Systemic administration of MPTP induces thalamic neuronal degeneration in mice

Connectivity of the corticostriatal and thalamostriatal systems in normal and parkinsonian states: An update

The striatum receives abundant glutamatergic afferents from the cortex and thalamus. These inputs play a major role in the functions of the striatal neurons in normal conditions, and are significantly altered in pathological states, such as Parkinson's disease. This review summarizes the current knowledge of the connectivity of the corticostriatal and thalamostriatal pathways, with emphasis on the most recent advances in the field. We also discuss novel findings regarding structural changes in cortico- and thalamostriatal connections that occur in these connections as a consequence of striatal loss of dopamine in parkinsonism.

Striatal synaptic adaptations in Parkinson's disease

The striatum is densely innervated by mesencephalic dopaminergic neurons that modulate acquisition and vigor of goal-directed actions and habits. This innervation is progressively lost in Parkinson's disease (PD), contributing to the defining movement deficits of the disease. Although boosting dopaminergic signaling with levodopa early in the course of the disease alleviates these deficits, later this strategy leads to the emergence of debilitating dyskinesia. Here, recent advances in our understanding of how striatal cells and circuits adapt to this progressive de-innervation and to levodopa therapy are discussed. First, we discuss how dopamine (DA) depletion triggers cell type-specific, homeostatic changes in spiny projection neurons (SPNs) that tend to normalize striatal activity but also lead to disruption of the synaptic architecture sculpted by experience. Second, we discuss the roles played by cholinergic and nitric oxide-releasing interneurons in these adaptations. Third, we examine recent work in freely moving mice suggesting that alterations in the spatiotemporal dynamics of striatal ensembles contributes to PD movement deficits. Lastly, we discuss recently published evidence from a progressive model of PD suggesting that contrary to the classical model, striatal pathway imbalance is necessary but not sufficient to produce frank parkinsonism.

Thalamic degeneration in MPTP-treated Parkinsonian monkeys: impact upon glutamatergic innervation of striatal cholinergic interneurons

In both Parkinson's disease (PD) patients and MPTP-treated non-human primates, there is a profound neuronal degeneration of the intralaminar centromedian/parafascicular (CM/Pf) thalamic complex. Although this thalamic pathology has long been established in PD (and other neurodegenerative disorders), the impact of CM/Pf cell loss on the integrity of the thalamo-striatal glutamatergic system and its regulatory functions upon striatal neurons remain unknown. In the striatum, cholinergic interneurons (ChIs) are important constituents of the striatal microcircuitry and represent one of the main targets of CM/Pf-striatal projections. Using light and electron microscopy approaches, we have analyzed the potential impact of CM/Pf neuronal loss on the anatomy of the synaptic connections between thalamic terminals (vGluT2-positive) and ChIs neurons in the striatum of parkinsonian monkeys treated chronically with MPTP. The following conclusions can be drawn from our observations: (1) as reported in PD patients, and in our previous monkey study, CM/Pf neurons undergo profound degeneration in monkeys chronically treated with low doses of MPTP. (2) In the caudate (head and body) nucleus of parkinsonian monkeys, there is an increased density of ChIs. (3) Despite the robust loss of CM/Pf neurons, no significant change was found in the density of thalamostriatal (vGluT2-positive) terminals, and in the prevalence of vGluT2-positive terminals in contact with ChIs in parkinsonian monkeys. These findings provide new information about the state of thalamic innervation of the striatum in parkinsonian monkeys with CM/Pf degeneration, and bring up an additional level of intricacy to the consequences of thalamic pathology upon the functional microcircuitry of the thalamostriatal system in parkinsonism. Future studies are needed to assess the importance of CM/Pf neuronal loss, and its potential consequences on the neuroplastic changes induced in the synaptic organization of the thalamostriatal system, in the development of early cognitive impairments in PD.

Acute histopathological responses and long-term behavioral outcomes in mice with graded controlled cortical impact injury

While animal models of controlled cortical impact often display short-term motor dysfunction after injury, histological examinations do not show severe cortical damage. Thus, this model requires further improvement. Mice were subjected to injury at three severities using a Pin-Point™-controlled cortical impact device to establish secondary brain injury mouse models. Twenty-four hours after injury, hematoxylin-eosin staining, Fluoro-Jade B histofluorescence, and immunohistochemistry were performed for brain slices. Compared to the uninjured side, we observed differences of histopathological findings, neuronal degeneration, and glial cell number in the CA2 and CA3 regions of the hippocampus on the injured side. The Morris water maze task and beam-walking test verified long-term (14–28 days) spatial learning/memory and motor balance. To conclude, the histopathological responses were positively correlated with the degree of damage, as were the long-term behavioral manifestations after controlled cortical impact. All animal procedures were approved by the Institutional Animal Care and Use Committee at Shanghai Jiao Tong University School of Medicine.

A new outlook on cholinergic interneurons in Parkinson's disease and L-DOPA-induced dyskinesia

Traditionally, dopamine (DA) and acetylcholine (ACh) striatal systems were considered antagonistic and imbalances or aberrant signaling between these neurotransmitter systems could be detrimental to basal ganglia activity and pursuant motor function, such as in Parkinson's disease (PD) and L-DOPA-induced dyskinesia (LID). Herein, we discuss the involvement of cholinergic interneurons (ChIs) in striatally-mediated movement in a healthy, parkinsonian, and dyskinetic state. ChIs integrate numerous neurotransmitter signals using intrinsic glutamate, serotonin, and DA receptors and convey the appropriate transmission onto nearby muscarinic and nicotinic ACh receptors to produce movement. In PD, severe DA depletion causes abnormal rises in ChI activity which promote striatal signaling to attenuate normal movement. When treating PD with L-DOPA, hyperkinetic side effects, or LID, develop due to increased striatal DA; however, the role of ChIs and ACh transmission, until recently has been unclear. Fortunately, new technology and pharmacological agents have facilitated understanding of ChI function and ACh signaling in the context of LID, thus offering new opportunities to modify existing and discover future therapeutic strategies in movement disorders.

Striatal cholinergic interneurons and Parkinson's disease

Giant, aspiny cholinergic interneurons (ChIs) have long been known to be key nodes in the striatal circuitry controlling goal-directed actions and habits. In recent years, new experimental approaches, like optogenetics and monosynaptic rabies virus mapping, have expanded our understanding of how ChIs contribute to the striatal activity underlying action selection and the interplay of dopaminergic and cholinergic signaling. These approaches also have begun to reveal how ChI function is distorted in disease states affecting the basal ganglia, like Parkinson's disease (PD). This review gives a brief overview of our current understanding of the functional role played by ChIs in striatal physiology and how this changes in PD. The translational implications of these discoveries, as well as the gaps that remain to be bridged, are discussed as well.

Loss and remodeling of striatal dendritic spines in Parkinson's disease: from homeostasis to maladaptive plasticity?

In Parkinson's disease (PD) patients and animal models of PD, the progressive degeneration of the nigrostriatal dopamine (DA) projection leads to two major changes in the morphology of striatal projection neurons (SPNs), i.e., a profound loss of dendritic spines and the remodeling of axospinous glutamatergic synapses. Striatal spine loss is an early event tightly associated with the extent of striatal DA denervation, but not the severity of parkinsonian motor symptoms, suggesting that striatal spine pruning might be a form of homeostatic plasticity that compensates for the loss of striatal DA innervation and the resulting dysregulation of corticostriatal glutamatergic transmission. On the other hand, the remodeling of axospinous corticostriatal and thalamostriatal glutamatergic synapses might represent a form of late maladaptive plasticity that underlies changes in the strength and plastic properties of these afferents and the resulting increased firing and bursting activity of striatal SPNs in the parkinsonian state. There is also evidence that these abnormal synaptic connections might contribute to the pathophysiology of L-DOPA-induced dyskinesia. Despite the significant advances made in this field over the last thirty years, many controversial issues remain about the striatal SPN subtypes affected, the role of spine changes in the altered activity of SPNs in the parkinsonisn state, and the importance of striatal spine plasticity in the pathophysiology of L-DOPA-induced dyskinesia. In this review, we will examine the current state of knowledge of these issues, discuss the limitations of the animal models used to address some of these questions, and assess the relevance of data from animal models to the human-diseased condition.

