Striatal degeneration induced by mitochondrial blockade is prevented by biologically delivered NGF

Using gene or cell therapies to treat Huntington's disease

Huntington's disease is caused by a CAG repeat expansion in the first exon of the HTT gene, leading to the production of gain-of-toxic-function mutant huntingtin protein species and consequent transcriptional dysregulation and disrupted cell metabolism. The brunt of the disease process is borne by the striatum from the earliest disease stages, with striatal atrophy beginning approximately a decade prior to the onset of neurologic signs. Although the expanded CAG repeat in the HTT gene is necessary and sufficient to cause HD, other genes can influence the age at onset of symptoms and how they progress. Many of these modifier genes have roles in DNA repair and are likely to modulate the stability of the CAG repeat in somatic cells. Currently, there are no disease-modifying treatments for HD that can be prescribed to patients and few symptomatic treatments, but there is a lot of interest in therapeutics that can target the pathogenic pathways at the DNA and RNA levels, some of which have reached the stage of human studies. In contrast, cell therapies aim to replace key neural cells lost to the disease process and/or to support the host vulnerable striatum by direct delivery of cells to the brain. Ultimately it may be possible to combine gene and cell therapies to both slow disease processes and provide some level of neural repair. In this chapter we consider the current status of these therapeutic strategies along with their prospects and challenges.

3-Nitropropionic Acid and Similar Nitrotoxins

3-Nitropropionic acid as well as 3-nitro-1-propanol and its β-D-glucopyranoside (miserotoxin) are the plant and fungal toxins reported to interrupt mitochondrial electron transport resulting in cellular energy deficit. These nitrotoxins induce neurological degeneration in ruminants and humans. 3-Nitropropionic acid-intoxicated rats serve as the animal model for Huntington’s disease.

Cellular Delivery of Cntf but not Nt-4/5 Prevents Degeneration of Striatal Neurons in a Rodent Model of Huntington's Disease

The delivery of neurotrophic factors to the central nervous system (CNS) has gained considerable attention as a potential treatment strategy for neurodegenerative disorders such as Huntington's disease (HD). In the present study, we directly compared the ability of two neurotrophic factors, ciliary neurotrophic factor (CNTF), and neurotrophin-4/5 (NT-4/5), to prevent the degeneration of striatal neurons following intrastriatal injections of quinolinic acid (QA). Expression vectors containing either the human CNTF or NT-4/5 gene were transfected into a baby hamster kidney fibroblast cell line (BHK). Using a polymeric device, encapsulated BHK-control cells and those secreting either CNTF (BHK-CNTF) or NT-4/5 (BHK-NT-4/5) were transplanted unilaterally into the rat lateral ventricle. Seven days later, the same animals received unilateral injections of QA (225 nmol) into the ipsilateral striatum. Nissl-stained sections demonstrated that the BHK-CNTF cells significantly reduced the volume of striatal damage produced by QA. Quantitative analysis of striatal neurons further demonstrated that both choline acetyltransferase (ChAT)- and glutamic acid decarboxylase (GAD)-immunoreactive neurons were protected by CNTF implants. In contrast, the volume of striatal damage and loss of striatal ChAT and GAD-positive neurons in animals receiving BHK-NT-4/5 implants did not differ from control-implanted animals. These results help better define the scope of neuronal protection that can be afforded following cellular delivery of various neurotrophic factors. Moreover, these data further support the concept that implants of polymer-encapsulated CNTF-releasing cells can be used to protect striatal neurons from excitotoxic damage, and that this strategy may ultimately prove relevant for the treatment of HD.

Cellular Delivery of Human Cntf Prevents Motor and Cognitive Dysfunction in a Rodent Model of Huntington's Disease

The delivery of ciliary neurotrophic factor (CNTF) to the central nervous system has recently been proposed as a potential means of halting or slowing the neural degeneration associated with Huntington's disease (HD). The following set of experiments examined, in detail, the ability of human CNTF (hCNTF) to prevent the onset of behavioral dysfunction in a rodent model of HD. A DHFR-based expression vector containing the hCNTF gene was transfected into a baby hamster kidney fibroblast cell line (BHK). Using a polymeric device, encapsulated BHK-control cells and those secreting hCNTF were transplanted bilaterally into rat lateral ventricles. Eight days later, the same animals received bilateral injections of quinolinic acid (QA, 225 nmol) into the previously implanted striata. A third group received sham surgery (incision only) and served as a normal control group. Bilateral infusions of QA produced a significant loss of body weight and mortality that was prevented by prior implantation with hCNTF-secreting cells. Moreover, QA produced a marked hyperactivity, an inability to use the forelimbs to retrieve food pellets in a staircase test, increased the latency of the rats to remove adhesive stimuli from their paws, and decreased the number of steps taken in a bracing test that assessed motor rigidity. Finally, the QA-infused animals were impaired in tests of cognitive function — the Morris water maze spatial learning task, and the delayed nonmatching-to-position operant test of working memory. Prior implantation with hCNTF-secreting cells prevented the onset of all the above deficits such that implanted animals were nondistinguishable from sham-lesioned controls. At the conclusion of behavioral testing, 19 days following QA, the animals were sacrificed for neurochemical determination of striatal choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) levels. This analysis revealed that QA decreased striatal ChAT levels by 35% and striatal GAD levels by 45%. In contrast, hCNTF-treated animals did not exhibit any decrease in ChAT levels and only a 10% decrease in GAD levels. These results support the concepts that implants of polymer-encapsulated hCNTF-releasing cells can be used to protect striatal neurons from excitotoxic damage, produce extensive behavioral protection as a result of that neuronal sparing, and that this strategy may ultimately prove relevant for the treatment of HD.

Neural Transplantation for Huntington's Disease: Experimental Rationale and Recommendations for Clinical Trials

Huntington's disease (HD) is a neurodegenerative disorder affecting motor function, personality, and cognition. This paper reviews the experimental data that demonstrate the potential for transplantation of fetal striatum and trophic factor secreting cells to serve as innovative treatment strategies for HD. Transplantation strategies have been effective in replacing lost neurons or preventing the degeneration of neurons destined to die in both rodent and nonhuman primate models of HD. In this regard, a logical series of investigations has proven that grafts of fetal striatum survive, reinnervate the host, and restore function impaired following excitotoxic lesions of the striatum. Furthermore, transplants of cells genetically modified to secrete trophic factors such as nerve growth factor protect striatal neurons from degeneration due to excitotoxicity or mitochondrial dysfunction. Given the disabling and progressive nature of HD, coupled with the absence of any meaningful medical therapy, it is reasonable to consider clinical trials of neural transplantation for this disease. Fetal striatal implants will most likely be the first transplant strategy attempted for HD. This paper describes the variable parameters we believe to be critical for consideration for the design of clinical trials using fetal striatal implants for the treatment of HD.

Dose-Dependent Neurochemical and Functional Protection Afforded by Encapsulated CNTF-Producing Cells

Intracerebral delivery of hCNTF has shown considerable neuroprotective potential in animal models of Huntington's disease (HD). The present study describes the relationship between a range of hCNTF doses and the resulting behavioral and neurochemical (striatal ChAT and GAD activity) protection in a rodent model of HD. Encapsulated BHK delivering a range of hCNTF doses were implanted into the lateral ventricle ipsilateral to an intrastriatal quinolinic acid (QA) injection. Results demonstrated a dose-dependent effect of hCNTF with complete, partial, and no observable neuroprotection occurring with preimplant doses of hCNTF of 30.8, 8.6, and 0.8–2.1 ng hCNTF/24 h, respectively. These data continue to support the use of cellular delivery of hCNTF for HD and will facilitate the optimization of this approach in the clinical situation.

