Differential effects of excitatory amino acids on mesencephalic neurons expressing either calretinin or tyrosine hydroxylase in primary cultures

Age-dependent neuroprotective effect of an SK3 channel agonist on excitotoxity to dopaminergic neurons in organotypic culture

Background

Small conductance, calcium-activated (SK3) potassium channels control the intrinsic excitability of dopaminergic neurons (DN) in the midbrain and modulate their susceptibility to toxic insults during development.

Methods

We evaluated the age-dependency of the neuroprotective effect of an SK3 agonist, 1-Ethyl-1,3-dihydro-2H-benzimidazol-2-one (1-EBIO), on Amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) excitotoxicity to DN in ventral mesencephalon (VM) organotypic cultures.

Results

Most tyrosine hydroxylase (TH)+ neurons were also SK3+; SK3+/TH- cells (DN+) were common at each developmental stage but more prominently at day in vitro (DIV) 8. Young DN+ neurons were small bipolar and fusiform, whereas mature ones were large and multipolar. Exposure of organotypic cultures to AMPA (100 μm, 16 h) had no effect on the survival of DN+ at DIV 8, but caused significant toxicity at DIV 15 (n = 15, p = 0.005) and DIV 22 (n = 15, p<0.001). These results indicate that susceptibility of DN to AMPA excitotoxicity is developmental stage-dependent in embryonic VM organotypic cultures. Immature DN+ (small, bipolar) were increased after AMPA (100 μm, 16 h) at DIV 8, at the expense of the number of differentiated (large, multipolar) DN+ (p = 0.039). This effect was larger at DIV 15 (p<<<0.0001) and at DIV 22 (p<<<0.0001). At DIV 8, 30 μM 1-EBIO resulted in a large increase in DN+. At DIV 15, AMPA toxicity was prevented by exposure to 30 μM, but not 100 μM 1-EBIO. At DIV 22, excitotoxicity was unaffected by 30 μM 1-EBIO, and partially reduced by 100 μM 1-EBIO.

Conclusion

The effects of the SK3 channel agonist 1-EBIO on the survival of SK3-expressing dopaminergic neurons were concentration-dependent and influenced by neuronal developmental stage.

Glial cell-line derived neurotrophic factor is essential for electroconvulsive shock-induced neuroprotection in an animal model of Parkinson's disease

Sustained motor improvement in human patients with idiopathic Parkinson's disease has been described following electroconvulsive shock (ECS) treatment. In rats, ECS stimulates the expression of various trophic factors (TFs), some of which have been proposed to exert neuroprotective actions. We previously reported that ECS protects the integrity of the rat nigrostriatal dopaminergic system against 6-hydroxydopamine (6-OHDA)-induced toxicity; in order to shed light into its neuroprotective mechanism, we studied glial cell-line derived neurotrophic factor (GDNF) levels (the most efficient TF for dopaminergic neurons) in the substantia nigra (SN) and striatum of 6-OHDA-injected animals with or without ECS treatment. 6-OHDA injection decreased GDNF levels in the SN control animals, but not in those receiving chronic ECS, suggesting that changes in GDNF expression may participate in the ECS neuroprotective mechanism. To evaluate this possibility, we inhibit GDNF by infusion of GDNF function blocking antibodies in the SN of 6-OHDA-injected animals treated with ECS (or sham ECS). Animals were sacrificed 7 days after 6-OHDA infusion, and the integrity of the nigrostriatal system was studied by tyrosine hydroxylase immunohistochemistry and Cresyl Violet staining. Neuroprotection observed in ECS-treated animals was inhibited by GDNF antibodies in the SN. These results robustly demonstrate that GDNF is essential for the ECS neuroprotective effect observed in 6-OHDA-injected animals.

