Activation of caspase-3 in developmental models of programmed cell death in neurons of the substantia nigra

Chrysanthemum boreale Makino Inhibits Oxidative Stress-Induced Neuronal Damage in Human Neuroblastoma SH-SY5Y Cells by Suppressing MAPK-Regulated Apoptosis

Oxidative stress has been demonstrated to play a pivotal role in the pathological processes of many neurodegenerative diseases. In the present study, we demonstrated that Chrysanthemum boreale Makino extract (CBME) suppresses oxidative stress-induced neurotoxicity in human neuroblastoma SH-SY5Y cells and elucidated the underlying molecular mechanism. Our observations revealed that CBME effectively protected neuronal cells against H₂O₂-induced cell death by preventing caspase-3 activation, Bax upregulation, Bcl-2 downregulation, activation of three mitogen-activated protein kinases (MAPKs), cAMP response element-binding protein (CREB) and NF-κB phosphorylation, and iNOS induction. These results provide evidence that CBME has remarkable neuroprotective properties in SH-SY5Y cells against oxidative damage, suggesting that the complementary or even alternative role of CBME in preventing and treating neurodegenerative diseases is worth further studies.

Selective deletion of Caspase-3 gene in the dopaminergic system exhibits autistic-like behaviour

Apoptotic caspases are thought to play critical roles in elimination of excessive and non-functional synapses and removal of extra cells during early developmental stages. Hence, an impairment of this process may thus constitute a basis for numerous neurological and psychiatric diseases. This view is especially relevant for dopamine due to its pleiotropic roles in motor control, motivation and reward processing. Here, we have analysed the effect of caspase-3 depletion on the development of catecholaminergic neurons and performed a wide array of neurochemical, ultrastructural and behavioural assays. To achieve this, we performed selective deletion of the Casp3 gene in tyrosine hydroxylase (TH)-expressing cells using Cre-loxP-mediated recombination. Histological evaluation of most relevant catecholaminergic nuclei revealed the ventral mesencephalon as the most affected region. Stereological analysis demonstrated an increase in the number of TH-positive neurons in both the substantia nigra and ventral tegmental area along with enlarged volume of the ventral midbrain. Analysis of main innervating tissues revealed a rather contrasting profile. In striatum, basal extracellular levels and potassium-evoked DA release were significantly reduced in mice lacking Casp3, a clear indication of dopaminergic hypofunction in dopaminergic innervating tissues. This view was sustained by analysis of TH-labelled dopaminergic terminals by confocal and electron microscopy. Remarkably, at a behavioural level, Casp3-deficient mice exhibited impaired social interaction, restrictive interests and repetitive stereotypies, which are considered the core symptoms of autism spectrum disorder (ASD). Our study revitalizes the potential involvement of dopaminergic transmission in ASD and provides an excellent model to get further insights in ASD pathogenesis.

Loss of Collapsin Response Mediator Protein 4 Attenuates 6-Hydroxydopamine-Induced Impairments in a Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is a chronic neurodegenerative disorder characterized by impaired motor symptoms induced by the degeneration of dopaminergic neurons of the substantia nigra pars compacta (SNc). Many factors are speculated to operate in the mechanism of PD, including oxidative stress, mitochondrial dysfunction, abnormal protein handling, and PD induced apoptosis. Besides, researchers have recently shown that inflammatory secretions may engage neighboring cells such as astrocytes, which then induce autocrine and paracrine responses that amplify the inflammation, leading to neurodegeneration. In the present study, we analyzed the neuroprotective and anti-inflammatory effects of collapsin response mediator protein 4 (CRMP4) deletion in 6-hydroxydopamine (6-OHDA)-injected male mice, as well as its effects on motor impairments. Our findings indicated that the deletion of CRMP4 could maintain the TH-positive fibers in the striatum and the TH-positive cells in SNc, attenuate the inflammatory responses, and improve motor coordination and rotational behavior. Furthermore, based on our findings at the early time points, we hypothesized that primary differences between the Crmp4+/+ and Crmp4-/- mice may occur in microglia instead of neurons. Although further work should be carried out to clarify the specific role of CRMP4 in the pathogenesis of PD, our findings suggest that it could be a possible target for the treatment of PD.

Nimodipine attenuates the parkinsonian neurotoxin, MPTP-induced changes in the calcium binding proteins, calpain and calbindin

We have recently demonstrated neuroprotective abilities of nimodipine, an L-type voltage dependent calcium channel (VDCC) blocker in cellular and animal models of Parkinson's disease (PD). To understand the calcium regulatory mechanisms in the disease pathogenesis, the present study examined calcium regulatory proteins calbindin and calpain mRNA and protein levels employing quantitative PCR and western blot in 1-methyl-4-phenyl pyridinium ion (MPP⁺)-treated SH-SY5Y cell lines and in the striatum of mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). mRNA and protein levels of calbindin were lower, while that of calpain were higher in MPP⁺-treated SH-SY5Y cells and MPTP-treated mouse striatum as compared to their respective controls. Nimodipine pretreatment significantly attenuated these effects in the parkinsonian neurotoxin-treated SH-SY5Y cell line and in the mouse striatum. The activities of the apoptotic mediator, caspase-3 and calpain were increased in the neurotoxin-treated groups as compared to their respective controls, which was ameliorated by nimodipine pretreatment. These results suggest that parkinsonian neurotoxin-mediated dopaminergic neuronal death might involve defects in calcium regulatory proteins that control intracellular calcium homeostasis, and these could be corrected by inhibiting L-type VDCC activity. These findings support the notion that hypertensive patients who are on long-term intake of dihydropyridine have reduced risk for PD.

