Neurotrophins and basic fibroblast growth factor induce the differentiation of calbindin-containing neurons in the cerebral cortex

Electrical stimulation promotes functional recovery after spinal cord injury by activating endogenous spinal cord-derived neural stem/progenitor cell: an in vitro and in vivo study

BACKGROUND CONTEXT

Electrical stimulation is a noninvasive treatment method that has gained popularity in the treatment of spinal cord injury (SCI). Activation of spinal cord-derived neural stem/progenitor cell (SC-NSPC) proliferation and differentiation in the injured spinal cord may elicit considerable neural regenerative effects.

PURPOSE

This study aimed to explore the effect of electrical stimulation on the neurogenesis of SC-NSPCs.

STUDY DESIGN

This study analyzed the effects of electrical stimulation on neurogenesis in rodent SC-NSPCs in vitro and in vivo and evaluated functional recovery and neural circuitry improvements with electrical stimulation using a rodent SCI model.

METHODS

Rats (20 rats/group) were assigned to sham (Group 1), SCI only (Group 2), SCI + electrode implant without stimulation (Group 3), and SCI + electrode with stimulation (Group 4) groups to count total SC-NSPCs and differentiated neurons and to evaluate morphological changes in differentiated neurons. Furthermore, the Basso, Beattie, and Bresnahan scores were analyzed, and the motor- and somatosensory-evoked potentials in all rats were monitored.

RESULTS

Biphasic electrical currents enhanced SC-NSPC proliferation differentiation and caused qualitative morphological changes in differentiated neurons in vitro. Electrical stimulation promoted SC-NSPC proliferation and neuronal differentiation and improved functional outcomes and neural circuitry in SCI models. Increased Wnt3, Wnt7, and β-catenin protein levels were also observed after electrical stimulation.

CONCLUSIONS

Our study proved the beneficial effects of electrical stimulation on SCI. The Wnt/β-catenin pathway activation may be associated with this relationship between electrical stimulation and neuronal regeneration after SCI.

CLINICAL SIGNIFICANCE

The study confirmed the benefits of electrical stimulation on SCI based on cellular, functional, electrophysiological, and histological evidence. Based on these findings, we expect electrical stimulation to make a positive and significant difference in SCI treatment strategies.

SUN11602, a bFGF mimetic, modulated neuroinflammation, apoptosis and calcium-binding proteins in an in vivo model of MPTP-induced nigrostriatal degeneration

Background

Parkinson’s disease (PD) is the second most frequent neurodegenerative disease. PD etiopathogenesis is multifactorial and not yet fully known, however, the scientific world advised the establishment of neuroinflammation among the possible risk factors. In this field, basic fibroblast growth factor/fibroblast growth factor receptor-1 (bFGF/FGFR1) could be a promising way to treat CNS-mediated inflammation; unfortunately, the use of bFGF as therapeutic agent is limited by its side effects. The novel synthetic compound SUN11602 exhibited neuroprotective activities like bFGF. With this perspective, this study aimed to evaluate the effect of SUN11602 administration in a murine model of MPTP-induced dopaminergic degeneration.

Methods

Specifically, nigrostriatal degeneration was induced by intraperitoneal injection of MPTP (80 mg/kg). SUN11602 (1 mg/kg, 2.5 mg/kg, and 5 mg/kg) was administered daily by oral gavage starting from 24 h after the first administration of MPTP. Mice were killed 7 days after MPTP induction.

Results

The results obtained showed that SUN11602 administration significantly reduced the alteration of PD hallmarks, attenuating the neuroinflammatory state via modulation of glial activation, NF-κB pathway, and cytokine overexpression. Furthermore, we demonstrated that SUN11602 treatment rebalanced Ca²⁺ overload in neurons by regulating Ca²⁺-binding proteins while inhibiting the apoptotic cascade.

Conclusion

Therefore, in the light of these findings, SUN11602 could be considered a valuable pharmacological strategy for PD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02457-3.

Transplantation of Human Neural Progenitor Cells Reveals Structural and Functional Improvements in the Spastic Han-Wistar Rat Model of Ataxia

The use of regenerative medicine to treat nervous system disorders like ataxia has been proposed to either replace or support degenerating neurons. In this study, we assessed the ability of human neural progenitor cells (hNPCs) to repair and restore the function of dying neurons within the spastic Han-Wistar rat (sHW), a model of ataxia. The sHW rat suffers from neurodegeneration of specific neurons, including cerebellar Purkinje cells and hippocampal CA3 pyramidal cells leading to the observed symptoms of forelimb tremor, hind-leg rigidity, gait abnormality, motor incoordination, and a shortened life span. To alleviate the symptoms of neurodegeneration and to replace or augment dying neurons, neuronal human progenitor cells were implanted into the sHW rats. At 30 d of age, male sHW mutant rats underwent subcutaneous implantation of an Alzet osmotic pump that infused cyclosporine (15 mg/kg/d) used to suppress the rat's immune system. At 40 d, sHW rats received bilateral injections (500,000 cells in 5 µL media) of live hNPCs, dead hNPCs, live human embryonic kidney cells, or growth media either into the cerebellar cortex or into the hippocampus. To monitor results, motor activity scores (open-field testing) and weights of the animals were recorded weekly. The sHW rats that received hNPC transplantation into the cerebellum, at 60 d of age, displayed significantly higher motor activity scores and sustained greater weights and longevities than control-treated sHW rats or any hippocampal treatment group. In addition, cerebellar histology revealed that the transplanted hNPCs displayed signs of migration and signs of neuronal development in the degenerated Purkinje cell layer. This study revealed that implanted human progenitor cells reduced the ataxic symptoms in the sHW rat, identifying a future clinical use of these progenitor cells against ataxia and associated neurodegenerative diseases.

Developmental Expression of Calcium-Binding Protein-Containing Neurons in Neocortical Transplants

The present study examined the development of calcium binding protein-containing neurons in a timed series of fetal neocortical transplants. The immunoexpression of parvalbumin and calbindin, which are subpopulations of GABAergic neurons, have been widely studied in normal development and in disease and injury states. Because of their purported resistance to oxidative injury by their ability to buffer Ca++ influx, these neurons have been particularly studied following ischemia. Because it is likely that oxidative stress is associated with the grafting procedure, we sought to determine if these neurons displayed enhanced survival characteristics. Normally, parvalbumin and calbindin represent about 5-10% of cortical neurons. Within 2-4 wk after grafting the expression of both proteins increased markedly in that a relatively larger number of neurons (27% for parvalbumin) were immunopositive. This increase was transitory, however, and by 4 mo and beyond, confocal microscopic data showed a reduction of over 50% of parvalbumin (+) neurons and processes. Calbindin (+) processes showed a qualitative change in that they were smaller with less terminal branching. Electron microscopy confirmed a substantial reduction in parvalbumin synaptic contacts. Interestingly, in older grafts, remaining parvalbumin neurons were those that were strongly NSE (+) suggesting a link between normal metabolism and Ca++ buffering in grafted neurons. It is possible that in early grafts certain neuronal populations transiently upregulated calcium binding proteins as a defensive mechanism against Ca++ influx associated with oxidative stress. Over time, however, following physiological normalization within grafts, the calcium binding protein (+) neurons are diminished, possibly due to lack of appropriate afferent input to the interneuronal pool.

The building of the neocortex with non-hyperpolarizing neurotransmitters

The development of the neocortex requires the synergic action of several secreted molecules to achieve the right amount of proliferation, differentiation, and migration of neural cells. Neurons are well known to release neurotransmitters (NTs) in adult and a growing body of evidences describes the presence of NTs already in the embryonic brain, long before the generation of synapses. NTs are classified as inhibitory or excitatory based on the physiological responses of the target neuron. However, this view is challenged by the fact that glycine and GABA NTs are excitatory during development. Many reviews have described the role of nonhyperpolarizing GABA at this stage. Nevertheless, a global consideration of the inhibitory neurotransmitters and their downstream signaling during the embryonic cortical development is still needed. For example, taurine, the most abundant neurotransmitter during development is poorly studied regarding its role during cortical development. In the light of recent discoveries, we will discuss the functions of glycine, GABA, and taurine during embryonic cortical development with an emphasis on their downstream signaling. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1023-1037, 2017.