Brain Food at High Altitude

Scenic view at high altitude is a pleasure to the eyes, but it has some shortcoming effects as well. High altitude can be divided into different categories, i.e., high altitude (3000-5000 ft), very high altitude (5000-8000 ft), and extreme altitude (above 8000 ft). Much of the population resides at high altitude, and others go there for tourism. Military personnel are also posted there to defend boundaries. As we ascent to high altitude, partial pressure of oxygen reduces, whereas concentration remains the same; this reduces the availability of oxygen to different body parts. This pathophysiological condition is known as hypobaric hypoxia (HH) which leads to oxidative stress and further causes cognitive dysfunction in some cases. Hypoxia causes neurodegeneration in different brain regions; however, the hippocampus is found to be more prone in comparison to other brain regions. As the hippocampus is affected most, therefore, spatial memory is impaired most during such condition. This chapter will give a brief review of the damaging effect of high altitude on cognition and also throw light on possible herbal interventions at high altitude, which can improve cognitive performance as well as provide protection against the deteriorating effect of hypobaric hypoxia at high altitude.

Development and application of novel histochemical tracers for localizing brain connectivity and pathology

FLUORO-GOLD

A NEW FLUORESCENT RETROGRADE AXONAL TRACER WITH NUMEROUS UNIQUE PROPERTIES: A new fluorescent dye, Fluoro-Gold, has been demonstrated to undergo retrograde axonal transport. Its properties include (1) intense fluorescence, (2) extensive filling of dendrites, (3) high resistance to fading, (4) no uptake by intact undamaged fibers of passage, (5) no diffusion from labeled cells, (6) consistent and pure commercial source, (7) wide latitude of survival times and (8) compatibility with all other tested neuro-histochemical techniques. © 1986. Fluoro-Jade C results in ultra high resolution and contrast labeling of degenerating neurons: The causes and effects of neuronal degeneration are of major interest to a wide variety of neuroscientists. Paralleling this growing interest is an increasing number of methods applicable to the detection of neuronal degeneration. The earliest methods employing aniline dyes were methodologically simple, but difficult to interpret due to a lack of staining specificity. In an attempt to circumvent this problem, numerous suppressed silver methods have been introduced. However, these methods are labor intensive, incompatible with most other histochemical procedures and notoriously capricious. In an attempt to develop a tracer with the methodological simplicity and reliability of conventional stains but with the specificity of an ideal suppressed silver preparation, the Fluoro-Jade dyes were developed. Fluoro-Jade C, like its predecessors, Fluoro-Jade and Fluoro-Jade B, was found to stain all degenerating neurons, regardless of specific insult or mechanism of cell death. Therefore, the patterns of neuronal degeneration seen following exposure to either the glutamate agonist, kainic acid, or the inhibitor of mitochondrial respiration, 3-NPA, were the same for all of the Fluoro-Jade dyes. However, there was a qualitative difference in the staining characteristics of the three fluorochromes. Specifically, Fluoro-Jade C exhibited the greatest signal to background ratio, as well as the highest resolution. This translates to a stain of maximal contrast and affinity for degenerating neurons. This makes it ideal for localizing not only degenerating nerve cell bodies, but also distal dendrites, axons and terminals. The dye is highly resistant to fading and is compatible with virtually all histological processing and staining protocols. Triple labeling was accomplished by staining degenerating neurons with Fluoro-Jade C, cell nuclei with DAPI and activated astrocytes with GFAP immunofluoresence. © 2005.

ARTICLE ABSTRACT

The development of novel tracers and associated histochemical methods has always been need driven. One such need was the development of tracers that could be administered to discrete brain regions in vivo to subsequently reveal neuronal connectivity via axonal transport of the tracer. One such compound is Fluoro-Gold (F-G), which can be used to demonstrate retrograde axonal transport. Advantages of this fluorescent tracer include brightness, sensitivity, contrast, stability, permanence and compatibility with multiple labeling studies. It may be applied to resolve either the afferent or efferent connections of brain regions of interest. Another need addressed was for a simple and definitive way to localize degenerating neurons in brain tissue sections. This led to the development of Fluoro-Jade B (FJ-B) and Fluoro-Jade C (FJ-C). Advantages of these fluorescent histochemical tracers include high specificity, resolution, contrast, stability and suitability for use in multiple labeling studies. These methods can be applied to detect both apoptotic and necrotic neuronal degeneration following a variety of insults including physical trauma, neurodegenerative disease and a wide variety of neurotoxicants. This article is part of a Special Issue entitled SI:50th Anniversary Issue.

Morphological changes of glutamatergic synapses in animal models of Parkinson's disease

The striatum and the subthalamic nucleus (STN) are the main entry doors for extrinsic inputs to reach the basal ganglia (BG) circuitry. The cerebral cortex, thalamus and brainstem are the key sources of glutamatergic inputs to these nuclei. There is anatomical, functional and neurochemical evidence that glutamatergic neurotransmission is altered in the striatum and STN of animal models of Parkinson’s disease (PD) and that these changes may contribute to aberrant network neuronal activity in the BG-thalamocortical circuitry. Postmortem studies of animal models and PD patients have revealed significant pathology of glutamatergic synapses, dendritic spines and microcircuits in the striatum of parkinsonians. More recent findings have also demonstrated a significant breakdown of the glutamatergic corticosubthalamic system in parkinsonian monkeys. In this review, we will discuss evidence for synaptic glutamatergic dysfunction and pathology of cortical and thalamic inputs to the striatum and STN in models of PD. The potential functional implication of these alterations on synaptic integration, processing and transmission of extrinsic information through the BG circuits will be considered. Finally, the significance of these pathological changes in the pathophysiology of motor and non-motor symptoms in PD will be examined.

Neuronal loss in the caudal intralaminar thalamic nuclei in a primate model of Parkinson's disease

In light of postmortem human studies showing extensive degeneration of the center median (CM) and parafascicular (Pf) thalamic nuclei in Parkinson's disease patients, the present study assessed the extent of neuronal loss in CM/Pf of non-human primates that were rendered parkinsonian by repeated injections of low doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In order to determine the course of CM/Pf degeneration during the MPTP intoxication, motor-asymptomatic animals with partial striatal dopamine denervation were also used. The Cavalieri's principle for volume estimation and the unbiased stereological cell count method with the optical dissector technique were used to estimate the total number of neurons in the CM/Pf. We found substantial neurons loss in the CM/Pf in both, motor-symptomatic MPTP-treated monkeys in which the striatal dopamine innervation was reduced by more than 80%, and in motor-asymptomatic MPTP-treated animals with 40-50% striatal dopamine loss. In MPTP-treated parkinsonian monkeys, 60 and 62% neurons loss was found in CM and Pf, respectively, while partially dopamine-depleted asymptomatic animals displayed 59 and 52% neurons loss in the CM and Pf, respectively. Thus, our study demonstrates that the CM/Pf neurons loss is an early phenomenon that occurs prior to the development of parkinsonian motor symptoms in these animals. In contrast, the neighboring mediodorsal nucleus of the thalamus was only mildly affected (18% neurons loss) in the parkinsonian monkeys. Together with recent findings about the possible role of the CM/Pf-striatal system in cognition, our findings suggest that the pathology of the thalamostriatal system may precede the development of motor symptoms in PD, and may account for some of the cognitive deficits in attentional set-shifting often seen in these patients. Future studies in this animal model, and in monkeys with selective lesion of CM or Pf, are needed to further elucidate the role of the CM/Pf-striatal system in normal and parkinsonian conditions.

Visualization of fast calcium oscillations in the parafascicular nucleus

The parafascicular nucleus (Pf) is an ascending target of the pedunculopontine nucleus (PPN) and is part of the "non-specific" intralaminar thalamus. The PPN, part of the reticular activating system, is mainly involved in waking and rapid eye movement sleep. Gamma oscillations are evident in all Pf neurons and mediated by high threshold voltage-dependent N- and P/Q-type calcium channels. We tested the hypothesis that high-speed calcium imaging would reveal calcium-mediated oscillations in synchrony with patch clamp recorded oscillations during depolarizing current ramps. Patch-clamped 9 to 19-day-old rat Pf neurons (n = 148, dye filled n = 61, control n = 87) were filled with Fura 2, Bis Fura, or Oregon Green BAPTA-1. Calcium transients were generated during depolarizing current ramps and visualized with a high-speed, wide-field fluorescence imaging system. Cells manifested calcium transients with oscillations in both somatic and proximal dendrite fluorescence recordings. Fluorescent calcium transients were blocked with the nonspecific calcium channel blocker, cadmium, or the combination of ω-Agatoxin-IVA (AgA), a specific P/Q-type calcium channel blocker and ω-conotoxin-GVIA (CgTx), a specific N-type calcium channel blocker. We developed a viable methodology for studying high-speed oscillations without the use of multi-photon imaging systems.

