Striatal infarction in the rat causes a transient reduction of tyrosine hydroxylase immunoreactivity in the ipsilateral substantia nigra

Interaction of an α-synuclein epitope with HLA-DRB1∗15:01 triggers enteric features in mice reminiscent of prodromal Parkinson's disease

Enteric symptoms are hallmarks of prodromal Parkinson's disease (PD) that appear decades before the onset of motor symptoms and diagnosis. PD patients possess circulating T cells that recognize specific α-synuclein (α-syn)-derived epitopes. One epitope, α-syn32-46, binds with strong affinity to the HLA-DRB1∗15:01 allele implicated in autoimmune diseases. We report that α-syn32-46 immunization in a mouse expressing human HLA-DRB1∗15:01 triggers intestinal inflammation, leading to loss of enteric neurons, damaged enteric dopaminergic neurons, constipation, and weight loss. α-Syn32-46 immunization activates innate and adaptive immune gene signatures in the gut and induces changes in the CD4+ TH1/TH17 transcriptome that resemble tissue-resident memory (TRM) cells found in mucosal barriers during inflammation. Depletion of CD4+, but not CD8+, T cells partially rescues enteric neurodegeneration. Therefore, interaction of α-syn32-46 and HLA-DRB1∗15:0 is critical for gut inflammation and CD4+ T cell-mediated loss of enteric neurons in humanized mice, suggesting mechanisms that may underlie prodromal enteric PD.

Neuroprotective Effects of Salidroside on Cerebral Ischemia/Reperfusion-Induced Behavioral Impairment Involves the Dopaminergic System

Salidroside, a phenylpropanoid glycoside, is the main bioactive component of Rhodiola rosea L. Salidroside has prominent anti-stroke effects in cerebral ischemia/reperfusion models. However, the underlying mechanisms of its actions are poorly understood. This study examined the anti-stroke effects of salidroside in middle cerebral artery occlusion (MCAO)-induced rat model of stroke and its potential mechanisms involving the dopaminergic system. Salidroside administration increased the levels of dopamine (DA), homovanillic acid (HVA), and 3,4-dihydroxyphenylacetic acid (DOPAC) in the ipsilateral striatum after induction of transient ischemia, which were assessed using microdialysis with high-performance liquid chromatography coupled with electrochemical detection (HPLC-ECD). Furthermore, treatment with salidroside ameliorated neurobehavioral impairment, assessed with the modified neurological severity scores (mNSS), the balance beam test, and the foot fault test. Moreover, enzyme-linked immunosorbent assay (ELISA) suggested that MCAO-induced reduction in monoamine oxidase (MAO) was inhibited by salidroside. Immunohistochemical and immunofluorescence analyses revealed high level of tyrosine hydroxylase (TH) in the ipsilateral striatal caudate putamen (CPu) after cerebral ischemia/reperfusion, which could be further elevated by salidroside. In addition, salidroside could reverse the decreased immunoreactivity of TH in the substantia nigra pars compacta (SNpc). These results suggest that the anti-stroke effects of salidroside in MCAO-induced cerebral ischemia/reperfusion may involve the modulation of monoamine metabolism in the striatum and SNpc, which may be related to the function of the dopaminergic system in the rat brain.

Executive (dys)function after stroke: special considerations for behavioral pharmacology

Stroke is a worldwide leading cause of death and long-term disability with concurrent secondary consequences that are largely comprised of mood dysfunction, as well as sensory, motor, and cognitive deficits. This review focuses on the cognitive deficits associated with stroke specific to executive dysfunction (including decision making, working memory, and cognitive flexibility) in humans, nonhuman primates, and additional animal models. Further, we review some of the cellular and molecular underpinnings of the individual components of executive dysfunction and their neuroanatomical substrates after stroke, with an emphasis on the changes that occur during biogenic monoamine neurotransmission. We concentrate primarily on changes in the catecholaminergic (dopaminergic and noradrenergic) and serotonergic systems at the levels of neurotransmitter synthesis, distribution, reuptake, and degradation. We also discuss potential secondary stroke-related behavioral deficits (specifically, poststroke depression as well as drug-abuse potential and addiction) and their relationship with stroke-induced deficits in executive function, an especially important consideration given that the average age of the human stroke population is decreasing. In the final sections, we address pharmacological considerations for the treatment of ischemia and the subsequent functional impairment, as well as current limitations in the field of stroke and executive function research.

