Dopamine neurons in a simple GDNF-treated meso-striatal organotypic co-culture model

Microcontact Printing of Cholinergic Neurons in Organotypic Brain Slices

Alzheimer's disease is a severe neurodegenerative disorder of the brain, characterized by beta-amyloid plaques, tau pathology, and cell death of cholinergic neurons, resulting in loss of memory. The reasons for the damage of the cholinergic neurons are not clear, but the nerve growth factor (NGF) is the most potent trophic factor to support the survival of these neurons. In the present study we aim to microprint NGF onto semipermeable 0.4 μm pore membranes and couple them with organotypic brain slices of the basal nucleus of Meynert and to characterize neuronal survival and axonal growth. The brain slices were prepared from postnatal day 10 wildtype mice (C57BL6), cultured on membranes for 2–6 weeks, stained, and characterized for choline acetyltransferase (ChAT). The NGF was microcontact printed in 28 lines, each with 35 μm width, 35 μm space between them, and with a length of 8 mm. As NGF alone could not be printed on the membranes, NGF was embedded into collagen hydrogels and the brain slices were placed at the center of the microprints and the cholinergic neurons that survived. The ChAT+ processes were found to grow along with the NGF microcontact prints, but cells also migrated. Within the brain slices, some form of re-organization along the NGF microcontact prints occurred, especially the glial fibrillary acidic protein (GFAP)+ astrocytes. In conclusion, we provided a novel innovative microcontact printing technique on semipermeable membranes which can be coupled with brain slices. Collagen was used as a loading substance and allowed the microcontact printing of nearly any protein of interest.

The Organic Cation Transporter 2 Inhibitor Quinidine Modulates the Neuroprotective Effect of Nerve Growth Factor and Memantine on Cholinergic Neurons of the Basal Nucleus of Meynert in Organotypic Brain Slices

INTRODUCTION

Alzheimer's disease (AD) is a severe neurodegenerative disorder of the brain characterized by degeneration of cholinergic neurons which is directly linked to cognitive decline. Nerve growth factor (NGF) is the most potent protective factor for cholinergic neurons, additionally the NMDA antagonist memantine blocks glutamate-mediated excitotoxic activity. Quinidine is an inhibitor of organic cation transporter 2 (OCT2). OCT2 is located on cholinergic neurons and plays a role in presynaptic reuptake and recycling of acetylcholine in the brain. We hypothesize that quinidine can modulate the protective effects of NGF and memantine on cholinergic neurons in organotypic brain slices of the nucleus basalis of Meynert (nBM).

METHODS

Organotypic brain slices of nBM were incubated with 100 ng/mL NGF, 10 µM memantine, 10 µM quinidine, and combinations of these treatments for 2 weeks. Cholinergic neurons were immunohistochemically stained for choline acetyltransferase (ChAT).

RESULTS

Our data show that NGF as well as memantine counteracted the cell death of cholinergic nBM neurons. Quinidine alone had no toxic effect on cholinergic neurons but inhibited the protective effect of NGF and memantine when applied simultaneously.

DISCUSSION/CONCLUSION

Our data provide evidence that quinidine modulates the survival of cholinergic nBM neurons via OCT2.

Biomaterial based strategies to reconstruct the nigrostriatal pathway in organotypic slice co-cultures

Protection or repair of the nigrostriatal pathway represents a principal disease-modifying therapeutic strategy for Parkinson's disease (PD). Glial cell line-derived neurotrophic factor (GDNF) holds great therapeutic potential for PD, but its efficacious delivery remains difficult. The aim of this study was to evaluate the potential of different biomaterials (hydrogels, microspheres, cryogels and microcontact printed surfaces) for reconstructing the nigrostriatal pathway in organotypic co-culture of ventral mesencephalon and dorsal striatum. The biomaterials (either alone or loaded with GDNF) were locally applied onto the brain co-slices and fiber growth between the co-slices was evaluated after three weeks in culture based on staining for tyrosine hydroxylase (TH). Collagen hydrogels loaded with GDNF slightly promoted the TH+ nerve fiber growth towards the dorsal striatum, while GDNF loaded microspheres embedded within the hydrogels did not provide an improvement. Cryogels alone or loaded with GDNF also enhanced TH+ fiber growth. Lines of GDNF immobilized onto the membrane inserts via microcontact printing also significantly improved TH+ fiber growth. In conclusion, this study shows that various biomaterials and tissue engineering techniques can be employed to regenerate the nigrostriatal pathway in organotypic brain slices. This comparison of techniques highlights the relative merits of different technologies that researchers can use/develop for neuronal regeneration strategies.

What and How Can Physical Activity Prevention Function on Parkinson's Disease?

Aim

This study was aimed at investigating the effects and molecular mechanisms of physical activity intervention on Parkinson's disease (PD) and providing theoretical guidance for the prevention and treatment of PD.

Methods

Four electronic databases up to December 2019 were searched (PubMed, Springer, Elsevier, and Wiley database), 176 articles were selected. Literature data were analyzed by the logic analysis method.

Results

(1) Risk factors of PD include dairy products, pesticides, traumatic brain injury, and obesity. Protective factors include alcohol, tobacco, coffee, black tea, and physical activity. (2) Physical activity can reduce the risk and improve symptoms of PD and the beneficial forms of physical activity, including running, dancing, traditional Chinese martial arts, yoga, and weight training. (3) Different forms of physical activity alleviate the symptoms of PD through different mechanisms, including reducing the accumulation of α-syn protein, inflammation, and oxidative stress, while enhancing BDNF activity, nerve regeneration, and mitochondrial function.

Conclusion

Physical activity has a positive impact on the prevention and treatment of PD. Illustrating the molecular mechanism of physical activity-induced protective effect on PD is an urgent need for improving the efficacy of PD therapy regimens in the future.

Nerve growth factor released from collagen scaffolds protects axotomized cholinergic neurons of the basal nucleus of Meynert in organotypic brain slices

BACKGROUND

Alzheimeŕs disease is accompanied by cell death of cholinergic neurons, resulting in cognitive impairment and memory loss. Nerve growth factor (NGF) is the most potent protein to support survival of cholinergic neurons.