Neurotrophic Factor Protection against Excitotoxic Neuronal Death

Neurotrophic factors are polypeptides capable of promoting neuronal survival in both the developing and the adult brain. In addition to the neurotrophins, NGF, brain-derived neurotropic factor, and NT-3 to -6, other neurotrophic factors include ciliary neurotrophic factor, fibroblast growth factors, insulin-like growth factors, members of the transforming growth factor superfamily, members of the epidermal growth factor family, and other cytokines such as leukemia inhibitory factor, oncostatin M, and interleukins-6 and -11. One condition under which these factors promote survival is the challenge of neurons with analogs of excitatory amino acid transmitters. Such analogs, including quinolinic acid, kainic acid, and ibotenic acid, are frequently employed as models of neurological diseases such as Huntington's disease, Parkinson's disease, Alzheimer's disease, epilepsy, cerebellar degenerations, and amyotrophic lateral sclerosis. Excitotoxicity also plays a role in neu ronal death caused by focal ischemia, hypoglycemia, or trauma. Although much has been learned about the mechanisms of both the action of neurotrophic factors and of cell death in response to excitotoxins, the mechanism of protection by these factors remains uncertain. This review explores the biochemical and phys iological changes mediated by neurotrophic factors that may underlie their ability to protect against excito toxic cell death. Second messenger pathways used degenerately by both excitotoxins and neurotrophic factors are discussed as a potential site of interaction mediating the protective effects of neurotrophic factors. Particular attention is also paid to the importance of the route of neurotrophic factor delivery in conferring neuroprotection in particular excitotoxic models. The Neuroscientist 1:286-297, 1995

Postnatal expression of neurotrophic factors accessible to spiral ganglion neurons in the auditory system of adult hearing and deafened rats

Spiral ganglion neurons (SGNs) receive input from cochlear hair cells and project from the cochlea to the cochlear nucleus. After destruction of hair cells with aminoglycoside antibiotics or noise, SGNs gradually die. It has been assumed that SGN death is attributable to loss of neurotrophic factors (NTFs) derived from hair cells or supporting cells in the organ of Corti (OC). We used quantitative PCR (qPCR) to assay NTF expression-neurotrophin-3 (NT-3), BDNF, GDNF, neurturin, artemin, and CNTF-in the OC and cochlear nucleus at various ages from postnatal day 0 (P0) to P90 in control hearing and neonatally deafened rats. NT-3, neurturin, and CNTF were most abundant in the postnatal hearing OC; CNTF and neurturin most abundant in the cochlear nucleus. In the OC, NT-3 and CNTF showed a postnatal increase in expression approximately concomitant with hearing onset. In rats deafened by daily kanamycin injections (from P8 to P16), surviving inner hair cells were evident at P16 but absent by P19, with most postsynaptic boutons lost before P16. NT-3 and CNTF, which normally increase postnatally, had significantly reduced expression in the OC of deafened rats, although CNTF was expressed throughout the time that SGNs were dying. In contrast, neurturin expression was constant, unaffected by deafening or by age. CNTF and neurturin expression in the cochlear nucleus was unaffected by deafening or age. Thus, NTFs other than NT-3 are available to SGNs even as they are dying after deafening, apparently conflicting with the hypothesis that SGN death is attributable to lack of NTFs.

Nucleic Acid-Based Therapy Approaches for Huntington's Disease

Huntington's disease (HD) is caused by a dominant mutation that results in an unstable expansion of a CAG repeat in the huntingtin gene leading to a toxic gain of function in huntingtin protein which causes massive neurodegeneration mainly in the striatum and clinical symptoms associated with the disease. Since the mutation has multiple effects in the cell and the precise mechanism of the disease remains to be elucidated, gene therapy approaches have been developed that intervene in different aspects of the condition. These approaches include increasing expression of growth factors, decreasing levels of mutant huntingtin, and restoring cell metabolism and transcriptional balance. The aim of this paper is to outline the nucleic acid-based therapeutic strategies that have been tested to date.

The interrelationship between mitochondrial dysfunction and transcriptional dysregulation in Huntington disease

Huntington disease (HD) is an inherited neurodegenerative disease caused by an abnormal expansion of the CAG repeat region in the huntingtin (Htt) gene. Although the pathogenic mechanisms by which mutant Htt (mHtt) causes HD have not been fully elucidated, it is becoming increasingly apparent that mHtt can impair mitochondrial function directly, as well as indirectly by dysregulation of transcriptional processes. mHtt causes increased sensitivity to Ca(2+)-induced decreases in state 3 respiration and mitochondrial permeability transition pore (mPTP) opening concurrent with a reduction in mitochondrial Ca(2+) uptake capacity. Treatment of striatal cells expressing mHtt with thapsigargin results in a decrease in mitochondrial Ca(2+) uptake and membrane potential and an increase in reactive oxygen species (ROS) production. Transcriptional processes regulated by peroxisome proliferator-activated receptor gamma (PPAR gamma) coactivator-1 alpha (PGC-1 alpha), which are critical for mitochondrial biogenesis, have been shown to be impaired in HD. In addition, the PPAR gamma signaling pathway is impaired by mHtt and the activation of this pathway ameliorates many of the mitochondrial deficits, suggesting that PPAR gamma agonists may represent an important treatment strategy for HD.

Zonisamide: aspects in neuroprotection

Zonisamide is widely used as an antiepileptic drug. Two studies published recently in Experimental Neurology focus on the drug's neuroprotective effect. In the present commentary, we discuss the significance of their findings and aspects of zonisamide in neuroprotection.

The corticostriatal pathway in Huntington's disease

The corticostriatal pathway provides most of the excitatory glutamatergic input into the striatum and it plays an important role in the development of the phenotype of Huntington's disease (HD). This review summarizes results obtained from genetic HD mouse models concerning various alterations in this pathway. Evidence indicates that dysfunctions of striatal circuits and cortical neurons that make up the corticostriatal pathway occur during the development of the HD phenotype, well before there is significant neuronal cell loss. Morphological changes in the striatum are probably primed initially by alterations in the intrinsic functional properties of striatal medium-sized spiny neurons. Some of these alterations, including increased sensitivity of N-methyl-D-aspartate receptors in subpopulations of neurons, might be constitutively present but ultimately require abnormalities in the corticostriatal inputs for the phenotype to be expressed. Dysfunctions of the corticostriatal pathway are complex and there are multiple changes as demonstrated by significant age-related transient and more chronic interactions with the disease state. There also is growing evidence for changes in cortical microcircuits that interact to induce dysfunctions of the corticostriatal pathway. The conclusions of this review emphasize, first, the general role of neuronal circuits in the expression of the HD phenotype and, second, that both cortical and striatal circuits must be included in attempts to establish a framework for more rational therapeutic strategies in HD. Finally, as changes in cortical and striatal circuitry are complex and in some cases biphasic, therapeutic interventions should be regionally specific and take into account the temporal progression of the phenotype.

3-Nitropropionic acid: a mitochondrial toxin to uncover physiopathological mechanisms underlying striatal degeneration in Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder caused by a mutation in the gene encoding Huntingtin. The mechanisms underlying the preferential degeneration of the striatum, the most striking neuropathological change in HD, are unknown. Of those probably involved, mitochondrial defects might play an important role. The behavioural and anatomical similarities found between HD and models using the mitochondrial toxin 3-nitropropionic acid (3NP) in rats and primates support this hypothesis. Here, we discuss the recently identified mechanisms of 3NP-induced striatal degeneration. Two types of important factor have been identified. The first are the 'executioner' components that have direct roles in cell death, such as c-Jun N-terminal kinase and Ca2+-activated protease calpains. The second are 'environmental' factors, such as glutamate, dopamine and adenosine, which modulate the striatal degeneration induced by 3NP. Interestingly, these recent studies support the hypothesis that 3NP and mutated Huntingtin have certain mechanisms of toxicity in common, suggesting that the use of 3NP might give new insights into the pathogenesis of HD. Research on 3NP provides additional proof that the neurochemical environment of a given neurone can determine its preferential vulnerability in neurodegenerative diseases.