Calbindin-D28K is increased in the ventral horn of spinal cord by neuroprotective factors for motor neurons

Slow glutamate-mediated neuronal degeneration is implicated in the pathophysiology of motor neuron diseases such as amyotrophic lateral sclerosis (ALS). The calcium-binding proteins calbindin-D28K and parvalbumin have been reported to protect neurons against excitotoxic insults. Expression of calbindin-D28K is low in adult human motor neurons, and vulnerable motor neurons additionally may lack parvalbumin. Thus, it has been speculated that the lack of calcium-binding proteins may, in part, be responsible for early degeneration of the population of motor neurons most vulnerable in ALS. Using a rat organotypic spinal cord slice system, we examined whether the most potent neuroprotective factors for motor neurons can increase the expression of calbindin-D28K or parvalbumin proteins in the postnatal spinal cord. After 4 weeks of incubation of spinal cord slices with 1) glial cell line-derived neurotrophic factor (GDNF), 2) neurturin, 3) insulin-like growth factor I (IGF-I), or 4) pigment epithelium-derived factor (PEDF), the number of calbindin-D28K -immunopositive large neurons (>20 μm) in the ventral horn was higher under the first three conditions, but not after PEDF, compared with untreated controls. Under the same conditions, parvalbumin was not upregulated by any neuroprotective factor. The same calbindin increase was true of IGF-I and GDNF in a parallel glutamate toxicity model of motor neuron degeneration. Taken together with our previous reports from the same model, which showed that all these neurotrophic factors can potently protect motor neurons from slow glutamate injury, the data here suggest that upregulation of calbindin-D28K by some of these factors may be one mechanism by which motor neurons can be protected from glutamate-induced, calcium-mediated excitotoxicity.

A subpopulation of individual neural progenitors in the mammalian dorsal pallium generates both projection neurons and interneurons in vitro

There are two major classes of neurons in nervous systems: projection neurons and interneurons. During Drosophila nervous system development, a subpopulation of individual stem/progenitor cells gives rise to both motor neurons and interneurons. However, it remains unknown whether individual stem/progenitor cells in the mammalian brain also have the potential to give rise to both projection neurons and interneurons. Here we present evidence that single mouse neocortical progenitors generated both projection neurons and GABAergic interneurons based on studies using fluorescence-activated cell sorting (to obtain individual progenitors) and in vitro clonal analysis using time-lapse video microscopy and immunostaining. We determined that a subpopulation of individual dorsal pallial progenitors from E11.5 Dlx5/6-cre-IRES-EGFP and GAD67-GFP mice can generate both GFP-negative/Tbr1-positive (GFP(-) /Tbr1+)/Tuj1+ cells and GFP+/Sp8+/calretinin+/Tuj1+ cells. The GFP(-) /Tbr1+/Tuj1+ cells had morphological features of cultured projection neurons. Quantitative analysis of the reconstructed lineage trees derived from single progenitors showed that the projection neuron lineage appeared earlier than the interneuron lineage; however, more interneuron-like cells were produced than projection neuron-like cells. Thus, our results provide direct in vitro evidence that individual progenitors of the mammalian dorsal pallium can generate both projection neurons and interneurons.

Microfluidic investigation of BDNF-enhanced neural stem cell chemotaxis in CXCL12 gradients

In vivo studies have suggested that gradients of CXCL12 (aka stromal cell-derived factor 1α) may be critical for neural stem cell (NSC) migration during brain development and neural tissue regeneration. However, traditional in vitro chemotaxis tools are limited by unstable concentration gradients and the inability to decouple cell migration directionality and speed. These limitations have restricted the reproducible and quantitative analysis of neuronal migration, which is required for mechanism-based studies. Using a microfluidic gradient generator, nestin and Sox-2 positive human embryonic NSC chemotaxis is quantified within a linear and stable CXCL12 gradient. While untreated NSCs are not able to chemotax within CXCL12 gradients, pre-treatment of the cells with brain-derived neurotrophic factor (BDNF) results in significant chemotactic, directional migration. BDNF pre-treatment has no effect on cell migration speed, which averages about 1 μm min(-1). Quantitative analysis determines that CXCL12 concentrations above 9.0 nM are above the minimum activation threshold, while concentrations below 14.7 nM are below the saturation threshold. Interestingly, although inhibitor studies with AMD 3100 revealed that CXCL12 chemotaxis requires receptor CXCR4 activation, BDNF pre-treatment is found to have no profound effects on the mRNA levels or surface presentation of CXCR4 or the putative CXCR7 scavenger receptor. The microfluidic study of NSC migration within stable chemokine concentration profiles provides quantitative analysis as well as new insight into the migratory mechanism underlying BDNF-induced chemotaxis towards CXCL12.

A global transcriptome analysis reveals molecular hallmarks of neural stem cell death, survival, and differentiation in response to partial FGF-2 and EGF deprivation

Neurosphere cell culture is a commonly used model to study the properties and potential applications of neural stem cells (NSCs). However, standard protocols to culture NSCs have yet to be established, and the mechanisms underlying NSC survival and maintenance of their undifferentiated state, in response to the growth factors FGF-2 and EGF are not fully understood. Using cultures of embryonic and adult olfactory bulb stem cells (eOBSCs and aOBSCs), we analyzed the consequences of FGF-2 and EGF addition at different intervals on proliferation, cell cycle progression, cell death and differentiation, as well as on global gene expression. As opposed to cultures supplemented daily, addition of FGF-2 and EGF every 4 days significantly reduced the neurosphere volume and the total number of cells in the spheres, mainly due to increased cell death. Moreover, partial FGF-2 and EGF deprivation produced an increase in OBSC differentiation during the proliferative phase. These changes were more evident in aOBSC than eOBSC cultures. Remarkably, these effects were accompanied by a significant upregulation in the expression of endogenous Fgf-2 and genes involved in cell death and survival (Cryab), lipid catabolic processes (Pla2g7), cell adhesion (Dscaml1), cell differentiation (Dscaml1, Gpr17, S100b, Ndrg2) and signal transduction (Gpr17, Ndrg2). These findings support that a daily supply of FGF-2 and EGF is critical to maintain the viability and the undifferentiated state of NSCs in culture, and they reveal novel molecular hallmarks of NSC death, survival and the initiation of differentiation.

Therapeutic potentials of neural stem cells treated with fluoxetine in Alzheimer's disease

Recent studies have proposed that chronic treatment with antidepressants increases neurogenesis in the adult hippocampus. However, the effect of antidepressants on fetal neural stem cells (NSCs) has not been well defined. Our study shows the dose-dependent effects of fluoxetine on the proliferation and neural differentiation of NSCs. Fluoxetine, even at nanomolar concentrations, stimulated proliferation of NSCs and increased the number of βIII-tubulin (Tuj 1)- and neural nucleus marker (NeuN)-positive cells, but not glial fibrillary acidic protein (GFAP)-positive cells. These results suggest that fluoxetine can enhance neuronal differentiation. In addition, fluoxetine has protective effects against cell death induced by oligomeric amyloid beta (Aβ(42)) peptides. Taken together, these results clearly show that fluoxetine promotes both the proliferation and neuronal differentiation of NSCs and exerts protective effects against Aβ(42)-induced cytotoxicities in NSCs, which suggest that the use of fluoxetine is applicable for cell therapy for various neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases by its actions in NSCs.

Biphasic electrical currents stimulation promotes both proliferation and differentiation of fetal neural stem cells

The use of non-chemical methods to differentiate stem cells has attracted researchers from multiple disciplines, including the engineering and the biomedical fields. No doubt, growth factor based methods are still the most dominant of achieving some level of proliferation and differentiation control - however, chemical based methods are still limited by the quality, source, and amount of the utilized reagents. Well-defined non-chemical methods to differentiate stem cells allow stem cell scientists to control stem cell biology by precisely administering the pre-defined parameters, whether they are structural cues, substrate stiffness, or in the form of current flow. We have developed a culture system that allows normal stem cell growth and the option of applying continuous and defined levels of electric current to alter the cell biology of growing cells. This biphasic current stimulator chip employing ITO electrodes generates both positive and negative currents in the same culture chamber without affecting surface chemistry. We found that biphasic electrical currents (BECs) significantly increased the proliferation of fetal neural stem cells (NSCs). Furthermore, BECs also promoted the differentiation of fetal NSCs into neuronal cells, as assessed using immunocytochemistry. Our results clearly show that BECs promote both the proliferation and neuronal differentiation of fetal NSCs. It may apply to the development of strategies that employ NSCs in the treatment of various neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases.