Effect of wedelolactone and gallic acid on quinolinic acid-induced neurotoxicity and impaired motor function: significance to sporadic amyotrophic lateral sclerosis

Quinolinic acid (QUIN) is a well-known neuroactive metabolite of tryptophan degradation pathway or kynurenine pathway. The QUIN is involved in the development of several toxic cascades which leads to the neuronal degeneration processes. The QUIN-induced toxicity is also responsible for the impairment of the motor function and motor learning ability. This study seeks to investigate the several mechanisms which are involved in the intrastriatal administration of QUIN-induced neurodegeneration and the neuroprotective effects of wedelolactone (WL) and gallic acid (GA) over QUIN-induced toxicity. The Wistar rats were used for the study and conducted behavioral model to evaluate the effects of WL (100 & 200 mg/kg) and GA (100 & 200 mg/kg) on impaired motor function and motor learning ability. We also assessed the effects of WL and GA on the antioxidant profile, cytotoxicity, apoptosis, excitotoxicity, inflammatory cascades, and on growth factors which helps in neurogenesis. The compounds effectively improved the motor function, motor learning memory in the rats. Similarly, enhanced the activity of Glutathione peroxidase, SOD, catalase, and declined the lipid peroxidation and nitrite production in the brain. The treatment with WL and GA lowered the activities of LDH, m-calpain, and caspase-3. The reports strongly support that both compounds are useful in the prevention of glutamate excitotoxicity induced by QUIN. The NAA, IGF-1, and VEGF levels in the brain were improved after treatment with WL and GA. The neuroprotective effects of WL and GA further proved through the anti-inflammatory effects. The compounds significantly down-regulated the expression of TNF-α, IL-6, and IL-β in the brain. Immunohistochemical analysis shows that the WL and GA reduced the expression of NF-κB. The histopathological studies for cerebellum, hippocampus, striatum, and spinal cord confirms the toxic effects of QUIN and neuroprotective effects of WL and GA. The results suggest that WL and GA could ameliorate the toxic events triggered by QUIN and might be effective in the prevention and progression of several cascades which lead to the development of sALS.

Melandrii Herba Extract Attenuates H₂O₂-Induced Neurotoxicity in Human Neuroblastoma SH-SY5Y Cells and Scopolamine-Induced Memory Impairment in Mice

Oxidative stress plays a significant role in the etiology of a variety of neurodegenerative diseases. In this study, we found that Melandrii Herba extract (ME) attenuated oxidative-induced damage in cells. Mechanistically, ME exhibited protection from H₂O₂-induced neurotoxicity via caspase-3 inactivation, Bcl-2 downregulation, Bax upregulation, and MAPK activation (ERK 1/2, JNK 1/2, and p38 MAPK) in vitro. Moreover, our in vivo data showed that ME was able to attenuate scopolamine-induced cognitive impairment. These results provide in vitro and in vivo evidence that ME exhibits neuroprotective properties against oxidative stress, which suggests that ME is worthy of further investigation as a complementary, or even as an alternative, product for preventing and treating neurodegenerative disorders.

Downregulation of DEC1 contributes to the neurotoxicity induced by MPP+ by suppressing PI3K/Akt/GSK3β pathway

AIM

Differentiated embryonic chondrocyte gene 1 (DEC1) is involved in the neuronal differentiation and development. The aim of this study is to investigate the role of DEC1 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPP+ )-induced PD model.

METHODS

The location of DEC1 and tyrosine hydroxylase (TH)-positive neurons were detected by immunofluorescence. 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse subacute model of PD was established to evaluate the change of DEC1 expression in midbrain. Then, SH-SY5Y cells were used to investigate the role of DEC1 in MPP+ -induced neurotoxicity.

RESULTS

We showed that the co-expressed DEC1 and TH neurons took up more than 80% of the expressed TH neurons in the midbrain of mice. DEC1/TH double-positive neurons decreased by 40.6% in SNpc and 28.8% in VTA of MPTP-injured mice. Consistently, DEC1, TH and dopamine transporter (DAT) expression decreased in the midbrain of MPTP mice. In SY-SY5Y cells, MPP+ significantly suppressed DEC1 expression and increased the cleaved caspase 3/caspase 3 and Bax/Bcl-2. DEC1 overexpression relieved, whereas DEC1 knockdown aggravated MPP+ -induced cytotoxicity. Likewise, DEC1 overexpression and knockdown inversely regulated the expression of β-catenin and PI3Kp110α (PIK3CA), an essential role in Wnt/β-catenin and PI3K/Akt signaling pathways. Interestingly, LY294002, an inhibitor of PI3K/Akt signaling, aggravated, whereas LiCl, an activator of Wnt/β-catenin signaling, abolished the reduction in DEC1 by MPP+ . It is established that these two pathways are interconnected by the phosphorylation status of GSK3β. DEC1 overexpression increased but MPP+ and DEC1 knockdown decreased GSK3β phosphorylation.

CONCLUSION

Downregulation of DEC1 contributes to MPP+ -induced neurotoxicity by suppressing PI3K/Akt/GSK3β pathway.

Low Levels of Prohibitin in Substantia Nigra Makes Dopaminergic Neurons Vulnerable in Parkinson's Disease

Since substantia nigra (SN) and ventral tegmental area (VTA) dopaminergic neurons are, respectively, susceptible or largely unaffected in Parkinson's disease (PD), we searched for protein(s) that regulates this differential sensitivity. Differentially, expressed proteins in SN and VTA were investigated employing two-directional gel electrophoresis- matrix-assisted laser desorption ionization time of flight (MALDI-TOF-TOF) analyses. Prohibitin, which is involved in mitochondrial integrity, was validated using immunoblot, qRT-PCR, and immunohistochemistry in normal mice as well as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-model, PD postmortem human brains, and PD cybrids. In prohibitin over-expression, differentiated SH-SY5Y neurons were investigated for their susceptibility to PD neurotoxin, 1-methyl-4-phenyl-pyridnium (MPP⁺). Prohibitin, Hsc73, and Cu-Zn superoxide dismutase (Cu-Zn SOD) were highly expressed in VTA, whereas heat shock protein A8 (HSPA8) and 14-3-3ζ/δ were 2-fold more in SN. Prohibitin level was transiently increased in SN but unaltered in VTA on the third day of MPTP-induced mice, whereas in PD human brains, prohibitin was depleted in both these regions. Parallel to mouse SN, an enhanced prohibitin expression was found in human PD cybrids. In MPP⁺-induced cellular model of PD, reduction in prohibitin level was found to be associated with a loss in its binding with Ndufs3, a mitochondrial complex I protein partner. Prohibitin over-expression resisted MPP⁺-induced neuronal death by restoring mitochondrial membrane potential, preventing reactive oxygen species generation and cytochrome c release into cytosol. These protective phenomena exerted by prohibitin over-expression altogether hinder caspase 3 activation induced by MPP⁺. These results imply that prohibitin is an important negotiator protein that regulates dopaminergic cell death in SN and their protection in VTA in PD.