Neuroprotective changes of thalamic degeneration-related gene expression by acupuncture in an MPTP mouse model of parkinsonism: microarray analysis

Acupuncture stimulations at GB34 and LR3 inhibit the reduction of tyrosine hydroxylase in the nigrostriatal dopaminergic neurons in the parkinsonism animal models. Especially, behavioral tests showed that acupuncture stimulations improved the motor dysfunction in a previous study by almost 87.7%. The thalamus is a crucial area for the motor circuit and has been identified as one of the most markedly damaged areas in Parkinson's disease (PD), so acupuncture stimulations might also have an effect on the thalamic damage. In this study, gene expression changes following acupuncture at the acupoints were investigated in the thalamus of a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced parkinsonism model using a whole transcript array. It was confirmed that acupuncture at these acupoints could inhibit the decrease of tyrosine hydroxylase in the thalamic regions of the MPTP model, while acupuncture at the non-acupoints could not suppress this decrease by its level shown in the acupoints. GeneChip gene array analysis showed that 18 (5 annotated genes: Dnase1l2, Dusp4, Mafg, Ndph and Pgm5) of the probes down-regulated in MPTP, as compared to the control, were exclusively up-regulated by acupuncture at the acupoints, but not at the non-acupoints. In addition, 14 (3 annotated genes; Serinc2, Sp2 and Ucp2) of the probes up-regulated in MPTP, as compared to the control, were exclusively down-regulated by acupuncture at the acupoints, but not at the non-acupoints. The expression levels of the representative genes in the microarray were validated by real-time RT-PCR. These results suggest that the 32 probes (8 annotated genes) which are affected by MPTP and acupuncture may be responsible for exerting the inhibitory effect of acupuncture in the thalamus which can be damaged by MPTP intoxication.

Basal ganglia activity patterns in parkinsonism and computational modeling of their downstream effects

The availability of suitable animal models and the opportunity to record electrophysiologic data in movement disorder patients undergoing neurosurgical procedures has allowed researchers to investigate parkinsonism-related changes in neuronal firing patterns in the basal ganglia and associated areas of the thalamus and cortex. These studies have shown that parkinsonism is associated with increased activity in the basal ganglia output nuclei, along with increases in burst discharges, oscillatory firing and synchronous firing patterns throughout the basal ganglia. Computational approaches have the potential to play an important role in the interpretation of these data. Such efforts can provide a formalized view of neuronal interactions in the network of connections between the basal ganglia, thalamus, and cortex, allow for the exploration of possible contributions of particular network components to parkinsonism, and potentially result in new conceptual frameworks and hypotheses that can be subjected to biological testing. It has proven very difficult, however, to integrate the wealth of the experimental findings into coherent models of the disease. In this review, we provide an overview of the abnormalities in neuronal activity that have been associated with parkinsonism. Subsequently, we discuss some particular efforts to model the pathophysiologic mechanisms that may link abnormal basal ganglia activity to the cardinal parkinsonian motor signs and may help to explain the mechanisms underlying the therapeutic efficacy of deep brain stimulation for Parkinson's disease. We emphasize the logical structure of these computational studies, making clear the assumptions from which they proceed and the consequences and predictions that follow from these assumptions.

CCL20 Is Associated with Neurodegeneration Following Experimental Traumatic Brain Injury and Promotes Cellular Toxicity In Vitro

Traumatic brain injury (TBI) is complex and involves multiple processes that contribute to functional decline. Progressive neuropathies result from delayed cellular death following the initial impact. Although the precise mechanisms responsible for delayed injury are unknown, numerous data implicate a role for the peripheral immune system in perpetuating neuroinflammation after TBI. A previous report demonstrated that splenic CCL20 chemokine expression was upregulated 24 h after lateral fluid percussive impact (LFPI), prior to neuronal expression but consistent with neurodegeneration. Here, we expand on those data to report increased CCL20 protein expression in white matter 48 h after LFPI and demonstrate that CCL20 is directly toxic to primary neurons and oligodendrocytes subjected to oxygen glucose deprivation. The temporal expression profile of CCL20, coupled with in vitro toxicity to primary cells, suggests that this chemokine exerts deleterious effects on cell viability following TBI. These findings warrant further investigations into the use of CCL20 as a potential biomarker and/or therapeutic target.

The effects of nigrostriatal dopamine depletion on the thalamic parafascicular nucleus

Neuronal loss in Parkinson's disease (PD) is seen in a number of brain regions in addition to the substantia nigra (SN). Among these is the thalamic parafascicular nucleus (PF), which sends glutamatergic projections to the striatum and receives GABAergic inputs from the SN. Recent data suggest that lesions of nigrostriatal dopamine axons cause a loss of PF neurons, which has been interpreted to suggest that the PF cell loss seen in PD is secondary to dopamine denervation. However, the extent of a PF dopamine innervation in the rat is unclear, and it is possible that PF cell loss in parkinsonism is independent of nigrostriatal dopamine degeneration. We characterized the dopamine innervation of the PF in the rat and determined if 6-hydroxydopamine SN lesions cause PF neuron degeneration. Dual-label immunohistochemistry revealed that almost all tyrosine hydroxylase-immunoreactive (TH-ir) axons in the PF also expressed dopamine-beta-hydroxylase and were therefore noradrenergic or adrenergic. Moreover, an antibody directed against dopamine revealed only very rare PF dopaminergic axons. Retrograde-tract tracing-immunohistochemistry did not uncover an innervation of the PF from midbrain dopamine neurons. Nigrostriatal dopamine neuron lesions did not elicit degeneration of PF cells, as reflected by a lack of FluoroJade C staining. Similarly, neither unilateral 6-OHDA lesions of nigrostriatal axons nor the dorsal noradrenergic bundle decreased the number of PF neurons or the number of PF neurons retrogradely-labeled from the striatum. These data suggest that the loss of thalamostriatal PF neurons in Parkinson's Disease is a primary event rather than secondary to nigrostriatal dopamine degeneration.

Gamma band activity in the developing parafascicular nucleus

The parafascicular nucleus (Pf) receives cholinergic input from the pedunculopontine nucleus, part of the reticular activating system involved in waking and rapid eye movement (REM) sleep, and sends projections to the cortex. We tested the hypothesis that Pf neurons fire maximally at gamma band frequency (30-90 Hz), that this mechanism involves high-threshold voltage-dependent P/Q- and N-type calcium channels, and that this activity is enhanced by the cholinergic agonist carbachol (CAR). Patch-clamped 9- to 25-day-old rat Pf neurons (n = 299) manifested a firing frequency plateau at gamma band when maximally activated (31.5 ± 1.5 Hz) and showed gamma oscillations when voltage-clamped at holding potentials above -20 mV, and the frequency of the oscillations increased significantly with age (24.6 ± 3.8 vs. 51.6 ± 4.4 Hz, P < 0.001) but plateaued at gamma frequencies. Cells exposed to CAR showed significantly higher frequencies early in development compared with those without CAR (24.6 ± 3.8 vs. 41.7 ± 4.3 Hz, P < 0.001) but plateaued with age. The P/Q-type calcium channel blocker ω-agatoxin-IVA (ω-Aga) blocked gamma oscillations, whereas the N-type blocker ω-conotoxin-GVIA (ω-CgTx) only partially decreased the power spectrum amplitude of gamma oscillations. The blocking effect of ω-Aga on P/Q-type currents and ω-CgTx on N-type currents was consistent over age. We conclude that P/Q- and N-type calcium channels appear to mediate Pf gamma oscillations during development. We hypothesize that the cholinergic input to the Pf could activate these cells to oscillate at gamma frequency, and perhaps relay these rhythms to cortical areas, thus providing a stable high-frequency state for "nonspecific" thalamocortical processing.

The primate thalamostriatal systems: Anatomical organization, functional roles and possible involvement in Parkinson's disease

The striatum receives glutamatergic inputs from two main thalamostriatal systems that originate either from the centre median/parafascicular complex (CM/PF-striatal system) or the rostral intralaminar, midline, associative and relay thalamic nuclei (non-CM/PF-striatal system). These dual thalamostriatal systems display striking differences in their anatomical and, most likely, functional organization. The CM/PF-striatal system is topographically organized, and integrated within functionally segregated basal ganglia-thalamostriatal circuits that process sensorimotor, associative and limbic information. CM/PF neurons are highly responsive to attention-related sensory stimuli, suggesting that the CM/PF-striatal system, through its strong connections with cholinergic interneurons, may play a role in basal ganglia-mediated learning, behavioral switching and reinforcement. In light of evidence for prominent CM/PF neuronal loss in Parkinson's disease, we propose that the significant CM-striatal system degeneration, combined with the severe nigrostriatal dopamine loss in sensorimotor striatal regions, may alter normal automatic actions, and shift the processing of basal ganglia-thalamocortical motor programs towards goal-directed behaviors.