The Intersection of Central Dopamine System and Stroke: Potential Avenues Aiming at Enhancement of Motor Recovery

Dopamine, a major neurotransmitter, plays a role in a wide range of brain sensorimotor functions. Parkinson's disease and schizophrenia are two major human neuropsychiatric disorders typically associated with dysfunctional dopamine activity levels, which can be alleviated through the druggability of the dopaminergic systems. Meanwhile, several studies suggest that optimal brain dopamine activity levels are also significantly impacted in other serious neurological conditions, notably stroke, but this has yet to be fully appreciated at both basic and clinical research levels. This is of utmost importance as there is a need for better treatments to improve recovery from stroke. Here, we discuss the state of knowledge regarding the modulation of dopaminergic systems following stroke, and the use of dopamine boosting therapies in animal stroke models to improve stroke recovery. Indeed, studies in animals and humans show stroke leads to changes in dopamine functioning. Moreover, evidence from animal stroke models suggests stimulation of dopamine receptors may be a promising therapeutic approach for enhancing motor recovery from stroke. With respect to the latter, we discuss the evidence for several possible receptor-linked mechanisms by which improved motor recovery may be mediated. One avenue of particular promise is the subtype-selective stimulation of dopamine receptors in conjunction with physical therapy. However, results from clinical trials so far have been more mixed due to a number of potential reasons including, targeting of the wrong patient populations and use of drugs which modulate a wide array of receptors. Notwithstanding these issues, it is hoped that future research endeavors will assist in the development of more refined dopaminergic therapeutic approaches to enhance stroke recovery.

Neuroprotective effects of Aceglutamide on motor function in a rat model of cerebral ischemia and reperfusion

PURPOSE

To investigate the effect and underlying mechanism of Aceglutamide on motor dysfunction in rats after cerebral ischemia-reperfusion.

METHODS

Adult male Sprague-Dawley rats were subjected to 2 h transient middle cerebral artery occlusion (MCAO). Aceglutamide or vehicle was intraperitoneally given to rats at 24 h after reperfusion and lasted for 14 days. Subsequently functional recovery was assessed and number of tyrosine hydroxylase (TH)-positive neurons in substantia nigra (SN) was analyzed. Tumor necrosis factor receptor-associated factor 1(TRAF1), P-Akt and Bcl-2/Bax were determined in mesencephalic tissue by Western blot method. PC12 cells and primary cultured mesencephalic neurons were employed to further investigate the mechanism of Aceglutamide.

RESULTS

Aceglutamide treatment improved behavioral functions, reduced the infarction volume, and elevated the number of TH-positive neurons in the SN. Moreover, Aceglutamide significantly attenuated neuronal apoptosis in the SN. Meanwhile Aceglutamide treatment significantly inhibited the expression of TRAF1 and up-regulated the expression of P-Akt and Bcl-2/Bax ratio both in vitro and in vivo.

CONCLUSIONS

Aceglutamide ameliorated motor dysfunction and delayed neuronal death in the SN after ischemia, which involved the inhibition of pro-apoptotic factor TRAF1 and activation of Akt/Bcl-2 signaling pathway. These data provided experimental information for applying Aceglutamide to ischemic stroke treatment.

Environment- and activity-dependent dopamine neurotransmitter plasticity in the adult substantia nigra