The 6-hydroxydopamine model and parkinsonian pathophysiology: Novel findings in an older model

The neurotoxin 6-hydroxydopamine (6-OHDA) is widely used to induce models of Parkinson's disease (PD). We now know that the model induced by 6-OHDA does not include all PD symptoms, although it does reproduce the main cellular processes involved in PD, such as oxidative stress, neurodegeneration, neuroinflammation, and neuronal death by apoptosis. In this review we analyse the factors affecting the vulnerability of dopaminergic neurons as well as the close relationships between neuroinflammation, neurodegeneration, and apoptosis in the 6-OHDA model. Knowledge of the mechanisms involved in neurodegeneration and cell death in this model is the key to identifying potential therapeutic targets for PD.

Sexual Differences in Cell Loss during the Post-Hatch Development of Song Control Nuclei in the Bengalese Finch

Birdsongs and the regions of their brain that control song exhibit obvious sexual differences. However, the mechanisms underlying these sexual dimorphisms remain unknown. To address this issue, we first examined apoptotic cells labeled with caspase-3 or TUNEL in Bengalese finch song control nuclei - the robust nucleus of the archopallium (RA), the lateral magnocellular nucleus of the anterior nidopallium (LMAN), the high vocal center (HVC) and Area X from post-hatch day (P) 15 to 120. Next, we investigated the expression dynamics of pro-apoptotic (Bid, Bad and Bax) and anti-apoptotic (Bcl-2 and Bcl-xL) genes in the aforementioned nuclei. Our results revealed that the female RA at P45 exhibited marked cell apoptosis, confirmed by low densities of Bcl-xL and Bcl-2. Both the male and female LMAN exhibited apoptotic peaks at P35 and P45, respectively, and the observed cell loss was more extensive in males. A corresponding sharp decrease in the density of Bcl-2 after P35 was observed in both sexes, and a greater density of Bid was noted at P45 in males. In addition, we observed that RA volume and the total number of BDNF-expressing cells decreased significantly after unilateral lesion of the LMAN or HVC (two areas that innervate the RA) and that greater numbers of RA-projecting cells were immunoreactive for BDNF in the LMAN than in the HVC. We reasoned that a decrease in the amount of BDNF transported via HVC afferent fibers might result in an increase in cell apoptosis in the female RA. Our data indicate that cell apoptosis resulting from different pro- and anti-apoptotic agents is involved in generating the differences between male and female song control nuclei.

Quinolinic acid: an endogenous neurotoxin with multiple targets

Quinolinic acid (QUIN), a neuroactive metabolite of the kynurenine pathway, is normally presented in nanomolar concentrations in human brain and cerebrospinal fluid (CSF) and is often implicated in the pathogenesis of a variety of human neurological diseases. QUIN is an agonist of N-methyl-D-aspartate (NMDA) receptor, and it has a high in vivo potency as an excitotoxin. In fact, although QUIN has an uptake system, its neuronal degradation enzyme is rapidly saturated, and the rest of extracellular QUIN can continue stimulating the NMDA receptor. However, its toxicity cannot be fully explained by its activation of NMDA receptors it is likely that additional mechanisms may also be involved. In this review we describe some of the most relevant targets of QUIN neurotoxicity which involves presynaptic receptors, energetic dysfunction, oxidative stress, transcription factors, cytoskeletal disruption, behavior alterations, and cell death.

Activation of GSK-3β and caspase-3 occurs in Nigral dopamine neurons during the development of apoptosis activated by a striatal injection of 6-hydroxydopamine

The 6-Hydroxydopamine (6-OHDA) rat model of Parkinson's disease is essential for a better understanding of the pathological processes underlying the human disease and for the evaluation of promising therapeutic interventions. This work evaluated whether a single striatal injection of 6-OHDA causes progressive apoptosis of dopamine (DA) neurons and activation of glycogen synthase kinase 3β (GSK-3β) and caspase-3 in the substantia nigra compacta (SNc). The loss of DA neurons was shown by three neuron markers; tyrosine hydroxylase (TH), NeuN, and β-III tubulin. Apoptosis activation was determined using Apostain and immunostaining against cleaved caspase-3 and GSK-3β pY216. We also explored the possibility that cleaved caspase-3 is produced by microglia and astrocytes. Our results showed that the 6-OHDA caused loss of nigral TH(+) cells, progressing mainly in rostrocaudal and lateromedial directions. In the neostriatum, a severe loss of TH(+) terminals occurred from day 3 after lesion. The disappearance of TH(+) cells was associated with a decrease in NeuN and β-III tubulin immunoreactivity and an increase in Apostain, cleaved caspase-3, and GSK-3β pY216 in the SNc. Apostain immunoreactivity was observed from days 3 to 21 postlesion. Increased levels of caspase-3 immunoreactivity in TH(+) cells were detected from days 1 to 15, and the levels then decreased to day 30 postlesion. The cleaved caspase-3 also collocated with microglia and astrocytes indicating its participation in glial activation. Our results suggest that caspase-3 and GSK-3β pY216 activation might participate in the DA cell death and that the active caspase-3 might also participate in the neuroinflammation caused by the striatal 6-OHDA injection.

Neuroprotective effect of sulforaphane in 6-hydroxydopamine-lesioned mouse model of Parkinson's disease

Parkinson's disease (PD) is characterized by the selective loss of dopaminergic nigrostriatal neurons, which leads to disabling motor disturbances. Sulforaphane (SFN), found in cruciferous vegetables, is a potent indirect antioxidant and recent advances have shown its neuroprotective activity in various experimental models of neurodegeneration. This study was undertaken to examine the effects of SFN on behavioral changes and dopaminergic neurotoxicity in mice exposed to 6-hydroxydopamine (6-OHDA). For this purpose, mice were treated with SFN (5mg/kg twice a week) for four weeks after the unilateral intrastriatal injection of 6-OHDA. The increase in 6-OHDA-induced rotations and deficits in motor coordination were ameliorated significantly by SFN treatment. In addition, SFN protected 6-OHDA-induced apoptosis via blocking DNA fragmentation and caspase-3 activation. These results were further supported by immunohistochemical findings in the substantia nigra that showed that SFN protected neurons from neurotoxic effects of 6-OHDA. The neuroprotective effect of SFN may be attributed to its ability to enhance glutathione levels and its dependent enzymes (glutathione-S-transferase and glutathione reductase) and to modulate neuronal survival pathways, such as ERK1/2, in the brain of mice. These results suggest that SFN may potentially be effective in slowing down the progression of idiopathic PD by the modulation of oxidative stress and apoptotic machinery.