Functional reduction of SK3-mediated currents precedes AMPA-receptor-mediated excitotoxicity in dopaminergic neurons

In primary cultures of mesencephalon small-conductance calcium-activated potassium channels (SK) are expressed in dopaminergic neurons. We characterized SK-mediated currents (I(SK)) in this system and evaluated their role on homeostasis against excitotoxicity. I(SK) amplitude was reduced by the glutamatergic agonist AMPA through a reduction in SK channel number in the membrane. Blockade of I(SK) for 12 h with apamin or NS8593 reduced the number of dopaminergic neurons in a concentration-dependent manner. The effect of apamin was not additive to AMPA toxicity. On the other hand, two I(SK) agonists, 1-EBIO and CyPPA, caused a significant reduction of spontaneous loss of dopaminergic neurons. 1-EBIO reversed the effects of both AMPA and apamin as well. Thus, I(SK) influences survival and differentiation of dopaminergic neurons in vitro, and is part of protective homeostatic responses, participating in a rapidly acting negative feedback loop coupling calcium levels, neuron excitability and cellular defenses. This article is part of a Special Issue entitled 'Trends in neuropharmacology: in memory of Erminio Costa'.

Protection of dopaminergic neurons by electroconvulsive shock in an animal model of Parkinson’s disease

Electroconvulsive shock (ECS) improves motor function in Parkinson's disease. In rats, ECS stimulates the expression of various factors some of which have been proposed to exert neuroprotective actions. We have investigated the effects of ECS on 6-hydroxydopamine (6-OHDA)-injected rats. Three weeks after a unilateral administration of 6-OHDA, 85-95% nigral dopaminergic neurons are lost. Chronic ECS prevented this cell loss, protect the nigrostriatal pathway (assessed by FloroGold retrograde labeling) and reduce motor impairment in 6-OHDA-treated animals. Injection of 6-OHDA caused loss of expression of glial cell-line derived neurotrophic factor (GDNF) in the substantia nigra. Chronic ECS completely prevented this loss of GDNF expression in 6-OHDA-treated animals. We also found that protected dopaminergic neurons co-express GDNF receptor proteins. These results strongly suggest that endogenous changes in GDNF expression may participate in the neuroprotective mechanism of ECS against 6-OHDA induced toxicity.

Effects of Ginkgolide B on 6-OHDA-induced apoptosis and calcium over load in cultured PC12

Ginkgolide B, one of the major components of Ginkgo biloba extracts, is a potent platelet-activating factor (PAF) receptor antagonist, which is also regarded as having neuroprotective effects on the CNS. The aim of this research is to observe the effects of Ginkgolide B on the PC12 apoptosis induced by 6-hydroxydopamine (6-OHDA) and to explore whether these effects are related to the changes of intracellular Ca(2+) and Calbindin D28K mRNA in PC12 cells. In the present work, the damage of PC12 cells was induced by 100 microM 6-OHDA. The cells survival rate was examined by MTT assays. The intracellular free calcium concentration in PC12 cells was measured by using the fluorescent Ca(2+) indicator fluo-3/AM. Semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) was employed to determine the expression of Calbindin D28K mRNA in PC12. The data show that the Ginkgolide B inhibited PC12 cells apoptosis induced by 6-OHDA in a dose-dependent manner, and decreased the activity of caspase-3. In addition, Ginkgolide B increased the expression of Calbindin D28K mRNA and inhibited 6-OHDA-induced elevation in the intracellular calcium concentration. Our results showed that the Ginkgolide B inhibited the apoptosis of PC12 induced by 6-OHDA, and the protective effects of Ginkgolide B on PC12 cells are mediated, at least in part, by up-regulating the Calbindin D28K mRNA and by decreasing the intracellular calcium concentration.

