γ-Aminobutyric acid infusion in substantia nigra pars reticulata in rats inhibits ascorbate release in ipsilateral striatum

A relatively high level of extracellular ascorbate in the striatum, which is known to modulate impulse flow in striatal neurons, originates primarily from glutamate-containing corticostriatal afferents. Increasing evidence suggests that ascorbate release from these fibers is regulated by a multisynaptic loop that includes γ-aminobutyric acid (GABA) mechanisms in the substantia nigra. To assess the role that nigral GABA plays in striatal ascorbate release, extracellular ascorbate was monitored voltammetrically in the striatum during infusions of GABA into the substantia nigra pars reticulata (SNr) of awake, unrestrained rats. Compared to vehicle infusions, intranigral GABA lowered striatal ascorbate by >50%. In contrast, intranigral application of picrotoxin, a GABA antagonist, had the opposite effect. Neither GABA nor picrotoxin altered striatal 3,4-dihydroxyphenylacetic acid (DOPAC), a major dopamine metabolite. Collectively, these results indicate that intranigral GABA exerts a tonic inhibitory influence on ascorbate release in the striatum.     

Trauma-induced increase of extracellular ascorbate in rat cerebral cortex

Extracellular (EC) ascorbate concentrations were measured in microdialysates from the cerebral cortex in rats subjected to cortical compression-contusion trauma. The trauma induced a transient, dramatic increase in EC ascorbate compared to the basal level before the insult and compared to control animals. The data support the presence of a releasable intracellular pool of ascorbate in the neocortex. The possibility that ascorbate may influence traumatic brain damage by its proposed neuromodulatory property and/or by its ability to induce lipid peroxidation is considered.     

Circadian changes in extracellular ascorbate in rat cortex, accumbens, striatum and hippocampus: Correlations with motor activity

We have used linear sweep voltammetry with carbon-paste electrodes to monitor changes in the ascorbate signal simultaneously in rat frontal cortex, nucleus accumbens, striatum and hippocampus together with motor activity. The relative amplitude of the ascorbate signal recorded in the four regions corresponded to the relative density of excitatory amino acid (EAA) transmission determined by other methods; this result provides further evidence that the ascorbate signal may be used as an index of EAA release. Changes in motor activity were associated with changes in the ascorbate signal; linear regression analysis for motor activity versus the ascorbate signal revealed differences between the release of ascorbate in the four brain regions.     

Ascorbate modulates pentylenetetrazol-induced convulsions biphasically

Ascorbate is an antioxidant vitamin that is found in high concentrations in the brain which seems to have neuroprotective properties in some experimental models of excitotoxic neurological disorders, including convulsive behavior and reactive species-related damage. In this study we tested whether ascorbate (30, 100 or 300 mg/kg, i.p.) protects against the convulsions, protein carbonylation and inhibition of Na(+),K(+)-ATPase activity induced by pentylenetetrazol (PTZ; 1.8 micromol/striatum), a classical convulsant agent that has been fairly used for the study of epilepsy and screening of new compounds with antiepileptic activity. The intrastriatal injection of PTZ caused convulsive behavior in a dose-dependent manner and an increase in the total protein carbonyl content of the injected striatum. However, duration of PTZ-induced convulsive episodes did not correlate with protein carbonyl content of the injected striatum. Ascorbate, at high doses (300 mg/kg), protected against PTZ-induced convulsions, protein carbonylation and inhibition of Na(+),K(+)-ATPase activity in the rat striatum, further suggesting a anticonvulsant and neuroprotective role for this vitamin. Conversely, intermediate doses of ascorbate (100 mg/kg) potentiated the duration of the convulsive episodes, but had no additive effects on protein carbonylation or Na(+),K(+)-ATPase activity inhibition induced by PTZ. Low doses of ascorbate (30 mg/kg) prevented PTZ-induced increase of total striatal carbonyl protein content, but did not alter PTZ-induced convulsions and Na(+),K(+)-ATPase activity inhibition. Collectively, these data indicate that the anticonvulsant activity of ascorbate is not related to its antioxidant action and support a dual role for this compound as a neuroprotective agent, since while it protects against PTZ-induced cellular oxidative damage, it has a biphasic effect on PTZ-induced convulsions.     