NEW METHOD

Organotypic brain slices of the basal nucleus of Meynert (nBM) are a valuable tool to study cell death of axotomized cholinergic neurons, as well as protective effects of NGF added into the medium. The aim of the present study is to use collagen scaffolds crosslinked with polyethyleneglycole and load with NGF to target delivery of NGF to organotypic nBM brain slices.

RESULTS

Collagen scaffolds (visualized by incorporating AlexaFluor 488 antibodies) slowly degraded when applied onto organotypic brain slices within 2 weeks in culture. GFAP reactive astrocytes and Iba1+ microglia became visible around the collagen scaffolds 7days after incubation, showing reactive gliosis. Cholinergic neurons of the nBM survived (201±21, n=8) when incubated with 100ng/ml NGF in the medium compared to NGF-free medium (69±12, n=7). Collagen scaffolds loaded with NGF (1ng/2μl scaffold) significantly rescued cholinergic cell death in the nBM brain slices (175±12, n=10), which was counteracted by an anti-NGF antibody (77±5, n=5).

COMPARISON WITH EXISTING METHODS

The combination of coronal brain slices with biomaterial is a novel and potent tool to selectively study neuroprotective effects.

CONCLUSIONS

Collagen scaffolds loaded with low amounts of a protein/drug of interest can be easily applied directly onto organotypic brain slices, allowing slow targeted release of a protective molecule. Such an approach is highly useful to optimize CollScaff for further in vivo applications.

Organotypic brain slice cultures: A review

In vitro cell cultures are an important tool for obtaining insights into cellular processes in an isolated system and a supplement to in vivo animal experiments. While primary dissociated cultures permit a single homogeneous cell population to be studied, there is a clear need to explore the function of brain cells in a three-dimensional system where the main architecture of the cells is preserved. Thus, organotypic brain slice cultures have proven to be very useful in investigating cellular and molecular processes of the brain in vitro. This review summarizes (1) the historical development of organotypic brain slices focusing on the membrane technology, (2) methodological aspects regarding culturing procedures, age of donors or media, (3) whether the cholinergic neurons serve as a model of neurodegeneration in Alzheimer’s disease, (4) or the nigrostriatal dopaminergic neurons as a model of Parkinson’s disease and (5) how the vascular network can be studied, especially with regard to a synthetic blood–brain barrier. This review will also highlight some limits of the model and give an outlook on future applications.

Organotypic vibrosections from whole brain adult Alzheimer mice (overexpressing amyloid-precursor-protein with the Swedish-Dutch-Iowa mutations) as a model to study clearance of beta-amyloid plaques

Alzheimer's disease is a severe neurodegenerative disorder of the brain, pathologically characterized by extracellular beta-amyloid plaques, intraneuronal Tau inclusions, inflammation, reactive glial cells, vascular pathology and neuronal cell death. The degradation and clearance of beta-amyloid plaques is an interesting therapeutic approach, and the proteases neprilysin (NEP), insulysin and matrix metalloproteinases (MMP) are of particular interest. The aim of this project was to establish and characterize a simple in vitro model to study the degrading effects of these proteases. Organoytpic brain vibrosections (120 μm thick) were sectioned from adult (9 month old) wildtype and transgenic mice (expressing amyloid precursor protein (APP) harboring the Swedish K670N/M671L, Dutch E693Q, and Iowa D694N mutations; APP_SDI) and cultured for 2 weeks. Plaques were stained by immunohistochemistry for beta-amyloid and Thioflavin S. Our data show that plaques were evident in 2 week old cultures from 9 month old transgenic mice. These plaques were surrounded by reactive GFAP+ astroglia and Iba1+ microglia. Incubation of fresh slices for 2 weeks with 1-0.1-0.01 μg/ml of NEP, insulysin, MMP-2, or MMP-9 showed that NEP, insulysin, and MMP-9 markedly degraded beta-amyloid plaques but only at the highest concentration. Our data provide for the first time a potent and powerful living brain vibrosection model containing a high number of plaques, which allows to rapidly and simply study the degradation and clearance of beta-amyloid plaques in vitro.

Mesenchymal stem cells support neuronal fiber growth in an organotypic brain slice co-culture model

Mesenchymal stem cells (MSCs) have been identified as promising candidates for neuroregenerative cell therapies. However, the impact of different isolation procedures on the functional and regenerative characteristics of MSC populations has not been studied thoroughly. To quantify these differences, we directly compared classically isolated bulk bone marrow-derived MSCs (bulk BM-MSCs) to the subpopulation Sca-1(+)Lin(-)CD45(-)-derived MSCs(-) (SL45-MSCs), isolated by fluorescence-activated cell sorting from bulk BM-cell suspensions. Both populations were analyzed with respect to functional readouts, that are, frequency of fibroblast colony forming units (CFU-f), general morphology, and expression of stem cell markers. The SL45-MSC population is characterized by greater morphological homogeneity, higher CFU-f frequency, and significantly increased nestin expression compared with bulk BM-MSCs. We further quantified the potential of both cell populations to enhance neuronal fiber growth, using an ex vivo model of organotypic brain slice co-cultures of the mesocortical dopaminergic projection system. The MSC populations were cultivated underneath the slice co-cultures without direct contact using a transwell system. After cultivation, the fiber density in the border region between the two brain slices was quantified. While both populations significantly enhanced fiber outgrowth as compared with controls, purified SL45-MSCs stimulated fiber growth to a larger degree. Subsequently, we analyzed the expression of different growth factors in both cell populations. The results show a significantly higher expression of brain-derived neurotrophic factor (BDNF) and basic fibroblast growth factor in the SL45-MSCs population. Altogether, we conclude that MSC preparations enriched for primary MSCs promote neuronal regeneration and axonal regrowth, more effectively than bulk BM-MSCs, an effect that may be mediated by a higher BDNF secretion.