Ultrastructural characterization of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-induced cell death in embryonic dopaminergic neurons

Developing neuronal populations undergo significant attrition by natural cell death. Dopaminergic neurons in the substantia nigra pars compacta undergo apoptosis during synaptogenesis. Following this time window, destruction of the anatomic target of dopaminergic neurons results in dopaminergic cell death but the morphology is no longer apoptotic. We describe ultrastructural changes that appear unique to dying embryonic dopaminergic neurons. In primary cultures of mesencephalon, death of dopaminergic neurons is triggered by activation of glutamate receptors sensitive to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and differs ultrastructurally from both neuronal apoptosis or typical excitotoxicity. AMPA causes morphological changes selectively in dopaminergic neurons, without affecting other neurons in the same culture dishes. Two hours after the onset of treatment swelling of Golgi complexes is apparent. At 3 h, dopaminergic neurons display loss of membrane asymmetry (coinciding with commitment to die), as well as nuclear membrane invagination, irregular aggregation of chromatin, and mitochondrial swelling. Nuclear changes continue to worsen until loss of cytoplasmic structures and cell death begins to occur after 12 h. These changes are different from those described in neurons undergoing either apoptosis or excitotoxic death, but are similar to ultrastructural changes observed in spontaneous death of dopaminergic neurons in the natural mutant weaver mouse.

Neuroprotective effect of nitric oxide against NMDA-induced neurotoxicity in the rat retina is associated with tyrosine hydroxylase expression

N-methyl-D-aspartate (NMDA) may affect dopaminergic cells, which contain tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine synthesis. To clarify the involvement of TH in the neuroprotective effects of nitric oxide (NO), we investigated whether NMDA alters TH mRNA and TH protein levels and whether NO inhibits NMDA-induced changes in the rat retina. Dopamine levels in the retina were measured by high-performance liquid chromatography (HPLC). Reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR showed that intravitreal injection of NMDA caused a significant reduction in TH mRNA levels in the retina. Similarly, Western blot analysis showed that NMDA decreased the production of TH protein. These reductions in TH mRNA and TH protein levels were attenuated by concomitant injection of NOC 18, an NO donor. HPLC analysis showed that NMDA reduced dopamine levels in the retina and that NO attenuated this reduction. Furthermore, morphological analysis showed that NO prevents NMDA-induced neurotoxicity through dopamine D(1) receptors. These results suggest that the neuroprotective effect of NO may be associated with the induction of TH expression and increased levels of dopamine.

Nuclear translocation of nuclear transcription factor-kappa B by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors leads to transcription of p53 and cell death in dopaminergic neurons

We describe a new molecular mechanism of cell death by excitotoxicity mediated through nuclear transcription factor kappa B (NF kappa B) in rat embryonic cultures of dopaminergic neurons. Treatment of mesencephalic cultures with alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) resulted in a number of changes that occurred selectively in dopaminergic neurons, including persistent elevation in intracellular Ca(2+) monitored with Fura-2, and a significant increase in intramitochondrial oxidation of dihydrorhodamine 123, probably associated with transient increase of mitochondrial permeability, cytochrome c release, nuclear translocation of NF kappa B, and transcriptional activation of the oncogene p53. Interruption of any of these steps by specific antagonists prevented neurite pruning and programmed cell death. In contrast, cell death was not prevented by caspase antagonists and only partly prevented by nitric-oxide synthase inhibitors. This signal transduction pathway might be a contributing mechanism in ongoing neuronal death in Parkinson disease.

Differential changes of calcium binding proteins in the rat striatum after kainic acid-induced seizure

It has been suggested that calcium binding proteins protect against Ca2+ overload, thus rendering neurons more resistant against excitotoxicity. The influence of kainic acid, which induces status epilepticus, on the expressions of calbindin D28k, parvalbumin and calretinin was examined in the rat striatum by immunohistochemistry and microdensitometry. At 1, 3 and 6 days after kainic acid-induced seizure, the number of calretinin-positive neurons in the striatum was significantly lower than in control rats. However, no significant difference was observed in the number of calbindin D28k- and parvalbumin-positive neurons in control and seizure rats. At 1, 3 and 6 days after seizure the optical densities of calretinin- and parvalbumin-positive neurons in the striatum were significantly lower than in control rats. Our finding concerning the selective loss of calretinin-positive neurons in seizure groups suggests that calcium binding proteins in the striatum have differential vulnerabilities to kainic acid-induced seizure.