Selective vulnerability of neurons in primary cultures and in neurodegenerative diseases

Primary neuronal cultures are commonly used to dissect the molecular and cellular mechanisms that underlie human brain diseases. Neurons dissociated from an embryonic brain and grown in culture dishes are almost by definition different from those residing inside a living brain. Not only are the individual cells stripped of their normal chemical and physical contacts, but the cellular composition of the cultures (the ratio of cell types) can be affected by many intrinsic and extrinsic factors, including brain region, neuronal birthday, gender, genetic background and in vitro age. Changes in any of these factors may have a strong impact on the outcome of the experiment. In a recent study, Romito-DiGiacomo et al. /54/ demonstrated that when neurons were harvested from murine embryonic cortex, the typical protocol favored cells that were just finishing cell division at the time of harvest. By taking advantage of the fact that the date of the final cell division (birthday) of a neuron correlates with its final position in the cortical plate they were able to assay deeper layer neurons (layers V-VI) separately from the more superficial layers (layers II-III). They reported that while the superficial cells were sensitive to the toxic effect of beta-amyloid, the deeper layer neurons were virtually resistant to death in its presence. The findings recapitulate selective vulnerability in the neocortex of Alzheimer's disease. This is a beautiful example of how to turn the apparent weakness of primary cultures into strength through experimental design and data interpretation. Selective vulnerability is a common feature of neurodegenerative disease, thus it is critical to use the right primary culture. Do you know what is in your culture?

Immunoelectron microscopic analysis of the distribution of tyrosine kinase receptor B in olfactory axons

To determine the morphological basis for the neurotrophic effects of brain-derived neurotrophic factor (BDNF) in the primary olfactory pathway (POP), tyrosine kinase receptor B (TrkB), a membrane-bound receptor for BDNF, was identified and localized in axons of olfactory receptor cells (ORC) of neonatal rat olfactory mucosa using immuno-histochemical and -cytochemical techniques. Initially, the immunospecificity of an anti-TrkB antibody that had been used as a specific antibody for full-length TrkB was confirmed in the olfactory mucosa. Then, a combination of a reduced osmium-LR-White and post-embedding immunogold technique was applied to ORC axons in the lamina propria just beneath the olfactory epithelium. Immunogold particles, which indicate TrkB immunoreactivity, were noted either in close association with the plasma membranes of ORC axons, and designated plasma-lemmal (PL), or within their cytoplasm, and designated cytoplasmic (CP). Most PL particles were seen in the CP portion of the axonal plasma membranes, suggesting that the anti-TrkB antibody binds to the membrane-inserted TrkB that acts as a functional receptor. Some CP particles were on vesicular structures. Quantitative analysis demonstrated that the ratio of CP to PL particles was 7:3, and this ratio was constant between animals examined (n = 5). Because membrane proteins are wrapped in vesicles and transported within the axonal cytoplasm and inserted into the plasma membrane to function there, the present study suggests that TrkB is transported within the cytoplasm of ORC axons and is positioned as a functional receptor for BDNF in their membranes.

Glutamate and neurotrophic factors in neuronal plasticity and disease

Glutamate's role as a neurotransmitter at synapses has been known for 40 years, but glutamate has since been shown to regulate neurogenesis, neurite outgrowth, synaptogenesis, and neuron survival in the developing and adult mammalian nervous system. Cell-surface glutamate receptors are coupled to Ca(2+) influx and release from endoplasmic reticulum stores, which causes rapid (kinase- and protease-mediated) and delayed (transcription-dependent) responses that change the structure and function of neurons. Neurotrophic factors and glutamate interact to regulate developmental and adult neuroplasticity. For example, glutamate stimulates the production of brain-derived neurotrophic factor (BDNF), which, in turn, modifies neuronal glutamate sensitivity, Ca(2+) homeostasis, and plasticity. Neurotrophic factors may modify glutamate signaling directly, by changing the expression of glutamate receptor subunits and Ca(2+)-regulating proteins, and also indirectly by inducing the production of antioxidant enzymes, energy-regulating proteins, and antiapoptotic Bcl-2 family members. Excessive activation of glutamate receptors, under conditions of oxidative and metabolic stress, may contribute to neuronal dysfunction and degeneration in diseases ranging from stroke and Alzheimer's disease to psychiatric disorders. By enhancing neurotrophic factor signaling, environmental factors such as exercise and dietary energy restriction, and chemicals such as antidepressants may optimize glutamatergic signaling and protect against neurological disorders.

Retinal TrkB receptors regulate neural development in the inner, but not outer, retina

BDNF signaling through its TrkB receptor plays a pivotal role in activity-dependent refinement of synaptic connectivity of retinal ganglion cells. Additionally, studies using TrkB knockout mice have suggested that BDNF/TrkB signaling is essential for the development of photoreceptors and for synaptic communication between photoreceptors and second order retinal neurons. Thus the action of BDNF on refinement of synaptic connectivity of retinal ganglion cells could be a direct effect in the inner retina, or it could be secondary to its proposed role in rod maturation and in the formation of rod to bipolar cell synaptic transmission. To address this matter we have conditionally eliminated TrkB within the retina. We find that rod function and synaptic transmission to bipolar cells is not compromised in these conditional knockout mice. Consistent with previous work, we find that inner retina neural development is regulated by retinal BDNF/TrkB signaling. Specifically we show here also that the complexity of neuronal processes of dopaminergic cells is reduced in conditional TrkB knockout mice. We conclude that retinal BDNF/TrkB signaling has its primary role in the development of inner retinal neuronal circuits, and that this action is not a secondary effect due to the loss of visual signaling in the outer retina.

Morphology and synaptic input of substance P receptor-immunoreactive interneurons in control and epileptic human hippocampus

Substance P (SP) is known to be a peptide that facilitates epileptic activity of principal cells in the hippocampus. Paradoxically, in other models, it was found to be protective against seizures by activating substance P receptor (SPR)-expressing interneurons. Thus, these cells appear to play an important role in the generation and regulation of epileptic seizures. The number, distribution, morphological features and input characteristics of SPR-immunoreactive cells were analyzed in surgically removed hippocampi of 28 temporal lobe epileptic patients and eight control hippocampi in order to examine their changes in epileptic tissues. SPR is expressed in a subset of inhibitory cells in the control human hippocampus, they are multipolar interneurons with smooth dendrites, present in all hippocampal subfields. This cell population is considerably different from SPR-positive cells of the rat hippocampus. The CA1 (cornu Ammonis subfield 1) region was chosen for the detailed morphological analysis of the SPR-immunoreactive cells because of its extreme vulnerability in epilepsy. The presence of various neurochemical markers identifies functionally distinct interneuron types, such as those responsible for perisomatic, dendritic or interneuron-selective inhibition. We found considerable colocalization of SPR with calbindin but not with parvalbumin, calretinin, cholecystokinin and somatostatin, therefore we suppose that SPR-positive cells participate mainly in dendritic inhibition. In the non-sclerotic CA1 region they are mainly preserved, whereas their number is decreased in the sclerotic cases. In the epileptic samples their morphology is considerably altered, they possessed more dendritic branches, which often became beaded. Analyses of synaptic coverage revealed that the ratio of symmetric synaptic input of SPR-immunoreactive cells has increased in epileptic samples. Our results suggest that SPR-positive cells are preserved while principal cells are present in the CA1 region, but show reactive changes in epilepsy including intense branching and growth of their dendritic arborization.