The ability of neurons to change the amount or type of neurotransmitter they use, or 'neurotransmitter plasticity', is an emerging new form of adult brain plasticity. For example, it has recently been shown that neurons in the adult rat hypothalamus up- or down-regulate dopamine (DA) neurotransmission in response to the amount of light the animal receives (photoperiod), and that this in turn affects anxiety- and depressive-like behaviors (Dulcis et al., 2013). In this Chapter I consolidate recent evidence from my laboratory suggesting neurons in the adult mouse substantia nigra pars compacta (SNc) also undergo DA neurotransmitter plasticity in response to persistent changes in their electrical activity, including that driven by the mouse's environment or behavior. Specifically, we have shown that the amounts of tyrosine hydroxylase (TH, the rate-limiting enzyme in DA synthesis) gene promoter activity, TH mRNA and TH protein in SNc neurons increases or decreases after ∼20h of altered electrical activity. Also, infusion of ion-channel agonists or antagonists into the midbrain for 2 weeks results in ∼10% (∼500 neurons) more or fewer TH immunoreactive (TH+) SNc neurons, with no change in the total number of SNc neurons (TH+ and TH-). Targeting ion-channels mediating cell-autonomous pacemaker activity in, or synaptic input and afferent pathways to, SNc neurons are equally effective in this regard. In addition, exposing mice to different environments (sex pairing or environment enrichment) for 1-2 weeks induces ∼10% more or fewer TH+ SNc (and ventral tegmental area or VTA) neurons and this is abolished by concurrent blockade of synaptic transmission in midbrain. Although further research is required to establish SNc (and VTA) DA neurotransmitter plasticity, and to determine whether it alters brain function and behavior, it is an exciting prospect because: (1) It may play important roles in movement, motor learning, reward, motivation, memory and cognition; and (2) Imbalances in midbrain DA cause symptoms associated with several prominent brain and behavioral disorders such as schizophrenia, addiction, obsessive-compulsive disorder, depression, Parkinson's disease and attention-deficit and hyperactivity disorder. Midbrain DA neurotransmitter plasticity may therefore play a role in the etiology of these symptoms, and might also offer new treatment options.

MRI heralds secondary nigral lesion after brain ischemia in mice: a secondary time window for neuroprotection

Cerebral ischemia in the territory of the middle cerebral artery (MCA) can induce delayed neuronal cell death in the ipsilateral substantia nigra (SN) remote from the primary ischemic lesion. This exofocal postischemic neuronal degeneration (EPND) may worsen stroke outcomes. However, the mechanisms leading to EPND are poorly understood. Here, we studied the time course of EPND via sequential magnetic resonance imaging (MRI) and immunohistochemistry for up to 28 days after 30 minutes' occlusion of the MCA (MCAo) and reperfusion in the mouse. Furthermore, the effects of delayed treatment with FK506 and MK-801 on the development of EPND were investigated. Secondary neuronal degeneration in the SN occurred within the first week after MCAo and was characterized by a marked neuronal cell loss on histology. Sequential neuroimaging examinations revealed transient MRI changes, which were detectable as early as day 4 after MCAo and thus heralding histologic evidence of EPND. Treatment with MK-801, an established anti-excitotoxic agent, conferred protection against EPND even when initiated days after the initial ischemic event, which was not evident with FK506. Our findings define a secondary time window for delayed neuroprotection after stroke, which may provide a promising target for the development of novel therapies.

Striatal Infarction Elicits Secondary Extrafocal MRI Changes in Ipsilateral Substantia Nigra

Focal ischemia may induce pathological alterations in brain areas distant from the primary lesion. In animal models, exofocal neuron death in the ipsilateral midbrain has been described after occlusion of the middle cerebral artery (MCA). Using sequential magnetic resonance imaging (T2- and diffusion-weighted) at 3 Tesla, we investigated acute ischemic stroke patients on days 1, 2, 6, 8, and 10 after stroke onset. Sixteen consecutive patients who had suffered a stroke involving the caudate nucleus and/or putamen of either hemisphere were recruited into the study. Four additional patients with strokes sparing the caudate nucleus and putamen but encompassing at least one-third of the MCA territory served as controls. Ischemic lesions involving striatal structures resulted in hyperintense lesions in ipsilateral midbrain that emerged between days 6 and 10 after stroke and were not present on the initial scans. In contrast, none of the control stroke patients developed secondary midbrain lesions. Hyperintense lesions in the pyramidal tract or the brain stem caused by degeneration of the corticospinal tract could be clearly distinguished from these secondary midbrain gray matter lesions and were detectable from day 2 after ischemia. Co-registration of high-resolution images with a digitized anatomic atlas revealed localization of secondary lesions primarily in the substantia nigra pars compacta. Apparent diffusion coefficient (ADC) values in the secondary lesions showed a delayed sharp decline through day 10. Normalization of ADC values was observed at late measurements. Taken together, our study demonstrates that striatal infarction elicits delayed degenerative changes in ipsilateral substantia nigra pars compacta.

