ischemic insult at postnatal day 7-10, and discovered that, unlike adult granule cells, developing granule cells were irreversibly injured. Localization of calbindin-D28k-like immunoreactivity (LI) revealed that the vulnerable cells were the immature granule cells at the base of the cell layer that were not yet calbindin-immunoreactive. Adjacent granule cells that did not die in response to the hypoxic/ischemic insult were calbindin-immunoreactive. Whether the lack of calbindin-LI in immature granule cells is causally related to their vulnerability, or is a coincidental reflection of cellular immaturity, remains to be determined.

Calcium-binding proteins in the chick Edinger Westphal nucleus

It has been suggested that the calcium-binding proteins, parvalbumin and calbindin-D28K, are involved in the control of intracellular calcium levels but their exact functions are unknown. Immunoreactivity for parvalbumin has been associated with rapidly firing cells, while calbindin has been implicated in protecting neurons from excitotoxicity. Since the chick Edinger Westphal nucleus contains two populations of neurons with different firing patterns, parvalbumin and calbindin immunoreactivities were examined in the Edinger Westphal nuclei of posthatch chicks to determine whether a particular subpopulation of neurons is associated with either protein. Moderate levels of parvalbumin immunoreactivity were found consistently associated with repetitively firing neurons in the lateral Edinger Westphal nucleus. In contrast, medial neurons expressed much lower levels of parvalbumin immunoreactivity. Many medial neurons were negative for parvalbumin although occasionally a few medial neurons stained as strongly as lateral neurons. Definitive calbindin immunoreactivity was absent from Edinger Westphal nuclei despite robust staining of cells in other parts of the brainstem and in control sections of cerebellum.

Calbindin D-28K in the dopaminergic mesocortical projection of a monkey (Aotus trivirgatus)

Injections of fluorescent dyes were made in the prefrontal and motor cortex of owl monkeys and retrogradely labeled neurons in the mesencephalon were analyzed for tyrosine hydroxylase and calbindin-D28K immunostaining. Numbers of mesocortical dopaminergic neurons in the dorsal substantia nigra compacta and in the ventral tegmental area also contain calbindin-D28K. This cortically projecting calbindin-D28K containing subpopulation of the dopaminergic mesencephalic cells may be characterized by different electrophysiological properties and a lesser vulnerability to cell death.

Modulation of a neuronal calmodulin mRNA species in the rat brain stem by reserpine

Reserpine evokes transsynaptic impulse activity by depleting catecholaminergic neurotransmitters in the rat brain. Previous studies suggest a relationship between catecholaminergic activity and calmodulin concentration. In this report we employ Northern blot analysis to examine the effect of a single subcutaneous injection of reserpine on levels of calmodulin mRNA species which are preferentially expressed in neurons of the rat brain. Regional differences in mRNA levels were also investigated by in situ hybridization and drug-induced changes were noted particularly in specific regions of the rat brain stem. The riboprobe used in the in situ hybridization study recognized a 4.0 kilobase neuronal calmodulin mRNA species (NGB1), which was derived from the rat CaM1 gene. A calmodulin radio-immunoassay was utilized to demonstrate a drug-induced increased in calmodulin protein levels in a region which included the brain stem.

Rapid and protracted phases of retinal ganglion cell loss follow axotomy in the optic nerve of adult rats

To investigate the short- and long-term effects of axotomy on the survival of central nervous system (CNS) neurons in adult rats, retinal ganglion cells (RGCs) were labelled retrogradely with the persistent marker diI and their axons interrupted in the optic nerve (ON) by intracranial crush 8 or 10 mm from the eye or intraorbital cut 0.5 or 3 mm from the eye. Labelled RGCs were counted in flat-mounted retinas at intervals from 2 weeks to 20 months after axotomy. Two major patterns of RGC loss were observed: (1) an initial abrupt loss that was confined to the first 2 weeks after injury and was more severe when the ON was cut close to the eye; (2) a slower, persistent decline in RGC densities with one-half survival times that ranged from approximately 1 month after intraorbital ON cut to 6 months after intracranial ON crush. A small population of RGCs (approximately 5%) survived for as long as 20 months after intraorbital axotomy. The initial loss of axotomized RGCs presumably results from time-limited perturbations related to the position of the ON injury. A persistent lack of terminal connectivity between RGCs and their targets in the brain may contribute to the subsequent, more protracted RGC loss, but the differences between intraorbital cut and intracranial crush suggest that additional mechanisms are involved. It is unclear whether the various injury-related processes set in motion in both the ON and the retina exert random effects on all RGCs or act preferentially on subpopulations of these neurons.