Nifedipine and nimodipine protect dopaminergic substantia nigra neurons against axotomy-induced cell death in rat vibrosections via modulating inflammatory responses

Neurodegeneration of cholinergic and dopaminergic neurons is a major hallmark in Alzheimer's or Parkinson's disease, respectively. A dysregulation in calcium homeostasis may be part of this process and counteracting calcium influx may have neuroprotective properties in both diseases. Therefore, we investigated the putative neuroprotective or neurotoxic activity of L-type calcium channel (LTCC) inhibitors on cholinergic and dopaminergic neurons in a rat organotypic vibrosection model. Sagittal or coronal vibrosections (200 μm thick) of postnatal day 10 rats were cultured on 0.4 μm semipermeable membranes for 2 weeks with 10 ng/ml nerve growth factor (NGF) and/or glial-cell line derived neurotrophic factor (GDNF) to maintain survival of cholinergic or dopaminergic neurons, respectively. Thereafter, sections were incubated with 0.1, 1 or 10 μM isradipine, nicardipine or verapamil for 2 weeks to explore cytotoxicity. Alternatively, in order to explore neuroprotective activity, vibrosections were incubated without growth factors but with isradipine or verapamil or with nicardipine, nimodipine or nifedipine from the beginning for 4 weeks. Our data show that all LTCC inhibitors exhibited no neurotoxic effect on cholinergic and dopaminergic neurons. Further, LTCC inhibitors did not have any neuroprotective activity on cholinergic neurons. However, nimodipine and nifedipine significantly enhanced the survival of dopaminergic substantia nigra (SN) but not ventral tegmental area (VTA) neurons, while nicardipine, isradipine and verapamil had no effect. Nifedipine (and more potently GDNF) reduced inflammatory cytokines (macrophage inflammatory protein-2, tumor necrosis factor-α), but did not influence oxidative stress or caspase-3 activity and did not interfere with iron-mediated overload. Our data show that nifedipine and nimodipine are very potent to enhance the survival of axotomized SN neurons, possibly influencing inflammatory processes.

β-Amyloid induced effects on cholinergic, serotonergic, and dopaminergic neurons is differentially counteracted by anti-inflammatory drugs

β-Amyloid (Aβ) is a small peptide that plays a potent role in synaptic plasticity as well as forms amyloid plaques in Alzheimer's disease (AD). Recent studies suggest that Aβ deposition is deleterious not only in AD, but also in Parkinson's disease (PD) and depression. This Aβ effect is associated with inflammatory processes. However, further evaluation is needed to understand how Aβ and inflammation interact and contribute to the regulation of the cholinergic, serotonergic, and dopaminergic neuronal populations. The aim of the present study was to investigate the effects of Aβ(1-42) on cholinergic neurons of the nucleus basalis of Meynert (which degenerate in AD), on serotonergic neurons of the dorsal raphe nucleus (which play a role in depression), and on dopaminergic neurons of the ventral mesencephalon (which degenerate in PD) in rat organotypic brain slices. Furthermore, we investigated whether anti-inflammatory drugs (celecoxib, citalopram, cyclooxygenase-2 inhibitor, ibuprofen, indomethacin, piclamilast) modulate or counteract Aβ-induced effects. Two-week-old organotypic brain slices of the nucleus basalis of Meynert, dorsal raphe nucleus, and ventral mesencephalon were incubated with 50 ng/ml Aβ(1-42) with or without anti-inflammatory agents for 3 days. Our results reveal that Aβ significantly decreased the number of choline acetyltransferase-positive cholinergic, tryptophan hydroxylase-positive serotonergic, and tyrosine hydroxylase-positive dopaminergic neurons and that anti-inflammatory drugs partially counteracted the Aβ-induced neuronal decline. This decline was not due to apoptotic processes (as evaluated by TUNEL, propidium iodide, caspase), oxidative stress (as measured by nitrite, catalase, or superoxide dismutase-2), or inflammation, but was most likely caused by a downregulation of these key enzymes.

Organotypic vibrosections: novel whole sagittal brain cultures

In vitro cell culture models are of enormous importance in neuroscience research and organotypic brain slices are found to be a potent model very close to the in vivo situation. Brain slices can be cultured as single slices or as co-slices. However, there is need to culture whole brain sections, containing the complex functional architecture. The aim of the present study was to develop and characterize whole brain sagittal slice cultures (200μm organotypic vibrosections) from postnatal day 8 rats. We show that sagittal vibrosections can be cultured for several weeks and they maintain survival of cholinergic and dopaminergic neurons, as well as a strong capillary network. Partly long-distance cortico-striatal and cortico-hippocampal nerve fibers were found using Mini-Ruby neurotracing. Dopaminergic nerve fibers extended from the mesencephalon, but in the striato-nigral tract and in the striatum only strong dense varicosities were found. The model also allows to study pathological triggers, such as e.g. hydrogen peroxide markedly increased propidiumiodide-positive nuclei in the hippocampus. In conclusion, our novel model provides an easy potent whole sagittal brain culture system that allows to study cholinergic and dopaminergic neurons together but also in close interaction with all other cells of the brain and with capillaries. It will be a great challenge in future to use this model to re-construct whole pathways. This vibrosection model may partly represent a close adult in vivo situation, which allows to study neurodegeneration and neuroprotection of cholinergic and dopaminergic neurons, which plays an important role in Alzheimer's and Parkinson's disease, respectively.

Inflammatory stimuli reduce survival of serotonergic neurons and induce neuronal expression of indoleamine 2,3-dioxygenase in rat dorsal raphe nucleus organotypic brain slices

Neuroinflammation results in dysregulation of serotonergic neurons in the dorsal raphe nucleus (doR) and is considered to play an important role in the pathophysiology of depression. The aim of the present study was to induce neuroinflammation in a simple doR brain slice model using lipopolysaccharide (LPS), interferon-gamma (IFNγ), beta-amyloid₁₋₄₂ or tumor necrosis factor-alpha and to explore the survival of serotonergic neurons and the expression of the tryptophan degrading enzyme indoleamine 2,3-dioxygenase (IDO). Administration of pro-inflammatory stimuli reduced survival of serotonergic neurons in doR slices and increased IDO expression. IFNγ most potently induced IDO expression, which co-localized with neurons, including serotonergic neurons, but not with microglia or astrocytes. IFNγ did not induce PI-positive staining in slices, but increased the average nuclei size of IDO-positive cells. The inflammation-induced decline did not return to control levels, when slices were withdrawn from inflammation, pointing to neurodegeneration. The growth factors BDNF or GDNF did not counteract the inflammation-induced decrease in serotonergic neurons, except for LPS-induced neuronal decline. The inflammation-induced effect was not blocked by the NMDA-receptor antagonist MK-801. Further LPS, but not IFNγ increased inflammatory markers and microglia activity. In conclusion, our data show that a range of inflammatory stimuli decline serotonergic neurons in doR slices and upregulate IDO expression. The data suggest that IDO does not contribute to serotonergic decline, but may serve as a marker of neurodegeneration. Neuroinflammation may contribute to the development of depression.