Selective neuronal loss in ischemic stroke and cerebrovascular disease

As a sequel of brain ischemia, selective neuronal loss (SNL)-as opposed to pannecrosis (i.e. infarction)-is attracting growing interest, particularly because it is now detectable in vivo. In acute stroke, SNL may affect the salvaged penumbra and hamper functional recovery following reperfusion. Rodent occlusion models can generate SNL predominantly in the striatum or cortex, showing that it can affect behavior for weeks despite normal magnetic resonance imaging. In humans, SNL in the salvaged penumbra has been documented in vivo mainly using positron emission tomography and (11)C-flumazenil, a neuronal tracer validated against immunohistochemistry in rodent stroke models. Cortical SNL has also been documented using this approach in chronic carotid disease in association with misery perfusion and behavioral deficits, suggesting that it can result from chronic or unstable hemodynamic compromise. Given these consequences, SNL may constitute a novel therapeutic target. Selective neuronal loss may also develop at sites remote from infarcts, representing secondary 'exofocal' phenomena akin to degeneration, potentially related to poststroke behavioral or mood impairments again amenable to therapy. Further work should aim to better characterize the time course, behavioral consequences-including the impact on neurological recovery and contribution to vascular cognitive impairment-association with possible causal processes such as microglial activation, and preventability of SNL.

Activation of cerebral peroxisome proliferator-activated receptors γ (PPARγ) reduces neuronal damage in the substantia nigra after transient focal cerebral ischaemia in the rat

AIM

The function of brain (neuronal) peroxisome proliferator-activated receptor(s) γ (PPARγ) in the delayed degeneration and loss of neurones in the substantia nigra (SN) was studied in rats after transient occlusion of the middle cerebral artery (MCAO).

METHODS

The PPARγ agonist, pioglitazone, or vehicle was infused intracerebroventricularly over a 5-day period before, during and 5 days after MCAO (90 min). The neuronal degeneration in the SN pars reticularis (SNr) and pars compacta (SNc), the analysis of the number of tyrosine hydroxylase-immunoreactive (TH-IR) neurones and the expression of the PPARγ in these neurones were studied by immunohistochemistry and immunofluorescence staining. The effects of PPARγ activation on excitotoxic and oxidative neuronal damage induced by glutamate and 6-hydroxydopamine were investigated in primary cortical neurones expressing PPARγ.

RESULTS

Pioglitazone reduced the total and striatal infarct size, neuronal degeneration in both parts of the ipsilateral SN, the loss of TH-IR neurones in the SNc and increased the number of PPARγ-positive TH-IR neurones. Pioglitazone protected primary cortical neurones against oxidative and excitotoxic damage, prevented the loss of neurites and supported the formation of synaptic networks in neurones exposed to glutamate or 6-hydroxydopamine by a PPARγ-dependent mechanism.

CONCLUSIONS

Activation of cerebral PPARγ confers neuroprotection after ischaemic stroke by preventing both, neuronal damage within the peri-infarct zone and delayed degeneration of neurones and neuronal death in areas remote from the site of ischaemic injury. Pioglitazone and other PPARγ agonists may be useful therapeutic agents to prevent progression of brain damage after cerebral ischaemia.

Neuronal activity regulates expression of tyrosine hydroxylase in adult mouse substantia nigra pars compacta neurons

Striatal delivery of dopamine (DA) by midbrain substantia nigra pars compacta (SNc) neurons is vital for motor control and its depletion causes the motor symptoms of Parkinson's disease. While membrane potential changes or neuronal activity regulates tyrosine hydroxylase (TH, the rate limiting enzyme in catecholamine synthesis) expression in other catecholaminergic cells, it is not known whether the same occurs in adult SNc neurons. We administered drugs known to alter neuronal activity to mouse SNc DAergic neurons in various experimental preparations and measured changes in their TH expression. In cultured midbrain neurons, blockade of action potentials with 1 μM tetrodotoxin decreased TH expression beginning around 20 h later (as measured in real time by green fluorescent protein (GFP) expression driven off TH promoter activity). By contrast, partial blockade of small-conductance, Ca(2+) -activated potassium channels with 300 nM apamin increased TH mRNA and protein between 12 and 24 h later in slices of adult midbrain. Two-week infusions of 300 nM apamin directly to the adult mouse midbrain in vivo also increased TH expression in SNc neurons, measured immunohistochemically. Paradoxically, the number of TH immunoreactive (TH+) SNc neurons decreased in these animals. Similar in vivo infusions of drugs affecting other ion-channels and receptors (L-type voltage-activated Ca(2+) channels, GABA(A) receptors, high K(+) , DA receptors) also increased or decreased cellular TH immunoreactivity but decreased or increased, respectively, the number of TH+ cells in SNc. We conclude that in adult SNc neurons: (i) TH expression is activity-dependent and begins to change ∼20 h following sustained changes in neuronal activity; (ii) ion-channels and receptors mediating cell-autonomous activity or synaptic input are equally potent in altering TH expression; and (iii) activity-dependent changes in TH expression are balanced by opposing changes in the number of TH+ SNc cells.