Critical issues in gene therapy for neurologic disease

Gene therapy for the nervous system is a newly emerging field with special issues related to modes of delivery, potential toxicity, and realistic expectations for treatment of this vital and highly complex tissue. This review focuses on the potential for gene delivery to the brain, as well as possible risks and benefits of these procedures. This includes discussion of appropriate vectors, such as adeno-associated virus, lentivirus, gutless adenovirus, and herpes simplex virus hybrid amplicons, and cell vehicles, such as neuroprogenitor cells. Routes of delivery for focal and global diseases are enumerated, including use of migratory cells, facilitation of vascular delivery across the blood-brain barrier, cerebrospinal fluid delivery, and convection injection. Attention is given to examples of diseases falling into different etiologic types: metabolic deficiency states, including Canavan disease and lysosomal storage disorders; and degenerative conditions, including Parkinson's disease and other neurodegenerative conditions.

A bile acid protects against motor and cognitive deficits and reduces striatal degeneration in the 3-nitropropionic acid model of Huntington's disease

There is currently no effective treatment for Huntington's disease (HD), a progressive, fatal, neurodegenerative disorder characterized by motor and cognitive deterioration. It is well established that HD is associated with perturbation of mitochondrial energy metabolism. Tauroursodeoxycholic acid (TUDCA), a naturally occurring bile acid, can stabilize the mitochondrial membrane, inhibit the mitochondrial permeability transition, decrease free radical formation, and derail apoptotic pathways. Here we report that TUDCA significantly reduced 3-nitropropionic acid (3-NP)-mediated striatal neuronal cell death in cell culture. In addition, rats treated with TUDCA exhibited an 80% reduction in apoptosis and in lesion volumes associated with 3-NP administration. Moreover, rats which received a combination of TUDCA + 3-NP exhibited sensorimotor and cognitive task performance that was indistinguishable from that of controls, and this effect persisted at least 6 months. Bile acids have traditionally been used as therapeutic agents for certain liver diseases. This is the first demonstration, however, that a bile acid can be delivered to the brain and function as a neuroprotectant and thus may offer potential therapeutic benefit in the treatment of certain neurodegenerative diseases.

Cellular delivery of trophic factors for the treatment of Huntington's disease: is neuroprotection possible?

The elucidation of the genetic defect in patients with Huntington's disease (HD) has allowed for the detection of individuals at risk for HD prior to the onset of symptoms. Thus "neuroprotection strategies" aimed at preventing the neuropathological and behavioral sequelae of this disease might be powerful therapeutically since they could be introduced to healthy patients before the initiation of a massive degenerative cascade principally localized to the striatum. A variety of trophic factors potently protect vulnerable striatal neurons in animal models of HD. A number of experimental variables are critical in determining the success of trophic factors in animal models. In this regard, the method of trophic factor delivery may be crucial, as delivery via genetically modified cells often produces greater and more widespread effects on striatal neurons than infusions of that same factor. The mechanisms by which cellularly delivered trophic factors forestall degeneration and prevent behavioral deficits are complex and often appear to be unrelated to the trophic factor binding to its cognate receptor. In this regard, cells genetically modified to secrete nerve growth factor (NGF) or ciliary neurotrophic factor (CNTF) protect degenerating striatal neurons which do not express either NGF or CNTF receptors. This review will discuss some of the non-receptor-based events that might underlie these effects and present the hypothesis that cellular delivery of certain trophic factors using genetically modified cells may be ready for clinical testing in HD patients.

Clenbuterol induces growth factor mRNA, activates astrocytes, and protects rat brain tissue against ischemic damage

The induction of growth factor synthesis in brain tissue by beta2-adrenoceptor agonists, such as clenbuterol, is a promising approach to protect brain tissue from ischemic damage. Clenbuterol (0.01-0.5 mg/kg) reduced the cortical infarct volume in Long-Evans rats as measured 7 days after permanent occlusion of the middle cerebral artery. Dosages of clenbuterol higher than 1 mg/kg showed no cerebroprotective effect due to a decrease in blood pressure and an increase in plasma glucose level. The increase in the mRNA level of nerve growth factor (NGF), basic fibroblast growth factor (basic FGF), and transforming growth factor-beta1 (TGF-beta1) mRNA in cortical and hippocampal tissue occurred earlier after middle cerebral artery occlusion and was more pronounced in animals treated with clenbuterol than in controls. In addition, glial fibrillary acidic protein (GFAP) mRNA expression was enhanced in astrocytes 6 h after ischemia in clenbuterol-treated animals. The results suggest that growth factor synthesis is enhanced in activated astrocytes and that this could be the mechanism of clenbuterol-induced cerebroprotection after ischemia.

Herpes simplex virus type 1 vector-mediated expression of nerve growth factor protects dorsal root ganglion neurons from peroxide toxicity

Nerve growth factor beta subunit (beta-NGF) transgene delivery and expression by herpes simplex virus type 1 (HSV-1) vectors was examined in a cell culture model of neuroprotection from hydrogen peroxide toxicity. Replication-competent (tk- K mutant background) and replication-defective (ICP4(-);tk- S mutant background) vectors were engineered to contain the murine beta-NGF cDNA under transcriptional control of either the human cytomegalovirus immediate-early gene promoter (HCMV IEp) (e.g., KHN and SHN) or the latency-active promoter 2 (LAP2) (e.g., KLN and SLN) within the viral thymidine kinase (tk) locus. Infection of rat B103 and mouse N2A neuronal cell lines, 9L rat glioma cells, and Vero cells with the KHN or SHN vectors resulted in the production of beta-NGF-specific transcripts and beta-NGF protein reaching a maximum at 3 days postinfection (p.i.). NGF protein was released into the culture media in amounts ranging from 10.83 to 352.86 ng/ml, with the highest levels being achieved in B103 cells, and was capable of inducing neurite sprouting of PC-12 cells. The same vectors produced high levels of NGF in primary dorsal root ganglion (DRG) cultures at 3 days. In contrast to HCMV IEp-mediated expression, the LAP2-NGF vectors showed robust expression in primary DRG neurons at 14 days. The neuroprotective effect of vector produced NGF was assessed by its ability to inhibit hydrogen peroxide-induced neuron toxicity in primary DRG cultures. Consistent with the kinetics of vector-mediated NGF expression, HCMV-NGF vectors were effective in abrogating the toxic effects of peroxide at 3 but not 14 days p.i. whereas LAP2-NGF vector transduction inhibited apoptosis in DRG neurons at 14 days p.i. but was ineffective at 3 days p.i. Similar kinetics of NGF expression were observed with the KHN and KLN vectors in latently infected mouse trigeminal ganglia, where high levels of beta-NGF protein expression were detected at 4 wks p.i. only from the LAP2; HCMV-NGF-driven expression peaked at 3 days but could not be detected during HSV latency at 4 weeks. Together, these results indicate that (i) NGF vector-infected cells produce and secrete mature, biologically active beta-NGF; (ii) vector-synthesized NGF was capable of blocking peroxide-induced apoptosis in primary DRG cultures; and (iii) the HCMV-IEp functioned to produce high levels of NGF for several days; but (iv) only the native LAP2 was capable of long-term expression of a therapeutic gene product in latently infected neurons in vivo.

6-Hydroxydopamine injections into the nigrostriatal pathway attenuate striatal malonate and 3-nitropropionic acid lesions

The mitochondrial inhibitors malonate and 3-nitropropionic (3NP) acid are potent neurotoxins in vivo. Administration of these compounds results in neuronal loss similar to that seen in Huntington's disease. Although the mechanism of cell death produced by these compounds likely involves activation of N-methyl-D-aspartate receptors, it remains unclear why the striatum demonstrates regional susceptibility to the toxicity of these and other mitochondrial poisons. We hypothesized that dopamine, a weak neurotoxin that occurs in high concentrations in the striatum, may contribute to the neuronal damage caused by mitochondrial inhibition. We investigated whether depletion of striatal dopamine using the catecholaminergic toxin 6-hydroxydopamine would attenuate lesions induced by mitochondrial inhibition. We found that dopamine depletion reduced significantly the extent of histological damage in the striatum elicited by both intraparenchymal injections of 0.8 micromol malonate and 20 mg/kg systemic administration of 3NP. These data suggest that dopamine or one of its metabolites may contribute to mitochondrial toxin-induced cell death.