Rapid changes in striatal ascorbate in response to tail-pinch monitored by constant potential voltammetry

The first peak in the voltammogram recorded with linear sweep and a carbon paste electrode implanted in the rat striatum is due to the oxidation of ascorbic acid. When the potential is held at a level slightly positive to this peak a current is recorded which is abolished by the microinjection of ascorbic acid oxidase in the vicinity of the electrode; this suggests that it is due to the oxidation of ascorbate. This current shows the same diurnal variation as the size of the ascorbate peak and its rise and fall coincides with the onset and offset of motor activity. A tail-pinch applied through a paper clip causes an immediate rise in the ascorbate current which begins to fall as soon as the paper clip is removed. Measurement of the ascorbate current at constant potential provides a technique for monitoring rapid changes in extracellular brain ascorbate in response to physiological stimuli.     

Opposed locomotor asymmetries following lesions of the medial and lateral substantia nigra pars compacta or pars reticulata in the rat

In animals with lesions in the medial or lateral portions of the substantia nigra pars compacta (SNC) amphetamine produces circling in opposite directions. The present study examined the relationships between lesion site and the direction of circling using glyoxylic acid histofluorescence to visualize DA cells. Lesions were produced by 6-hydroxydopamine (2–6 μg) or 0.05% ascorbate injected into the SN. After lesions in the medial SNC, amphetamine caused rats to circle ipsiversive to the lesion while after lateral SNC lesions rats circled contraversively. When the lesion extended to the middle of the SNC, or deeper into the SN pars reticulata (SNR), the direction of circling was unpredictable. When the damage produced by the cannula track and ascorbate injection was in the lateral SNR animals circled ipsiversively while medial SNR damage led to contraversive circling. Thus the medial and lateral SN, and the pars compacta and pars reticulata, are functionally antagonistic. This four way division of the SN is consistent with the topographic mapping of SNC to striatum and striatum to SNR.     

Linear sweep voltammetry with carbon paste electrodes in the rat striatum

Voltammetry has been widely used in attempts to measure catecholamine release in vivo. The voltammogram recorded in the rat striatum using carbon paste electrodes and linear sweep voltammetry with semidifferentiation consists of a number of separate peaks; changes in the height of the first of these peaks have been attributed to changes in catecholamine release. We have found that ascorbate, either microinjected into the striatum or injected intraperitoneally, increases the height of the first peak without changing its potential. Microinjection of dopamine or 3,4-dihydroxyphenylacetic acid, or intraperitoneal injection of 3,4-dihydroxyphenylalanine, caused a shift in the potential of peak 1 of 25-50 mV in a positive direction. Amphetamine, administered intraperitoneally to freely moving animals, caused an increase in the height of the first peak but did not change its potential. Oxidation potentials in vitro and the effect of other drugs on the voltammogram obtained in vivo were also measured. Peak 1 is caused by the oxidation of both ascorbate and catechols whose oxidation potentials differ by only 50 mV in vivo; the contribution of catechols in control animals is negligible. Shifts in the potential of peak 1 caused by drugs are not due to changes in the oxidation potentials of the components but to a change in their relative contributions. Therefore changes in the height of peak 1 with no change in position do not represent changes in the extracellular concentration of catechols but are due to changes in ascorbate concentration. Changes in the concentration of catecholamine-related compounds can be detected at potentials some 50 mV greater than that of the first peak.     

Ascorbic acid does not modulate stimulated dopamine release: In vivo voltammetric data in the rat

Electrical stimulation of the nigrostriatal pathway released dopamine (DA) in the striatum of the anaesthetized rat. The level of DA released by 10-s stimulus trains was measured by high-speed cyclic voltammetry. Metoclopramide (10 mg/kg) increased DA release by 20%. Apomorphine (1.76 mg/kg) caused a 40% decrease in release which was blocked by metoclopramide. Ascorbate (1.76 g/kg) had no effect on stimulated DA release. Furthermore, pretreatment of rats with ascorbate trebled the striatal extracellular ascorbate level, but failed to modify the effects of metoclopramide and apomorphine on DA release. We conclude that ascorbate has no effect on the presynaptic autoreceptors that modulate striatal DA release in vivo.     