Long-term changes in the ipsilateral substantia nigra after transient focal cerebral ischaemia in rats

Transient focal cerebral ischaemia can cause neuronal damage in remote areas, including the ipsilateral thalamus and subsutantia nigra, as well as in the ischaemic core. In the present study, we investigated long-term changes in the ipsilateral substantia nigra from 1 up to 20 weeks after 90 min of transient focal cerebral ischaemia in rats, using tyrosine hydroxylase (TH), neuronal nuclei (NeuN), Iba-1, glial fibrillary acidic protein (GFAP) and brain-derived neurotrophic factor (BDNF) immunostaining. These results show that transient focal cerebral ischaemia in rats can cause a severe and prolonged neuronal damage in the ipsilateral striatum. Our results with TH and NeuN immunostaining also demonstrate that the atrophy of the ipsilateral substantia nigra after transient focal cerebral ischaemia was not static but progressive. Furthermore, our double-labelled immunohistochemical study suggests that BDNF released by GFAP-positive astrocytes may play a key role in the survival of dopaminergic neurones in the ipsilateral substantia nigra at the chronic stage after transient focal cerebral ischaemia, although the areas of the ipsilateral substantia nigra are decreased progressively after ischaemia. Thus our study provides further valuable information for the pathogenesis of neuronal damage after transient focal cerebral ischaemia.

Delayed increase of tyrosine hydroxylase expression in rat nigrostriatal system after traumatic brain injury

Tyrosine hydroxylase (TH) is the key enzyme for synthesizing dopamine (DA) in dopaminergic neurons and its terminals. Emerging experimental and clinical evidence support the hypothesis of a disturbance in dopamine neurotransmission following traumatic brain injury (TBI). However, the effect of controlled cortical impact (CCI) injury on TH in the nigrostriatal system is currently unknown. To determine if there is an alteration in TH after CCI injury, we examined TH levels at 1 day, 7 days, and 28 days post-injury by utilizing a commercially available antibody specific to TH. Rats were anesthetized and surgically prepared for CCI injury (4 m/s, 3.2 mm) or sham surgery. Injured (N=6) and sham animals (N=6) were sacrificed and coronally sectioned (35 microm thick) through the striatum and substantia nigra (SN) for immunohistochemistry. Additionally, semiquantitative measurements of TH protein in striatal and SN homogenates from injured (N=6) and sham (N=6) rats sacrificed at the appropriate time post-surgery were assessed using Western blot analysis. TH protein is bilaterally increased at 28 days post-injury in nigrostriatal system revealed by immunohistochemistry in injured rats compared to sham controls. Western blot analysis confirms the findings of immunohistochemistry in both striatum and SN. We speculate that the increase in TH in the nigrostriatal system may reflect a compensatory response of dopaminergic neurons to upregulate their synthesizing capacity and a delayed increase in the efficiency of DA neurotransmission after TBI.

Improvement of focal ischemia-induced rat dopaminergic dysfunction by striatal transplantation of mouse embryonic stem cells

Middle cerebral artery occlusion (MCAO) caused behavioral dysfunction with massive neuronal loss. Cell transplantation may recover this deficit by replacing damaged brain cells. In this study, we examined the effects of transplantation of mouse embryonic stem (ES) cells or ES cell-derived neuron-like (ES-N) cells on behavioral function in ischemic rats. Seven days after MCAO, ES or ES-N cells were transplanted into ipsilateral striata (but not the substantia nigra) of ischemic rats. Transplanted rats exhibited a gradual reduction in the number of rotations induced by methamphetamine compared to vehicle-injected rats. These rats also showed a significant improvement in rota-rod performance. At 15 weeks after transplantation, immunoreactivities for tyrosine hydroxylase (TH) and dopamine transporter (DAT) in the striatum were significantly recovered in rats grafted with ES or ES-N cells compared to vehicle-injected rats. These results suggest that intrastriatal-transplantation of ES or ES-N cells improved the dopaminergic function and subsequently recover behavioral dysfunction in focal ischemic rats.