Clonal analysis by distinct viral vectors identifies bona fide neural stem cells in the adult zebrafish telencephalon and characterizes their division properties and fate

Neurogenesis is widespread in the zebrafish adult brain through the maintenance of active germinal niches. To characterize which progenitor properties correlate with this extensive neurogenic potential, we set up a method that allows progenitor cell transduction and tracing in the adult zebrafish brain using GFP-encoding retro- and lentiviruses. The telencephalic germinal zone of the zebrafish comprises quiescent radial glial progenitors and actively dividing neuroblasts. Making use of the power of clonal viral vector-based analysis, we demonstrate that these progenitors follow different division modes and fates: neuroblasts primarily undergo a limited amplification phase followed by symmetric neurogenic divisions; by contrast, radial glia are capable at the single cell level of both self-renewing and generating different cell types, and hence exhibit bona fide neural stem cell (NSC) properties in vivo. We also show that radial glial cells predominantly undergo symmetric gliogenic divisions, which amplify this NSC pool and may account for its long-lasting maintenance. We further demonstrate that blocking Notch signaling results in a significant increase in proliferating cells and in the numbers of clones, but does not affect clone composition, demonstrating that Notch primarily controls proliferation rather than cell fate. Finally, through long-term tracing, we illustrate the functional integration of newborn neurons in forebrain adult circuitries. These results characterize fundamental aspects of adult progenitor cells and neurogenesis, and open the way to using virus-based technologies for stable genetic manipulations and clonal analyses in the zebrafish adult brain.

Brain-derived neurotrophic factor regulates early postnatal developmental cell death of dopamine neurons of the substantia nigra in vivo

Brain-derived neurotrophic factor (BDNF) was the first purified molecule identified to directly support the development of mesencephalic dopamine neurons. However, its physiologic role has remained unknown. Based on patterns of expression, it is unlikely to serve as a target-derived neurotrophic factor, but it may instead act locally in the mesencephalon, either released by afferent projections, or in autocrine fashion. To assess a possible local role, we blocked BDNF signaling in the substantia nigra (SN) of postnatal rats by injection of either neutralizing antibodies or a peptide antagonist. These treatments increased the magnitude of developmental cell death in the SN, indicating that endogenous local BDNF does play a regulatory role. However, we also find that elimination of BDNF in brain throughout postnatal development in BDNF(fl/fl):Nestin-Cre mice has no effect on the adult number of SN dopamine neurons. We postulate that other forms of trophic support may compensate for the elimination of BDNF during early development. Although the number of SN dopamine neurons is unchanged, their organization is disrupted. We conclude that BDNF plays a physiologic role in the postnatal development of SN dopamine neurons.

Regulation of the postnatal development of dopamine neurons of the substantia nigra in vivo by Akt/protein kinase B

Following mitosis, specification and migration during embryogenesis, dopamine neurons of the mesencephalon undergo a postnatal naturally occurring cell death event that determines their final adult number, and a period of axonal growth that determines pattern and extent of target contacts. While a number of neurotrophic factors have been suggested to regulate these developmental events, little is known, especially in vivo, of the cell signaling pathways that mediate these effects. We have examined the possible role of Akt/Protein Kinase B by transduction of these neurons in vivo with adeno-associated viral vectors to express either a constitutively active or a dominant negative form of Akt/protein kinase B. We find that Akt regulates multiple features of the postnatal development of these neurons, including the magnitude of the apoptotic developmental cell death event, neuron size, and the extent of target innervation of the striatum. Given the diversity and magnitude of its effects, the regulation of the development of these neurons by Akt may have implications for the many psychiatric and neurologic diseases in which these neurons may play a role.

Genetic dissection of gamma-secretase-dependent and -independent functions of presenilin in regulating neuronal cell cycle and cell death

Cell cycle markers have been shown to be upregulated and proposed to lead to apoptosis of postmitotic neurons in Alzheimer's disease (AD). Presenilin (PS) plays a critical role in AD pathogenesis, and loss-of-function studies in mice established a potent effect of PS in cell proliferation in peripheral tissues. Whether PS has a similar activity in the neuronal cell cycle has not been investigated. PS exhibits gamma-secretase-dependent and -independent functions; the former requires aspartate 257 (D257) as part of the active site, and the latter involves the hydrophilic loop domain encoded by exon 10. We used two novel mouse models, one expressing the PS1 D257A mutation on a postnatal PS conditional knock-out background and the other deleting exon 10 of PS1, to dissect the gamma-secretase-dependent and -independent activities of PS in the adult CNS. Whereas gamma-secretase plays a dominant role in neuronal survival, our studies reveal potent neuronal cell cycle regulation mediated by the PS1 hydrophilic loop. Although neurons expressing cell cycle markers do not directly succumb to apoptosis, they are more vulnerable under stress conditions. Importantly, our data identify a novel pool of cytoplasmic p53 as a downstream mediator of this cellular vulnerability. These results support a model whereby the PS gamma-secretase activity is essential in maintaining neuronal viability, and the PS1 loop domain modulates neuronal homeostasis through cell cycle and cytoplasmic p53 control.

Histochemical methods for the detection of apoptosis in the nervous system

Neuroscientists often need to detect neuron death at the light microscope level in tissue sections derived from animal models of neurological disease. In many instances there is a need to detect apoptosis, the most common morphology of programmed cell death. This unit provides two protocols for the detection of apoptosis by immunostaining for either activated forms of caspases or their cleavage products. When used in conjunction with nuclear dyes, these protocols permit visualization not only of caspase activation, but also the nuclear chromatin clumps characteristic of apoptosis. The first protocol utilizes peroxidase-mediated chromogen deposition to visualize antibodies by brightfield microscopy. The second protocol utilizes fluorophores to visualize antibodies by epifluorescence. Double immunofluorescence labeling can be performed to identify the phenotype of cells in which caspases are activated. Not all cell death is apoptotic. Therefore, a third protocol is presented for suppressed silver staining, a useful method to screen for all morphologic forms of cell death.

Progressive degeneration of dopamine neurons in 6-hydroxydopamine rat model of parkinson's disease does not involve activation of caspase-9 and caspase-3

6-Hydroxydopamine (6-OHDA), a neurotoxin that causes the death of dopamine (DA) neurons, is commonly used to produce experimental models of Parkinson's disease (PD) in rodents. In the rat model of PD first described by Sauer and Oertel, DA neurons progressively die over several weeks following a striatal injection of 6-OHDA. It is generally assumed that DA neurons die through apoptosis after exposure to 6-OHDA, but data supporting activation of a caspase enzymatic cascade are lacking. In this study, we sought to determine if caspases involved in the intrinsic apoptotic cascade play a role in the initial stages of 6-OHDA-induced death of DA neurons in the progressively lesioned rat model of PD. We found that injection of 6-OHDA into adult rat striatum did not activate caspase-9 or caspase-3 or increase levels of caspase-dependent cleavage products in the substantia nigra at various survival times up to 7 days after the lesion, even though this paradigm produced DA neuronal loss. These data suggest that in the adult rat brain DA neurons whose terminals are challenged with 6-OHDA do not die through a classical caspase-dependent apoptotic mechanism.