Voltammetrically monitored brain ascorbate as an index of excitatory amino acid release in the unrestrained rat

To discover the significance of changes in the extracellular concentration of brain ascorbate, we used linear sweep voltammetry to monitor the ascorbate signal. Recordings were made with carbon paste electrodes implanted in the striatum and hippocampus of anaesthetised and unanaesthetised rats under a variety of conditions. Intraperitoneal administration of excitatory amino acid transmitters, but not tyrosine or glycine, increased extracellular striatal ascorbate; similarly, microinfusion of L-glutamate beside striatal electrodes enhanced the ascorbate signal. Electrical stimulation of the perforant path increased the extracellular concentration of dentate ascorbate in the unanaesthetised, but not in the anaesthetised, rat. These results support our hypothesis that changes in the extracellular concentration of brain ascorbate monitored by voltammetry reflect the release of excitatory amino acids.     

Generalized induction of 72-kDa heat-shock protein after transient focal ischemia in rat brain

The time course of 72-kDa heat-shock protein (hsp72) induction was evaluated by immunoblotting in cerebral cortex, striatum, hippocampus, cerebellum, liver, and kidney of rats subjected to 60-min focal cerebral ischemia following proximal unilateral occlusion of the right middle cerebral artery (MCA). Neurological examinations indicated that maximum deficits in reflex and sensorimotor functions occurred 24-48 h after reperfusion (40% lower than baseline), while significant recovery occurred at 72 h (33% higher than 48 h). hsp72 was present in all tissues at 6 h. The regions perfused by the occluded MCA showed a higher induction than the corresponding contralateral ones. hsp72 reached its maximum level in ipsilateral cerebral cortex and striatum at 24 h, whereas in the contralateral cortex and cerebellum the protein reached its maximum expression at 48 h, that is 24 h before functional recovery. This delay suggests a role of the protein in plastic events sustaining neurological recovery.     

Hyperactive striatal neurons in symptomatic Huntington R6/2 mice: variations with behavioral state and repeated ascorbate treatment

Membrane and morphological abnormalities occur in the striatum of R6/2 transgenics, a widely used mouse model of Huntington's disease. To assess changes in behavior-related neuronal activity, we implanted micro-wire bundles in the striatum of symptomatic R6/2 mice and wild-type controls. Unit activity was recorded in an open-field arena once weekly for the next several weeks. For each recording session, firing rate was monitored before, during, and after a period of light anesthesia to assess the influence of behavioral arousal. Because low ascorbate in striatal extracellular fluid may contribute to Huntington's disease symptoms, all animals received an injection of either 300 mg/kg sodium ascorbate or vehicle for three consecutive days prior to each recording session. In R6/2 mice, regardless of treatment, striatal unit activity was significantly faster than in wild-type controls. The difference in mean (+/-S.E.M.) firing was most apparent during wakefulness (6.4+/-0.8 vs. 3.5+/-0.3 spikes/s) but also persisted during anesthesia (2.0+/-0.3 vs. 0.7+/-0.1 spikes/s). Assessment of treatment duration indicated that R6/2 mean waking discharge rate was significantly slower after three weeks than after one week of ascorbate treatment (3.1+/-0.6 vs. 10.2+/-2.7 spikes/s). Vehicle-treated R6/2s showed no such decline in striatal activity ruling out an age- or injection-related effect. Slow-scan voltammetry in separate animals confirmed that ascorbate-injections returned the level of striatal extracellular ascorbate in R6/2 mice to that of wild-type controls. Our results indicate that although striatal neurons modulate firing in relation to behavioral state, impulse activity is consistently elevated in transgenic relative to wild-type mice. Restoring extracellular ascorbate to the wild-type level reverses this effect suggesting a role for ascorbate in normalizing neuronal function in Huntington's disease striatum.     