Calretinin and calbindin D-28k delay the onset of cell death after excitotoxic stimulation in transfected P19 cells

In some neurological diseases, injury to neurones reflects an over-stimulation of their receptors for excitatory amino acids. This response may disturb the Ca(2+)-homeostasis and lead to a pronounced and sustained increase in the intracellular concentration of this ion. On the basis of data derived from correlative studies, calcium-binding proteins have been postulated to play a protective role in these pathologies. We tested, directly, the capacity of the three calcium-binding proteins calretinin (CR), calbindin D-28k (CB) and parvalbumin (PV) to buffer [Ca(2+)], and to protect cells against excitotoxic death. We used P19 murine embryonic carcinoma cells, which can be specifically induced (by retinoic acid) to transform into nerve-like ones. The differentiated cells express functional glutamate-receptors and are susceptible to excitotoxic shock. Undifferentiated P19-cells were stably transfected with the cDNA for CR, CB or PV, induced to differentiate, and then exposed to NMDA, a glutamate-receptor agonist. The survival rates of clones expressing CR, CB or PV were compared with those of untransfected P19-cells using the lactate-dehydrogenase assay. CR- and CB-expressing cells were protected from death during the first 2 h of exposure to NMDA. This protection was, however, transient, and did not suffice to rescue P19-cells after prolonged stimulation. Two of the three PV-transfected clones raised were vulnerable to NMDA-induced excitotoxicity; the third, which expressed the lowest level of PV, was protected to a similar degree as that found for the CR- and CB-transfected clones. Our results indicate that in the P19-cell model, CR and CB can help to delay the onset of cell death after excitotoxic stimulation.

On the altered expression of tyrosine hydroxylase and calbindin-D 28kD immunoreactivities and viability of neurons in the ventral tegmental area of Tsai following injections of 6-hydroxydopamine in the medial forebrain bundle in the rat

Calbindin-D 28kD is a calcium binding protein reported to protect neurons from degeneration by buffering intracellular calcium. It is expressed in midbrain dopaminergic neurons reported to be relatively resistant to degeneration in Parkinson's disease and certain of its animal models. Lesions of the nigrostriatal pathway produced in rats following injection of 6-hydroxydopamine result in a neurochemical profile similar to that seen in patients with Parkinson's disease. In the present study, brains were processed to exhibit tyrosine hydroxylase- and calbindin-D 28kD immunoreactivities in sections through the ventral mesencephalon at 3, 7, 10, 14 and 21 days after 6-hydroxydopamine had been injected into the medial forebrain bundle. Numbers of ventral mesencephalic calbindin-D 28kD immunoreactive neurons were significantly reduced ipsilateral to the lesions at 3 days post-lesion and, following slight recovery, remained significantly depleted through post-lesion day 21. The densities of calbindin-D 28kD and tyrosine hydroxylase immunoreactive neurons were different only at the 3 day post-lesion time point, when the apparent loss of calbindin-D 28 kD immunoreactive profiles was significantly greater. A lesion-induced increase in the proportion of neurons exhibiting both calbindin-D 28kD and tyrosine hydroxylase immunoreactivities, expected if calbindin-D 28kD is neuroprotective, was observed in the substantia nigra, pars compacta, but not in the ventral tegmental area. It is concluded that, while the observed losses of tyrosine hydroxylase and calbindin-D 28kD immunoreactivities do not necessarily reflect neuronal degeneration, they are not consistent with CB confering a neuroprotective advantage in the ventral tegmental area following 6-OHDA lesions as administered in this study.