Different calcium-binding proteins identify subpopulations of vestibular ganglion neurons in the rat

Vestibular neurons were studied by cytochrome oxidase (CO) histochemistry and by immunocytochemistry using antibodies against parvalbumin (PV), calbindin (CaBP), calretinin (CaR) and 160 KD neurofilament protein (NF). All the neurons present a high level of CO activity and a high content of PV. CaBP and CaR are restricted to a specific population of about 16% of the neurons and are among the largest ones. The latter neurons also have a high density of NF 160 KD protein. In conclusion the biochemical characteristics of the vestibular ganglion neurons are discussed in relation to their morphological and physiological properties.

Glutathione peroxidase, glial cells and Parkinson's disease

Hyperoxidation phenomena are suspected to be involved in dopaminergic cell death in Parkinson's disease, which affects preferentially the neuromelanin-containing dopaminergic neurons of the substantia nigra. Glutathione peroxidase is the major protective enzyme against hydrogen peroxide toxicity. The distribution of glutathione peroxidase-containing cells was investigated by immunohistochemistry in the midbrain of four control subjects and four patients with Parkinson's disease. (1) Glutathione peroxidase-like immunoreactivity was detected exclusively in glial cells. (2) In control brains, the density of glutathione peroxidase-positive cells was higher in the vicinity of the dopaminergic cell groups known to be resistant to the pathological process of Parkinson's disease. (3) In Parkinson's disease, an increased density of glutathione peroxidase-immunostained cells was observed, surrounding the surviving dopaminergic neurons. The increase in glutathione peroxidase-containing cells was correlated with the severity in dopaminergic cell loss in the respective cell groups. The data suggest that in control brains, a low density of glutathione peroxidase-positive cells surround the dopaminergic neurons the most vulnerable to Parkinson's disease, and that in parkinsonian brains, the increased number of glutathione peroxidase-positive cells may contribute to protect neurons against pathological death. Thus, the amount of glutathione peroxidase protein-containing cells may be critical for a protective effect against oxidative stress, although it cannot be excluded that the level of the enzyme activity remains the crucial factor.

Ca(2+)-binding proteins in rat synaptic fractions surveyed by the 45Ca2+ overlay method

Ca(2+)-binding proteins in the synaptic and subsynaptic fractions (P2, synaptosome, synaptic plasma membrane, and postsynaptic density [PSD]-enriched fractions) and soluble fraction of rat brain were surveyed by a 45Ca2+ overlay method. The PSD-enriched fraction from cerebral cortex contained two major Ca(2+)-binding proteins (55,000 M(r) and 19,000 M(r)) and a distinct group (in 140,000 M(r) region), and two minor ones (66,000 M(r) and 16,000 M(r)); and the fraction from cerebellum contained two (55,000 M(r) and 19,000 M(r)). The proteins with 55,000 M(r) and 19,000 M(r) were identified as tubulin and calmodulin, respectively, and present in all the fractions investigated. The Ca(2+)-binding proteins of 140,000 M(r) region were found only in the PSD-enriched fraction isolated from cerebral cortex: neither the PSD-enriched fraction isolated from cerebellum nor other subcellular fractions prepared from cerebral cortex and cerebellum contained the proteins. The 140,000 M(r) Ca(2+)-binding proteins were the substrates for the Ca2+/calmodulin-dependent protein kinase II associated with PSD, and no change in the Ca(2+)-binding was detected by the 45Ca2+ overlay method after phosphorylation of the proteins by the protein kinase. The 16,000 M(r) Ca(2+)-binding protein might be the beta-subunit of calcineurin. Calretinin and calbindin-D28k were also detected as Ca(2+)-binding proteins in the soluble fractions of both cerebral cortex and cerebellum.

Calretinin in rat ovary: an in situ hybridization and immunohistochemical study

Calretinin is a cytosolic calcium-binding protein of the calmodulin superfamily, with high homology with calbindin D28k. The only cells in which calretinin has been described so far are neurons, in the central nervous system and in retina. In the present work, we describe the expression of the calretinin gene in the interstitial cells of rat ovary. Immunohistochemistry, using a calretinin-specific antibody, allowed to detect the protein from 19 days after birth. Western blot from ovary homogenates confirmed the labelling of a 29 kDa band, the size of calretinin. In situ hybridization confirmed immunochemical data; calretinin transcripts were clearly shown in the same cell population. This represents the first description of calretinin outside the nervous system. Its function in ovary remains to be determined.