Age-related changes in dopaminergic and serotonergic indices in the rat forebrain

Age-related changes in the content of dopamine (DA), homovanillic acid (HVA), dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3-MT), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in anterior cerebral cortex, hippocampus and striatum of the rat have been investigated using HPLC with electrochemical detection. A significant decrease in HVA was observed in the striatum and hippocampus of the aged (27 months) animals, as compared to the controls (2.4 to 2.6 months). A significant decrease in DA levels was also observed in the hippocampus but not in the striatum. In contrast, the level of DA in the cerebral cortex was markedly increased in the aged animals. A concomitant increase in 3-MT level was observed. Finally the level of 5-HIAA was significantly increased in striatum and hippocampus.     

Neuronal damage in the striatum following forebrain ischemia: lack of effect of selective lesions of mesostriatal dopamine neurons

Summary Transient periods of global cerebral ischemia lead to selective neuronal damage in the striatum. We investigated the effects of unilateral 6-hydroxydopamine lesions of the mesostriatal dopamine (DA) system on the density and distribution of neuronal necrosis in the rat striatum following ischemia induced by bilateral occlusion of the common carotid arteries combined with hypotension. After both 12 and 15 min of ischemia, which caused slight and extensive striatal damage, respectively, there was no difference in the density of neuronal necrosis in the striatum between DA-lesioned and shamoperated animals. We conclude that the DA system alone does not modulate injury following complete cerebral ischemia, but may contribute significantly to damage following conditions such as during hypoglycemia and incomplete cerebral ischemia.     

The organization of the projection from the cerebral cortex to the striatum in the rat

The detailed organization of the corticostriate projection has been investigated in the brain of the rat using the technique of retrograde transport of horseradish peroxidase following the placement of small, iontophoretic injections of horseradish peroxidase conjugated to lectin throughout all major regions of the striatum (caudate-putamen, nucleus accumbens and olfactory tubercle). The results demonstrate that all major regions of the cerebral cortex project to the striatum on both sides of the brain with an ipsilateral predominance. The cells of origin of both the ipsilateral and contralateral corticostriate projections lie mainly in lamina V (especially lamina Va) with very small numbers in lamina III of the neocortex and mesocortex, and in the deep laminae of the allocortex. The results show that each striatal locus receives inputs from several cortical regions, i.e. there is extensive overlap in the corticostriate projection, and that, in general terms, each cortical region projects onto a longitudinally oriented region of the striatum. In particular, the major subdivisions of the cerebral cortex--the neocortex, mesocortex and allocortex--project onto defined but partially overlapping regions of the striatum: the neocortex projects to the caudate-putamen; the mesocortex projects mainly to the medial and ventral regions of the caudate-putamen but also to the ventral striatum (nucleus accumens and olfactory tubercle); and the allocortex projects mainly to the ventral striatum but also to the medial and ventral parts of the caudate-putamen. Within each of these major projection systems there is a further organization, with the constituent parts of each major cortical region projecting to smaller longitudinal components of the major projection fields. Each neocortical area projects to a longitudinal region of the dorsal striatum (caudate-putamen): the sensory and motor areas project topographically onto the dorsolateral striatum such that the rostral sensorimotor cortex (head areas) projects to central and ventral regions and the more caudal sensorimotor cortex (limb areas) projects to dorsal regions of the dorsolateral striatum; the visual area projects to the dorsomedial striatum; and the auditory area projects to the medial striatum. Each mesocortical area projects to a longitudinal area of the striatum: the most posteromedial mesocortex (the retrosplenial area) projects to the dorsomedial striatum; more anterior and lateral parts of the mesocortex project to more ventral parts of the striatum: and the most lateral mesocortex (the agranular insular and perirhinal areas) project to the ventrolateral striatum.(ABSTRACT TRUNCATED AT 400 WORDS)     