Metabolic compromise with systemic 3-nitropropionic acid produces striatal apoptosis in Sprague-Dawley rats but not in BALB/c ByJ mice

Metabolic compromise with systemic 3-nitropropionic acid (3-NP) results in the degeneration of striatal cells, mimicking the pathology of Huntington's disease (HD). Here we show that 10-week- and 8-month-old BALB/c ByJ mice show an unexpected striatal resilience to single and multiple systemic injections of 3-NP, while Sprague-Dawley rats are vulnerable, albeit in a variable manner. Identification of lesions was made by staining of DNA fragmentation with terminal deoxytransferase-mediated dUTP-biotin nick-end labeling (TUNEL) and hematoxylin/eosin, 1-10 days after injection. Quantitative imaging of histochemistry for succinate dehydrogenase (SDH) activity, the target of 3-NP inhibition, revealed that vulnerable rats reached maximal inhibition in brain at 1 day after 3-NP, whereas mice and resilient rats took 7 days to reach maximal inhibition. All groups of animals reached similar maximal decreases in SDH activity in striatum and cortex. Remarkably, only the fast decline in SDH activity seen in vulnerable rats was associated with TUNEL labeling. In addition, vulnerable rats developed a region within striatum where SDH activity was fully depleted and a similarly depleted region in CA1 hippocampus. While mice did not develop this region in striatum, some developed one in CA1. These regions of SDH depletion in both structures were associated with widespread TUNEL staining, with maximal labeling at 3 days after 3-NP. The existence of an animal strain resilient to 3-NP suggests that there are mediating factors involved in the preferential vulnerability of striatum to metabolic lesioning. The identification of these factors could provide strategies for therapeutic intervention in HD.

The role of neuronal growth factors in neurodegenerative disorders of the human brain

Recent evidence suggests that neurotrophic factors that promote the survival or differentiation of developing neurons may also protect mature neurons from neuronal atrophy in the degenerating human brain. Furthermore, it has been proposed that the pathogenesis of human neurodegenerative disorders may be due to an alteration in neurotrophic factor and/or trk receptor levels. The use of neurotrophic factors as therapeutic agents is a novel approach aimed at restoring and maintaining neuronal function in the central nervous system (CNS). Research is currently being undertaken to determine potential mechanisms to deliver neurotrophic factors to selectively vulnerable regions of the CNS. However, while there is widespread interest in the use of neurotrophic factors to prevent and/or reduce the neuronal cell loss and atrophy observed in neurodegenerative disorders, little research has been performed examining the expression and functional role of these factors in the normal and diseased human brain. This review will discuss recent studies and examine the role members of the nerve growth factor family (NGF, BDNF and NT-3) and trk receptors as well as additional growth factors (GDNF, TGF-alpha and IGF-I) may play in neurodegenerative disorders of the human brain.

Mitochondrial membrane potential and nuclear changes in apoptosis caused by serum and nerve growth factor withdrawal: time course and modification by (-)-deprenyl

Studies in non-neural cells have suggested that a fall in mitochondrial membrane potential (DeltaPsiM) is one of the earliest events in apoptosis. It is not known whether neural apoptosis caused by nerve growth factor (NGF) and serum withdrawal involves a decrease in DeltaPsiM. We used epifluorescence and laser confocal microscopy with the mitochondrial potentiometric dyes chloromethyl-tetramethylrosamine methyl ester and 5,5',6, 6'-tetrachloro-1,1',3,3'-tetraethybenzimidazol carbocyanine iodide to estimate DeltaPsiM. PC12 cells were differentiated in media containing serum and NGF for 6 d before withdrawal of trophic support. After washing, the cells were incubated with media containing serum and NGF (M/S+N), media without serum and NGF, or media with the "trophic-like" monoamine oxidase B inhibitor, (-)-deprenyl. Mitochondria in cells without trophic support underwent a progressive shift to lower DeltaPsiM values that was significant by 3 hr after washing. The percentages of cells with nuclear chromatin condensation or nuclear DNA fragmentation were not significantly increased above those for cells in M/S+N until 6 hr after washing. Replacement of cells into M/S+N or treatment with (-)-deprenyl markedly reduced the proportion of mitochondria with decreased DeltaPsiM. Measurements of cytoplasmic peroxyl radical levels with 2',7'-dihydrodichlorofluorescein fluorescence and intramitochondrial Ca2+ with dihydro-rhodamine-2-acetylmethyl ester indicated that cytoplasmic peroxyl radical levels were not increased until after 6 hr, whereas increases in intramitochondrial Ca2+ paralleled the decreases in DeltaPsiM. (-)-Deprenyl appeared to alter the relationship between intramitochondrial Ca2+ levels and DeltaPsiM, possibly through its reported capacity to increase the synthesis of proteins such as BCL-2.

Bioenergetics of rat prostate cancer cell migration

BACKGROUND

Increased cell motility and increased glycolysis are two well-known hallmarks of cancer. We undertook these studies to determine whether increased glycolysis is required for prostate cancer cell locomotion.

METHODS

We studied the highly metastatic MatLu cell line, which is a variant of the Dunning R-3327 rat prostate adenocarcinoma model. Using videomicroscopy and computer image analysis, we compared the speed of migration of cells grown in serum-free medium in either the presence or absence of glucose.

RESULTS

We found that cells grown in glucose-free, conditioned medium maintained speeds of migration and intracellular ATP levels for 24 hr which were equivalent to those of cells grown in conditioned medium containing glucose. In contrast, migration was significantly inhibited by growth in glucose-free, unconditioned medium. We also tested the effect of antimycin A and rotenone, two inhibitors of mitochondrial electron transport, on cell migration and ATP levels. Antimycin A had no significant effect on either feature, while rotenone slightly inhibited cell migration without affecting ATP levels.

CONCLUSIONS

1) Glycolysis is not necessary for rat prostate cancer cell locomotion in the presence of conditioned medium. 2) MatLu cells grown in the absence of both serum and conditioned medium require glucose to maintain cellular ATP levels and cell migration. 3) MatLu cells in conditioned medium adapt to inhibition of glycolysis or mitochondrial respiration by increasing the activity of the uninhibited pathway.

Neurobehavioral alteration in rodents following developmental exposure to aluminum

Aluminum (Al) is one of the most abundant metals in the earth's crust, and humans can be exposed to it from several sources. It is present in food, water, pharmaceutical compounds, and in the environment, e.g., as a result of acid rain leaching it from the soil. Exposure to Al has recently been implicated in a number of human pathologies, but it has not yet been definitely proved that it plays a major causal role in any of them. In this paper we review the effects of developmental exposure of laboratory animals to Al salts as a model for human pathological conditions. The data presented show behavioral and neurochemical changes in the offspring of AL-exposed mouse dams during gestation, which include alterations in the pattern of ultrasonic vocalizations and a marked reduction in central nervous system (CNS) choline acetyltransferase activity. Prenatal Al also affects CNS cholinergic functions under Nerve Growth Factor (NGF) control, as shown by increased central NGF levels and impaired performances in a maze learning task in young-adult mice. The need for more detailed studies to evaluate the risks for humans associated with developmental exposure to Al, as well as the importance of using more than one strain of laboratory animal in the experimental design, is emphasized.