Calretinin-containing axons and neurons are resistant to an intrastriatal 6-hydroxydopamine lesion

Relative preservation of dopaminergic axons in patches and a subcallosal layer was observed in the dorsal, lateral and caudal striatum 4 weeks after intrastriatal injection of 6-hydroxydopamine (6-OHDA), a neurotoxin selective for catecholaminergic neurons. Since calcium binding proteins are reported to provide neuroprotective influence in neurons, differences in the distribution of the calcium binding proteins might be related to the different vulnerabilities of dopaminergic neurons and axons to neurotoxins. To address this possibility, we characterized patches of relatively dense tyrosine hydroxylase-immunoreactive (TH-IR) axons in intrastriatal 6-OHDA lesioned rats, focusing on two calcium binding proteins, calbindin (CB) and calretinin (CR). The patches and subcallosal layer of preserved dopaminergic axons in the striatum of rats lesioned with 6-OHDA contained CR, a 31-kDa calcium-binding protein, but interestingly not CB. Dopaminergic neurons containing CR in the substantia nigra pars compacta (SNpc) were relatively spared compared to those that did not contain CR. Taken together, our data indicate that dopaminergic axons and neurons containing CR in the nigrostriatal pathway are more resistant to 6-OHDA lesion than those that do not contain CR.

Differential vulnerabilities of substantia nigra catecholamine neurons to excitatory amino acid-induced degeneration in rat midbrain slices

Although differential vulnerability in different regions of the central nervous system is a characteristic feature of neurodegenerative disorders in vivo, its cellular basis is not well understood. In the present study we investigated whether catecholamine neurons in different regions of the substantia nigra (SN) are differentially vulnerable to excitatory amino acid-induced damage in a midbrain slice preparation. Rats were anesthetized by halothane inhalation and killed, the brain was rapidly removed, and 300-microm-thick midbrain slices were cut horizontally on a vibratome. The slices were incubated at 35 degrees C for 2 h in saline buffer containing either kainic acid (KA) or N-methyl-d-aspartate (NMDA) (10-50 microM). They were then fixed and cut into 30-microm sections that were coplanar with the horizontal slice. Individual catecholamine neurons were identified in these thin sections using an antibody to tyrosine hydroxylase coupled to diaminobenzidine. Catecholaminergic neurons in the dorsal and ventral tiers of the SN were readily identified by reference to an atlas of the distribution of catecholamine neurons in the horizontal plane. Using dendritic degeneration as a sensitive index of damage, and submaximal concentrations of KA and NMDA, we found that catecholamine neurons in the dorsal tier were more vulnerable than those in the ventral tier. For example, KA (10 microM) caused a significant reduction in the proportion of neurons with dendrites in the dorsal tier (from 60 to 34%) without altering the dendritic arbor of ventral tier neurons. After treatment with 50 microM KA, only 11% of dorsal tier neurons retained any dendrites while 45% of ventral tier neurons retained their dendrites. These differences were statistically significant (P<0.001). A similar differential vulnerability was apparent in slices treated with NMDA; neurons in the dorsal tier lost dendrites before detectable damage in the ventral tier. An understanding of the comparative anatomical, neurochemical, and physiological properties of vulnerable (dorsal tier) and resistant (ventral tier) catecholamine neurons in rat SN may provide significant insights into the mechanisms and treatment of neurodegenerative disorders involving catecholamine neurons.

Dendrite loss is a characteristic early indicator of toxin-induced neurodegeneration in rat midbrain slices