Cholinergic neurons regulate secretion of glial cell line-derived neurotrophic factor by skeletal muscle cells in culture

Glial cell line-derived neurotrophic factor (GDNF) has been identified as a potent survival factor for both central and peripheral neurons. GDNF has been shown to be a potent survival factor for motor neurons during programmed cell death and continuous treatment with GDNF maintains hyperinnervation of skeletal muscle in adulthood. However, little is known about factors regulating normal production of endogenous GDNF in skeletal muscle. This study aimed to examine the role that motor neurons play in regulating GDNF secretion by skeletal muscle. A co-culture of skeletal muscle cells (C2C12) and cholinergic neurons, glioma×neuroblastoma hybrid cells (NG108-15) were used to create nerve-muscle interactions in vitro. Acetylcholine receptors (AChRs) on nerve-myotube co-cultures were blocked with alpha-bungarotoxin (α-BTX). GDNF protein content in cells and in culture medium was analyzed by enzyme-linked immunosorbant assay (ELISA) and western blotting. GDNF localization was examined by immunocytochemistry. The nerve-muscle co-culture study indicated that the addition of motor neurons to skeletal muscle cells reduced the secretion of GDNF by skeletal muscle. The results also showed that blocking AChRs with α-BTX reversed the action of neural cells on GDNF secretion by skeletal muscle. Although ELISA results showed no GDNF in differentiated NG108-15 cells grown alone, immunocytochemical analysis showed that GDNF was localized in NG108-15 cells co-cultured with C2C12 myotubes. These results suggest that motor neurons may be regulating their own supply of GDNF secreted by skeletal muscle and that activation of AChRs may be involved in this process.

Effects of intrastriatal GDNF on the response of dopamine neurons to 6-hydroxydopamine: time course of protection and neurorestoration

Glial cell line-derived neurotrophic factor (GDNF) protects dopamine (DA) neurons from 6-hydroxydopamine (6-OHDA) toxicity. We have now explored this protection over 8 weeks following toxin administration. Infusion of Fluoro-Gold (FG) into the striatum was followed 1 week later by GDNF (9μg) or its vehicle. Six hours later, animals received 6-OHDA (4 μg) into the same site. 6-OHDA caused a loss of cells in the substantia nigra that expressed both FG and tyrosine hydroxylase (TH) and striatal terminals expressing TH, the high affinity dopamine transporter (DAT), and the vesicular monoamine transporter 2 (VMAT2) as assessed 2-8 weeks later. Loss of FG(+) cells, and striatal DA was completely blocked by GDNF by 2 weeks. In contrast, GDNF only slightly attenuated the loss of TH, DAT, or VMAT2 in the striatum at 2 weeks, but had restored these markers by 4-8 weeks. Thus, GDNF prevents DA cell death and loss of striatal DA content, but several weeks are required to fully restore the dopaminergic phenotype. These results provide insight into the mechanism of GDNF protection of DA neurons, and may help avoid incorrect interpretations of temporary phenotypic changes.

Rotenone induces cell death of cholinergic neurons in an organotypic co-culture brain slice model

In Alzheimer and Parkinson's disease cell death of cholinergic and dopaminergic neurons are characteristic hallmarks, respectively. It is well established that rotenone, an inhibitor of complex I of the electron transport chain, induces cell death of dopaminergic neurons, however, not much is known on the effects of rotenone on cholinergic neurons. The aim of the present study was to evaluate the effects of rotenone on cholinergic neurons in an organotypic in vitro brain co-slice model. When co-cultures were treated with 10 μM rotenone for 24 h a significantly decreased number of cholinergic neurons was found in the basal nucleus of Meynert but not in the dorsal striatum. This cell death exhibited apoptotic DAPI-positive malformed nuclei and enhanced TUNEL-positive cells. In summary, inhibition of complex I of the electron transport chain may play a role in neurodegeneration of cholinergic neurons.

The pro-apoptotic substance thapsigargin selectively stimulates re-growth of brain capillaries

Thapsigargin is a pro-apoptotic chemical, which has been shown to be useful to study cell death of cholinergic or dopaminergic neurons, or cells, which degenerate in Alzheimer's disease or Parkinson's disease, respectively. The aim of the present work was to study the effects of thapsigargin in the well established organotypic brain co-slice model composed of the basal nucleus of Meynert (nBM), ventral mesencephalon (vMes), dorsal striatum (dStr) and parietal cortex (Ctx). Cholinergic acetyltransferase-positive neurons in the nBM and dStr and dopaminergic tyrosine hydroxylase-positive neurons in the vMes survived, when cultured for 4 weeks with nerve growth factor and glial cell line-derived neurotrophic factor. Nerve fibers of cholinergic nBM neurons grew into the cortex and dopaminergic nerve fibers sprouted into dopamine D2 receptor-positive dStr. The whole co-slice contained a dense laminin-positive capillary network. Treatment of co-cultures with 3 microM thapsigargin for 24 hr significantly decreased the number of cholinergic neurons and dopaminergic neurons. This cell death displayed apoptotic DAPI-positive malformed nuclei and enhanced TUNEL-positive cells. Thapsigargin selectively stimulated the laminin-positive capillary growth between the nBM and Ctx. In conclusion, the induced cell death of cholinergic and dopaminergic neurons may be accompanied by enhanced angiogenic activity.