Deep brain stimulation of the center median-parafascicular complex of the thalamus has efficient anti-parkinsonian action associated with widespread cellular responses in the basal ganglia network in a rat model of Parkinson's disease

The thalamic centromedian-parafascicular (CM/Pf) complex, mainly represented by Pf in rodents, is proposed as an interesting target for the neurosurgical treatment of movement disorders, including Parkinson's disease. In this study, we examined the functional impact of subchronic high-frequency stimulation (HFS) of Pf in the 6-hydroxydopamine-lesioned hemiparkinsonian rat model. Pf-HFS had significant anti-akinetic action, evidenced by alleviation of limb use asymmetry (cylinder test). Whereas this anti-akinetic action was moderate, Pf-HFS totally reversed lateralized neglect (corridor task), suggesting potent action on sensorimotor integration. At the cellular level, Pf-HFS partially reversed the dopamine denervation-induced increase in striatal preproenkephalin A mRNA levels, a marker of the neurons of the indirect pathway, without interfering with the markers of the direct pathway (preprotachykinin and preprodynorphin). Pf-HFS totally reversed the lesion-induced changes in the gene expression of cytochrome oxidase subunit I in the subthalamic nucleus, the globus pallidus, and the substantia nigra pars reticulata, and partially in the entopeduncular nucleus. Unlike HFS of the subthalamic nucleus, Pf-HFS did not induce per se dyskinesias and directly, although partially, alleviated L-3,4-dihydroxyphenylalanine (L-DOPA)-induced forelimb dyskinesia. Conversely, L-DOPA treatment negatively interfered with the anti-parkinsonian effect of Pf-HFS. Altogether, these data show that Pf-DBS, by recruiting a large basal ganglia circuitry, provides moderate to strong anti-parkinsonian benefits that might, however, be affected by L-DOPA. The widespread behavioral and cellular outcomes of Pf-HFS evidenced here demonstrate that CM/Pf is an important node for modulating the pathophysiological functioning of basal ganglia and related disorders.

Acetylcholinesterase inhibitors enhance cognitive functions in rats following hypobaric hypoxia

Hypobaric hypoxia (HBH) can produce neuropsychological disorders such as insomnia, dizziness, memory deficiencies, headache and nausea. It is well known that exposure to HBH cause alterations of neurotransmitters and cognitive impairment in terms of learning and memory. But the mechanisms are poorly understood. The present study aimed to investigate the cholinergic system alterations associated with simulated HBH induced cognitive impairment. Male Sprague-Dawley rats were exposed to HBH equivalent to 6100 m for 7 days in a simulation chamber. The cognitive performance was assessed using Morris Water Maze (MWM) task. Cholinergic markers like acetylcholine (ACh) and acetylcholinesterase (AChE) were evaluated in hippocampus and cortex of rats. Neuronal damage was also studied through morphological changes. Exposure to HBH led to impairment in relearning ability and memory retrieval and it was accompanied by decrease in ACh level and increase in AChE and led to morphological damage. Administration of AChE inhibitor (AChEI), physostigmine (PHY) and galantamine (GAL) to rats during HBH exposure resulted in amelioration of the deleterious effects induced by HBH. The AChEIs were able to improve the cholinergic activity by restoring the level of ACh by blocking the AChE activity. In addition, the AChEIs also prevented neurodegeneration by reducing the AChE level in cortical and hippocampal neurons.

Preinduction of HSP70 promotes hypoxic tolerance and facilitates acclimatization to acute hypobaric hypoxia in mouse brain

It has been shown that induction of HSP70 by administration of geranylgeranylacetone (GGA) leads to protection against ischemia/reperfusion injury. The present study was performed to determine the effect of GGA on the survival of mice and on brain damage under acute hypobaric hypoxia. The data showed that the mice injected with GGA survived significantly longer than control animals (survival time of 9.55 +/- 3.12 min, n = 16 vs. controls at 4.28 +/- 4.29 min, n = 15, P < 0.005). Accordingly, the cellular necrosis or degeneration of the hippocampus and the cortex induced by sublethal hypoxia for 6 h could be attenuated by preinjection with GGA, especially in the CA2 and CA3 regions of the hippocampus. In addition, the activity of nitric oxide synthase (NOS) of the hippocampus and the cortex was increased after exposure to sublethal hypoxia for 6 h but could be inhibited by the preinjection of GGA. Furthermore, the expression of HSP70 was significantly increased at 1 h after GGA injection. These results suggest that administration of GGA improved survival rate and prevented acute hypoxic damage to the brain and that the underlying mechanism involved induction of HSP70 and inhibition of NOS activity.

The thalamostriatal systems: anatomical and functional organization in normal and parkinsonian states

Although we have gained significant knowledge in the anatomy and microcircuitry of the thalamostriatal system over the last decades, the exact function(s) of these complex networks remain(s) poorly understood. It is now clear that the thalamostriatal system is not a unique entity, but consists of multiple neural systems that originate from a wide variety of thalamic nuclei and terminate in functionally segregated striatal territories. The primary source of thalamostriatal projections is the caudal intralaminar nuclear group which, in primates, comprises the centromedian and parafascicular nuclei (CM/Pf). These two nuclei provide massive, functionally organized glutamatergic inputs to the whole striatal complex. There are several anatomical and physiological features that distinguish this system from other thalamostriatal projections. Although all glutamatergic thalamostriatal neurons express vGluT2 and release glutamate as neurotransmitter, CM/Pf neurons target preferentially the dendritic shafts of striatal projection neurons, whereas all other thalamic inputs are almost exclusively confined to the head of dendritic spines. This anatomic arrangement suggests that transmission of input from sources other than CM/Pf to the striatal neurons is likely regulated by dopaminergic afferents in the same manner as cortical inputs, while the CM/Pf axo-dendritic synapses do not display any particular relationships with dopaminergic terminals. A better understanding of the role of these systems in the functional circuitry of the basal ganglia relies on future research of the physiology and pathophysiology of these networks in normal and pathological basal ganglia conditions. Although much remains to be known about the role of these systems, recent electrophysiological studies from awake monkeys have provided convincing evidence that the CM/Pf-striatal system is the entrance for attention-related stimuli to the basal ganglia circuits. However, the processing and transmission of this information likely involves intrinsic GABAergic and cholinergic striatal networks, thereby setting the stage for complex physiological responses of striatal output neurons to CM/Pf activation. Finally, another exciting development that will surely generate significant interest towards the thalamostriatal systems in years to come is the possibility that CM/Pf may be a potential surgical target for movement disorders, most particularly Tourette syndrome and Parkinson's disease. Although the available clinical evidence is encouraging, these procedures remain empirical at this stage because of the limited understanding of the thalamostriatal systems.

Effects of stimulation of the centromedian nucleus of the thalamus on the activity of striatal cells in awake rhesus monkeys

Although the existence of a massive projection from the caudal intralaminar nuclei of the thalamus [i.e. the centromedian (CM) and parafascicular nuclei] to the striatum is well documented, the effects of CM activation upon striatal cells remain poorly understood. Therefore, we studied the effects of electrical stimulation of CM on the electrophysiological activity of striatal neurons, and on striatal levels of gamma-aminobutyric acid (GABA) and acetylcholine in rhesus monkeys. Striatal cells did not respond to single-pulse stimulation (bipolar biphasic stimulation, 175-500 muA), but the large majority of recorded neurons responded to burst stimulation (100 Hz, 1 s, 150-175 muA) of CM, often with a delay of tens of milliseconds. Striatal phasically active neurons, which likely correspond to projection neurons, responded mainly with increases in firing (13/28 cells), while tonically active neurons (likely cholinergic interneurons) often showed combinations of increases and decreases in firing (24/46 cells). In microdialysis studies, CM stimulation led to a reduction of striatal acetylcholine levels. This effect was prevented by addition of the GABA-A receptor antagonist gabazine to the microdialysis fluid. We conclude that CM stimulation frequently results in striatal response patterns with excitatory and inhibitory components. Under the conditions chosen here, the specific patterns of striatal responses to CM stimulation are likely the result of striatal processing of thalamic inputs. Through these indirect effects, local CM stimulation may engage large portions of the striatum. These effects may be relevant in the interpretation of the therapeutic effects of CM stimulation for the treatment of neurological disorders.