In rat brain substantia nigra catecholamine neurons in vitro, a sensitive indicator of excitatory amino-acid-induced damage is dendritic degeneration that precedes the loss of the cell body. The present study has shown that dendritic loss is not specific for excitatory amino acids and is an early indicator of neurodegeneration produced by numerous agents that initiate damage by different primary cellular actions. Rats were anesthetised by fluothane inhalation and killed, and the brain was rapidly removed. Three-hundred-micrometer-thick slices containing substantia nigra were incubated for 2 h at 35 degrees C in the presence or absence of kainic acid (50 microM), 1-methyl-4-phenylpyridinium ion (10 or 50 microM), ouabain (10 or 30 microM), 6-hydroxydopamine (10 or 100 microM), potassium cyanide (100 microM or 1 mM), or elevated extracellular potassium chloride (25, 50, or 100 mM). The slices were fixed and recut into thin sections (30 micrometer) and substantia nigra dopamine neurons were immunolabeled for tyrosine hydroxylase coupled to diaminobenzidine. Both the cell body and the extensive dendritic projections were immunolabeled. Each agent caused a similar pattern of toxicity including loss of tyrosine-hydroxylase-immunolabeled dendrites at lower concentrations and damage to, or disintegration of, the cell bodies at higher concentrations. For example, 100 microM potassium cyanide reduced the proportion of substantia nigra neurons which exhibited dendrites from 66 +/- 4% (SEM) in controls to 54 +/- 7%, without obvious changes in cell bodies. After 1 mM potassium cyanide, only 13 +/- 2% of substantia nigra neurons retained dendrites and cell bodies were shrunken or disintegrated. Loss of dendrites was also evident in substantia nigra neurons stained with cresyl violet or immunolabeled for microtubule-associated protein 2. The findings suggest that disruption of the dendritic arbor is an early indicator of neurodegeneration, irrespective of how this is initiated. The approach that we have developed may therefore prove valuable in investigating the mechanisms of degeneration of catecholamine neurons.

Calbindin-D 28kD immunofluorescence in ventral mesencephalic neurons labeled following injections of Fluoro-Gold in nucleus accumbens subterritories: inverse relationship relative to known neurotoxin vulnerabilities

The shell and core of the nucleus accumbens exhibit different vulnerabilities to neurotoxins. Calcium binding proteins are reported to offer some neuroprotection against excitotoxicity by suppressing or buffering intracellular calcium. Differences in the distributions of the calbindin-D 28kD (CB) and calretinin (CR) might be related to the different vulnerabilities to neurotoxins of dopaminergic neurons in the ventral mesencephalon that project to the core and medial shell of the nucleus accumbens. To address this possibility, Fluoro-Gold (FG) was injected into accumbens subterritories and numbers of retrogradely labeled neurons in the ventral tegmental area containing CB and CR immunoreactivities (ir) were expressed as a percentage of total numbers of labeled neurons. The perikaryal diameters and lengths of the immunoreactive dendrites of FG labeled neurons were also measured. About 70% and 35% of retrogradely labeled cells observed following core and medial shell injections, respectively, exhibited CB immunoreactivity. Differences were not observed in the percentages of FG labeled cells exhibiting CR immunoreactivity following medial shell (13%) and core (15%) injections. The mean perikaryal diameters and median summed lengths of dendrites of retrogradely labeled neurons containing CB were smaller than in labeled neurons lacking CB following injections in both core and medial shell of the nucleus accumbens. The data indicate that the different 6-hydroxydopamine (6-OHDA) vulnerabilities of ventral mesencephalic dopaminergic neurons are not obviously related to the presence of CB and CR.

Odor-induced, activity-dependent transneuronal gene induction in vitro: mediation by NMDA receptors

Expression of tyrosine hydroxylase (TH) by juxtaglomerular (JG) neurons of the olfactory bulb (OB) requires innervation of the bulb by olfactory receptor neurons (ORNs). ORN lesion selectively downregulates TH in JG neurons. In reversible odor deprivation, TH expression is downregulated as the naris is closed and then upregulated upon naris reopening. The mechanism or mechanisms regulating this dependence are unknown. TH expression could be regulated by trophic factor release and/or synaptic activity from ORN terminals. We investigated TH expression in cocultures of dissociated postnatal rat OB cells and embryonic olfactory neuroepithelium (OE) slice explants. TH-positive neurons in control dissociated OB cell cultures alone comprise only a small fraction of the total population of cells present in the culture. However, when OE slice explants are cocultured with dispersed OB cells, there is a mean 2.4-fold increase in the number of TH-positive neurons. ORNs in vivo use glutamate as a neurotransmitter. Broad spectrum excitatory amino acid antagonists (kyurenic acid) or selective antagonists of the NMDA receptor (APV) both prevent induction of TH expression in OE-OB cocultures. Furthermore, pulse application of NMDA stimulates TH expression in OB neurons in the absence of OE. In vitro, OB TH neurons express NMDA receptors, suggesting that NMDA stimulation is acting directly on TH neurons. Exposure of OE explants to natural odorants results in upregulation of TH, presumably through increased ORN activity, which could be blocked by APV. These findings indicate that odorant-stimulated glutamate release by ORN terminals regulates TH expression via NMDA receptors on JG dopaminergic neurons.