GDNF control of the glutamatergic cortico-striatal pathway requires tonic activation of adenosine A receptors

Glial cell line-derived neurotrophic factor (GDNF) affords neuroprotection in Parkinson's disease in accordance with its ability to bolster nigrostriatal innervation. We previously found that GDNF facilitates dopamine release in a manner dependent on adenosine A(2A) receptor activation. As motor dysfunction also involves modifications of striatal glutamatergic innervation, we now tested if GDNF and its receptor system, Ret (rearranged during transfection) and GDNF family receptor alpha1 controlled the cortico-striatal glutamatergic pathway in an A(2A) receptor-dependent manner. GDNF (10 ng/mL) enhanced (by approximately 13%) glutamate release from rat striatal nerve endings, an effect potentiated (up to approximately 30%) by the A(2A) receptor agonist CGS 21680 (10 nM) and prevented by the A(2A) receptor antagonist, SCH 58261 (50 nM). Triple immunocytochemical studies revealed that Ret and GDNF family receptor alpha1 were located in 50% of rat striatal glutamatergic terminals (immunopositive for vesicular glutamate transporters-1/2), where they were found to be co-located with A(2A) receptors. Activation of the glutamatergic system upon in vivo electrical stimulation of the rat cortico-striatal input induced striatal Ret phosphorylation that was prevented by pre-treatment with the A(2A) receptor antagonist, MSX-3 (3 mg/kg). The results provide the first functional and morphological evidence that GDNF controls cortico-striatal glutamatergic pathways in a manner largely dependent on the co-activation of adenosine A(2A) receptors.

Dopaminergic development of prenatal ventral mesencephalon and striatum in organotypic co-cultures

Using organotypic co-cultures of rat embryonic day 14 (E14) ventral mesencephalon (VM) and E21 striatum, we have described the developmental changes in (i) dopamine (DA) neurochemistry; (ii) numbers of DA neurons; and (iii) protein expression of tyrosine hydroxylase (TH), DA transporter (DAT), and glutamic acid decarboxylase (GAD 65/67), over 17 days in vitro (DIV). Co-cultures demonstrated changes in DA development similar to those observed in vivo. The numbers of VM DA neurons remained relatively constant, while levels of VM DA progressively increased through 10 DIV. After 3 DIV, the levels of striatal DA increased substantially, through 10 DIV. Tissue levels of DA metabolites homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) reflected changes in tissue DA concentrations, indicating that release and metabolism of DA are similar to these characteristics observed in vivo. Western blot analysis of TH protein expression revealed large increases in VM TH after only 3 DIV, followed by a decline in levels through 17 DIV; levels of striatal TH, in contrast, increased through this period. Additionally, DAT and GAD 65/67 expression increased, in both the VM and striatum, over 17 DIV. By 17 DIV, many measures of DA function had decreased from those assessed at 10 DIV, thus providing an approximate limit to the effective duration of use of this co-culture model. Our results provide a much-needed description of the neurochemical changes that occur during the maturation of VM and striatum in organotypic co-cultures. Additionally, these results provide a foundation for future studies to assess toxic challenges of the developing nigrostriatal DA system, in vitro.

Characterization of organotypic ventral mesencephalic cultures from embryonic mice and protection against MPP toxicity by GDNF

We characterized organotypic ventral mesencephalic (VM) cultures derived from embryonic day 12 (E12) mice (CBL57/bL6) in terms of number of dopaminergic neurons, cell soma size and dopamine production in relation to time in vitro and tested the effects of 1-methyl-4-phenylpyridinium (MPP(+)) and glial derived neurotrophic factor (GDNF) to validate this novel culture model. Dopamine production and dopaminergic neuron soma size increased dramatically with time in vitro, whereas the number of dopamine neurons declined by approximately 30% between week 1 and week 2, which was further reduced after week 4. GDNF treatment (100 ng/mL) increased dopaminergic neuron soma size (up to 43%) and DOPAC production (approximately three-fold), but not the number of dopamine neurons in control cultures. One-week-old cultures were more vulnerable to MPP(+), than three-week-old cultures. The EC(50) for dopamine depletion after 2 days exposure and 15 days of recovery were 0.6 and 7 microm, respectively. Both pre-treatment and post-treatment with GDNF are important to obtain maximal protection against MPP(+) toxicity. In one-week-old cultures (5 microm MPP(+), 2 days) GDNF provided potent neuroprotection with dopamine contents reaching control levels and number of tyrosine hydroxylase (TH)(+) cells up to 80% of control, but in three-week-old cultures (10 microm MPP(+), 2 days) the protective potential of GDNF was markedly reduced. Long recovery periods after MPP(+) exposure are required to distinguish between reversible or irreversible toxic and/or trophic effects.

Protein delivery of caspase-3 induces cell death in malignant C6 glioma, primary astrocytes and immortalized and primary brain capillary endothelial cells

Most brain tumors consist of transformed glia cells and are highly vascularized by capillary endothelial cells. The aim of the present study therefore was to deliver pro-apoptotic caspase-3 into malignant C6 glioma and immortalized rBCEC4 brain endothelial cells to induce cell death. Both cell lines were transfected with a reporter protein (beta-galactosidase) using lipid-mediated gene transfer (FuGENE6) or using the novel protein delivery reagent BioPORTER. beta-Galactosidase protein was successfully delivered into both cells, the protein expression peaked around day 2 and was transient. Delivery of caspase-3 induced TUNEL-positive cell death of both cell types. As a control, caspase-3 was also delivered to non-neoplastic primary astrocytes and endothelial cells and induced cell death. In conclusion BioPORTER-protein delivery of pro-apoptotic molecules may provide a potent tool to cause death of the cells in brain tumors, however, this method is limited due to its toxicity to non-malignant cells.