Involvement of multitargets in paeoniflorin-induced preconditioning

Paeoniflorin (PF) is the principal component of Paeoniae radix prescribed in traditional Chinese medicine. The delayed neuroprotection induced by PF preconditioning and its underlying mechanisms were investigated in rat middle cerebral artery occlusion (MCAO) and reperfusion model. At a dosage of 20 or 40 mg/kg, PF preconditioning 48 h before MCAO followed by 24-h reperfusion significantly reduced the mortality and infarct volume and reversed the neurological deficits caused by ischemia. Likewise, the ameliorative effects on mortality, infarct size, and neurological impairment induced by MCAO emerged as well when PF was administered 24 h, 48 h, or 5 days before MCAO at the dose of 20 mg/kg. Furthermore, comparative proteomics analysis was adopted to identify the differentially expressed proteins induced by PF preconditioning itself. The relative levels of 42 proteins were altered after PF preconditioning, among which 20 were elevated and 22 reduced. In summary, A(1) receptor-regulator of G protein signaling-K(ATP) signaling, arachidonic acid cascade, nitric oxide system, markers of neuronal damage, mitochondrial damage-related molecules, and the mitogen-activated protein kinase and nuclear factor-kappaB pathway are associated with the mechanisms of PF preconditioning.

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.

Erythropoietin protects dopaminergic neurons and improves neurobehavioral outcomes in juvenile rats after neonatal hypoxia-ischemia

Brain injury as a result of hypoxia-ischemia remains a common cause of morbidity and mortality in neonates. No effective therapy is currently available. The hematopoietic cytokine erythropoietin (Epo) provides neuroprotection in many adult models of brain injury and is currently being investigated as a therapeutic agent for human stroke and spinal cord injury. We tested the hypothesis that recombinant Epo (rEpo) would improve neurobehavioral outcomes after neonatal hypoxic-ischemic brain injury. Postnatal day 7 rats underwent right common carotid artery occlusion followed by a 90-min exposure to 8% oxygen. Rats were subsequently treated with rEpo or placebo. Sensory neglect and apomorphine-induced rotation were measured at P27 and P28. Rats were killed at P30, blood was drawn, and the brains were perfusion-fixed for histology and immunohistochemistry. No differences in gross brain injury between rEpo and placebo-treated rats were found. Neonatal rEpo treatment protected dopamine neurons as indicated by the preservation of tyrosine hydroxylase-positive cells in the substantia nigra pars compacta and ventral tegmental area. rEpo treatment also improved functional outcomes by reducing sensory neglect and preventing the rotational asymmetry seen in control animals. No differences in hematocrit, white blood cell counts, neutrophil counts, or platelet counts were measured. We observed that rEpo treatment protected mesencephalic dopamine neurons and reduced the degree of behavioral asymmetries at 4 wk of life. On the basis of these findings, we conclude that further studies investigating the safety and efficacy of high-dose rEpo as a neuroprotective strategy are indicated in neonatal models of hypoxic-ischemic brain injury.

Caspase-dependent and caspase-independent signalling of apoptosis in the penumbra following middle cerebral artery occlusion in the adult rat