Effect of lead on cytoskeletal proteins expressed in E14 mesencephalic primary cultures

Several lines of evidence indicated that Pb exposure in vivo and in vitro altered neurite morphology in central and peripheral neurons. The present report shows that neurite length in mesencephalic primary cultures, consisting of neurons and glia, was decreased by Pb exposure when serum factors, presumably essential for glial functions, were absent in the culture medium. We studied whether a serum factor might control the mechanisms involved in the uptake and accumulation of Pb and its effect on cytoskeleton proteins. The total amount of Pb taken up in cell cultures was measured by atomic absorption spectroscopy and appeared to be down-regulated by a non-albumin-like serum component. In presence of serum, Pb exposure failed to alter cytoskeletal proteins. Instead, in serum-free neurobasal medium, Pb uptake failed to reach saturation within 6 h. Western blot analysis showed that the tau, 280 kDa MAP-2b, 70 kDa MAP-2c and GAP-43 protein bands were decreased 24 h after a 3 h exposure to 3 or 6 microM Pb in absence of serum. However, if cultures were maintained in serum-containing media after a 3 h Pb exposure without serum, the immunoblots did not differ from those of controls. It can be inferred that a serum factor prevents cytoskeletal protein alterations by Pb. In serum free medium, Pb that is primarily scavenged by the metallothionein I/II isoforms present in glial cells, may bind to thiol residues of proteins involved in either oxidative stress response or transcriptional regulation of cytoskeletal proteins.

Brain-derived neurotrophic factor stimulates neurite outgrowth in a calretinin-enriched neuronal culture system

A calretinin enriched cell culture system which comprised approximately 40% of the total neuronal population of the E14 rat embryo was established from the region of the thalamic eminence (TE), and the effects of several neurotrophins on the neurite growth of calretinin-immunoreactive (CR-IR) neurons was investigated. A 4-day treatment of BDNF significantly increased the ratio of CR-IR to microtubule-associated protein 2-immunoreactive neurons at concentrations between 50 and 250 ng/ml. IGF-I at 100 ng/ml and TGF-alpha at 250 ng/ml also increased this ratio. None of the neurotrophins examined increased the number of primary neurites. BDNF did, however, increase the number of secondary neurites. BDNF-treated primary and secondary neurites were also significantly longer than neurites from neurons in control cultures. IGF-I elicited an increase in primary neurite length, but did not affect either number or length of secondary neurites. TGF-alpha had no effect on either number or length of the primary and secondary neurites. These results indicate that the maturation and development of CR-IR neurites is specifically affected by BDNF. It is suggested that BDNF increases the CR concentration above the threshold of detection by immunohistochemistry in cells and stimulates the sprouting of secondary CR-IR neurites.

A method for the rapid analysis of neuronal proportions and neurite morphology in primary cultures

This article provides basic guidelines for a rapid analysis of subpopulation proportions and neurite morphology in primary cultures. We describe, in E14 mesencephalic primary cultures, an immunohistochemical method for the simultaneous identification of multiple neuronal phenotypes and an estimation of the ratio of subpopulations. In addition, we describe the use of the Renaissance TSA-Direct kit (NEN, DuPont) to enhance the visualization of neurites when the antigen is in low abundance. Finally, a modified sholl analysis is used to rapidly and reliably estimate neurite number and length.