Effect of GDNF on differentiation of cultured ventral mesencephalic dopaminergic and non-dopaminergic calretinin-expressing neurons

Glial cell line-derived neurotrophic factor (GDNF) is a potent survival factor for ventral mesencephalic (VM) dopaminergic neurons. Subpopulations of dopaminergic and non-dopaminergic VM neurons express the calcium-binding proteins calbindin (CB) and calretinin (CR). Characterization of the actions of GDNF on distinct subpopulations of VM cells is of great importance for its potential use as a therapeutic molecule and for understanding its role in neuronal development. The present study investigated the effects of GDNF on the survival and morphological differentiation of dopaminergic and non-dopaminergic neurons in primary cultures of embryonic day (E) 18 rat VM. As expected from our results obtained using E14 VM cells, GDNF significantly increased the morphological complexity of E18 CB-immunoreractive (CB-ir), tyrosine hydroxylase (TH)-ir, and CR-ir neurons and also the densities of CB-ir and TH-ir neurons. Interestingly, densities of E18 CR-ir neurons, contrarily to our previous observations on E14 CR-ir neurons, were significantly higher after GDNF treatment (by 1.5-fold). Colocalization analyses demonstrated that GDNF increased the densitiy of dopaminergic neurons expressing CR (TH+/CR+/CB-), while no significant effects were observed for TH-/CR+/CB- cell densities. In contrast, we found that GDNF significantly increased the total fiber length (2-fold), number of primary neurites (1.4-fold), number of branching points (2.5-fold), and the size of neurite field per neuron (1.8-fold) of the non-dopaminergic CR-expressing neurons (TH-/CR+/CB-). These cells were identified as GABA-expressing neurons. In conclusion, our findings recognize GDNF as a potent differentiation factor for the development of VM dopaminergic and non-dopaminergic CR-expressing neurons.

GDNF and GFRalpha1 promote differentiation and tangential migration of cortical GABAergic neurons

Cortical GABAergic neurons are generated in the ventral telencephalon and migrate dorsally into the cortex following a tangential path. GDNF signaling via GFRalpha1 was found to promote the differentiation of ventral precursors into GABAergic cells, enhancing their neuronal morphology and motility. GDNF stimulated axonal growth in cortical GABAergic neurons and acted as a potent chemoattractant of GABAergic cells. These effects required GFRalpha1 but neither RET nor NCAM, the two transmembrane signaling receptors known for GDNF. Mutant mice lacking GDNF or GFRalpha1, but neither RET nor NCAM, showed reduced numbers of GABAergic cells in the cerebral cortex and hippocampus. We conclude that one of the normal functions of GDNF signaling via GFRalpha1 in the developing brain is to promote the differentiation and migration of cortical GABAergic neurons. The lack of involvement of RET or NCAM in these processes suggests the existence of additional transmembrane effectors for GDNF.

Potential of progenitors from postnatal cerebellar neuroepithelium and white matter: lineage specified vs. multipotent fate

Progenitors that migrate through the white matter of the postnatal cerebellum give rise to interneurons, astrocytes, and oligodendrocytes. To investigate the lineage potential of progenitors from the neuroepithelium and the white matter, we performed an in vitro clonal analysis in the presence or absence of various growth factors. Clonal progeny of cells labeled with a green fluorescent protein (GFP)-expressing retrovirus was characterized using morphological features and lineage markers. The large majority of clones were homogeneous, containing astrocytes, oligodendrocytes, neurons, or hybrid progenitors-cells labeled with markers for astrocytes and oligodendrocytes. Heterogeneous clones consisted of astrocytes and oligodendrocytes, with only a few mixed glial-neuronal clones. The neuroepithelium contains a higher number of multipotent progenitors than the white matter, pointing to a lineage specification of most of the cerebellar progenitors before their migration to the white matter.

Neuropsychiatric problems in tuberous sclerosis complex

Tuberous sclerosis complex is an autosomal dominant disorder characterized by abnormal cellular differentiation and proliferation, as well as abnormal neuronal migration. It is a disease affecting multiple organ systems and typically has brain involvement, causing severe disabilities. This article reviews the literature of the commonly associated neuropsychiatric complications, including mental retardation, autism-like features, and other behavior problems, which are discussed in the context of the neuropathology and epilepsy observed in tuberous sclerosis complex. The potential pathogenesis of neuropsychiatric problems is explored, including links to the genetics, neuropathology, neurotrophins, and epilepsy factors associated with tuberous sclerosis complex. Treatment of neuropsychiatric symptoms, including autism-like features, attention deficits, and sleep disorders, is also discussed.

Excitotoxic and excitoprotective mechanisms: abundant targets for the prevention and treatment of neurodegenerative disorders

Activation of glutamate receptors can trigger the death of neurons and some types of glial cells, particularly when the cells are coincidentally subjected to adverse conditions such as reduced levels of oxygen or glucose, increased levels of oxidative stress, exposure to toxins or other pathogenic agents, or a disease-causing genetic mutation. Such excitotoxic cell death involves excessive calcium influx and release from internal organelles, oxyradical production, and engagement of programmed cell death (apoptosis) cascades. Apoptotic proteins such as p53, Bax, and Par-4 induce mitochondrial membrane permeability changes resulting in the release of cytochrome c and the activation of proteases, such as caspase-3. Events occurring at several subcellular sites, including the plasma membrane, endoplasmic reticulum, mitochondria and nucleus play important roles in excitotoxicity. Excitotoxic cascades are initiated in postsynaptic dendrites and may either cause local degeneration or plasticity of those synapses, or may propagate the signals to the cell body resulting in cell death. Cells possess an array of antiexcitotoxic mechanisms including neurotrophic signaling pathways, intrinsic stress-response pathways, and survival proteins such as protein chaperones, calcium-binding proteins, and inhibitor of apoptosis proteins. Considerable evidence supports roles for excitotoxicity in acute disorders such as epileptic seizures, stroke and traumatic brain and spinal cord injury, as well as in chronic age-related disorders such as Alzheimer's, Parkinson's, and Huntington's disease and amyotrophic lateral sclerosis. A better understanding of the excitotoxic process is not only leading to the development of novel therapeutic approaches for neurodegenerative disorders, but also to unexpected insight into mechanisms of synaptic plasticity.

Synaptic reorganization of calbindin-positive neurons in the human hippocampal CA1 region in temporal lobe epilepsy

The distribution, morphology, synaptic coverage and postsynaptic targets of calbindin-containing interneurons and afferent pathways have been analyzed in the control and epileptic CA1 region of the human hippocampus. Numerous calbindin-positive interneurons are preserved even in the strongly sclerotic CA1 region. The morphology of individual cells is altered: the cell body and dendrites become spiny, the radially oriented dendrites disappear, and are replaced by a large number of curved, distorted dendrites. Even in the non-sclerotic epileptic samples, where pyramidal cells are present and calbindin-immunoreactive interneurons seem to be unchanged, some modifications could be observed at the electron microscopic level: they received more inhibitory synaptic input, and the calbindin-positive excitatory afferents - presumably derived from the CA1, the CA2 and/or the dentate gyrus - are sprouted. In the strongly sclerotic tissue, with the death of pyramidal cells, calbindin-positive terminals (belonging to interneurons and the remaining excitatory afferents) change their targets. Our data suggest that an intense synaptic reorganization takes place in the epileptic CA1 region, even in the non-sclerotic tissue, before the death of considerable numbers of pyramidal cells. Calbindin-positive interneurons participate in this reorganization: they show plastic changes in response to epilepsy. The enhanced inhibition of inhibitory interneurons may result in the disinhibition of pyramidal cells or in an abnormal synchrony in the output region of the hippocampus.

Fibroblast growth factor 1 regulates signaling via the glycogen synthase kinase-3beta pathway. Implications for neuroprotection

We hypothesize that in neurodegenerative disorders such as Alzheimer's disease and human immunodeficiency virus encephalitis the neuroprotective activity of fibroblast growth factor 1 (FGF1) against several neurotoxic agents might involve regulation of glycogen synthase kinase-3beta (GSK3beta), a pathway important in determining cell fate. In primary rat neuronal and HT22 cells, FGF1 promoted a time-dependent inactivation of GSK3beta by phosphorylation at serine 9. Blocking FGF1 receptors with heparinase reduced this effect. The effects of FGF1 on GSK3beta were dependent on phosphatidylinositol 3-kinase (PI3K)-protein kinase B (Akt) because inhibitors of this pathway or infection with dominant negative Akt adenovirus blocked inactivation. Furthermore, treatment of neuronal cells with FGF1 resulted in ERK-independent Akt phosphorylation and beta-catenin translocation into the nucleus. On the other hand, infection with wild-type GSK3beta recombinant adenovirus-associated virus increased activity of GSK3beta and cell death, both of which were reduced by FGF1 treatment. Moreover, FGF1 protection against glutamate toxicity was dependent on GSK3beta inactivation by the PI3K-Akt but was independent of ERK. Taken together these results suggest that neuroprotective effects of FGF1 might involve inactivation of GSK3beta by a pathway involving activation of the PI3K-Akt cascades.