Fetal lateral ganglionic eminence attracts one of two morphologically different types of tyrosine hydroxylase-positive nerve fibers formed by cultured ventral mesencephalon

The purpose of this study was to investigate the influence of fetal lateral ganglionic eminence (LGE) on nerve fiber outgrowth formed by fetal ventral mesencephalon (VM). Organotypic tissue cultures of fetal VM and LGE plated as single or cocultures were employed. Survival time was 3-21 days in vitro. Nerve fiber outgrowth and migration of astrocytes were analyzed using immunohistochemistry for tyrosine hydroxylase (TH) and S100. In addition, cultures were labeled with the TUNEL technique and with antibodies directed against neurofilament (NF) in order to study apoptosis and retraction of nerve fibers, respectively. The results revealed two morphologically different types of TH-positive outgrowth growing into the substrate. The initially formed TH-positive outgrowth radiated continuously without changing direction, while a second wave of TH-positive outgrowth became obvious when the initial growth already had reached a distance of approximately 1000 microm. The second wave of TH-positive outgrowth radiated from the tissue, but at a certain distance changed direction and formed a network surrounding the culture. The initially formed TH-positive growth was not associated with the presence of S100-positive astrocytes and avoided to grow into the LGE. At longer time points the first wave of TH-positive nerve fibers appeared dotted, with disrupted NF-immunoreactive fibers and in most cultures these long distance growing fibers had disappeared at 21 days in vitro. The second wave of TH-positive nerve fibers was growing onto a layer of glia and never reached the distance of the first wave. LGE became innervated by TH-positive fibers at the time point for when the second wave of TH-positive growth had been initiated, and the innervation appeared in TH-dense patches that also showed a high density of S100-positive astrocytes. Significantly increased TUNEL activity within LGE portion of cocultures was observed when TH-positive fibers entered the LGE and formed patches. In conclusion, two morphologically different types of TH-positive outgrowth were found and the initially formed fibers neither targeted the LGE nor were they guided by glial cells, but their potential to grow for long distances was high.

Can the brain be protected through exercise? Lessons from an animal model of parkinsonism☆

Evidence suggests that following injury the brain has the capacity for self-repair and that this can be promoted through a variety of experiences including motor activity. In their article, Döbrössy and Dunnett have provided further evidence that this is the case in an animal model in which an excitotoxin is applied to the neostriatum. Under standard conditions, such a toxin would cause considerable damage to the GABAergic cells of this region and produce behavioral deficits. This model has been used to explore certain aspects of Huntington's disease, which also involves the loss of these neurons. However, Döbrössy and Dunnett show that the damage can be reduced by prior motor training. We have been exploring the neuroprotective effects of motor exercise in a different model, one involving 6-hydroxydopamine, which normally destroys dopamine neurons. Our results indicate that forced exercise can reduce the vulnerability of dopamine neurons to 6-hydroxydopamine. The results further suggest that this protection is due in part to an increase in the availability of the trophic factor GDNF, which can in turn stimulate certain signaling cascades, including one that activates ERK. Our results, together with those of Döbrössy and Dunnett and others, raise the possibility that exercise will protect against a variety of neurodegenerative conditions.

Differential effects of phencyclidine application on secretogranin II expression in organotypic slices of rat prefrontal cortex

Phencyclidine (PCP) is a non-competitive NMDA glutamate receptor antagonist that induces psychotomimetic effects in humans and experimental animals. Chronic PCP exposure elicits signs of persistently altered frontal brain activity and related behaviors which are also seen in patients with schizophrenia. Secretogranin II (sg II) belongs to the chromogranin family of proteins that exist in large dense core vesicles in nervous tissue. In the brain, 90% of sg II is processed to the small peptide secretoneurin. We previously detected differential effects of single-dose and subchronic PCP administration on sg II expression in the rat prefrontal cortex (PFC). In the present study, we applied PCP to organotypic PFC slices. PCP application for 28 h induced decreased tissue and culture medium secretoneurin content. In contrast, incubation with the adenylate cyclase activator forskolin caused significantly increased secretoneurin levels after 8 h. PCP for 4 h followed by 24 h without PCP resulted in increased culture medium secretoneurin content but no change in tissue levels. sg II mRNA expression was decreased after 28 h PCP application in cortical neurons. Immunohistochemical and TUNEL staining profiles indicated that the alterations were not due to neurodegeneration. PCP for 5 days changed neither the secretoneurin tissue or culture medium levels, nor the sg II mRNA expression. These results demonstrate that PCP modulates sg II expression in PFC tissue in the absence of afferent inputs and that the nature of these changes is dependent upon the duration of exposure to and/or withdrawal from PCP.

Tumor necrosis factor-alpha triggers cell death of sensitized potassium chloride-stimulated cholinergic neurons

Cell death of cholinergic neurons of the basal forebrain plays an important role in neurodegenerative disorders, such as Alzheimer's disease. Inflammatory cytokines, such as, for example, tumor necrosis factor-alpha (TNF-alpha), may be involved in these neurodegenerative processes. The aim of this project was to study the role of TNF-alpha in the survival and nerve fiber growth of cholinergic neurons of the basal nucleus of Meynert in organotypic brain slices and in adult rats. Cholinergic neurons were visualized by immunohistochemistry for the enzyme choline acetyltransferase and nerve fibers by histochemistry for the enzyme acetylcholinesterase. When co-slices of basal nucleus of Meynert and neocortex were sensitized for 15 min with 30 mM potassium chloride and subsequently incubated for 1 week with 20 ng/ml TNF-alpha, cholinergic neurons and nerve fibers markedly degenerated. Incubation with different growth factors rescued the loss of cholinergic cell bodies and cholinergic nerve fibers. Injection of 30 mM potassium chloride and 50 ng TNF-alpha into four defined cortical regions of anesthetized adult rats resulted in predominant cell death of cholinergic neurons on the ipsilateral side. In conclusion, our data show that TNF-alpha potentiated cell death of cholinergic neurons possibly via retrograde axonal damage in vitro and in vivo. Cortical overactivation combined with an increased expression of pro-inflammatory cytokines may contribute to the cell death observed in Alzheimer's disease and ageing.

Neuroprotective effects of prior limb use in 6-hydroxydopamine-treated rats: possible role of GDNF

Unilateral administration of 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle (MFB) causes a loss of dopamine (DA) in the ipsilateral striatum and contralateral motor deficits. However, if a cast is placed on the ipsilateral limb during the first 7 days following 6-OHDA infusion, forcing the animal to use its contralateral limb, both the behavioral and neurochemical deficits are reduced. Here, we examine the effect of forced reliance on a forelimb during the 7 days prior to ipsilateral infusion of 6-OHDA on the deficits characteristic of this lesion model. Casted animals displayed no behavioral asymmetries as measured 14-28 days postlesion and a marked attenuation in the loss of striatal DA and its metabolites at 30 days. In addition, animals receiving a unilateral cast alone had an increase in glial cell-line derived neurotrophic factor (GDNF) protein in the striatum corresponding to the overused limb. GDNF increased within 1 day after the onset of casting, peaked at 3 days, and returned to baseline within 7 days. These results suggest that preinjury forced limb-use can prevent the behavioral and neurochemical deficits to the subsequent administration of 6-OHDA and that this may be due in part to neuroprotective effects of GDNF.