Transient focal ischaemia by middle cerebral artery occlusion (MCAO) may produce cell death, but the mechanisms leading to cell death differ in the infarct core and in the penumbra, the immediate zone surrounding the infarct core. In the present study, transient focal ischaemia to adult rats was produced by intraluminal occlusion of the middle cerebral artery for 1 h followed by 0 h (n=6), 1 h (n=10), 4 h (n=8), 6 h (n=2) and 12 h (n=3) of reperfusion. The present model of ischaemia causes a large cortico-striatal infarct extending through the mediolateral cortex and dorsolateral striatum at 12 h. The expression and subcellular distribution of several proteins involved in apoptosis have been examined in the penumbra and in the infarct core by using combined methods of immunohistochemistry, cell subfractionation and Western blotting. Transient focal ischaemia by MCAO results in activation of complex signal pathways for cell death in the penumbra. Increased expression of Bcl-2 and Bax, but not of Bcl-x, occurs in the penumbra at the time when Bax translocates from the cytosol to the mitochondria, cytochrome c is released to the cytoplasm and active caspase-3 is expressed. Bax translocation, cytochrome c release and active caspase-3 are observed at 4 h, but not at 1 h, following reperfusion, and together indicate activation of the caspase-dependent pathway of apoptosis in the penumbra. In contrast, reduced Bax expression but not Bax translocation and cytochrome c release occurs in the infarct core, thus suggesting apoptosis signals restricted to the penumbra. In addition, increased expression of an apoptosis-inducing factor in the cytoplasm and nuclei of selected cells shows, for the first time, activation of the caspase-independent mitochondrial pathway in the penumbra following transient focal ischaemia and reperfusion.

Microglial activation and tyrosine hydroxylase immunoreactivity in the substantia nigral region following transient focal ischemia in rats

The temporal profiles of the changes of dopaminergic cells and microglial activation induced by transient cerebral ischemia were investigated in the substantia nigra pars compacta (SNc) located outside ischemic areas of rat brain. Transient cerebral ischemia was induced by intraluminal occlusion of the right middle cerebral artery for 2 h and reperfusion was continued for 1, 2, 3, 4, 7, 10, 14, 28, 60, and 120 days. Dopaminergic cells immunostained with tyrosine hydroxylase (TH)-antibody in the ipsilateral SNc were significantly decreased at 7 days post-ischemia compared with those in the contralateral side (P<0.05). However, at 60 and 120 days, there were no significant differences between ipsilateral and contralateral side of the SNc. Unlike the TH immunoreactivity, activated microglial cells immunostained with OX-42 antibody were significantly increased at 2 and 3 days and then decreased gradually until 10 days post-ischemia. Activated microglial cells were increased at 2 weeks post-ischemia, and this pattern remained until 60 days. These results suggest that the transient changes of TH-immunoreactive cells in the SNc caused by transient focal ischemia are correlated with a biphasic microglial cell activation response.

Enhanced noradrenergic transmission in the spontaneously hypertensive rat anococcygeus muscle

There is a long-known hyper-responsiveness of vascular adrenergic transmission in the spontaneously hypertensive rat (SHR) that is uncovered specifically in the presence of cocaine and attributed to blockade of the neuronal monoamine transporter. We have now used the rat anococcygeus muscle to investigate whether this phenomenon is generic to sympathetic transmission to smooth muscle rather than a purely vascular phenomenon. We sought the origin of the effect by successively blocking the buffering effects of the neuronal monoamine transporter, prejunctional alpha2-adrenoceptors and NO from nitrergic nerves with desipramine (0.1 microm), rauwolscine (0.01 microm) and l-NG-nitro-arginine (100 microm). In the presence of desipramine, contractile responses to electrical field stimulation but not to noradrenaline (1 nm-100 microm) were greater in SHR than in Wistar-Kyoto (WKY). Neither inhibition of prejunctional alpha2-adrenoceptors nor the blockade of neuronal nitric oxide synthase (nNOS) accounted for the differential enhancement of response in SHR. The enhanced effectiveness of motor neurotransmission in SHR becomes most apparent when all known major buffering mechanisms are removed. When nitrergic responses were isolated pharmacologically (phentolamine 1 microm and guanethidine 30 microm; tone raised with carbachol 50 microm), they were not different between SHR and WKY. Western blots showed that both nNOS and tyrosine hydroxylase are expressed to a similar extent in anococcygeus muscle from SHR and WKY, suggesting similar adrenergic and nitrergic innervations in the two strains. This suggests that enhanced motor transmission is due to increased transmitter release per varicosity rather than there being normal transmission from a greater number of sites. We conclude that there is a generic enhancement of sympathetic transmission in SHR rather than this being a vascular phenomenon.