孕酮对脑缺血再灌注大鼠纹状体水、钠、钾及钙含量的影响

目的:孕酮(PROG)已被证明是一种"神经活性甾体",本文探讨PROG对缺血脑的神经保护作用。方法:采用大鼠局灶性脑缺血再灌注模型,测定大脑中动脉阻塞(MCAO)2h再灌注22h后纹状体水、钠、钾、钙含量。结果:①I/R和DMSO组MCAO侧纹状体的水、钠、钙明显高于、钾显著低于非MCAO侧,I/R和DMSO组之间相比无显著差异;②与I/R和DMSO组相比,PROG预防及防治组MCAO侧纹状体的水、钠、钙明显减少,钾明显增加(P＜0.01);PROG治疗组则水、钠明显减少,但钾和钙无显著差异(P＞0.05);③PROG各组与阳性对照DEXA组相比,MCAO侧纹状体水、钠、钙、钾的差别均无显著(P＞0.05)。结论:PROG可减轻脑缺血/再灌注大鼠纹状体的损伤。     

N400 involvement in the processing of action sequences

Basic fibroblast growth factor (bFGF) is a neurotrophic and vasoactive factor, and has therapeutic potential for some central nervous system (CNS) disorders. In this study, we used the intranasal pathway to administer bFGF in adult rats, and evaluated its neuroprotective benefits and effects on endogenous neural stem cells. The bFGF levels after intranasal administration in normal rats were determined by western blot. Transient focal ischemia was achieved by occlusion of the right middle cerebral artery for 2 h. bFGF was given intranasally 2 h after reperfusion and daily thereafter on 3 successive days. Dividing progenitor cells were labeled with bromodeoxyuridine (BrdU) on day 3 of reperfusion. Rats were killed the next day after BrdU labeling. bFGF levels were significantly raised in the olfactory bulb (OB) and striatum following intranasal administration. Intranasal bFGF treatment improved neurological function and reduced infarct volume after cerebral ischemia/reperfusion, while no influence was observed on the blood pressure. And the BrdU incorporation was enhanced in the ipsilateral subventricular zone (SVZ) and striatum following intranasal administration of bFGF. These results demonstrated that bFGF can be directly delivered into brain following intranasal administration, and protects against cerebral ischemia/reperfusion. The protective effects may be attributed to the reduction of infarct volume and enhancement of endogenous progenitors in brain. Therefore, intranasal administration of bFGF may provide an alternative treatment for brain ischemia and some other CNS disorders.     

Enhanced activity of GABA receptors inhibits glutamate release induced by focal cerebral ischemia in rat striatum

Cerebral ischemia causes an excess release of glutamate, which can injure neurons. The striatum is one of the important regions vulnerable to hypoxia and ischemia. Using push–pull perfusion technique, we investigated the regulatory role of γ-aminobutyric acid (GABA) and its receptors in modifying the amount of glutamate in rat striatum with ischemia. Perfusion with exogenous GABA (1 mM) inhibited cerebral ischemia-induced glutamate release by as much as 47%. We further characterized relative roles of subtype receptors of GABA on glutamate release by using pharmacological tools. While baclofen (500 μM), a GABA_B receptor agonist, suppressed ischemia-induced glutamate release by 52%, GABA_B receptor antagonist saclofen (500 μM) failed to produce a significant increase of glutamate release. The GABA_A receptor agonist muscimol (500 μM) also reduced by 38% the release of glutamate induced by cerebral ischemia but the GABA_A receptor antagonist bicuculline (500 μM) had very little effect. The present study demonstrates that the excessive release of glutamate or the overly activated glutamate receptor, triggered by cerebral ischemia, can be down-regulated by exogenous GABA or by increased activity of GABA receptors, especially the presynaptic GABA_B receptors, which might be one of the important mechanisms to protect against striatum neuronal damage from over stimulation by excessive glutamate during ischemia.     

Nitrergic neurons make synapses on dual-input dendritic spines of neurons in the cerebral cortex and the striatum of the rat: implication for a postsynaptic action of nitric oxide