Interactions of cyclic adenosine monophosphate, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor treatment on the survival and growth of postnatal mesencephalic dopamine neurons in vitro

The survival of rat postnatal mesencephalic dopamine (DA) neurons in dissociated cell cultures was studied by examining the combinatorial effects of dibutyryl cyclic adenosine monophosphate (db-cAMP), glial cell line-derived neurotrophic factor (GDNF), and brain-derived neurotrophic factor (BDNF), as well as selective inhibitors of protein kinase A (PKA), and mitogen-activated protein kinase (MAPK). Postnatal DA neurons were maintained for 14 days in vitro, and were identified by immunohistochemistry using tyrosine hydroxylase antibody. The survival and growth of DA neurons was significantly increased by the inclusion of either >100 microM db-cAMP or 10 microM Forskolin plus 100 microM IBMX in the culture medium. Neither 10-50 ng/ml GDNF nor 50 ng/ml BDNF alone significantly increased DA neuron survival in vitro. However, the combined use of GDNF and BDNF did increase DA neuron survival, and the addition of either db-cAMP or IBMX/Forskolin to media containing these neurotrophins markedly increased DA neuron survival and growth. The cAMP inhibitor Rp-cAMP, the cAMP-dependent protein kinase A inhibitor H89, and the MAP kinase (MAPK) pathway inhibitor PD98059 significantly reduced the survival of DA neurons when applied alone in the absence of added growth factors. Application of GDNF plus BDNF, or db-cAMP significantly protected the DA neurons from the deleterious effects on survival of either 20 microM H89 or 20 microM PD 98059. The results suggest that BDNF, GDNF, and cAMP produce convergent signals to activate PKA and MAPK pathways which are involved in the survival of postnatal mesencephalic DA neurons in vitro.

Nerve growth factor and cholinergic CNS neurons studied in organotypic brain slices. Implication in Alzheimer's disease?

Nerve growth factor (NGF) is a potent growth factor for cholinergic neurons. The aim of the present study was to investigate if NGF affects cholinergic neurons of the basal nucleus of Meynert (nBM) in organotypic brain slices. In single nBM slices cholinergic neurons rapidly degenerated when incubated without NGF. The number of remaining neurons was rescued by NGF application at any time point. When nBM slices were co-cultured with a cortex slice the number of cholinergic neurons was significantly increased pointing to a trophic influence of the cortex. Incubation with acetylcholine precursors did not affect the survival of cholinergic neurons. There was no significant difference when postnatal day 3 or day 10 nBM slices were cultured. In conclusion, NGF is the most potent growth factor for cholinergic neurons and is a promising candidate for treating Alzheimers disease, however, the delivery of NGF to the brain must the solved.

Additive effect of glial cell line-derived neurotrophic factor and neurotrophin-4/5 on rat fetal nigral explant cultures

Transplantation of embryonic dopaminergic neurons is an experimental therapy for Parkinson's disease, but limited tissue availability and suboptimal survival of grafted dopaminergic neurons impede more widespread clinical application. Glial cell line-derived neurotrophic factor (GDNF) and neurotrophin-4/5 (NT-4/5) exert neurotrophic effects on dopaminergic neurons via different receptor systems. In this study, we investigated possible additive or synergistic effects of combined GDNF and NT-4/5 treatment on rat embryonic (embryonic day 14) nigral explant cultures grown for 8 days. Contrary to cultures treated with GDNF alone, cultures exposed to NT-4/5 and GDNF+NT-4/5 were significantly larger than controls (1.6- and 2.0-fold, respectively) and contained significantly more protein (1.6-fold). Treatment with GDNF, NT-4/5 and GDNF+NT-4/5 significantly increased dopamine levels in the culture medium by 1.5-, 2.5- and 4.7-fold, respectively, compared to control levels, and the numbers of surviving tyrosine hydroxylase-immunoreactive neurons increased by 1.7-, 2.1-, and 3.4-fold, respectively. Tyrosine hydroxylase enzyme activity was moderately increased in all treatment groups compared to controls. Counts of nigral neurons containing the calcium-binding protein, calbindin-D28k, revealed a marked increase in these cells by combined GDNF and NT-4/5 treatment. Western blots for neuron-specific enolase suggested an enhanced neuronal content in cultures after combination treatment, whereas the expression of glial markers was unaffected. The release of lactate dehydrogenase into the culture medium was significantly reduced for GDNF+NT-4/5-treated cultures only. These results indicate that combined treatment with GDNF and NT4/5 may be beneficial for embryonic nigral donor tissue either prior to, or in conjunction with, intrastriatal transplantation in Parkinson's disease.

Nestin expression persists in astrocytes of organotypic slice cultures from rat cortex

Nestin is an intermediate filament protein typical for neural precursor cells that is down-regulated in the post-natal rodent brain. Re-expression of nestin has been observed in reactive astrocytes after injury. In this study, organotypic slice cultures from rat cortex were examined for expression of nestin and glial fibrillary acidic protein between 2 and 8 weeks in culture. Immunoreactivity for nestin and glial fibrillary acidic protein was seen in astrocytes which persisted throughout the observation period. Immunofluorescence double labeling showed widespread co-localization of nestin and glial fibrillary acidic protein. Image analysis revealed that levels of nestin-immunoreactivity plateaued after 5 weeks in culture. By comparison nestin immunoreactivity was absent from glial cells of the cortex in mature rats. These immunohistochemical findings of a persistent expression of nestin in glial cells of organotypic slice culture of the rat cortex indicate a different time course of glial maturation in vitro. This difference could be related to the altered trophic stimulation in vitro; differences in neuronal maturation, activity or survival; slow degeneration of the vasculature; or intrinsic properties of astrocytes.