Apoptotic natural cell death in developing primate dopamine midbrain neurons occurs during a restricted period in the second trimester of gestation

Natural cell death (NCD) by apoptosis is a normal developmental event in most neuronal populations, and is a determinant of the eventual size of a population. We decided to examine the timing and extent of NCD of the midbrain dopamine system in a primate species, as dopamine deficiency or excess has been implicated in several disorders. Genetic or environmental differences may alter the extent of NCD and predispose individuals to neurological or psychiatric diseases. In developing rats, NCD in the midbrain dopamine system has been observed to start at the end of gestation and peak in the postnatal period. In fetal monkey brains, apoptosis in midbrain DA neurons was identified histologically by chromatin clumping in tyrosine hydroxylase-positive cells, and confirmed by TUNEL and active caspase-3 staining. A distinct peak of NCD occurred at about E80, midway through gestation in this species. We estimate that at least 50% of the population may be lost in this process. In other brains we determined biochemically that the onset of apoptosis coincides with the time of greatest rate of increase of striatal DA concentration. Thus, marked apoptotic NCD occurs in the primate midbrain dopamine system half-way through gestation, and appears to be associated with the rapid developmental increase in striatal dopamine innervation.

Time-course of nigrostriatal damage, basal ganglia metabolic changes and behavioural alterations following intrastriatal injection of 6-hydroxydopamine in the rat: new clues from an old model

Despite the progressive development of innovative animal models for Parkinson's disease, the intracerebral infusion of neurotoxin 6-hydroxydopamine (6-OHDA) remains the most widely used means to induce an experimental lesion of the nigrostriatal pathway in the animal, due to its relatively low complexity and cost, coupled with the high reproducibility of the lesion obtained. To gain new information from such a classic model, we studied the time-course of the nigrostriatal damage, metabolic changes in the basal ganglia nuclei (cytochrome oxidase activity) and behavioural modifications (rotational response to apomorphine) following unilateral injection of 6-OHDA into the corpus striatum of rat, over a 4-week period. Striatal infusion of 6-OHDA caused early damage of dopaminergic terminals, followed by a slowly evolving loss of dopaminergic cell bodies in the substantia nigra pars compacta, which became apparent during the second week post-injection and peaked at the 28th day post-infusion; the rotational response to apomorphine was already present at the first time point considered (Day 1), and remained substantially stable throughout the 4-week period of observation. The evolution of the nigrostriatal lesion was accompanied by complex changes in the metabolic activity of the other basal ganglia nuclei investigated (substantia nigra pars reticulata, entopeduncular nucleus, globus pallidus and subthalamic nucleus), which led, ultimately, to a generalized, metabolic hyperactivity, ipsilaterally to the lesion. However, peculiar patterns of metabolic activation, or inhibition, characterized the post-lesional responses of each nucleus, in the early and intermediate phases, with peculiar response profiles that varied closely related to the functional position occupied within the basal ganglia circuitry.

Apoptosis in the rat basal forebrain during development and following lesions of connections

Evidence suggests that neurotrophins are essential for the survival and phenotypic maintenance of cholinergic basal forebrain (BF) neurons. We evaluated the pattern of programmed cell death in the BF of the rat during development and after ablations of the cerebral cortex, a major target area and source of neurotrophins for BF neurons. We identified dying cells using the TUNEL (terminal deoxynucleotidyl-transferase-mediated dUTP-biotin nick end labelling) method and confirmed their apoptotic morphology with electron microscopy. Moreover, we demonstrated the expression of the apoptotic marker active caspase-3 in cells with features of apoptosis. TUNEL(+) cells were present in the developing BF during the first two postnatal weeks. Their frequency peaked at postnatal day (P)1 and at P5. TUNEL used in conjunction with immunofluorescence for neuronal nuclear protein (NeuN) showed that, at both peak stages, the majority of apoptotic cells were neurons. Extensive lesions of the cerebral cortex at different ages (P0, P7 and P14) did not induce significant changes in the frequency of apoptotic BF neurons. However, they resulted in alterations in the morphological phenotype of choline acetyltransferase (ChAT)-immunoreactive neurons in the BF, and a reduction in their number which was inversely proportional to the age at which the lesions were performed. We suggest that: (i) apoptosis is temporally coordinated with the morphological and neurochemical differentiation of BF neurons and the establishment of connections with their target areas; and (ii) cortical ablations do not affect the survival of BF neurons, but they influence the phenotype of cholinergic BF neurons.

Dynamic changes of apoptosis and expression of Bcl-2 family members in the posthatch hippocampus of Bengalese finches

The hippocampus of songbirds plays an important role in spatial memory, and probably in song learning. Although prolonged neuronal generation and apoptosis are thought to be closely correlated with memory function, natural changes of the number of neurons and in apoptosis in the hippocampus of songbirds have not been fully investigated during development and in the adult. In the current study, we examined developmental changes in the volume and the number of neurons and apoptotic cells in the hippocampus of songbirds (Lonchura striata) from posthatch day (P5) to adulthood. Apoptotic cells were determined by Nissl staining and immunohistochemistry for cleaved caspase-3, a key apoptotic caspase executioner. The expression levels of Bcl-2 family member mRNA and protein, including Bcl-2, Bcl-xL and Bax, were also investigated. Our results indicated that: (1) the hippocampus volume significantly increased from P5 to P60, although the number of neurons remained stable in all studied stages; (2) the number of apoptotic cells was highest at P45, based either on the Nissl staining or on the immunohistochemistry for caspase-3; (3) Bcl-2 mRNA expression was high from P5 to adulthood, while Bax mRNA declined abruptly from P5 to adulthood, and Bcl-x mRNA was high after P45. Bcl-2 protein was only detected at P5 and P15, while detection of Bcl-xL and Bax proteins paralleled levels of mRNA expression. Our study provides detailed changes of apoptosis in the posthatch songbird hippocampus, suggesting an important role for caspase-3 and Bcl-2 family members in hippocampus apoptosis.