Regional differences in neurotrophin availability regulate selective expression of VGF in the developing limbic cortex

Gene and protein expression patterns in the cerebral cortex are complex and often change spatially and temporally through development. The signals that regulate these patterns are primarily unknown. In the present study, we focus on the regulation of VGF expression, which is limited to limbic cortical areas early in development but later expands into sensory and motor areas. We isolated neurons from embryonic day 17 rat cortex and demonstrate that the profile of VGF expression in perirhinal (expressing) and occipital (nonexpressing) populations in vitro is similar to that in the perinatal cortex in vivo. The addition of neutralizing neurotrophin antibodies indicates that endogenous brain-derived neurotrophic factor (BDNF) is necessary for the normal complement of VGF-expressing neurons in the perirhinal cortex, although endogenous neurotrophin-3 (NT-3) regulates the expression of VGF in a subpopulation of cells. ELISA analysis demonstrates that there is significantly more BDNF present in the perirhinal cortex compared with the occipital cortex in the perinatal period. However, the total amount of NT-3 is similar between the two regions and, moreover, there is considerably more NT-3 than BDNF in both areas, a finding seemingly in conflict with regional VGF expression. Quantification of the extracellular levels of neurotrophins in perirhinal and occipital cultures using ELISA in situ analysis indicates that perirhinal neurons release significantly more BDNF than the occipital population. Furthermore, the amount of NT-3 released by the perirhinal neurons is significantly less than the amount of BDNF. Local injection of BDNF in vivo into a normally negative VGF region results in robust ectopic expression of VGF. These data suggest that the local availability of specific neurotrophins for receptor occupation, rather than the total amount of neurotrophin, is a critical parameter in determining the selective expression of VGF in the developing limbic cortex.

Brain-derived neurotrophic factor alters cell migration of particular progenitors in the developing mouse cerebral cortex

Effects of brain-derived neurotrophic factor (BDNF) on cell migration from the ventricular zone to the cortical plate (CP) in developing mouse cerebral cortex were examined. BDNF (700 ng) was injected into the brain ventricle of 13- or 14-day-old embryos (E13 or E14) after the intraperitoneal administration of 5-bromodeoxyuridine (BrdU) to pregnant mice. BDNF injection at E13 increased the number of BrdU-positive cells migrated into the CP until E15, and caused them to become localized in much deeper layers (V-VI) than expected (IV-V, as in the vehicle-treated mice) by postnatal day 1. However, when the injections were made at E14, BrdU-positive cells predominantly migrated to layers II/III irrespective of BDNF administration. These results demonstrate that BDNF affects particular progenitors at limited stages, and suggest the presence of a Reelin-independent mechanism(s) to regulate cell migration.

Astrocytes mediate cerebral cortical neuronal axon and dendrite growth, in part, by release of fibroblast growth factor

Astrocytes occupy a central role in central nervous system (CNS) function. In particular astyrocytes can support neurite growth, in part, by release of diffusable factors. We therefore performed biochemical analysis of astrocyte conditioned medium to examine possible mechanisms of astrocyte mediated axon and dendrite growth in the mammalian CNS. Culture medium was conditioned on purified astrocyte monolayers derived from P3 rat cerebral cortex or on fibroblasts. Conditioned medium (CM) was subject to protein denaturation, molecular weight fractionation, and heparin affinity chromatography. E18 mouse cerebral cortical neurons were then cultured in the various media or directly on astrocyte monolayers and axon and dendrite growth from 50 neurons in each condition quantified after 3 DIV using double-labeled immunohistochemical techniques. Axon and dendrite growth was supported by astrocyte CM and both were significantly greater than process growth from neurons incubated in fibroblast CM. Protein denaturation significantly reduced astrocyte CM support of axon and dendrite growth. Following ultrafiltration and dialysis dendrite and axon growth was observed in the molecular weight fraction between 10 and 100 kDa. Axon growth also was observed in the CM molecular weight fraction greater than 100 kDa. Conditioned medium was eluted on a heparin column; when the bound fragment was reconstituted in chemically defined medium extensive dendrite and axon growth was observed. Since fibroblast growth factor (FGF) has these biochemical characteristics we added anti-bFGF neutralizing antibodies to astrocyte monolayers or CM; this significantly reduced astrocyte support of process growth. By contrast, the addition of heparin, which helps activate FGF receptors, to astrocyte CM further enhanced process growth. Western blot analysis confirmed that bFGF was present in astrocyte CM. We then examined axon and dendrite growth from cortical neurons after the addition of various growth factors to chemically defined medium. Axon and dendrite growth, similar to that found in astrocyte CM was observed after the addition of bFGF or aFGF. Astrocyte support of cerebral cortical neuron axon and dendrite growth in vitro may be explained, in part, by FGF release.

Differential cellular expression of neurotrophins in cortical tubers of the tuberous sclerosis complex

Neurotrophins and their receptors modulate cerebral cortical development. Tubers in the tuberous sclerosis complex (TSC) are characterized histologically by disorganized cortical cytoarchitecture and thus, we hypothesized that expression of neurotrophin mRNAs and proteins might be altered in tubers. Using in situ transcription and mRNA amplification to probe cDNA arrays, we found that neurotrophin-3 (NT3) and trkB mRNA expression were reduced whereas neurotrophin-4 (NT4) and trkC mRNA expression were increased in whole tuber sections. Alterations in mRNA abundance were defined in single microdissected dysplastic neurons (DNs) and giant cells (GCs). NT3 mRNA expression was reduced in GCs and trkB mRNA expression was reduced in DNs. NT4 mRNA expression was increased in DNs and trkC mRNA expression was increased in both DNs and GCs. In three patients, TSC2 locus mutations were confirmed and the mean tuberin mRNA expression levels was reduced across all nine cases. Consistent with these observations, NT3 mRNA expression was reduced but trkC mRNA expression was increased in vitro in human NTera2 neurons (NT2N) transfected with a tuberin antisense construct that reduced tuberin expression. Western analysis of tuber homogenates and computer-assisted densitometry of immunolabeled sections confirmed the neurotrophin mRNA expression data in whole sections and single neurotrophin immunoreactive cells. We conclude that alterations in NT4/trkB and NT3/trkC expression may contribute to tuber formation during brain development as downstream effects of the hamartin and tuberin pathway in TSC.

Overexpression of calbindin-D28K induces neurite outgrowth in dopaminergic neuronal cells via activation of p38 MAPK

An MN9D dopaminergic neuronal cell line overexpressing calbindin-D28K (MN9D/Calbindin) was established in order to investigate directly the potential role of calcium-binding protein in neuronal differentiation. Overexpression of calbindin-D28K in MN9D cells resulted in significant increases in the number of neurites, the length of primary neurites, and the total extent of neurites. This robust neurite outgrowth occurred without cessation of cell division. Analysis of immunoblots revealed that this morphological differentiation was accompanied by increased expression of such markers of maturation as the synaptosomal protein SNAP-25. During calbindin-D28K-evoked neurite outgrowth in MN9D cells, phosphorylation of p38 mitogen-activated protein kinase (MAPK) dramatically increased while the levels and extent of phosphorylation of such other MAPKs as c-Jun N-terminal kinase (JNK) or extracellular response kinase (ERK) were not altered. Consequently, calbindin-D28K-induced neurite outgrowth was largely abolished by treatment with a p38 inhibitor, PD 169316, while the level of SNAP-25 in MN9D/Calbindin cells was not altered by this treatment. These data support an idea that calbindin-D28K and its associated p38 signaling pathway play a role in dopaminergic neuronal differentiation.