Extranigral neurodegeneration in Parkinson's disease

It is widely known that the pathophysiology of idiopathic Parkinson's disease (PD) is associated with neurodegeneration and inflammatory responses in the midbrain substantia nigra. However, the possibility of neurodegeneration and inflammatory responses in other areas of the central nervous system (CNS) in course of the pathogenesis of PD remains to be explored. In this investigation, we provide evidence in support of the hypothesis that spinal cord, the final coordinator of movement, is also involved during parkinsonian degeneration using two distinct experimental parkinsonism models induced by the neurotoxin 1-methyl-4-phenyl 1,2,3,6-tetrahydropyridine (MPTP) and the environmental toxin rotenone. A key focus of our study is the role that calpain, a Ca(2+)-activated neutral protease, plays in disrupting the structural-functional integrity of the spinal cord in the context of spinal cord degeneration in experimental parkinsonism. We examined the mechanisms of calpain-mediated neuronal death in differentiated spinal cord motoneuron cultures following exposure to the active parkinsonian toxins 1-methyl-4-phenyl-pyridinium ion (MPP(+)) and rotenone and also tested the neuroprotective efficacy of calpeptin, a calpain inhibitor, in these cell culture models of experimental parkinsonism. Our results implied that spinal cord motoneurons could be a potential extranigral target of neurodegeneration during pathogenesis of PD in the CNS and that calpain inhibition could provide neuroprotection.

Impact of surgery targeting the caudal intralaminar thalamic nuclei on the pathophysiological functioning of basal ganglia in a rat model of Parkinson's disease

There is accumulating evidence that the centre median-parafascicular (CM/Pf) complex of the thalamus is implicated in basal ganglia-related movement disorders and notably in Parkinson's disease. However, the impact of the changes affecting CM/Pf on the pathophysiological functioning of basal ganglia in parkinsonian state remains poorly understood. To address this issue, we have examined the effects of excitotoxic lesion of CM/Pf and of 6-hydroxydopamine-induced lesion of nigral dopamine neurons, separately or in association, on gene expression of markers of neuronal activity in the rat basal ganglia (striatal neuropeptide precursors, GAD67, cytochrome oxidase subunit I) by quantitative in situ hybridization histochemistry. CM/Pf lesion prevented the changes produced by the dopamine denervation in the components of the indirect pathway connecting the striatum to the output structures (striatopallidal neurons, globus pallidus, subthalamic nucleus), and among the output structures, in the entopeduncular nucleus. Preliminary data on the effects of deep brain stimulation of CM/Pf in rats with nigral dopamine lesion show that this surgical approach produces efficient anti-akinetic effect associated with partial reversal of the dopamine lesion-induced increase in striatal preproenkephalin A mRNA levels, a marker of the striatopallidal neurons. These data, which provide substrates for the potential of CM/Pf surgery in the treatment of movement disorders, are discussed in comparison with the effects of lesion or deep brain stimulation of the subthalamic nucleus, the currently preferred target for the surgical treatment of PD.

The search for a role of the caudal intralaminar nuclei in the pathophysiology of Parkinson's disease

The situation of the caudal intralaminar thalamic nuclei within basal ganglia circuits has gained increased attention over the past few years. Although initially considered as a "non-specific" thalamic nuclei, tract-tracing studies carried out over the past two decades have demonstrated that the centromedian-parafascicular thalamic complex (CM-Pf) is connected to virtually all basal ganglia components and related nuclei. Although the anatomical basis sustaining the thalamic modulation of basal ganglia circuits has long been characterized, the functional significance of these transverse circuits still remain to be properly accommodated within the basal ganglia model, both under normal conditions as well as in situations of dopaminergic depletion. However, the recent demonstration of primary (e.g., non-dopamine related) neurodegenerative phenomena restricted to the CM-Pf in Parkinson's disease (PD) has renewed interest in the role played by the caudal intralaminar nuclei in the pathophysiology of PD. Concomitantly, evidence has become available of increased metabolic activity in the caudal intralaminar nuclei in rodent models of PD. Finally, CM-Pf neurosurgery in patients suffering from PD has produced contrasting outcomes, indicating that a consensus is still to be reached regarding the potential usefulness of targeting the caudal intralaminar nuclei to treat movement disorders of basal ganglia origin.

Behavioural effects of a selective NMDA NR1A/2B receptor antagonist in rats with unilateral 6-OHDA+parafascicular lesions

Experimental lesions involving the parafascicular (Pf) nucleus and medial forebrain bundle (MFB) may model to some extent the pathological loss of glutamatergic neurons from the centromedian-parafascicular (CM-Pf) complex and nigral dopaminergic cell loss observed clinically at post-mortem in Parkinson's disease (PD) cases. Our study investigated whether there were alterations in symptomatology in such rats with unilateral 6-OHDA+Pf lesions after treatment with either a selective NR1A/NR2B NMDA antagonist and/or l-dopa. Rats were given dual surgery to the MFB with 6-hydroxydopamine (6-OHDA) and Pf with N-methyl-d-aspartate (NMDA). (i) An NR1A/NR2B selective NMDA antagonist (BZAD-01; 10mg/kg), (ii) l-dopa (25mg/kg), (iii) BZAD-01+l-dopa (10mg/kg; 25mg/kg) or (iv) vehicle solution were administered for 6 weeks, during which behavioural testing was performed. BZAD-01 improved postural asymmetry in the first month as well as apomorphine-induced rotation. The latter was also improved by l-dopa in this model. These data support the use of selective NR1/NR2B NMDA antagonists in the therapeutics of PD.

Evaluation of Fluoro-Jade C as a marker of degenerating neurons in the rat retina and optic nerve

Detection of neuronal death is an essential requirement for researchers investigating retinal degeneration. Fluoro-Jade C (FJC) is a novel, fluorescent dye that has been successfully used to label degenerating neurons in the brain, but its effectiveness in the eye has not been ascertained. In the current study, we determined the efficacy of FJC for detection of neuronal degeneration in the retina and optic nerve in various paradigms of injury. N-methyl-D-aspartate (NMDA) and kainic acid-induced excitotoxicity, optic nerve transection, and bilateral occlusion of the common carotid arteries (BCCAO) were performed using standard techniques. Rats were killed at various time points and the retinas with optic nerves attached were removed for tissue processing prior to labelling for FJC, for DNA fragmentation by TUNEL or for immunohistochemical analysis. Retinas from RCS rats of different ages were also analysed. After excitotoxicity-induced injury, cell bodies and dendrites within the ganglion cell and inner plexiform layers were specifically labelled by FJC within 6h, a time point comparable to the appearance of TUNEL-positive nuclei and to reductions in mRNA levels of retinal ganglion cell-specific proteins, but in advance of alterations in some immunohistochemical markers. The number of FJC-labelled cell bodies in the retina declined over time as cell loss proceeded, although dendritic staining remained prominent. Colocalisation of FJC with TUNEL and with immunohistochemical neuronal markers was achieved. FJC was successful at identifying somato-dendritic degeneration following ischemia induced by BCCAO, but surprisingly, not after optic nerve transection. FJC visualised photoreceptor degeneration in the RCS rat, albeit less effectively than with the TUNEL assay, and was also effective for imaging and quantifying degenerating axons in the optic nerve after multiple injuries. In addition to labelling degenerating neurons, however, FJC also bound non-specifically to astrocytes and to blood cells in unperfused rats. Since the ganglion cell layer is adjacent to astrocytes within the nerve fibre layer, caution is needed when using FJC as a quantitative tool for detecting ganglion cell death.

Lesion of the centromedian thalamic nucleus in MPTP-treated monkeys

The caudal intralaminar nuclei are a major source of glutamatergic afferents to the basal ganglia. Experiments in the 6-hydroxydopamine rat model have shown that the parafascicular nucleus is overactive and its lesion alleviates basal ganglia neurochemical abnormalities associated with dopamine depletion. Accordingly, removal of this excitatory innervation of the basal ganglia could have a beneficial value in the parkinsonian state. To test this hypothesis, unilateral kainate-induced chemical ablation of the centromedian thalamic nucleus (CM) has been performed in MPTP-treated monkeys. Successful lesions restricted to the CM boundaries (n = 2) without spreading over other neighboring thalamic nuclei showed an initial, short-lasting, and mild change in the parkinsonian motor scale but no effect against levodopa-induced dyskinesias. The lack of significant and persistent motor improvement leads us to conclude that unilateral selective lesion of the CM alone cannot be considered as a suitable surgical approach for the treatment of PD or levodopa-induced dyskinesias. The role of the caudal intralaminar nuclei in the pathophysiology of movement disorders of basal ganglia origin remains to be clarified.