Pramipexole protects against H2O2-induced PC12 cell death

Pramipexole, a novel non-ergot dopamine (DA) agonist, has been successfully applied to the treatment of Parkinson's disease (PD). Although the specific cause of PD remains unknown, recent studies have provided evidence that oxidative stress plays a role in the parthenogenesis of the disease. In the present study, we examined the effect of pramipexole on hydrogen peroxide (H2O2, 100 microM)-induced PC12 cell death, and the intracellular mechanism of this effect. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) assay revealed that pretreatment of PC12 cells with pramipexole (1-100 microM) resulted in significant protection against H2O2-induced cell death in a concentration-dependent manner. The protective effect of pramipexole was not affected by pretreatment with the DA receptor antagonists sulpiride, spiperone or domperidone, suggesting that the effect of pramipexole is not mediated by DA receptors. In PC12 cells, pramipexole inhibited H2O2-induced lactate dehydrogenase (LDH) leakage, as well as H2O2-induced cytochrome c release and caspase-3 activation with the resultant apoptosis. It was also observed in PC12 cells that H2O2 stimulated phosphorylation of mitogen-activated protein (MAP) kinases, i.e., extracellular signal-regulated kinase1/2 (ERK1/2), c-Jun NH2-terminal kinase (JNK) and p38 MAP kinase. Pramipexole inhibited H2O2-induced JNK and p38 MAP kinase, but not ERK1/2 phosphorylation. Furthermore, in these cells experiments with a fluorescent probe, 2-[6-(4'-amino)phenoxy-3H-xanthen-3-on-9-yl]benzoic acid, revealed that pramipexole, the JNK inhibitor SP600125 and the p38 MAP kinase inhibitor SB203580 inhibited the generation of H2O2-induced reactive oxygen species. Caspase inhibitors Z-DEVD-FMK and Z-IETD-FMK, as well as SP600125 and SB203580, inhibited H2O2-induced PC12 cell death to a similar extent as pramipexole. These results suggest that pramipexole exerts a protective effect against oxidative stress-induced PC12 cell death in part through an inhibition of JNK and p38 MAP kinase.

CHOP/GADD153 is a mediator of apoptotic death in substantia nigra dopamine neurons in an in vivo neurotoxin model of parkinsonism

There is increasing evidence that neuron death in neurodegenerative diseases, such as Parkinson's disease, is due to the activation of programmed cell death. However, the upstream mediators of cell death remain largely unknown. One approach to the identification of upstream mediators is to perform gene expression analysis in disease models. Such analyses, performed in tissue culture models induced by neurotoxins, have identified up-regulation of CHOP/GADD153, a transcription factor implicated in apoptosis due to endoplasmic reticulum stress or oxidative injury. To evaluate the disease-related significance of these findings, we have examined the expression of CHOP/GADD153 in neurotoxin models of parkinsonism in living animals. Nuclear expression of CHOP protein is observed in developmental and adult models of dopamine neuron death induced by intrastriatal injection of 6-hydroxydopamine (6OHDA) and in models induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). CHOP is a mediator of neuron death in the adult 60HDA model because a null mutation results in a reduction in apoptosis. In the chronic MPTP model, however, while CHOP is robustly expressed, the null mutation does not protect from the loss of neurons. We conclude that the role of CHOP depends on the nature of the toxic stimulus. For 6OHDA, an oxidative metabolite of dopamine, it is a mediator of apoptotic death.

Protective effects of silybin on human umbilical vein endothelial cell injury induced by H2O2 in vitro

Oxidative injury induces cellular and nuclear damages that lead to cell injury. Agents or antioxidants that can inhibit production of reactive oxygen species can prevent injury. We tested the hypothesis that silybin can inhibit H2O2-induced injury in human umbilical vein endothelial cells. Eighteen hours of treatment with 750 micromol l(-1) H2O2 significantly stimulated expression of caspase-3 and cell apoptosis. In addition, it is observed that H2O2 increased the amounts of malondialdenhyde (MDA), the dehydrogenase (LDH) leakage, and decreased the activity of GSH-Px and NO contents in ECV-304 cells. In the H2O2 apoptosis model, the addition of 6.25-25 mg/L of silybin, which has in vitro radical scavenging activity, partially restored cell viability with a reduction in H2O2-induced apoptotic DNA damage, and decreased the expression of caspase-3. Moreover, it decreased other H2O2-induced damage in a concentration-dependent manner. The endothelial cell apoptosis was detected by AO/EB dual staining as well as flow cytometry, and the activity of pro-apoptotic factor caspase-3 was detected by immunocytochemical method. Our results suggest that the antioxidant, silybin, protects ECV-304 cells against H2O2-induced injury probably through its antioxidant activity, increasing the NO content, the activity GSH-Px and inhibiting signaling pathways mediated by caspase-3.

Endogenous oxidative stress in sporadic Alzheimer's disease neuronal cybrids reduces viability by increasing apoptosis through pro-death signaling pathways and is mimicked by oxidant exposure of control cybrids

Although oxidative stress and mitochondrial dysfunction have been linked to neurodegenerative diseases such as Alzheimer's disease (AD), it is not fully understood how mitochondrial oxidative stress may induce neuronal death. We used mitochondrial transgenic neuronal cell cybrid models of sporadic AD (SAD) to investigate the effects of endogenously generated reactive oxygen species (ROS) on viability and cell death mechanisms. Compared to control (CTL) cybrids, SAD cybrids have increased accumulation of oxidative stress markers and increased apoptosis that is blocked by N-acetylcysteine (NAC) and zVAD.fmk. SAD cybrids also have increased basal activation of the MAPKs, Akt, and NF-kappa B. NF-kappa B activation and cybrid viability are enhanced by NAC. Inhibiting the activity of the PI3K pathway or NF-kappa B aggravates neuronal death. Exposure of CTL cybrids to H2O2 decreased viability and activated in a NAC-sensitive manner, the same intracellular signaling pathways active under basal conditions in SAD cybrids.

Ontogenic cell death in the nigrostriatal system

Like most neural systems, dopamine neurons of the substantia nigra undergo apoptotic natural cell death during development. In rodents, this occurs largely postnatally and is biphasic with an initial major peak just after birth and a second minor peak on postnatal day 14. As envisioned by classic neurotrophic theory, this event is regulated by interactions with the target of these neurons, the striatum, because a developmental target lesion results in an augmented natural cell death event with fewer nigral dopamine neurons surviving into adulthood. Until recently, the striatal target-derived neurotrophic factors providing developmental support of dopamine neurons were unknown, but there is now growing evidence that glial-cell-line-derived neurotrophic factor (GDNF) serves as a physiologic limiting neurotrophic factor for these neurons during the first phase of natural cell death. During this phase, intrastriatal injection of GDNF diminishes the natural cell death event and neutralizing antibodies augment it. Sustained overexpression of GDNF in the striatum throughout development in a unique double transgenic mouse model results in an increased number of dopamine neurons surviving the first phase of natural cell death. However, this increase does not persist into adulthood. Therefore, other factors or mechanisms must play important roles in the determination of the mature number of nigral dopamine neurons. Further elucidation of these mechanisms will be important in the development of neuroprotective and cell replacement therapies for Parkinson's disease.