The mouse calretinin gene promoter region: structural and functional components

The 5' flanking region of the mouse calretinin gene was cloned and a 1.8 kbp region adjacent to exon 1 was sequenced. Putative upstream promoter and enhancer elements were identified, including appropriately positioned TATA and CAAT boxes (positions -50 and -68, respectively). There was considerable sequence and structural homology between mouse and human upstream elements. Neuron-restrictive activity was demonstrated via transfection of calretinin promoter-reporter constructs into primary embryonic mouse brain cultures expressing calretinin. In promoterless reporter constructs, the proximal upstream 1.5 kbp of the mouse calretinin gene boosted luciferase activity (up to 100-fold) exclusively in the neuronal population. Deletion analysis revealed the minimal promoter to be within the 95-bp proximal to the transcription start site. Transfections with SV40 promoter constructs in these cultures resulted in reporter gene expression predominantly in non-neuronal cells. Inserting the proximal 1.5 kbp of mouse calretinin upstream in SV40 promoter-reporter constructs reduced luciferase activity. Thus, calretinin upstream sequences increased reporter expression in cultured neurons and decreased expression from the SV40 promoter in non-neuronal cultured brain cells. The calretinin promoter contained relevant regulatory element consensus motifs and demonstrated in vitro neuron-restrictive bioactivity.

Development and survival of rat embryonic mesencephalic dopaminergic neurones in serum-free, antioxidant-rich primary cultures

Mesencephalic dopaminergic neurones typically require the presence of serum for their survival in culture. However, the present study, outlines how neurones from the rat ventral mesencephalon (E14-16) were successfully cultured in serum-free, antioxidant-rich Neurobasal medium supplemented with B27 components. Moreover, immunostaining with mouse monoclonal microtubule-associated protein 2 (MAP2) and glial fibrillary acidic protein (GFAP) from day 1 to 7 in vitro revealed these cultures were primarily neuronal (80-95%). Additionally, immunostaining with tyrosine hydroxylase (TH) revealed these cultures contained a relatively constant population of TH-positive neurones (5%) which were presumed to be dopaminergic. These primary cultures offer considerable advantages for the study of mesencephalic, TH-positive, dopaminergic neurones under conditions where milieu can be readily manipulated in the virtual absence of glia and without the confounding influence of serum.

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.

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.

Calcium-binding proteins in primate basal ganglia

This paper describes the distribution of the calcium-binding proteins calbindin-D28k. Parvalbumin and calretinin in primate basal ganglia. The data derive from immunocytochemical studies undertaken in squirrel monkeys (Saimiri sciureus) and in normal human individuals. In the striatum, calbindin labels medium-sized spiny projection neurons whereas parvalbumin and calretinin mark two separate classes of aspiny interneurons. The striatal matrix compartment is markedly enriched with calbindin while striatal patches (striosomes) display a calretinin-rich neuropil. In the pallidum, virtually all neurons contain parvalbumin but none express calbindin. Calretinin occurs only in a small subpopulation of both large and small pallidal neurons. In the subthalamic nucleus, there exists a multitude of parvalbumun-positive cells and fibers but the number of calretinin and calbindin-positive neuronal elements is small. In the substantia nigra/ventral tegmental area complex, calbindin and calretinin occur principally in dopaminergic neurons of the dorsal tier of the pars compacta and in those of the ventral tegmental area. Parvalbumin is strictly confined to the GABAergic neurons of the pars reticulata and lateralis. Calbindin-rich fibers abound in the pars reticulata and lateralis, while calretinin-positive axons are confined to the pars compacta. These results indicate that calbindin and parvalbumin are distributed according to a strikingly complementary pattern in primate basal ganglia. Calretinin is less ubiquitous but occurs in all basal ganglia components where it labels distinct subsets of neurons. Such highly specific patterns of distribution indicate that calbindin, parvalbumin and calretinin may work in synergy within primate basal ganglia.