Early modifications in the expression of mitogen-activated protein kinase (MAPK/ERK), stress-activated kinases SAPK/JNK and p38, and their phosphorylated substrates following focal cerebral ischemia

Focal ischemia induced by middle cerebral artery occlusion (MCAO) to adult rats results in necrosis at the infarct core and activation of complex signal pathways for cell death and cell survival in the penumbra. Upstream from the cell death promoters and executioners are several kinases that, once activated by phosphorylation, may activate several transcription factor substrates involved in cell death and cell survival. In the present study we examined, by immunohistochemistry, the expression of phosphorylated (active) mitogen-activated protein kinase, extracellular signal-regulated kinase (MAPK/ERK), stress-activated protein kinase (SAPK), c-Jun N-terminal kinase (JNK) and p-38 kinase at early stages (1-4 h) following 1 h of MCAO in the rat. The expression of phosphorylation-dependent, active transcription substrates of these kinases, including cyclic AMP-responsive element-binding protein (CREB) Alk-1, ATF-2, c-Myc and c-Jun was examined at early stages following reperfusion. Increased nuclear phosphorylated SAPK/JNK (SAPK/JNK-P) and c-Jun-PSer63, and reduced CREB-P, occurred in the infarct core at 1 h following reperfusion, suggesting increased phosphorylated SAPK/JNK and c-JunSer63, together with decreased phospho-CREB associated with cell death in the infarct core. However, increased cytoplasmic expression of MAPK/ERK-P, SAPK/JNK-P, p38-P, CREB-P, Elk-1-P, c-Myc-P, ATF-2-P and c-Jun-P occurred in the region bordering the infarct core (penumbra) at 4 h following reperfusion. This indicates that different signals converge in the cytoplasm of neurons located at the borders of the infarct at 4 h following reperfusion, revealing the struggle of death promoters and life facilitators at the penumbra. Whether phosphorylated kinases and specific substrates participate in promoting cell death or survival in the penumbra probably depends on additional factors and on the interaction with other proteins.

Tyrosine hydroxylase, but not dopamine beta-hydroxylase, is increased in rat frontal cortex after traumatic brain injury

Chronic frontal lobe functional deficits after traumatic brain injury (TBI) may be associated with altered catecholamine systems in the frontal cortex. To test this, tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) levels were examined by immunohistochemistry and Western blot at 1, 7, 14, and 28 days after TBI or sham surgery. No alterations in DBH levels were observed by Western blot at any time point examined, but there was a significant increase in TH expression 28 days after TBI (optical density 334 +/- 68% or 3.3-fold, ipsilateral and 218 +/- 39% or 2.2-fold, contralateral) relative to the sham controls. The increase in TH may reflect a compensatory response of dopaminergic neurons to upregulate their synthesizing capacity and increase the efficiency of dopamine neurotransmission chronically after TBI.

MPP(+) injection into rat substantia nigra causes secondary glial activation but not cell death in the ipsilateral striatum

Injection of MPP(+) into the substantia nigra causes extensive necrosis and anterograde degeneration of pars compacta dopaminergic neurons. We studied secondary effects in the ipsilateral striatum by examining dopaminergic terminals, signs of neuronal damage, and glial reactivity at 1, 2, 3, and 7 days after injection of MPP(+) into the substantia nigra. Dopaminergic terminals and uptake sites were evaluated with [(3)H]GBR-12935 binding and tyrosine hydroxylase immunoreactivity. Glial reaction was examined with markers of astrocytes and microglia. Stereology was used to evaluate any changes in neuronal density. Tyrosine hydroxylase immunoreactivity and [(3)H]GBR-12935 binding markedly decreased (74%) from days 2 to 7. Loss of dopaminergic terminals in the ipsilateral striatum was accompanied by an intense astroglial and, to a lesser extent, microglial reaction. However, no signs of cell damage, neuronal loss, or disruption of the blood-brain barrier were found in the striatum. Resident astroglial and microglial cells showed a morphological shift and notable changes in protein expression typical of glial reactivity, yet the presence of macrophage-like cells was not detected. This study shows that injection of MPP(+) in the substantia nigra causes a secondary reaction within the ipsilateral striatum involving the transformation of quiescent glia to reactive glia. It is suggested that stimuli derived from damaged dopaminergic terminals within the striatum are able to activate resident glia and that this glial transformation may promote repair and regeneration.