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Ebselen inhibits p38 mitogen-activated protein kinase-mediated endothelial cell death by hydrogen peroxide

Ebselen (2-phenyl-1, 2-benzisoselenazol-3[2H]-one) is a seleno-organic compound exhibiting both glutathione peroxidase and antioxidant activity. Although it has been reported that ebselen is effective against hydrogen peroxide (H(2)O(2))-induced cell death in several cell types, its effect on endothelial cell damage has not yet been elucidated. In the present study, we examined the effect of ebselen on H(2)O(2)-induced human umbilical vein endothelial cells (HUVECs) death, and its intracellular mechanism. Our findings showed that pretreatment of HUVECs with ebselen resulted in a significant recovery from H(2)O(2)-induced cell death in a concentration-dependent manner. In addition to the inhibition of lactate dehydrogenase (LDH) leakage, ebselen inhibited H(2)O(2)-induced cytochrome c release and caspase-3 activation and the resultant apoptosis in HUVECs. Moreover, it was observed that H(2)O(2) significantly stimulated activation of mitogen-activated protein (MAP) kinases, i.e., p38 MAP kinase, c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK1/2). Ebselen inhibited H(2)O(2)-induced p38 MAP kinase, but not JNK or ERK1/2 activation. Furthermore, SB203580 (4-[4-fluorophenyl]-2-[4-methylsulfinylphenyl]-5-[4-pyridyl]-1H-imidazole), a specific p38 MAP kinase inhibitor, inhibited H(2)O(2)-induced p38 MAP kinase phosphorylation, cytochrome c release, caspase-3 activation, as well as cell death in HUVECs. These findings suggest that ebselen attenuates H(2)O(2)-induced endothelial cell death through the inhibition of signaling pathways mediated by p38 MAP kinase, caspase-3, and cytochrome c release. Thus, inhibition of p38 MAP kinase by ebselen may imply its usefulness for prevention and/or treatment of endothelial cell dysfunction, which was suggested to be the first step in the development of atherosclerosis.

CEP11004, a novel inhibitor of the mixed lineage kinases, suppresses apoptotic death in dopamine neurons of the substantia nigra induced by 6-hydroxydopamine

There is much evidence that the kinase cascade which leads to the phosphorylation of c-jun plays an important signaling role in the mediation of programmed cell death. We have previously shown that c-jun is phosphorylated in a model of induced apoptotic death in dopamine neurons of the substantia nigra in vivo. To determine the generality and functional significance of this response, we have examined c-jun phosphorylation and the effect on cell death of a novel mixed lineage kinase inhibitor, CEP11004, in the 6-hydroxydopamine model of induced apoptotic death in dopamine neurons. We found that expression of total c-jun and Ser73-phosphorylated c-jun is increased in this model and both colocalize with apoptotic morphology. CEP11004 suppresses apoptotic death to levels of 44 and 58% of control values at doses of 1.0 and 3.0 mg/kg, respectively. It also suppresses, to approximately equal levels, the number of profiles positive for the activated form of capase 9. CEP11004 markedly suppresses striatal dopaminergic fiber loss in these models, to only 22% of control levels. We conclude that c-jun phosphorylation is a general feature of apoptosis in living dopamine neurons and that the mixed lineage kinases play a functional role as up-stream mediators of cell death in these neurons.

Down-regulation of Bcl-2, activation of caspases, and involvement of reactive oxygen species in 6-hydroxydopamine-induced thymocyte apoptosis

OBJECTIVE

Our previous work showed that 6-hydroxydopamine (6-OHDA) induced mouse thymocytes to undergo apoptosis both in vivo and in vitro. In the present study, we further investigated the mechanisms of 6-OHDA-induced apoptosis in vitro.

METHODS

Naive mouse thymocytes were cultured with 6-OHDA. The percentages of apoptotic cells were quantified by propidium iodide staining, and DNA fragmentation was detected by agarose gel electrophoresis. Intracellular Bcl-2 was analyzed by immunofluorescence staining. Cu/Zn superoxide dismutase (Cu/Zn-SOD) activities were measured by the SOD-525 method.

RESULTS

The apoptotic effect of 6-OHDA was blocked by desipramine, a catecholamine uptake blocker. Treatment with 6-OHDA caused a reduction in Bcl-2 expression. VAD-FMK, a broad-spectrum caspase inhibitor, and DEVD-CHO, a potent inhibitor of caspase-3, could block 6-OHDA-induced thymocyte apoptosis. However, the specific caspase-1 (ICE) inhibitor YVAD-CMK had no effect. This cell death process was prevented by the protein synthesis inhibitor cycloheximide and by antioxidants. The level of Cu/Zn-SOD activities also decreased after cells were exposed to 6-OHDA.

CONCLUSION

These results suggest an apoptotic effect of 6-OHDA via the uptake of this neurotoxin by thymocytes, and that down-regulation of Bcl-2, activation of caspases, such as caspase-3 but not caspase-1, generation of reactive oxygen species, and new synthesis of proteins are involved in this process.

Postnatal developmental programmed cell death in dopamine neurons

The prenatal development of dopamine (DA) neurons of the substantia nigra (SN) is characterized by their birth, specification, and migration to their final positions. Their postnatal development is characterized by the establishment of contact and interactions between the SN and other neural nuclei, particularly the striatal target, by extension of axons, terminal differentiation, and synapse formation. In this postnatal context there is a natural cell death event, which is apoptotic in nature and biphasic in time course, with an initial peak on postnatal day (PND) 2, and a second on PND14. By PND20 the event has largely subsided. This natural cell death event is regulated in vivo by interaction with striatal target: it is augmented by axon-sparing target lesion, DA terminal destruction, and medial forebrain bundle axotomy. This target dependence is present largely within only the first two postnatal weeks. The striatal target-derived neurotrophic factor(s) that regulate this death event are unknown. We have shown, in a postnatal primary culture model of mesencephalic DA neurons, that glia-derived neurotrophic factor (GDNF) is unique in its ability to support their viability by suppressing apoptosis. We have also recently found that intrastriatal injection of GDNF in vivo suppresses apoptosis, and injection of neutralizing antibodies augments it. Thus, GDNF is a leading candidate for a striatum-derived neurotrophic factor for DA neurons during development.