Glial cell line-derived neurotrophic factor attenuates the locomotor hypofunction and striatonigral neurochemical deficits induced by chronic systemic administration of the mitochondrial toxin 3-nitropropionic acid

The present study investigated whether glial cell line-derived neurotrophic factor prevents the progressive striatal degeneration induced by chronic systemic administration of the mitochondrial toxin, 3-nitropropionic acid. In addition, the effects of delayed treatment with glial cell line-derived neurotrophic factor on toxin-induced behavioural and neurochemical deficits were determined. Locomotor activity in rats infused with 3-nitropropionic acid (15 mg/kg/day, for four weeks) via subcutaneous osmotic minipumps was considerably reduced compared to control rats. However, in rats given a single intracerebroventricular injection of 100 micrograms of glial cell line-derived neurotrophic factor, locomotor activity was significantly higher than in rats injected with the vehicle, an effect that was most pronounced at the onset of toxin infusion. Consistent with a protective or restorative effect in this model of striatal neurodegeneration, toxin-induced deficits in markers of neurotransmitter function were attenuated by glial cell line-derived neurotrophic factor. Thus, [3H]GABA uptake and [3H]tiagabine/GABA uptake sites in striatal target tissues (globus pallidus and substantia nigra), as well as [3H]choline uptake, choline acetyltransferase activity and dopamine receptor binding in the striatum were decreased by the toxin and restored to varying degrees by glial cell line-derived neurotrophic factor administration. As with locomotor abnormalities, effects on neurochemical deficits were most prominent when glial cell line-derived neurotrophic factor was given at the start of toxin infusion, but remained significantly higher than in the vehicle-injected rats when given up to two weeks after. Substance P, dynorphin A and [Met]enkephalin levels in the striatal target tissues also were reduced by 3-nitropropionic acid. The results show that glial cell line-derived neurotrophic factor protects striatal neurons from slow excitotoxic cell death resulting from energy deprivation, secondary to mitochondrial dysfunction. Moreover, they suggest that glial cell line-derived neurotrophic factor may be a viable therapeutic agent for slowly progressive central nervous system disorders, like Huntington's disease, that may be caused by secondary excitotoxicity resulting from abnormal energy utilization.

Generation and transplantation of EGF-responsive neural stem cells derived from GFAP-hNGF transgenic mice

EGF-responsive neural stem cells isolated from murine striatum have the capacity to differentiate into both neurons and glia in vitro. Genetic modification of these cells is hindered by a number of problems such as gene stability and transfection efficiency. To circumvent these problems we generated transgenic mice in which the human GFAP promoter directs the expression of human NGF. Neural stem cells isolated from the forebrain of these transgenic animals proliferate and form clusters, which appear identical to stem cells generated from control animals. Upon differentiation in vitro, the transgenic stem cell-derived astrocytes express and secrete bioactive hNGF. Undifferentiated GFAP-hNGF or control stem cells were transplanted into the striatum of adult rats. One and 3 weeks after transplantation, hNGF was detected immunocytochemically in an halo around the transplant sites. In GFAP-hNGF-grafted animals, intrinsic striatal neurons proximal to the graft appear to have taken up hNGF secreted by the grafted cells. Ipsilateral to implants of GFAP-hNGF-secreting cells, choline acetyltransferase-immunoreactive neurons within the striatum were hypertrophied relative to the contralateral side or control-grafted animals. Further, GFAP-hNGF-grafted rats displayed a robust sprouting of p75 neurotrophin receptor-positive fibers emanating from the underlying basal forebrain. These studies indicate that EGF-responsive stem cells which secrete hNGF under the direction of the GFAP promoter display in vitro and in vivo properties similar to that seen following other methods of NGF delivery and this source of cells may provide an excellent avenue for delivery of neurotrophins such as NGF to the central nervous system.

Grafts of EGF-responsive neural stem cells derived from GFAP-hNGF transgenic mice: trophic and tropic effects in a rodent model of Huntington's disease

The present study examined whether implants of epidermal growth factor (EGF)-responsive stems cells derived from transgenic mice in which the glial fibrillary acid protein (GFAP) promoter directs the expression of human nerve growth factor (hNGF) could prevent the degeneration of striatal neurons in a rodent model of Huntington's disease (HD). Rats received intrastriatal transplants of GFAP-hNGF stem cells or control stem cells followed 9 days later by an intrastriatal injection of quinolinic acid (QA). Nissl stains revealed large striatal lesions in rats receiving control grafts, which, on average, encompassed 12.78 mm3. The size of the lesion was significantly reduced (1.92 mm3) in rats receiving lesions and GFAP-hNGF transplants. Rats receiving QA lesions and GFAP-hNGF-secreting grafts stem cell grafts displayed a sparing of striatal neurons immunoreactive (ir) for glutamic acid decarboxylase, choline acetyltransferase, and neurons histochemically positive for nicotinamide adenosine diphosphate. Intrastriatal GFAP-hNGF-secreting implants also induced a robust sprouting of cholinergic fibers from subjacent basal forebrain neurons. The lesioned striatum in control-grafted animals displayed numerous p75 neurotrophin-ir (p75NTR) astrocytes, which enveloped host vasculature. In rats receiving GFAP-hNGF-secreting stem cell grafts, the astroglial staining pattern was absent. By using a mouse-specific probe, stem cells were identified in all animals. These data indicate that cellular delivery of hNGF by genetic modification of stem cells can prevent the degeneration of vulnerable striatal neural populations, including those destined to die in a rodent model of HD, and supports the emerging concept that this technology may be a valuable therapeutic strategy for patients suffering from this disease.

Basic FGF attenuates amyloid beta-peptide-induced oxidative stress, mitochondrial dysfunction, and impairment of Na+/K+-ATPase activity in hippocampal neurons

Basic fibroblast growth factor (bFGF) exhibits trophic activity for many populations of neurons in the brain, and can protect those neurons against excitotoxic, metabolic and oxidative insults. In Alzheimer's disease (AD), amyloid beta-peptide (A beta) fibrils accumulate in plaques which are associated with degenerating neurons. A beta can be neurotoxic by a mechanism that appears to involve induction of oxidative stress and disruption of calcium homeostasis. Plaques in AD brain contain high levels of bFGF suggesting a possible modulatory role for bFGF in the neurodegenerative process. We now report that bFGF can protect cultured hippocampal neurons against A beta25-35 toxicity by a mechanism that involves suppression of reactive oxygen species (ROS) accumulation and maintenance of Na+/K+-ATPase activity. A beta25-35 induced lipid peroxidation, accumulation of H2O2, mitochondrial ROS accumulation, and a decrease in mitochondrial transmembrane potential; each of these effects of A beta25-35 was abrogated in cultures pre-treated with bFGF. Na+/K+-ATPase activity was significantly reduced following exposure to A beta25-35 in control cultures, but not in cultures pre-treated with bFGF. bFGF did not protect neurons from death induced by ouabain (a specific inhibitor of the Na+/K+-ATPase) or 4-hydroxynonenal (an aldehydic product of lipid peroxidation) consistent with a site of action of bFGF prior to induction of oxidative stress and impairment of ion-motive ATPases. By suppressing accumulation of oxyradicals, bFGF may slow A beta-induced neurodegenerative cascades.

Protective effect of encapsulated cells producing neurotrophic factor CNTF in a monkey model of Huntington's disease

Huntington's disease is a genetic disorder that results from degeneration of striatal neurons, particularly those containing GABA (gamma-aminobutyric acid). There is no effective treatment for preventing or slowing this neuronal degeneration. Ciliary neurotrophic factor (CNTF) is a trophic factor for striatal neurons and therefore a potential therapeutic agent for Huntington's disease. Here we evaluate CNTF as a neuroprotective agent in a nonhuman primate model of Huntington's disease. We gave cynomolgus monkeys intrastriatal implants of polymer-encapsulated baby hamster kidney fibroblasts that had been genetically modified to secrete human CNTF. One week later, monkeys received unilateral injections of quinolinic acid into the previously implanted striatum to reproduce the neuropathology seen in Huntington's disease. Human CNTF was found to exert a neuroprotective effect on several populations of striatal cells, including GABAergic, cholinergic and diaphorase-positive neurons which were all destined to die following administration of quinolinic acid. Human CNTF also prevented the retrograde atrophy of layer V neurons in motor cortex and exerted a significant protective effect on the GABAergic innervation of the two important target fields of the striatal output neurons (the globus pallidus and pars reticulata of the substantia nigra). Our results show that human CNTF has a trophic influence on degenerating striatal neurons as well as on critical non-striatal regions such as the cerebral cortex, supporting the idea that human CNTF may help to prevent the degeneration of vulnerable striatal populations and cortical-striatal basal ganglia circuits in Huntington's disease.