Neuroprotection of striatal neurons against kainate excitotoxicity by neurotrophins and GDNF family members

Neurotrophic factors are regarded as potential therapeutic tools in neurodegenerative disorders. Here, we analysed the protective effects of brain-derived neurotrophic factor, neurotrophin-3, glial cell line-derived neurotrophic factor and neurturin against the excitotoxic damage induced by kainate in striatal neurons in vitro and in vivo. Our results show that the decrease in the number of cultured striatal calbindin-positive neurons induced by kainate was prevented by treatment with any of these factors. To characterize their protective effects in vivo, cell lines overexpressing brain-derived neurotrophic factor, neurotrophin-3, glial cell line-derived neurotrophic factor or neurturin were grafted into the striatum. We found that the numbers of striatal projection neurons (calbindin-positive) and striatal interneurons (parvalbumin- or choline acetyltransferase-positive) were differentially decreased after kainate lesion. These neurotrophic factors prevented the loss of striatal projection neurons and interneurons with differing efficiency: brain-derived neurotrophic factor was the most efficient, whereas neurturin was the least. Our findings show that brain-derived neurotrophic factor, neurotrophin-3, glial cell line-derived neurotrophic factor and neurturin have specific neuroprotective profiles in striatal neurons and indicate that they are specific modulators of the survival of distinct subsets of striatal neurons in pathophysiological conditions.

Locally reduced levels of acidic FGF lead to decreased expression of 28-kda calbindin and contribute to the selective vulnerability of the neurons in the entorhinal cortex in Alzheimer's disease

Recent studies demonstrate that a disturbed calcium-homeostasis leading to increased susceptibility to excitotoxic triggers plays a major role in the neurodegenerative process initiating in layer 2 of the entorhinal cortex (EC2) during Alzheimer's disease (AD). Thus, proteins binding free Ca++ (i.e. calbindin) and factors regulating these proteins are of great importance for the neuroprotective-neurotoxic balance in the affected brain regions. In the present combined human and in vitro study evidence is provided that altered levels of the acidic fibroblast growth factor (aFGF) and calbindin expression are concomitantly present in EC2 neurons and have interactive effects. A dramatic loss of aFGF- and calbindin-labeled EC2 neurons was found. Further analysis of the surviving EC2 neurons revealed a strong immunoreactivity to calbindin and aFGF. In vitro experiments show that aFGF regulates calbindin expression, because treatment of differentiating neurons with recombinant aFGF increases calbindin expression in a time-dependent fashion. The data imply that a reduced expression of aFGF in EC2 neurons of AD brains leads to lower levels of calbindin resulting in decreased neuroprotective capacity.

Amelioration of neurotoxic effects of HIV envelope protein gp120 by fibroblast growth factor: a strategy for neuroprotection

Approximately two thirds of patients with human immunodeficiency virus encephalitis (HIVE) show cognitive impairment and neurodegeneration, while one third are cognitively unimpaired and their neuronal populations are preserved. Thus, it is possible that these individuals might have the capacity to produce neurotrophic factors capable of protecting neurons against the deleterious effects of HIV. In this context, the main objective of this study was to determine whether fibroblast growth factor 1 (FGF1) is protective against HIV. For this purpose levels of FGF1 immunoreactivity were determined in the frontal cortex of 35 AIDS cases subdivided into 4 groups according to the presence or absence of HIVE and neurodegeneration. In cases without both HIVE and neurodegeneration, mild to moderate levels of FGFI immunoreactivity were observed in pyramidal neurons, while in cases with HIVE but without neurodegeneration, levels were significiantly elevated. In contrast, individuals with both HIVE and neurodegeneration showed low levels of neuronal FGF1 immunoreactivity. Furthermore, studies in primary human neuronal cultures treated with the HIV envelope protein-gp120 in the presence or absence of FGF1 showed that FGF1 was protective against gpl20 neurotoxicity in a dose-dependent manner. Taken together, these results support the notion that upregulation of certain neurotrophic factors, such as FGF1, might protect the central nervous system from the neurotoxic effects of HIV.

Brain-derived neurotrophic factor in the control human brain, and in Alzheimer's disease and Parkinson's disease

Brain-derived neurotrophic factor (BDNF) is a small dimeric protein, structurally related to nerve growth factor, which is abundantly and widely expressed in the adult mammalian brain. BDNF has been found to promote survival of all major neuronal types affected in Alzheimer's disease and Parkinson's disease, like hippocampal and neocortical neurons, cholinergic septal and basal forebrain neurons, and nigral dopaminergic neurons. In this article, we summarize recent work on the molecular and cellular biology of BDNF, including current ideas about its intracellular trafficking, regulated synthesis and release, and actions at the synaptic level, which have considerably expanded our conception of BDNF actions in the central nervous system. But our primary aim is to review the literature regarding BDNF distribution in the human brain, and the modifications of BDNF expression which occur in the brain of individuals with Alzheimer's disease and Parkinson's disease. Our knowledge concerning BDNF actions on the neuronal populations affected in these pathological states is also reviewed, with an aim at understanding its pathogenic and pathophysiological relevance.

Cytokine and growth factor involvement in schizophrenia--support for the developmental model

Medical treatment with various cytokines can provoke psychiatric symptoms. Conversely, psychiatric patients can display abnormalities in cytokine and neurotrophic factor expression. Such observations have pointed to the potential contribution of cytokines and growth factors to schizophrenic pathology and/or etiology. The cellular targets of the relevant factors and the nature of their actions remain to be explored in mental illness, however. Recent physiological studies demonstrate that cytokines and neurotrophic factors can markedly influence synaptic transmission and plasticity upon acute or chronic application. Moreover, many of the molecular alterations observed in the schizophrenic brain are consistent with abnormalities in cytokine and neurotrophic factor regulation of these molecules. In this review, we summarize these molecular pathology findings for schizophrenia and highlight the neurodevelopmental activities of cytokines and neurotrophic factors that may contribute to the etiology or pathology of this illness.

Glial cell line-derived neurotrophic factor stimulates the morphological differentiation of cultured ventral mesencephalic calbindin- and calretinin-expressing neurons

Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor for mesencephalic dopaminergic neurons. Subpopulations of these neurons express the calcium-binding proteins calbindin (CB) and calretinin (CR). Understanding the specific effects of GDNF on these neurons is important for the development of an optimal cell replacement therapy for Parkinson's disease. To investigate the effects of GDNF on the morphological complexity of mesencephalic tyrosine hydroxylase (TH)-immunoreactive (-ir), CB-ir, and CR-ir neurons, dissociated cultures of embryonic (E14) rat ventral mesencephalon were prepared. Chronic administration of GDNF (10 ng/ml) for 7 days promoted the survival of TH-ir and CB-ir neurons but did not alter the density of CR-ir neurons. Total fiber length/neuron and number of branching points/neuron of CB-ir and CR-ir cells were significantly increased after GDNF treatment (2x for CB-ir cells and 1.4x and 1.7x, respectively, for CR-ir cells), which resulted in a significantly larger size of neurite field/neuron (2.9x and 1.5x for CB-ir and CR-ir neurons, respectively). The number of primary neurites/neuron of CB-ir neurons was found to be 1.5x larger, while no difference could be detected for CR-ir cells. Assessment of the effects of GDNF on TH-ir neurons unveiled a similar outcome with an increased total fiber length/neuron (1.5x), an increased number of primary neurites/neuron (1.6x), and a twofold larger size of neurite field/neuron. In conclusion, our findings recognize GDNF as a neurotrophic factor that stimulates the morphological differentiation of ventral mesencephalic CB-ir and CR-ir neurons.