Hypobaric hypoxia damages the hippocampal pyramidal neurons in the rat brain

Hypobaric hypoxia (HH), a predisposing environmental condition at high altitude (HA), encountered by many mountaineers, jeopardizes their normal physiology like motor coordination and cognitive functions. A large body of evidence shows that HH has deleterious effect on cognitive functions. Among them the hippocampal dependent memory deficit is well known. However, our current understanding of the mechanistic details of cognitive deficits at HA remains largely unclear and hence limits a solution for this problem. Therefore, the present study was designed to investigate the temporal component of the hippocampal pyramidal neuron damage in the rat brain subjected to chronic HH exposure. Three groups (sham HH, 3 days HH and 7 days HH) of rats were exposed to simulated HH equivalent to 6100 m in an animal decompression chamber for 3 or 7 days. Later, the hippocampal (CA1 and CA3) neurons were analysed for the cell morphology, neurodegeneration and DNA fragmentation. The CA1 and CA3 neurons showed HH induced neuronal pyknosis, cell shrinkage, and consequent inter-cellular vacuolization in the CA1 and CA3 areas. In addition, the total neuron (intact) numbers and mean surface area were decreased. The number of dead neurons increased significantly following exposure to HH for 3 or 7 days. The neurodegenerative (Fluoro jade B) and apoptotic (TUNEL) markers were more positive in CA1 and CA3 neurons. The magnitude of morphological changes, neurodegeneration and apoptosis was enhanced in 7 days HH group than 3 days HH group. Our studies indicate that CA3 neurons are more vulnerable to HH than CA1 neurons, and that may destabilize the neural circuits in the hippocampus and thus cause memory dysfunction.

Fluoro-Jade C can specifically stain the degenerative neurons in the substantia nigra of the 1-methy-4-phenyl-1,2,3,6-tetrahydro pyrindine-treated C57BL/6 mice

Fluoro-Jade C, a new-developed fluorescent dye, has been successfully applied for identification of neuronal degeneration in the substantia nigra of 1-methyl-4-phenyl-1,2,3,6-tetrahydro pyridine (MPTP)-treated mice in the present study. The animal model was first prepared by intraperitoneal injection of neurotoxicant MPTP that can specifically induce degeneration of dopamine neurons in the substantia nigra of C57BL/6 mice. Fluoro-Jade C was then utilized to stain the midbrain sections and semiquantitation analysis was carried out in comparison with controls. It revealed that Fluoro-Jade C-positive cells showed strong green color in neuronal profile and were observed in the substantia nigra of MPTP-treated mice whereas they were not detected in that of controls. The Fluoro-Jade C-positive cells were mostly shrunken or smaller-sized in their cell bodies in comparing with that of normal dopamine neurons of controls. In the midbrain of MPTP-treated mice, Fluoro-Jade C-positive neuronal cells were exclusively distributed in the substantia nigra pars compacta, but rarely seen in the ventral tegemental area where dopamine neurons were numerously distributed. Double-labeling experiments indicated that a population of Fluoro-Jade C-positive cells (23%) exhibited neuron-specific nuclear protein-immunoreactivity and none of them showed immunoreactivity to glial cell marker glial fibrillary acid protein. However, most of Fluoro-Jade C-positive degenerative neurons (98%) lost their immunoreactivity to dopaminergic marker tyrosine hydroxylase in the substantia nigra of MPTP-treated mice. Taken together with previous observations, this study has presented that Fluoro-Jade C can be sensitively and specifically utilized to identify the neuronal degeneration in the substantia nigra of rodent animals receiving MPTP insult.

On the variety of cell death pathways in the Lurcher mutant mouse

Apoptosis as well as autophagy have been implicated in the death of cerebellar Purkinje cells (PCs) in the Lurcher (Lc/+) mutant mouse and at least two different apoptotic pathways participate in the transsynaptic death of granule cells (GC) and inferior olivary (IO) neurones. The relative contribution of these pathways can only be assessed from their momentary involvement at any stage of the complete course of neurodegeneration. Here we used quantitative labelling for activated caspase-3 (Casp-3) and Fluoro-Jade B (FJ-B) to investigate the spatio-temporal pattern of neuronal death from P6 to P67 in Lc/+ mutants. Activated Casp-3 was present only in narrow time intervals (P14 to P22 in PCs; P14 to P28 in GCs) and in small subpopulations of PCs, GCs, and IO neurones. FJ-B positive PCs were detected during a broader period (P14 to P28), and outnumbered Casp-3 labelled PCs by a factor exceeding eight. Nevertheless, FJ-B labelling was restricted to PCs and never found in either GC or IO neurones. In conclusion, we present the first complete time course and extent of Casp-3 activation in Lc/+ mutants and show that the majority of dying neurones in Lc/+ mutants undergo Casp-3 independent cell death. The cellular overload produced by the initial gene defect in Lc/+ mutants apparently activates a variety of apoptotic and non-apoptotic pathways within the same neuronal population. Moreover, we present the first evidence for the ability of FJ-B to selectively label a discrete population of dying PCs, implying a higher selectivity of FJ-B than previously supposed.

Fluoro-Jade B staining as useful tool to identify activated microglia and astrocytes in a mouse transgenic model of Alzheimer's disease

Fluoro-Jade B is known as a high affinity fluorescent marker for the localization of neuronal degeneration during acute neuronal distress. However, one study suggested that fluoro-Jade B stains reactive astroglia in the primate cerebral cortex. In this study, we analyzed the staining of fluoro-Jade B alone or combined with specific markers for detection of glial fibrillary acidic protein (GFAP) or activated CD68 microglia in the double APP(SL)/PS1 KI transgenic mice of Alzheimer's disease (AD), which display a massive neuronal loss in the CA1 region of the hippocampus. Our results showed that fluoro-Jade B did not stain normal and degenerating neurons in this double mouse transgenic model. Fluoro-Jade B was co-localized with Abeta in the core of amyloid deposits and in glia-like cells expressing Abeta. Furthermore, fluoro-Jade B was co-localized with CD68/macrosialin, a specific marker of activated microglia, and with GFAP for astrocytes in APP(SL)/PS1 KI transgenic mice of AD. Taken together, these findings showed that fluoro-Jade B can be used to label activated microglia and astrocytes which are abundant in the brain of these AD transgenic mice. It could stain degenerating neurons as a result of acute insult while it could label activated microglia and astrocytes during a chronic neuronal degenerative process such as AD for example.

Deficiency of TNF receptors suppresses microglial activation and alters the susceptibility of brain regions to MPTP-induced neurotoxicity: role of TNF-alpha

Enhanced expression of tumor necrosis factor (TNF) -alpha, is associated with the neuropathological effects underlying disease-, trauma- and chemically induced neurodegeneration. Previously, we have shown that deficiency of TNF receptors protects against MPTP-induced striatal dopaminergic neurotoxicity, findings suggestive of a role for TNF-alpha in neurodegeneration. Here, we demonstrate that deficiency of TNF receptors suppresses microglial activation and alters the susceptibility of brain regions to MPTP. MPTP-induced expression of microglia-derived factors, TNF-alpha, MCP-1, and IL-1alpha, preceded the degeneration of striatal dopaminergic nerve terminals and astrogliosis, as assessed by loss of striatal dopamine and TH, and an increase in striatal GFAP. Pharmacological neuroprotection with the dopamine reuptake inhibitor, nomifensine, abolished striatal dopaminergic neurotoxicity and associated microglial activation. Similarly, in mice lacking TNF receptors, microglial activation was suppressed, findings consistent with a role for TNF-alpha in striatal MPTP neurotoxicity. In the hippocampus, however, TNF receptor-deficient mice showed exacerbated neuronal damage after MPTP, as evidenced by Fluoro Jade-B staining (to identify degenerating neurons) and decreased microtubule-associated protein-2 (MAP-2) immunoreactivity. These effects were not accompanied by microglial activation, but were associated with increased oxidative stress (nitrosylation of tyrosine residues). These findings suggest that TNF-alpha exerts a neurotrophic/neuroprotective effect in hippocampus. The marked differences we observed in the regional density, distribution and/or activity of microglia and microglia-derived factors may influence the region-specific role for this cell type. Taken together, our results are indicative of a region-specific and dual role for TNF-alpha in the brain: a promoter of neurodegeneration in striatum and a protector against neurodegeneration in hippocampus.