Pre-embedding electron microscopic immunocytochemistry was used to examine the ultrastructure of neurons containing nitric oxide synthase and to evaluate their synaptic relationships with target neurons in the striatum and sensorimotor cerebral cortex. Intense nitric oxide synthase immunoreactivity was found by light and electron microscopy in a type of aspiny neuron scattered in these two regions. The intensity of the labeling was uniform in the soma, dendrites and axon terminals of these neurons. In both forebrain regions, nitric oxide synthase-immunoreactive neurons received synaptic contacts from unlabeled terminals, which were mostly apposed to small-caliber dendrites. The unlabeled symmetric contacts were generally about four times as abundant as the unlabeled asymmetric contacts on the nitric oxide synthase-immunoreactive neurons. Terminals labeled for nitric oxide synthase were filled with synaptic vesicles and were observed to contact unlabeled neurons. Only 54% (in the cerebral cortex) and 44.3% (in the striatum) of the nitric oxide synthase-immunoreactive terminals making apposition with the target structures were observed to form synaptic membrane specializations within the plane of the randomly sampled sections. The most common targets of nitric oxide synthase-immunoreactive terminals were thin dendritic shafts (54% of the immunoreactive terminals in the cortex and 75.7% of the immunoreactive terminals in the striatum), while dendritic spines were a common secondary target (42% of the immunoreactive terminals in the cortex and 20.6% of the immunoreactive terminals in the striatum). The spines contacted by nitric oxide synthase-immunoreactive terminals typically also received an asymmetric synaptic contact from an unlabeled axon terminal.These findings suggest that: (i) nitric oxide synthase-immunoreactive neurons in the cortex and striatum preponderantly receive inhibitory input; (ii) nitric oxide synthase-containing terminals commonly make synaptic contact with target structures in the cortex and striatum; (iii) spines targeted by nitric oxide synthase-containing terminals in the cortex and striatum commonly receive an asymmetric contact as well, which may provide a basis for a synaptic interaction of nitric oxide with excitatory input to individual spines.     

Projections from eye movement-evoking cerebral cortices to the striatum and claustrum in the cat

Projection fields in the striatum and claustrum from eye movement-evoking cerebral cortices (EMECs) in the cat were investigated using the WGA-HRP tracing method under electrophysiological guidance to place WGA-HRP in the appropriate sites. The EMECs in the frontal cortex, which are located in the medial wall under the cruciate sulcus (CRUo), the medial and lateral banks of the presylvian sulcus the the knee portion of the coronal sulcus (CORo), projected to the rostral part of the striatum. The EMEC in the temporal cortex, which is located in the ventral bank of the anterior ectosylvian sulcus, projected to the middle part of the striatum. Concerning the EMECs in the frontal cortex, the medially situated CRUo projected to the dorsomedial portion of the striatum, and the laterally situated CORo projected to the ventrolateral portion of the striatum. The dorsal half of the claustrum had reciprocal connections with all of the EMECs.     

Poly(ADP-ribose) polymerase inhibition protect neurons and the white matter and regulates the translocation of apoptosis-inducing factor in stroke

Focal cerebral ischemia activates the nuclear protein poly(ADP-ribose) polymerase (PARP). Apoptosis-inducing factor (AIF) is a flavoprotein that is normally confined to the mitochondria, but translocates to the nucleus, as shown by in vitro models of neuronal injury. Using INO-1001, a novel potent inhibitor of PARP, we determined the role of PARP activation in the process of AIF translocation in a rat model of focal cerebral ischemia. The potency of INO-1001 as a PARP inhibitor and its cytoprotective potential in oxidant-challenged human neuronal SK-N-MC cells was first confirmed in vitro. PARP inhibition markedly reduced infarct size and improved neurological status in both transient and permanent models of MCA occlusion in Sprague-Dawley rats, with a therapeutic window of 6 h and 2 h in the transient and permanent ischemia models, respectively. The PARP inhibitor reduced the accumulation of poly(ADP-ribose) in the ischemic/reperfused hemisphere and reduced the accumulation of APP in the white matter of the affected hemisphere, consistently with protection against neuronal necrosis and axonal damage, respectively. Immunohistochemical analysis showed the appearance of AIF labeling in neuronal nuclei of the border zone ischemic area in the striatum after stroke. Cytoplasmatic (axonal) AIF staining was significantly diminished in the necrotic core of the striatum, while it was somewhat enhanced at the borderline ischemic territories of the white matter. Inhibition of PARP with INO-1001 reshifted the location of the apoptotic marker to the axons in the ipsilateral striatum. Thus, PARP inhibition is neuroprotective and regulates the ischemic nuclear translocation of AIF in stroke.