Colchicine induces apoptosis in organotypic hippocampal slice cultures

The microtubule-disrupting agent colchicine is known to be particular toxic for certain types of neurons, including the granule cells of the dentate gyrus. In this study we investigated whether colchicine could induce such neuron-specific degeneration in developing (1 week in vitro) and mature (3 weeks in vitro) organotypic hippocampal slice cultures and whether the induced cell death was apoptotic and/or necrotic. When applied to 1-week-old cultures for 48 h, colchicine induced primarily apoptotic, but also a minor degree of necrotic cell death in the dentate granule cells, as investigated by cellular uptake of the fluorescent dye propidium iodide (PI), immunostaining for active caspase 3 and c-Jun/AP-1 (N) and fragmentation of nuclei as seen in Hoechst 33342 staining. All four markers appeared after 12 h of colchicine exposure. Two of them, active caspase 3 and c-Jun/AP-1 (N) displayed a similar time course and reached a maximum after 24 h of exposure, 24 h ahead of both PI uptake and Hoechst 33342 staining, which together displayed similar time profiles and a close correlation. In 3-week-old cultures, colchicine did not induce apoptotic or necrotic cell death. Attempts to interfere with the colchicine-induced apoptosis in 1-week-old cultures showed that colchicine-induced PI uptake and formation of apoptotic nuclei were temporarily prevented by coapplication of the protein synthesis inhibitor cycloheximide. Application of the pancaspase inhibitor z-VAD-fmk almost completely abolished the formation of active caspase 3 protein and apoptotic nuclei induced by colchicine, but the formation of necrotic nuclei increased correspondingly and the PI uptake was unaffected. We conclude that colchicine induces caspase 3-dependent apoptotic cell death of dentate granule cells in hippocampal brain slice cultures, but the apoptotic cell death is highly dependent on the developmental stage of the cultures.

Ectopic expression of cell cycle markers in models of induced programmed cell death in dopamine neurons of the rat substantia nigra pars compacta

There is increasing evidence that proteins normally involved in the cell cycle can regulate neuronal programmed cell death (PCD). However, it remains unknown whether cell cycle markers are expressed in normal, postmitotic, postmigratory neurons undergoing PCD in vivo. We have previously shown that natural cell death occurs postnatally in dopamine neurons of the substantia nigra pars compacta (SNpc). PCD can be induced postnatally in these neurons either by intrastriatal injection of the neurotoxin 6-hydroxydopamine (6-OHDA) or by medial forebrain bundle (MFB) axotomy. At the time of induction of death in these models, these neurons are long postmitotic and postmigratory. We have studied three cell cycle markers in these models: 5-bromo-2'-deoxyuridine (BrdU) incorporation (a marker of S phase), cdc2 protein expression (a marker of G2 phase), and expression of MPM2 (a marker of M phase), an epitope phosphorylated by cdc2. We report here that postmitotic dopaminergic neurons undergoing PCD in the SNpc following 6-OHDA and axotomy lesions incorporate BrdU and overexpress cdc2, but do not express MPM2. This is the first in vivo evidence that postmitotic dopamine neurons of the SNpc undergoing apoptosis express markers for S phase and G2 phase. These results raise the possibility that cell cycle regulatory proteins may play a role in the demise of dopaminergic neurons in Parkinson's disease, in which PCD has been postulated to play a role.

Physiological and pathological roles of Apaf1 and the apoptosome

Different cellular pathways can lead to apoptosis. Apaf1 is the molecular core of the apoptosome, a multiproteic complex mediating the so-called mitochondrial pathway of cell death. The importance of this pathway during development has been clearly demonstrated by knocking out key genes. Also, the relevance of Apaf1 dosage during development has been recently underlined. Moreover, a growing body of evidences seems to point out a possible role of the mitochondria-dependent apoptosis in different pathologies. In particular, we discuss here some recent evidences regarding the putative role of the apoptosome in neurodegeneration and cancer.

Nitric oxide synthase inhibition during development: effect on apoptotic death of dopamine neurons

Naturally occurring cell death via apoptosis occurs in the substantia nigra pars compacta (SNc) during rat development, culminating during the perinatal period. We previously showed that lipid peroxidation-mediated oxidative stress is not involved in this cell death process. Nitric oxide (NO) has been proposed to be critical for many developmental processes in brain and has been shown to mediate cell death in neurotoxin models of neurodegenerative disorders. Here, we reported that in vivo pre- and postnatal treatment with the non-specific NO synthase (NOS) inhibitor, L-NAME (60 mg/kg), or with the neuronal NOS inhibitor, 7-NI (30 mg/kg), dramatically decreased the NOS activity as well as the NADPH-diaphorase staining in brain. However, those treatments did not rescue dopamine neurons from developmental death, suggesting that NO is not involved in vivo in developmental death of these neurons or in the overall development of the SNc.

Medial forebrain bundle axotomy during development induces apoptosis in dopamine neurons of the substantia nigra and activation of caspases in their degenerating axons

There is growing evidence that programmed cell death may play a role in degenerative neurologic disease. The caspases are a family of cell death proteins that mediate proteolytic cascades in the death process. Although there is clear evidence that caspases play a role in the destruction of the components of the neuronal soma, it has been controversial whether they play a role in the degeneration of axons that accompanies the death of the cell body. It is important to define the molecular mechanisms of axonal degeneration, because terminal degeneration may occur early in neurodegenerative disease. We have therefore investigated whether caspases play a role in axonal degeneration in the dopaminergic nigrostriatal system following axotomy of the median forebrain bundle during development. We find that this lesion induces apoptosis in midbrain dopaminergic neurons at the level of the cell soma. Concomitantly with this induction of apoptosis, degeneration of dopaminergic axons occurs and is characterized by the formation of axonal swellings and spheroids. Immunohistochemical analysis reveals that the activated form of caspase-3 and a caspase cleavage product of beta-actin are abundantly expressed in these degenerating fibers. We conclude that caspases are activated in degenerating dopaminergic axons as the somata undergo programmed cell death in this model. These results raise the possibility that caspase activation may occur in other programmed cell death contexts for these neurons, and, if this is so, then their inhibition may be a useful therapeutic target.