Modeling Neurodegenerative Diseases in vivo Review

Parkinson's disease (PD) is one of the major neurodegenerative disorders. The etiology of this disease is likely due to combinations of environmental and genetic factors. Symptomatic hallmarks of PD are tremor, bradykinesia, rigidity and postural instability. On the morphological and anatomical level, PD is characterized by massive degeneration of dopaminergic neurons in the substantia nigra pars compacta, leading to a severe loss of striatal dopaminergic fibers and to a massive reduction of dopamine levels in the striatum. In addition, PD is characterized by the appearance of Lewy bodies within the surviving dopaminergic neurons. Animal models of PD allow getting insight into the mechanisms of several symptoms of PD thereby providing indispensable tools for basic and applied research. The biochemical and cellular changes that occur following administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in rodents or monkeys are remarkably similar to those seen in idiopathic PD. In this review, the main characteristics of experimental models of PD induced by the neurotoxic compound MPTP are reviewed.

Consequences of unilateral nigrostriatal denervation on the thalamostriatal pathway in rats

The position of the caudal intralaminar nuclei within basal ganglia circuitry has largely been neglected in most studies dealing with basal ganglia function. During the past few years, there has been a growing body of evidence suggesting that the thalamic parafascicular nucleus in rodents (PF) exerts a multifaceted modulation of basal ganglia nuclei, at different levels. Our aim was to study the activity of the thalamostriatal pathway in rats with unilateral dopaminergic depletion. The experimental approach comprised first unilateral delivery of 6-OHDA in the medial forebrain bundle. Thirty days post-lesioning, animals showing a clear asymmetry were then subjected to bilateral injection of Fluoro-Gold (FG) within the striatum. Subsequently, expression of the mRNA encoding the vesicular glutamate transporter 2 (vGLUT2) was detected within thalamostriatal-projecting neurons (FG-labeled) by in situ hybridization and the results were confirmed by laser-guided capture microdissection microscopy followed by real-time PCR. The data showed that there was a marked neuronal loss restricted to PF neurons projecting to the dopamine-depleted striatum. Moreover, PF neurons innervating the dopamine-depleted striatum were intensely hyperactive. These neurons showed a marked increase on the expression of vGLUT2 mRNA as well as for the mRNA encoding the subunit I of cytochrome oxidase as compared with those neurons projecting to the striatum with normal dopamine content. Thus, the selective neurodegeneration of PF neurons innervating the striatum together with the increased activity of the thalamostriatal pathway coexist after nigrostriatal denervation.

Inflammation in areas of remote changes following focal brain lesion

Focal brain lesions can lead to metabolic and structural changes in areas distant from but connected to the lesion site. After focal ischemic or excitotoxic lesions of the cortex and/or striatum, secondary changes have been observed in the thalamus, substantia nigra pars reticulata, hippocampus and spinal cord. In all these regions, inflammatory changes characterized by activation of microglia and astrocytes appear. In the thalamus, substantia nigra pars reticulata and hippocampus, an expression of proinflammatory cytokine like tumor necrosis factor-alpha and interleukin-1beta is induced. However, time course of expression and cellular localisation differ between these regions. Neuronal damage has consistently been observed in the thalamus, substantia nigra and spinal cord. It can be present in the hippocampus depending on the procedure of induction of focal cerebral ischemia. This secondary neuronal damage has been linked to antero- and retrograde degeneration. Anterograde degeneration is associated with somewhat later expression of cytokines, which is localised in neurons. In case of retrograde degeneration, the expression of cytokines is earlier and is localised in astrocytes. Pharmacological intervention aiming at reducing expression of tumor necrosis factor-alpha leads to reduction of secondary neuronal damage. These first results suggest that the inflammatory changes in remote areas might be involved in the pathogenesis of secondary neuronal damage.

Behavioural effects of parafascicular thalamic lesions in an animal model of parkinsonism

We recently reported that the centromedian-parafascicular thalamic complex (CM-Pf) degenerates in Parkinson's disease and progressive supranuclear palsy. The contribution of such thalamic pathology to disease symptoms has not yet been established. The present study therefore investigated the behavioural impact of lesioning the corresponding thalamic region (termed Pf) on a range of behaviours present in rodents. There were four surgical groups: (1) sham medial forebrain bundle (mfb)+sham Pf, (2) 6-OHDA mfb lesion+sham Pf, (3) sham mfb+NMDA Pf lesion, (4) 6-OHDA+NMDA Pf lesions. Posture, sensory functions and apomorphine-induced rotational asymmetry were assessed before and after each surgery. Other assessments performed including a timed motivational task, grooming behaviours and piloerection. 6-OHDA lesions induced postural (ipsilateral curling and head position biases), sensorimotor (increased latency to respond to tactile stimulation of the contralateral side when eating or grooming) and rotational abnormalities (contralateral circling after apomorphine). The main effects of combined 6-OHDA+Pf lesions were improved performance in a motivational task (decreased latency to retrieve reward) but worsened piloerection, relative to animals with either 6-OHDA or Pf lesions alone. The thalamic zone common to all lesioned animals involved the posterior Pf. Our data suggests that the posterior CM-Pf may be involved in motivational responses and autonomic dysfunction in parkinsonian disorders.

Organophosphorus compound-induced delayed neurotoxicity in white leghorn hens assessed by Fluoro-Jade

Certain organophosphorus (OP) compounds can induce a delayed neuropathy, termed OPIDN, that involves central and peripheral nervous system axons, terminals, and perikarya. Historically, OPIDN has been characterized by staining neural sections with silver or hematoxylin and eosin (H and E). This study utilized a novel staining method, Fluoro-Jade, for evaluating the distribution and extent of OPIDN in the central nervous system of hens. Results were then compared to synoptically sectioned and stained H and E preparations. White Leghorn hens were injected with phenyl saligenin phosphate (PSP, 2.5 mg/kg, intramuscular [im]), triphenyl phosphite (TPPi, 500 mg/kg, subcutaneous [sc]), or dimethyl sulfoxide vehicle (DMSO, 0.5 ml/kg, im or sc) and evaluated clinically for signs of neurological dysfunction associated with OPIDN. Hens were sacrificed 7, 14, and 21 days post dosing. Brains and spinal cords were removed immediately following sacrifice, fixed in formalin, and embedded in paraffin. Microtome-cut sections (7 micro m) were then stained with Fluoro-Jade (0.001%, w/v) or H&E. Staining with Fluoro-Jade revealed time-dependent degeneration of nerve fibers and terminals (with PSP and TPPi), or cell bodies (with TPPi) in lamina VII, spinocerebellar, and medial pontine-spinal tracts of the lumbar spinal cord, in white matter and mossy fibers of foliae I-V and IX of the cerebellum, and in medullary, pontine, and midbrain nuclei and paleostriatal fibers surrounding the optic tract. TPPi-induced degeneration was more extensive than that induced by PSP and affected additional cerebellar folia, medullary, pontine, midbrain, and forebrain nuclei and fiber tracts. H&E-stained sections revealed fewer sites of neurodegeneration when compared to Fluoro-Jade. These results demonstrate that Fluoro-Jade is a sensitive method for staining neural tissue affected by OPIDN.

Fluoro-Jade C results in ultra high resolution and contrast labeling of degenerating neurons

The causes and effects of neuronal degeneration are of major interest to a wide variety of neuroscientists. Paralleling this growing interest is an increasing number of methods applicable to the detection of neuronal degeneration. The earliest methods employing aniline dyes were methodologically simple, but difficult to interpret due to a lack of staining specificity. In an attempt to circumvent this problem, numerous suppressed silver methods have been introduced. However, these methods are labor intensive, incompatible with most other histochemical procedures and notoriously capricious. In an attempt to develop a tracer with the methodological simplicity and reliability of conventional stains but with the specificity of an ideal suppressed silver preparation, the Fluoro-Jade dyes were developed. Fluoro-Jade C, like its predecessors, Fluoro-Jade and Fluoro-Jade B, was found to stain all degenerating neurons, regardless of specific insult or mechanism of cell death. Therefore, the patterns of neuronal degeneration seen following exposure to either the glutamate agonist, kainic acid, or the inhibitor of mitochondrial respiration, 3-NPA, were the same for all of the Fluoro-Jade dyes. However, there was a qualitative difference in the staining characteristics of the three fluorochromes. Specifically, Fluoro-Jade C exhibited the greatest signal to background ratio, as well as the highest resolution. This translates to a stain of maximal contrast and affinity for degenerating neurons. This makes it ideal for localizing not only degenerating nerve cell bodies, but also distal dendrites, axons and terminals. The dye is highly resistant to fading and is compatible with virtually all histological processing and staining protocols. Triple labeling was accomplished by staining degenerating neurons with Fluoro-Jade C, cell nuclei with DAPI and activated astrocytes with GFAP immunofluoresence.