Magnetic stimulation induces neuronal c-fos via tetrodotoxin-sensitive sodium channels in organotypic cortex brain slices of the rat

Repetitive transcranial magnetic stimulation is a novel non-invasive method with antidepressant properties, where electromagnetic fields are applied via an electrode. The aim of the present study was to investigate in an in vitro model if magnetic stimulation may activate the transcription factor c-fos. Organotypic brain slices of the parietal cortex were cultured for 2 weeks and then treated with a magnetic stimulator. Immunohistochemistry was used to detect c-fos like immunoreactivity. We show that magnetic stimulation (1 Hz, 10 min, 75% machine output/magstim 200 rapid stimulator) transiently enhanced c-fos 3-6 h after stimulation. Co-localization experiments revealed that c-fos was expressed in neurons but not astroglia. The activation of c-fos by magnetic stimulation was inhibited by the sodium-channel blocker tetrodotoxin (TTX) (10 microM). It is concluded that magnetic stimulation induces neuronal c-fos via TTX-sensitive sodium channels in organotypic cortex slices.

Nerve growth factor and glial cell line-derived neurotrophic factor restore the cholinergic neuronal phenotype in organotypic brain slices of the basal nucleus of Meynert

Loss of cholinergic neurons is found in the medial septum and nucleus basalis of Meynert in Alzheimer's disease. Recent observations suggest that cholinergic neurons down-regulate their phenotype and that growth factors may rescue cholinergic neurons. The aim of this study was to investigate whether cholinergic neurons of the basal nucleus of Meynert can be cultured in rat organotypic slices, and if nerve growth factor and glial cell line-derived neurotrophic factor can rescue the cholinergic phenotype. In the organotypic slices, glial cells, GABAergic and cholinergic neurons were visualized using immunohistochemistry. The number of cholinergic neurons was found to be very low in slices cultured without exogenous nerve growth factor. Analysis of nerve growth factor tissue levels by enzyme-linked immunosorbent assay revealed very low endogenous tissue levels. When slices were incubated with 100ng/ml nerve growth factor during the initial phase of culturing, a stable expression of choline acetyltransferase was found for up to several weeks. After eight weeks in culture with nerve growth factor or two to three weeks after nerve growth factor withdrawal, numbers of detected cholinergic neurons decreased. Neurons incubated with nerve growth factor displayed a significantly enlarged cell soma compared to neurons without growth factors. In cultures incubated for up to nine weeks, it was also found that glial cell line-derived neurotrophic factor was capable of restoring the cholinergic phenotype. The low-affinity p75 and high-affinity trkA receptors, as well as the glial cell line-derived neurotrophic factor receptor GFRalpha-1, could be visualized in slices using immunohistochemistry. In conclusion, it is shown that, in the axotomized organotypic slice model, the number of cholinergic neurons is decreased, but can be partly restored by nerve growth factor and glial cell line-derived neurotrophic factor.

Retinoic acid treatment enhances the acetylcholine contents in the human teratocarcinoma cell line NTera-2

Human NTera-2/clone D1 teratocarcinoma cells are induced by retinoic acid (RA) to differentiate into postmitotic cells with morphological and biochemical characteristics of embryonic human neurones. Currently only limited information concerning peptide-contents and neurotransmitter pools of these cells is available. Zeller and Strauss [Int. J. Dev. Neurosci. 1995;13(5):437] described an increase in choline acetyltransferase (ChAT) activity in RA-treated, but not in untreated NTera-2 cells, suggesting the induction of a cholinergic phenotype during treatment with RA. In the present study we investigated the effect of RA-differentiation on the amount of the neurotransmitters acetylcholine (ACh), and dopamine in NTera-2 in order to specify the transmitter phenotype induced by RA-differentiation. We found that a 4-week treatment of NTera-2 cells with 10 microM RA markedly increased the ACh-content of these cells, while dopamine levels were unchanged. Depolarisation with potassium (60 mM) enhanced ACh-outflow in the differentiated cells in a Ca(++) dependent way. Also neuropeptides like substance P and NPY were detectable in the undifferentiated NTera-2 cells, while vasointestinal peptide (VIP) could not be found in either precursor or RA-differentiated cells. Differentiation was accompanied by a marked reduction of neutral endopeptidase enzyme activity and aminopeptidase activity. From these observations it was concluded that RA induces a cholinergic neurochemical differentiation of this human teratocarcinoma cell line, and that these cells might provide a model system to investigate cholinergic properties of human origin.

3,4-Methylenedioxymetamphetamine (ecstasy) induces c-fos-like protein and mRNA in rat organotypic dorsal striatal slices

3,4-Methylenedioxymetamphetamine (MDMA, "ecstasy") is an increasingly abused drug, which has significant effects on the dopamine system in the striatum. The isolated single organotypic slice model allows investigation of the effects of drugs of abuse on the expression of transcription factors in the striatum without dopaminergic and glutamatergic interactions. In this study the effects of MDMA on the expression of c-fos mRNA by in situ hybridization as well as the c-fos-like protein by immunohistochemistry in isolated dorsal striatum was investigated. It was shown that 100 microM MDMA induced c-fos mRNA expression 30 min after treatment. Expression of c-fos-like protein was transiently detected 3 h afterwards. The c-fos expression was inhibited by MK 801 and metoclopramide, indicating the involvement of dopaminergic D2 receptors and glutamatergic NMDA receptors. The dopaminergic D1 receptor antagonist SCH 23390 did not affect c-fos expression. We conclude that MDMA treatment leads to the induction of c-fos expression in isolated rat striatal slices. This effect is independent of extrinsic neuronal circuitry and seems to be associated with direct interactions between MDMA and the dopamine/glutamate receptor system.

Chronic repetitive transcranial magnetic stimulation enhances c-fos in the parietal cortex and hippocampus

Repetitive transcranial magnetic stimulation (rTMS) is a novel non-invasive method with anti-depressant properties. However, the mechanism of activation on the cellular level is unknown. Twelve hours after the last chronic rTMS treatment (14 days, once per day, 20 Hz, 10 s, 75% machine output, the transcription factor c-fos was markedly increased in neurons in layers I-IV and VI of the parietal cortex and in few scattered neurons in the hippocampus of Sprague-Dawley rats. The cortical activation was not blocked by the NMDA antagonist MK-801. The increase of c-fos was not paralleled by an increased glial response and activation of cortical growth factors. Thus, it is concluded that chronic rTMS differentially activates parietal cortical layers and this might be involved in mediating anti-depressant activity in other brain areas.