Apoptosis in neurodegenerative disorders: potential for therapy by modifying gene transcription

Apoptotic, rather than necrotic, nerve cell death now appears as likely to underlie a number of common neurological conditions including stroke, Alzheimer's disease, Parkinson's disease, hereditary retinal dystrophies and Amyotrophic Lateral Sclerosis. Apoptotic neuronal death is a delayed, multistep process and therefore offers a therapeutic opportunity if one or more of these steps can be interrupted or reversed. Research is beginning to show how specific macromolecules play a role in determining the apoptotic death process. We are particularly interested in the critical nature of gradual mitochondrial failure in the apoptotic process and propose that a maintenance of mitochondrial function through the pharmacological modulation of gene expression offers an opportunity for the effective treatment of some types of neurological dysfunction. Our research into the development of small diffusible molecules that reduce apoptosis has grown from studies of the irreversible MAO-B inhibitor (-)-deprenyl. (-)-Deprenyl can reduce neuronal death independently of MAO-B inhibition even after neurons have sustained seemingly lethal damage. (-)-Deprenyl can also influence the process outgrowth of some glial and neuronal populations and can reduce the concentrations of oxidative radicals in damaged cells at concentrations too small to inhibit MAO. In accord with earlier work of others, we showed that (-)-deprenyl alters the expression of a number of mRNAs or of proteins in nerve and glial cells and that the alterations in gene expression/protein synthesis are the result of a selective action on transcription. The alterations in gene expression/protein synthesis are accompanied by a decrease in DNA fragmentation characteristic of apoptosis and the death of responsive cells. The onco-proteins Bcl-2 and Bax and the scavenger proteins Cu/Zn superoxide dismutase (SOD1) and Mn superoxide dismutase (SOD-2) are among the 40-50 proteins whose synthesis is altered by (-)-deprenyl. Since mitochondrial membrane potential correlates with mitochondrial ATP production, we have used confocal laser imaging techniques in living cells to show that the transcriptional changes induced by (-)-deprenyl result in a maintenance of mitochondrial membrane potential, a decrease in intramitochondrial calcium and a decrease in cytoplasmic oxidative radical levels. We therefore propose that (-)-deprenyl acts on gene expression to maintain mitochondrial function and decrease cytoplasmic oxidative radical levels and thereby reduces apoptosis. An understanding of the molecular steps by which (-)-deprenyl selectively alters transcription may lead to the development of new therapies for neurodegenerative diseases.

Neural transplantation as an experimental treatment modality for cerebral ischemia

Cerebrovascular disease exemplifies the poor regenerative capacity of the CNS. While there are methods to prevent cerebral infarction, there is no effective therapy available to ameliorate the anatomical, neurochemical and behavioral deficits which follow cerebral ischemia. Focal and transient occlusion of the middle cerebral artery (MCA) in rodents has been reported to result in neuropathology similar to that seen in clinical cerebral ischemia. Using specific techniques, this MCA occlusion can result in a well-localized infarct of the striatum. This review article will provide data accumulated from animal studies using the MCA occlusion technique in rodents to examine whether neural transplantation can ameliorate behavioral and morphological deficits associated with cerebral infarction. Recent advances in neural transplantation as a treatment modality for neurodegenerative disorders such as Parkinson's disease, have revealed that fetal tissue transplantation may produce neurobehavioral recovery. Accordingly, fetal tissue transplantation may provide a potential therapy for cerebral infarction. Preliminary findings in rodents subjected to unilateral MCA occlusion, and subsequently transplanted with fetal striatal tissue into the infarcted striatum have produced encouraging results. Transplanted fetal tissue, assessed immunohistochemically, has been demonstrated to survive and integrate with the host tissue, and, more importantly, ameliorate the ischemia-related behavioral deficits, at least in the short term. Although, this review will focus primarily on cerebral ischemia, characterized by a localized CNS lesion within the striatum, it is envisioned that this baseline data may be extrapolated and applied to cerebral infarction in other brain areas.

Implants of encapsulated human CNTF-producing fibroblasts prevent behavioral deficits and striatal degeneration in a rodent model of Huntington's disease

Delivery of neurotrophic molecules to the CNS has gained considerable attention as a potential treatment strategy for neurological disorders. In the present study, a DHFR-based expression vector containing the human ciliary neurotrophic factor (hCNTF) was transfected into a baby hamster kidney fibroblast cell line (BHK). Using a polymeric device, encapsulated BHK-control cells and those secreting hCNTF (BHK-hCNTF) were transplanted unilaterally into the rat lateral ventricle. Twelve days later, the same animals received unilateral injections of quinolinic acid (QA; 225 nmol) into the ipsilateral striatum. After surgery, animals were behaviorally tested for apomorphine-induced rotation behavior and for skilled forelimb function using the staircase test. Rats receiving BHK-hCNTF cells rotated significantly less than animals receiving BHK-control cells. No behavioral effects of hCNTF were observed on the staircase test. Nissl-stained sections demonstrated that BHK-hCNTF cells significantly reduced the extent of striatal damage produced by QA. Quantitative analysis of striatal neurons further demonstrated that both choline acetyltransferase- and GAD-immunoreactive neurons were protected by BHK-hCNTF implants. In contrast, a similar loss of NADPH-diaphorase-positive cells was observed in the striatum of both implant groups. Analysis of retrieved capsules revealed numerous viable and mitotically active BHK cells that continued to secrete hCNTF. These results support the concepts that implants of polymer-encapsulated hCNTF-releasing cells can be used to protect striatal neurons from excitotoxic damage and that this strategy may ultimately prove relevant for the treatment of Huntington's disease.

Dopamine-glutamate interactions in the striatum: behaviourally relevant modification of excitotoxicity by dopamine receptor-mediated mechanisms

The two most important afferent projections to the striatum contain glutamate and dopamine, respectively. Excitotoxic damage resulting from excessive stimulation of the N-methyl-D-aspartate subtype of glutamate receptor has been implicated in pathophysiology of ischaemic stroke, hypoglycaemic brain damage and Huntington's disease. We studied the ability of the dopamine system to modify the anatomical, neurochemical and behavioural consequences of glutamatergic toxicity in the striatum. In a first set of experiments, the specific N-methyl-D-aspartate receptor agonist quinolinate was injected unilaterally into the striatum of rats pretreated with one of (i) intraperitoneal (i.p.) saline (controls); (ii) i.p. haloperidol, a D2 dopamine receptor agonist; or (iii) 6-hydroxydopamine lesion of the ipsilateral nigrostriatal tract. Quinolinate-induced striatal damage, as assessed by morphometric and neurochemical criteria, was significantly attenuated in the animals with 6-hydroxydopamine lesions and in those pretreated with haloperidol, compared with saline-pretreated controls. There were no significant differences between the 6-OHDA and haloperidol groups. In a second set of experiments, animals received (i) bilateral intrastriatal quinolinate plus perioperative i.p. saline; (ii) bilateral intrastriatal quinolinate plus i.p. haloperidol; or (iii) bilateral intrastriatal saline. Again, the quinolinate-lesioned animals treated with perioperative haloperidol had significantly less striatal damage than the bilateral quinolinate rats. Behavioural assessment in the Morris Water Maze showed the bilateral quinolinate+haloperidol group to be significantly less impaired on a spatial acquisition task than the bilateral quinolinate animals. Measures of spontaneous daytime motor activity showed significant differences in average speed and rest time between the bilateral quinolinate+haloperidol rats and the bilateral quinolinate group. The performance of the bilateral quinolinate+haloperidol group was not significantly different from that of controls on any of the behavioural tasks. These results indicate an important role for D2 dopamine receptor-mediated mechanisms in striatal excitotoxicity. Since the excitotoxic process involves the same fundamental signalling mechanism that is involved in normal glutamatergic transmission, these findings imply an ability of D2 receptor blockade to modify glutamate signalling in the striatum. These results may have implications for treatment strategies in ischaemic stroke, hypoglycaemic brain damage and schizophrenia.