Opposite regulation of calbindin and calretinin expression by brain-derived neurotrophic factor in cortical neurons

Regulation of calbindin and calretinin expression by brain-derived neurotrophic factor (BDNF) was examined in primary cultures of cortical neurons using immunocytochemistry and northern blot analysis. Here we report that regulation of calretinin expression by BDNF is in marked contrast to that of calbindin. Indeed, chronic exposure of cultured cortical neurons for 5 days to increasing concentrations of BDNF (0.1-10 ng/ml) resulted in a concentration-dependent decrease in the number of calretinin-positive neurons and a concentration-dependent increase in the number of calbindin-immunoreactive neurons. Consistent with the immunocytochemical analysis, BDNF reduced calretinin mRNA levels and up-regulated calbindin mRNA expression, providing evidence that modifications in gene expression accounted for the changes in the number of calretinin- and calbindin-containing neurons. Among other members of the neurotrophin family, neurotrophin-4 (NT-4), which also acts by activating tyrosine kinase TrkB receptors, exerted effects comparable to those of BDNF, whereas nerve growth factor (NGF) was ineffective. As for BDNF and NT-4, incubation of cortical neurons with neurotrophin-3 (NT-3) also led to a decrease in calretinin expression. However, in contrast to BDNF and NT-4, NT-3 did not affect calbindin expression. Double-labeling experiments evidenced that calretinin- and calbindin-containing neurons belong to distinct neuronal subpopulations, suggesting that BDNF and NT-4 exert opposite effects according to the neurochemical phenotype of the target cell.

Abnormal expression of brain-derived neurotrophic factor and its receptor in the corticolimbic system of schizophrenic patients

Previous neuropathological studies have revealed that the corticolimbic system of schizophrenic patients expresses abnormal levels of various synaptic molecules, which are known to be influenced by the neuronal differentiation factors, neurotrophins. Therefore, we determined levels of neurotrophins and their receptors in the postmortem brains of schizophrenic patients and control subjects in relation to molecular impairments in schizophrenia. Among the neurotrophins examined, levels of brain-derived neurotrophic factor (BDNF) were elevated specifically in the anterior cingulate cortex and hippocampus of schizophrenic patients, but levels of nerve growth factors and neurotrophin-3 showed no change in any of the regions examined. In parallel, the expressions of TrkB receptor and calbindin-D, which are both influenced by BDNF, were reduced significantly in the hippocampus or the prefrontal cortex. However, neuroleptic treatment did not appear to mimic the neurotrophic change. Neither withdrawal of drug treatment in patients nor chronic administration of haloperidol to rats altered levels of BDNF. These findings suggest that neurotrophic abnormality is associated with the corticolimbic structures of schizophrenic patients and might provide the molecular substrate for pathological manifestations of the illness.

Parvalbumin in cortical epithelial cells of the pigeon thymus

We examined the distribution of parvalbumin in the pigeon thymus by light and electron microscopic immunohistochemistry. Tissues were also examined by conventional electron microscopy to determine the ultrastructure of immunoreactive cells. Parvalbumin immunoreaction was located in epithelial cells of the cortex, which formed dense mesh-like structures. Parvalbumin-positive epithelial cells were classified into 2 types. The first comprised elongated cells. In these, the nucleus was spindle-shaped, oval, or triangular, with a slightly irregular contour and contained rich heterochromatin peripherally. The cytoplasm was pale and processes extended laterally or ramified among the surrounding thymocytes. This type of cell formed the majority of immunoreactive cells. The other cell type consisted of polygonal epithelial cells. The nucleus was oval with deep indentations. Euchromatin occupied a large part of the nucleus. The cytoplasm contained numerous cell organelles compared with the elongated type, in particular, electron-dense vacuoles of various sizes and often bundles of tonofilaments. Both types of epithelial cell were interconnected by desmosomes. No secretory granules were found in the cytoplasm of elongated or polygonal cells. These results indicate the presence of heterogeneous group of parvalbumin-immunoreactive epithelial cells and suggest the likelihood of different functional roles for parvalbumin in the pigeon thymus.

Hippocampal stem cells differentiate into excitatory and inhibitory neurons

Stem cell technology promises new and rapid advances in cell therapy and drug discovery. Clearly, the value of this approach will be limited by the differentiated functions displayed by the progeny of stem cells. The foetal and adult central nervous system (CNS) harbour stem cells that can be expanded in vitro and differentiate into immature neurons and glia. Surprisingly, we do not know if neurons derived from stem cells form synapses, a definitive feature of neuronal function. Neuronal differentiation is a complex process and in this paper we establish conditions that permit extensive maturation of neurons in the presence of neurotrophins. These conditions permit the differentiation of rat hippocampal stem cells into both excitatory (glutamatergic) and inhibitory (GABAergic) neurons. The proportion of excitatory and inhibitory synapses was strongly influenced by specific neurotrophins, and these responses reflect the region of origin of the stem cells in the brain. These data show that stem cells can be used to study mechanisms of excitation and inhibition in the nervous system.

Evidence that brain-derived neurotrophic factor from presynaptic nerve terminals regulates the phenotype of calbindin-containing neurons in the lateral septum

Brain-derived neurotrophic factor (BDNF) is transported anterogradely in neurons of the CNS and can be released by activity-dependent mechanisms to regulate synaptic plasticity. However, few neural networks have been identified in which the production, transport, and effects of BDNF on postsynaptic neurons can be analyzed in detail. In this study, we have identified such a network. BDNF has been colocalized by immunocytochemistry with tyrosine hydroxylase (TH) in nerve fibers and nerve terminals within the lateral septum of rats. BDNF-containing nerve fibers terminate on a population of calbindin-containing neurons in lateral septum that contain TrkB, the high-affinity receptor for BDNF. Overexpression of BDNF in noradrenergic neurons increased levels of calbindin in septum, as well as in whole-brain lysates. Septal levels of calbindin and BDNF partially decreased after unilateral lesions of the medial forebrain bundle (MFB), induced with 6-hydroxydopamine, a treatment that abolished TH staining. These data suggest that BDNF is anterogradely transported within the MFB in catecholaminergic neurons arising from brainstem nuclei. To determine whether BDNF affects the production of calbindin in lateral septal neurons directly, we tested the effects of BDNF on cultures of septal neurons from embryonic day 16-17 rats. BDNF promoted the expression of calbindin, as well as the arborization of calbindin-containing neurons, but BDNF had no effect on cell division or survival. Together, these results suggest that BDNF, anterogradely transported in catecholaminergic neurons, regulates calbindin expression within the lateral septum.

Growth factor effects on survival and development of calbindin immunopositive cultured septal neurons

Alzheimer's disease (AD) is a neurodegenerative disease characterized by dementia, senile plaques, fibrillary tangles, and a reduction of cholinergic neurons in areas of the brain, including the septal nucleus. Certain growth factors may promote the long-term survival of this subpopulation of neurons at risk. This study was undertaken to characterize growth factors' long-term effects on survival and development of neurons expressing the calcium-binding protein calbindin. In order to accomplish this, embryonic day 16 rat septal neurons were grown in bilaminar culture with astrocytes and in the absence of serum. These cultures were chronically treated with estrogen (Es), insulin-like growth factors I/II (IGF-I, IGF-II), basic fibroblast growth factor (bFGF), and nerve growth factor (NGF). Insulin-like growth factor II significantly increased the number of neurons immunoreactive for calbindin by 155%, suggesting either an increase in the survival of this subpopulation or an increase in the percentage of cells expressing calbindin. Chronic treatment with NGF, IGF-II, and Es significantly increased the number of primary neuritic processes on calbindin-positive neurons, whereas NGF and Es caused significant increases in the number of secondary processes and in the total lengths of the neuritic processes. Thus, effects of IGF-II, estrogen, and NGF on survival and maintenance of this neuronal subpopulation may be dependent on alterations in neurons which are immunopositive for calbindin.

Induction of a physiologically active brain-derived neurotrophic factor in the infant rat brain by peripheral administration of 4-methylcatechol

Effects of 4-methylcatechol (4MC), a known potent stimulator of nerve growth factor (NGF) synthesis, on expression of brain-derived neurotrophic factor (BDNF) mRNA and BDNF-like immunoreactivity (BDNF-LI) was investigated in infant rat brains. A single intraperitoneal administration of 4MC caused transient increases in the levels of BDNF mRNA and BDNF-LI in neurons of the cerebral cortex from 1 to 3 h and 3 to 12 h, respectively, after the injection. Repetitive injections of 4MC to newborn rats (12-h intervals for 10 days) caused a marked and dose-dependent elevation of the level of BDNF mRNA in the whole brain besides elevating the number of cells containing calbindin D-28 and enhancing its immunoreactive intensity in the pyriform cortex and hippocampus. These findings demonstrate that 4MC stimulates de novo synthesis of BDNF in the infant rat brain, resulting in acceleration of the developmental expression of calbindin D-28.