Pathological dynamics of activated microglia following medial forebrain bundle transection

To elucidate the role and pathological dynamics of activated microglia, this study assessed the phagocytic, immunophenotypic, morphological, and migratory properties of activated microglia in the medial forebrain bundle (MFB) axotomized rat brain. Activated microglia were identified using two different monoclonal antibodies: ED1 for phagocytic activity and OX6 for major histocompatibility complex (MHC) class II. Phagocytic microglia, characterized by ED1-immunoreactivity or ED1- and OX6-immunoreactivity, appeared in the MFB and substantia nigra (SN) as early as 1-3 days post-lesion (dpl), when there was no apparent loss of SN dopamine (DA) neurons. Thereafter, a great number of activated microglia selectively adhered to degenerating axons, dendrites and DA neuronal somas of the SN. This was followed by significant loss of these fibers and nigral DA neurons. Activation of microglia into phagocytic stage was most pronounced between 14 approximately 28 dpl and gradually subsided, but phagocytic microglia persisted until 70 dpl, the last time point examined. ED1 expression preceded MHC II expression in phagocytic microglia. All phagocytic microglia sticking to DA neurons showed activated but ramified form with enlarged somas and thickened processes. They were recruited to the SNc from cranial, dorsal and ventral aspects along various structures and finally stuck to DA neurons of the SNc. Characteristic rod-shaped microglia in the white matter were thought to migrate a long distance. The present study strongly suggests that neurons undergoing delayed neurodegeneration may be phagocytosed by numerous phagocytic, ramified microglia at various sites where specific surface signals are exposed or diffusible molecules are released.

Immunofluorescent labeling of increased calpain expression and neuronal death in the spinal cord of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice

Parkinson's disease (PD) is a movement disorder characterized by rigidity, tremor, and bradykinesia, originating from degeneration of dopaminergic neurons in the substantia nigra (SN), retrorubral area, and locus ceoruleus (LC). Calpain has been implicated in the pathophysiology of neurodegenerative diseases. Since the spinal cord (SC) and brain are integrally connected and calpain is involved in cell death and mitochondrial dysfunction, we hypothesized that SC neurons are also affected in PD. In order to examine this hypothesis, we examined both brain and SC from mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). To identify cells expressing calpain, double immunofluorescent labeling was performed with antibodies specific for calpain and a cell type (OX-42, GFAP, or NeuN). Combined terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) and double immunofluorescent labeling were used to identify death of specific cells in the central nervous system (CNS). There was an increase in calpain expression in microglia, astrocytes, and neurons in the SC of MPTP-treated mice at 1 and 7 days, as compared to controls. TUNEL-positive neurons in the SC and SN showed apoptotic characteristics. These results demonstrated that neuronal death occurred not only in SN but also in the SC of MPTP-treated mice and has provided evidence for a possible calpain-mediated SC neuronal death in MPTP-induced parkinsonism in mice.

A unilateral 6-hydroxydopamine lesion decreases the expression of metabotropic glutamate receptors in rat substantia nigra

Loss of dopaminergic neurons in the substantia nigra pars compacta (SNc) in Parkinson's disease (PD) leads to augmentation of glutamatergic activity in the subthalamic nucleus (STN). Moreover, antagonizing excitotoxicity has yielded mostly symptomatic improvements in experimental animals of PD. Therefore, we used immunocytochemistry to examine the effect of unilateral 6-hydroxydopamine lesions of SNc on the expression of metabotropic glutamate receptors (mGluR1a, 2/3, 5, 4, 8) and tyrosine hydroxylase (TH). 6-Hydroxydopamine causes a fall in the number of mGluRs and TH in the lesioned lateral substantia nigra. Pharmacological activation of group II or III mGluRs or blockade of group I mGluRs for 1 week significantly increased the expression of the same group receptors. The alteration in the receptor expression may be a compensatory mechanism developed after mGluRs ligands neuroprotective treatment.

Antagonist, CP-101,606, Enhances the Functional Recovery The NMDA NR2B Subunit-Selective Receptor and Reduces Brain Damage after Cortical Compression-Induced Brain Ischemia

Using a novel in vivo model for cerebral ischemia produced by short-lasting compression of a well-defined brain area of sensorimotor cortex we studied neuroprotective effects of the NMDA NR2B subunit selective antagonist, CP-101,606, in Sprague-Dawley rats. Cortical compression for 30 min produced a consistent and highly reproducible functional impairment, that is paresis of contralateral hind and fore limbs. The neurological deficit was accompanied by marked brain damage in cerebral cortex, hippocampus and thalamus as identified by Fluoro-Jade, a marker of general neuronal cell death. Using a daily performed beam walking test it was shown that untreated animals recovered from their functional impairment within 5-7 days following surgery. Intravenous administration of increasing doses (1, 5, 10, 20 mg/kg) of the NMDA NR2B subunit receptor specific antagonist, CP-101,606, dose-dependently improved the rate of functional recovery and protected against the ischemic brain damage in cerebral cortex, hippocampus, and thalamus as identified 2 days after the ischemic insult. Based upon these results, we conclude that NMDA NR2B receptor subunits represent potential targets to reduce not only the functional deficits, but also neuronal death in cortex and several midbrain regions produced by moderate, transient, cerebral ischemia.

Role of nitric oxide in rotenone-induced nigro-striatal injury

Rotenone, a widely used pesticide, causes a syndrome in rats that mimics, both behaviorally and pathologically, the symptoms of Parkinson's disease. The present study evaluated the role of nitric oxide in rotenone-induced nigro-striatal injury. After administration of rotenone in rats for 40 days, there was a moderate but significant injury of the nigro-striatal pathway indicated by a 47% decrease in striatal dopamine levels and a 28% loss of substantia nigra tyrosine hydroxylase-immunopositive neurons. Furthermore, a significant (37%) increase in the number of cells positive for nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) in the striatum was observed, accompanied by a 83% increase in nitric oxide synthase (NOS) activity and a significant increase in the production of 3-nitrotyrosine (3-NT). There was a significant increase (45%) in the optical density of NADPH-d staining and an increase (72%) in NOS activity in the substantia nigra. Moreover, administration of the neuronal NOS inhibitor 7-nitroindazole significantly attenuated the increased NOS activity and 3-NT production, and provided significant protection against rotenone-induced nigro-striatal injury. Our data suggest that chronic rotenone administration can lead to significant injury to the nigro-striatal system, mediated by increased generation of nitric oxide.

Fluoro-jade identification of cerebellar granule cell and purkinje cell death in the alpha1A calcium ion channel mutant mouse, leaner

Cell death is a critical component of normal nervous system development; too little or too much results in abnormal development and function of the nervous system. The leaner mouse exhibits excessive, abnormal cerebellar granule cell and Purkinje cell death during postnatal development, which is a consequence of a mutated calcium ion channel subunit, alpha(1A). Previous studies have shown that leaner cerebellar Purkinje cells die in a specific pattern that appears to be influenced by functional and anatomical boundaries of the cerebellum. However, the mechanism of Purkinje cell death and the specific timing of the spatial pattern of cell death remain unclear. By double labeling both leaner and wild-type cerebella with Fluoro-Jade and terminal deoxynucleotide transferase-mediated, deoxyuridine triphosphate nick-end labeling or Fluoro-Jade and tyrosine hydroxylase immunohistochemistry we demonstrated that the relatively new stain, Fluoro-Jade, will label neurons that are dying secondary to a genetic mutation. Then, by staining leaner and wild-type cerebella between postnatal days 20 and 80 with Fluoro-Jade, we were able to show that Purkinje cell death begins at approximately postnatal day 25, peaks in the vermis about postnatal day 40 and in the hemispheres at postnatal day 50 and persists at a low level at postnatal day 80. In addition, we showed that there is a significant difference in the amount of cerebellar Purkinje cell death between rostral and caudal divisions of the leaner cerebellum, and that there is little to no Purkinje cell death in the wild type cerebellum at the ages we examined. This is the first report of the use of Fluoro-Jade to identify dying neurons in a genetic model for neuronal cell death. By using Fluoro-Jade, we have specifically defined the temporospatial pattern of postnatal Purkinje cell death in the leaner mouse. This information can be used to gain insight into the dynamic mechanisms controlling Purkinje cell death in the leaner cerebellum.

Signal transduction and neurosurvival in experimental models of brain injury

Brain injury and neurodegenerative disease are linked by their primary pathological consequence-death of neurons. Current approaches for the treatment of neurodegeneration are limited. In this review, we discuss animal models of human brain injury and molecular biological data that have been obtained from their analysis. In particular, signal transduction pathways that are associated with neurosurvival following injury to the brain are presented and discussed.