Intrastriatal implants of polymer encapsulated cells genetically modified to secrete human nerve growth factor: trophic effects upon cholinergic and noncholinergic striatal neurons

Nerve growth factor selectively prevents the degeneration of cholinergic neurons following intrastriatal infusion but rescues both cholinergic and noncholinergic striatal neurons if the nerve growth factor is secreted from grafts of genetically modified fibroblasts. The present study evaluated whether grafted fibroblasts genetically modified to secrete human nerve growth factor could provide trophic influences upon intact cholinergic and noncholinergic striatal neurons. Unilateral striatal grafts of polymer-encapsulated cells genetically modified to secrete human nerve growth factor induced hypertrophy and significantly increased the optical density of choline acetyltransferase-immunoreactive striatal neurons one, two, and four weeks post-transplantation relative to rats receiving identical grafts missing only the human nerve growth factor construct. Nerve growth factor secreting grafts also induced a hypertrophy of noncholinergic neuropeptide Y-immunoreactive striatal neurons one, two, and four weeks post-transplantation. Glutamic acid decarboxylase-immunoreactive neurons were unaffected by the human nerve growth factors secreting grafts. The effects upon choline acetyltransferase-immunoreactive and neuropeptide Y-immunoreactive striatal neurons dissipated following retrieval of the implants. Immunocytochemistry for nerve growth factor revealed intense graft-derived immunoreactivity for up to 1000 microns from the capsule extending along the dorsoventral axis of the striatum. Nerve growth factor-immunoreactivity was also observed within a subpopulation of striatal neurons and may represent nerve growth factor consumer neurons which retrogradely transported graft-derived nerve growth factor. When explanted, grafts produced 2-4 ng human nerve growth factor/24 h over the time course of this study indicating that this level of continuous human nerve growth factor secretion was sufficient to mediate the effects presently observed.

Chronic intrastriatal administration of quinolinic acid produces transient nocturnal hypermotility in the rat

Adult male Sprague-Dawley rats were exposed to 15 mM quinolinic acid solution or vehicle via bilateral intrastriatal dialytic administration for a period of 3 weeks. Animals were tested twice weekly for spontaneous behaviors and nocturnal activity during the 3-week dialysis period and for the 3 weeks following cessation of the dialysis period treatment. Nocturnal activity increased significantly (p < 0.005) during the first week of quinolinic acid exposure compared to vehicle exposed animals. The increase in nocturnal activity subsequently diminished to near control levels by the end of the 3-week dialysis period. During the 3-week period following cessation of dialysis, no significant differences were seen between quinolinic acid and vehicle-exposed animals. In addition, no differences were noted between quinolinic acid and vehicle-exposed animals in spontaneous behaviors either in the 3-week dialysis period or the 3-week period following cessation of dialysis. The results of this study are in agreement with other recent findings of transient nocturnal hyperactivity following striatal damage in rats. One possible explanation for the transient nature of this behavioral change is a transient effect of excitotoxicity in the striatum. During initial exposure to excitotoxins, nocturnal hypermotility could result from premorbid changes in neural function. With continued exposure, this behavioral effect may then diminish as a result of subsequent widespread striatal cell death.

Specific lesions in the extrapyramidal system of the rat brain induced by 3-nitropropionic acid (3-NPA)

The irreversible mitochondrial toxin 3-nitropropionic acid (3-NPA) is a specific inhibitor of succinate dehydrogenase. We performed stereotaxic unilateral injections of 3-NPA into the nigrostriatal dopaminergic pathway in rats in order to examine its specific effects on the dopamine system. The 3-NPA-treated rats displayed unidirectional apomorphineinduced rotations, suggesting that 3-NPA selectively damages dopaminergic neurons when injected into the nigrostriatal pathway. In situ hybridization 7 weeks postinjection indicated a decrease in tyrosine hydroxylase (TH) mRNA to 30% of the noninjected side in the substantia nigra pars compacta (P < 0.05) and decreased to 62% of the noninjected side in the ventral tegmental area (VTA) (nonsignificant) of 3-NPA-lesioned rats. The number of TH mRNA positive cells showed statistically significant decreases in substantia nigra and VTA (P < 0.001) within the lesioned side. In contrast, expression of mRNAs encoding choline acetyltransferase, p75 low-affinity NGF receptor, neurotrophin tyrosine kinase receptors Trk and TrkB, and brain-derived neurotrophic factor showed neuronal sparing in several other regions of the brain. The results suggest that the nigrostriatal dopaminergic system might be selectively vulnerable to 3-NPA and demonstrate that it is possible to employ 3-NPA in a model of partial lesion of the nigrostriatal dopaminergic system resembling early stages of Parkinson's disease.

TrkA-immunoreactive profiles in the central nervous system: colocalization with neurons containing p75 nerve growth factor receptor, choline acetyltransferase, and serotonin

The present investigation used an antibody directed against the extracellular domain of the signal transducing nerve growth factor receptor, trkA, to reveal immunoreactive perikarya or fibers within the olfactory bulb and tubercle, cingulate cortex, nucleus accumbens, striatum, endopiriform nucleus, septal/diagonal band complex, nucleus basalis, hippocampal complex, thalamic paraventricular and reuniens nuclei, periventricular hypothalamus, interpeduncular nucleus, mesencephalic nucleus of the fifth nerve, dorsal nucleus of the lateral lemniscus, prepositus hypoglossal nucleus, ventral cochlear nucleus, ventral lateral tegmentum, medial vestibular nucleus, spinal trigeminal nucleus oralis, nucleus of the solitary tract, raphe nuclei, and spinal cord. Colocalization experiments revealed that virtually all striatal trkA-immunoreactive neurons (> 99%) coexpressed choline acetyltransferase (ChAT) but not p75 nerve growth factor receptor (NGFR). Within the septal/diagonal band complex virtually all trkA neurons (> 95%) coexpressed both ChAT and p75 NGFR. More caudally, dual stained sections revealed numerous trkA/ChAT (> 80%) and trkA/p75 NGFR (> 95%) immunoreactive neurons within the nucleus basalis. In the brainstem, raphe serotonergic neurons (45%) coexpressed trkA. Sections stained with a pan-trk antibody that recognizes primarily trkA, as well as trkB and trkC, labeled neurons within all of these regions as well as within the hypothalamic arcuate, supramammilary, and supraoptic nuclei, hippocampus, inferior and superior colliculus, substantia nigra, ventral tegmental area of T'sai, and cerebellular Purkinje cells. Virtually all of these other regions with the exception of the cerebellum also expressed pan-trk immunoreactivity in the monkey. The widespread expression of trkA throughout the central neural axis suggests that this receptor may play a role in signal transduction mechanisms linked to NGF-related substances in cholinergic basal forebrain and noncholinergic systems. These findings suggest that pharmacological use of ligands for trkA could have beneficial effects on the multiple neuronal systems that are affected in such disorders as Alzheimer's disease.

trk-immunoreactivity in the monkey central nervous system: forebrain

Neurotrophins such as nerve growth factor (NGF) mediate their effects through interactions with high-affinity tropomycin-related kinase (trk) receptors. The present study employed a polyclonal antibody to characterize the distribution of trk-immunoreactive neurons within the nonhuman primate brain. Both young adult and aged cebus and rhesus monkeys displayed trk-immunoreactive neurons within all subdivisions of the basal forebrain. Colocalization studies revealed that between 66% and 76% of trk-immunoreactive basal forebrain neurons also expressed immunoreactivity for the low-affinity p75 NGF receptor, an excellent marker for cholinergic basal forebrain cells. In this experiment, most single-labeled basal forebrain neurons contained only trk immunoreactivity, whereas 4% of basal forebrain neurons expressed only the low-affinity p75 NGF receptor. Scattered trk-immunoreactive neurons also were observed within the caudate nucleus and putamen. Although dual-localization studies with choline acetyltransferase (ChAT) were not performed, striatal neurons codistributed with ChAT-immunoreactive cells, and both types of cells were similar in size and morphology. This suggests that trk immunoreactivity is expressed within cholinergic interneurons within the primate striatum. Finally, lightly stained trk-immunoreactive neurons were observed within the stratum oriens of the hippocampal formation and within the hypothalamus. These data indicate that both cholinergic and, possibly, noncholinergic forebrain neurons express the protein for the high-affinity trk receptor, which transduces the signal mediating the trophic effects of neurotrophins. In addition, the pattern of trk immunoreactivity was preserved in two aged (26 and 29 years old) rhesus monkeys, suggesting that the expression of trk, for the most part, is sustained throughout the lifetime of the organism.