Neurotrophic factors and neuro-muscular disease: II. GDNF, other neurotrophic factors, and future directions

This is the second of two reviews in which we discuss the essential aspects of neurotrophic factor neurobiology, the characteristics of each neurotrophic factor, and their clinical relevance to neuromuscular diseases. The previous paper reviewed the neurotrophin family and neuropoietic cytokines. In the present article, we focus on the GDNF family and other neurotrophic factors and then consider future approaches that may be utilized in neurotrophic factor treatment.

Ontogeny of neurotrophin receptor trkC expression in the rat forebrain and anterior hypothalamus with emphasis on the suprachiasmatic nucleus

There is little information about neurotrophic regulation in the developing rat hypothalamus. In the present study, we therefore examined the expression of neurotrophin receptor TrkC in the developing forebrain and hypothalamus. In situ hybridization of coronal sections revealed that on the 15th day of gestation, trkC messenger RNA expression is homogeneously distributed over the neocortex, septum, thalamus, hypothalamus, hippocampus, rhinencephalon and the amygdala. Exceptions were the anteroventral nucleus of the hypothalamus and the striatum, which showed higher levels of trkC messenger RNA expression, and the germinal zones which were devoid of trkC messenger RNA. After birth, the homogeneous staining pattern changes into a heterogeneous staining pattern like that found in adulthood. TrkC expression is observed in the area of the suprachiasmatic nucleus as early as E17 and continues until adulthood. The presence of the TrkC receptor in the E17 suprachiasmatic nucleus suggests that neurotrophin-3 plays a role in development of this structure and that application of neurotrophin-3 could stimulate neuronal survival and neuritic outgrowth in a suprachiasmatic nucleus transplantation model.

Sequential pharmacotherapy with magnesium chloride and basic fibroblast growth factor after fluid percussion brain injury results in less neuromotor efficacy than that achieved with magnesium alone

Combinational pharmacotherapy with individually efficacious agents is a potential strategy for the treatment of traumatic central nervous system (CNS) injury. Basic fibroblast growth factor (bFGF) has been shown to be neuroprotective against excitotoxic, ischemic, and traumatic injury to the CNS, while acute posttraumatic treatment with magnesium (Mg2+) has been shown to decrease the motor and cognitive deficits following experimental brain injury. In this study, bFGF and Mg2+ were evaluated separately and in combination to assess their potential additive effects on posttraumatic neurological recovery and histological cell loss (lesion volume). Twenty minutes after fluid percussion (FP) brain injury of moderate severity (2.2-2.4 atm), anesthetized rats received a 15-min intravenous infusion of either 125 mumol of MgCl2 or vehicle, followed 5 min later by a 24-h constant intravenous infusion of either bFGF (16 micrograms/h) or vehicle. Injured animals had a significant motor deficit when compared to sham (uninjured) animals at both 48 h and 7 days postinjury. At 48 h postinjury, there were no significant differences among injured animals when compared by treatment. By 7 days postinjury, injured animals treated with MgCl2 alone displayed significantly improved motor function when compared to brain-injured, vehicle-treated animals (p < 0.05). Animals treated with either bFGF alone or a combination of MgCl2 and bFGF displayed no significant neurological improvement relative to vehicle-treated injured animals at 7 days. No effect of any drug treatment of combination was observed on the extent of the postinjury lesion volume in the injured cortex. These results suggest that caution must be exercised when combining "cocktails" of potentially neuroprotective compounds in the setting of traumatic brain injury.

Cellular distribution of the calcium-binding proteins parvalbumin, calbindin, and calretinin in the neocortex of mammals: phylogenetic and developmental patterns

The three calcium-binding proteins parvalbumin, calbindin, and calretinin are found in morphologically distinct classes of inhibitory interneurons as well as in some pyramidal neurons in the mammalian neocortex. Although there is a wide variability in the qualitative and quantitative characteristics of the neocortical subpopulations of calcium-binding protein-immunoreactive neurons in mammals, most of the available data show that there is a fundamental similarity among the mammalian species investigated so far, in terms of the distribution of parvalbumin, calbindin, and calretinin across the depth of the neocortex. Thus, calbindin- and calretinin-immunoreactive neurons are predominant in layers II and III, but are present across all cortical layers, whereas parvalbumin-immunoreactive neurons are more prevalent in the middle and lower cortical layers. These different neuronal populations have well defined regional and laminar distribution, neurochemical characteristics and synaptic connections, and each of these cell types displays a particular developmental sequence. Most of the available data on the development, distribution and morphological characteristics of these calcium-binding proteins are from studies in common laboratory animals such as the rat, mouse, cat, macaque monkey, as well as from postmortem analyses in humans, but there are virtually no data on other species aside of a few incidental reports. In the context of the evolution of mammalian neocortex, the distribution and morphological characteristics of calcium-binding protein-immunoreactive neurons may help defining taxon-specific patterns that may be used as reliable phylogenetic traits. It would be interesting to extend such neurochemical analyses of neuronal subpopulations to other species to assess the degree to which neurochemical specialization of particular neuronal subtypes, as well as their regional and laminar distribution in the cerebral cortex, may represent sets of derived features in any given mammalian order. This could be particularly interesting in view of the consistent differences in neurochemical typology observed in considerably divergent orders such as cetaceans and certain families of insectivores and metatherians, as well as in monotremes. The present article provides an overview of calcium-binding protein distribution across a large number of representative mammalian species and a review of their developmental patterns in the species where data are available. This analysis demonstrates that while it is likely that the developmental patterns are quite consistent across species, at least based on the limited number of species for which ontogenetic data exist, the distribution and morphology of calcium-binding protein-containingneurons varies substantially among mammalian orders and that certain species show highly divergent patterns compared to closely related taxa. Interestingly, primates, carnivores, rodents and tree shrews appear closely related on the basis of the observed patterns, marsupials show some affinities with that group, whereas prototherians have unique patterns. Our findings also support the relationships of cetaceans and ungulates, and demonstrates possible affinities between carnivores and ungulates, as well as the existence of common, probably primitive, traits in cetaceans and insectivores.

Expression of trkB and trkC mRNAs by adult midbrain dopamine neurons: a double-label in situ hybridization study

The documented trophic actions of the neurotrophins brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4/5 (NT-4/5) upon ventral mesencephalic dopamine neurons in vitro and in vivo are presumed to be mediated through interactions with their high-affinity receptors TrkB (for BDNF and NT-4/5) and TrkC (for NT-3). Although both neurotrophin receptor mRNAs have been detected within the rat ventral midbrain, their specific association with mesencephalic dopaminergic cell bodies remains to be elucidated. The present study was performed to determine the precise organization of trkB and trkC mRNAs within rat ventral midbrain and to discern whether the neurotrophin receptor mRNAs are expressed specifically by dopaminergic neurons. In situ hybridization with isotopically labeled cRNA probes showed that trkB and trkC mRNAs were expressed in all mesencephalic dopamine cell groups, including all subdivisions of the substantia nigra and ventral tegmental area, and in the retrorubral field, rostral and caudal linear raphe nuclei, interfascicular nucleus, and supramammillary region. Combined isotopic/nonisotopic double-labeling in situ hybridization demonstrated that virtually all of the tyrosine hydroxylase (the catecholamine biosynthetic enzyme) mRNA-containing neurons in the ventral midbrain also expressed trkB or trkC mRNAs. Additional perikarya within these regions expressed the neurotrophin receptor mRNAs but were not dopaminergic. The present results demonstrate that essentially all mesencephalic dopaminergic neurons synthesize the neurotrophin receptors TrkB and TrkC and thus exhibit the capacity to respond directly to BDNF and NT-3 in the adult midbrain in vivo. Moreover, because BDNF and NT-3 are produced locally by subpopulations of the dopaminergic cells, the present data support the notion that the neurotrophins can influence the dopaminergic neurons through autocrine or paracrine mechanisms.