Implants of polymer-encapsulated human NGF-secreting cells in the nonhuman primate: rescue and sprouting of degenerating cholinergic basal forebrain neurons

Baby hamster kidney (BHK) cells were genetically modified to secrete high levels of human nerve growth factor (BHK-hNGF). Following polymer encapsulation, these cells were implanted into the lateral ventricle of four cynomolgus monkeys immediately following a unilateral transection/aspiration of the fornix. Three control monkeys received identical implants, with the exception that the BHK cells were not genetically modified to secrete hNGF and thus differed only by the hNGF construct. One monkey received a fornix transection only. All monkeys displayed complete transections of the fornix as revealed by a comprehensive loss of acetylcholinesterase-containing fibers within the hippocampus ipsilateral to the lesion. Control monkeys that were either unimplanted or received BHK-control (non-NGF secreting) cell implants did not differ from each other and displayed extensive losses of choline acetyltransferase and p75 NGF receptor (NGFr)-immunoreactive neurons within the medial septum (MS; 53 and 54%, respectively) and vertical limb of the diagonal band (VLDB; 21 and 30%, respectively) ipsilateral to the lesion. In contrast, monkeys receiving implants of BHK-hNGF cells exhibited a only a modest loss of cholinergic neurons within the septum (19 and 20%, respectively) and VLDB (7%). Furthermore, only implants of hNGF-secreting cells induced a dense sprouting of cholinergic fibers within the septum, which ramified against the ependymal lining of the ventricle adjacent to the transplant site. Examination of the capsules retreived from monkeys just prior to their death revealed an abundance of cells that produced detectable levels of hNGF in a sufficient concentration to differentiate PC12A cells in culture. These findings support the use of polymer-encapsulated cell therapy as a potential treatment for neurodegenerative diseases such as Alzheimer disease where basal forebrain degeneration is a consistent pathological feature. Moreover, this encapsulated xenogeneic system may provide therapeutically effective levels of a number of neurotrophic factors, alone or in combination, to select populations of neurons within the central nervous system.

Mitochondrial enzyme deficiencies in Down's syndrome

Defects in cytochrome oxidase (CO; complex 4) have recently been demonstrated in blood platelets and in brain tissue from patients with Alzheimer's disease (AD) with possible etiological implications. Because of pathogenetic similarities with AD, we have measured the activities of several mitochondrially localised enzymes in the blood platelets of individuals afflicted with trisomy-21 (Down's syndrome). The activities of monoamine oxidase, cytochrome oxidase, isocitrate dehydrogenase, and glutamate dehydrogenase were assayed in washed platelets from sixty caucasian, male and female control individuals (ages 18-60) and ten, young Down's Syndrome patients (ages 9-21). Significant reductions in the activities of monoamine oxidase, cytochrome oxidase, and isocitrate dehydrogenase were found. In all cases the average activities in Down's syndrome individuals were approximately two-thirds those of controls (DS/Controls = 0.68, 0.67, 0.64 respectively). The activity of the fourth enzyme studied, glutamate dehydrogenase, was found to be similar to controls. Results suggest that these reductions are a consequence of a generalised mitochondrial disturbance which may lie behind some pathogenetic aspect(s) of the disease.

Intravenous administration of a transferrin receptor antibody-nerve growth factor conjugate prevents the degeneration of cholinergic striatal neurons in a model of Huntington disease

Intrastriatal injections of quinolinic acid induce a pattern of neuronal degeneration similar to that seen in Huntington disease. In the present study, nerve growth factor (NGF) crossed the blood-brain barrier in a dose-dependent fashion following intravenous infusion when conjugated to an antibody directed against the transferrin receptor (OX-26). Intravenous injections of the OX-26-NGF conjugate selectively prevented the loss of striatal choline acetyltransferase-immunoreactive neurons which normally occurs following quinolinic acid administration relative to control rats receiving vehicle or a nonconjugated mixture of OX-26 and NGF. These data demonstrate that a neurotrophic factor-antibody conjugate can prevent the degeneration of central NGF-responsive neurons following systemic administration.

Intrastriatal infusion of nerve growth factor after quinolinic acid prevents reduction of cellular expression of choline acetyltransferase messenger RNA and trkA messenger RNA, but not glutamate decarboxylase messenger RNA

Excitotoxic striatal lesions induced by quinolinic acid, a model for Huntington's disease, were used to test for neuroprotective actions of nerve growth factor on striatal cholinergic and GABAergic neurons. Expressions of the trkA receptor for nerve growth factor, choline acetyltransferase and glutamate decarboxylase were analysed by messenger RNA in situ hybridization in adult rats following quinolinic acid lesion (150 nmol) and daily striatal administration of nerve growth factor (1 microgram) or control protein (cytochrome C) for one week. One week after toxin administration, the numbers of cells expressing trkA or choline acetyltransferase messenger RNAs were decreased when compared with unlesioned animals. Moreover, the surviving cells showed a strong down-regulation of these messenger RNAs as deduced from grain count analysis of sections processed for emulsion autoradiography. Daily intrastriatal nerve growth factor administration for one week completely prevented the reduction in the number of cells expressing either of the two markers. Nerve growth factor treatment increased the cellular expression of choline acetyltransferase messenger RNA three times above control levels and restored the levels of trk A messenger RNA expression to control levels. In contrast to the protective effects on cholinergic cells, nerve growth factor treatment failed to attenuate the quinolinic acid-induced decrease in glutamate decarboxylase messenger RNA levels. Optical density measurements of the entire striatum on autoradiographs of brain sections from quinolinic acid-lesioned animals revealed a reduction of the glutamate decarboxylase messenger RNA-specific hybridization signal, which was unaltered by infusion of nerve growth factor or control protein. Our findings strongly suggest that in both the intact and the quinolinic acid-lesioned adult rat striatum, nerve growth factor action is confined to trk A-expressing cholinergic neurons. Striatal glutamate decarboxylase messenger RNA-expressing GABAergic neurons which degenerate in Huntington's disease are not responsive to nerve growth factor.

Systemic 3-nitropropionic acid: long-term effects on locomotor behavior

Systemic administration of 3-nitropropionic acid (3-NP) results in striatal atrophy by irreversibly inhibiting the citric acid cycle, and thereby resulting in cellular ATP depletion. The neuropathological outcome following 3-NP injections is thought to resemble that seen in Huntington's disease (HD) [1]. The current study administered systemic injections in 6- and 10-week-old rats of low-dose 3-NP every other 4 days for a period of 28 days in order to investigate the effects on locomotor behavior and striatal D1 dopamine receptor binding. Experimental and control animals received intraperitoneal injections of 3-NP (10 mg/kg in 0.9% saline) and 0.9% saline, respectively. Animals were tested behaviorally prior to the first and after the last 3-NP administration. Brains were then removed and striatal tissue samples were analyzed for D1 dopamine receptor binding using [3H]SCH23390. Behaviorally, 6-week-old injected animals developed bradykinesia with no signs of stiffness or rigidity, while 10-week-old injected animals displayed an uncoordinated gait, stiffness and ventral recumbency with hind limbs extended in a rigid or fixed position. These visual observations of hypoactivity were supported by a significant decline in both experimental groups' locomotor activity as measured by Digiscan monitors. Furthermore, [3H]SCH23390 specific binding to D1 dopamine receptors revealed a small but significant decrease in 10-week-old injected animals compared to controls. These results demonstrate that both 6- and 10-week-old rats do exhibit behavioral alterations after long-term 3-NP administration, however the former may not show accompanying gross D1 receptor changes.