Aminoguanidine prevented the impairment of learning behavior and hippocampal long-term potentiation following transient cerebral ischemia

Polyamine and aminoguanidine treatments to promote structural and functional recovery in the adult mammalian brain after injury: a brief literature review and preliminary data about their combined administration

The regeneration potential of the adult mammalian central nervous system (CNS) is very modest, due to, among other factors, the presence of either a glial scar, or myelin-associated regeneration inhibitors such as Nogo-A, MAG and OMgp, which all interact with the same receptor (NgR). After a brief review of the key proteins (Rho and PKC) implicated in NgR-mediated signalling cascades, we will tackle the implications of cAMP and Arginase I in overcoming myelin growth-inhibitory influence, and then will focus on the effects of polyamines and aminoguanidine to propose (and to briefly support this proposal by our own preliminary data) that their association might be a potent way to enable functionally-relevant regeneration in the adult mammalian CNS.

Neuropsychological disorders indicative of postresuscitation encephalopaty in rats

The aim of this research was to study the effect of 12-minute clinical death on innate and acquired behavior, biogenic amine concentration, and the composition and quantity of neural populations in specific brain regions of white rats. The study shows that in animals during the postresuscitation period with formal restoration of neurological status, there are changes in emotional reactivity, orientation-exploration reactions, impairment of learning and memory, decrease in exercise tolerance and pain sensitivity. These processes are accompanied by alterations in serotonin and norepinephrine levels in the frontal cerebral cortex, dopamine and serotonin levels in the striatum, certain biochemical indices in blood plasma and neural loss in the CA1 sector of the hippocampus and lateral portions of the cerebellum.

Electrophysiological correlates of neural plasticity compensating for ischemia-induced damage in the hippocampus

Injury to the brain often results in loss of synapses or cell death in the damaged area. Subsequent to the injury, the areas that are not directly affected often exhibit enhanced neuronal plasticity. Although there are many reports of morphological changes resulting from such plasticity, their functional consequences are poorly understood. In this study we examined electrophysiological changes associated with ischemia-induced neurogenesis in the hippocampus, a brain region that is particularly vulnerable but also exceptionally plastic. Transient global ischemia was induced in Sprague-Dawley rats by occlusion of both carotid arteries and a reduction in blood pressure for 12 min. The procedure resulted in delayed cell death in the CA1 field of the hippocampus while the dentate gyrus (DG) was spared. To assess neurogenesis and synaptic changes in parallel we used both hemispheres from each animal. One side was used for immunohistochemistry and the other for in vitro electrophysiological experiments in brain slices. Synaptic field responses and synaptic plasticity (LTP) in perforant path within the DG were reduced by 50% at 10 days after the ischemic injury but recovered at 35 days. Synaptic responses in non-neurogenic CA1 were abolished in parallel with cell death and did not recover. Gamma irradiation applied focally to the head selectively prevented neurogenesis and the synaptic recovery in the DG. These experiments reveal electrophysiological changes associated with reactive neural plasticity in the hippocampus.

Glial nitric oxide-mediated long-term presynaptic facilitation revealed by optical imaging in rat spinal dorsal horn

We investigated a presynaptic form of long-term potentiation (LTP) in horizontal slices of the rat spinal cord by visualizing presynaptic and postsynaptic excitation with a voltage-sensitive dye. To record presynaptic excitation, we stained primary afferent fibers anterogradely from the dorsal root. A single-pulse test stimulation of C fiber-activating strength to the dorsal root elicited action potential (AP)-like or compound AP-like optical signals throughout the superficial dorsal horn. After conditioning (240 pulses at 2 Hz for 2 min), the presynaptic excitation was augmented. Furthermore, new excitation was elicited in the areas that were silent before conditioning. For postsynaptic recording, projection neurons in spinal lamina I were stained retrogradely from the periaqueductal gray in the brain stem. The test stimulation elicited AP-like or EPSP-like optical signals in the stained neurons. After conditioning, the EPSP-like responses were augmented, and previously silent neurons were converted to active ones. Results obtained with a nitric oxide (NO) donor, NO synthase inhibitors, metabotropic glutamate receptor (mGluR) agonist and mGluR1 antagonist, and a glial metabolism inhibitor suggest that after conditioning, presynaptic excitation is facilitated by NO released from glial cells via the activation of mGluR1. The results also indicate the possible presence of additional presynaptic and postsynaptic mechanism(s) for the LTP induction. Activity-dependent LTP of nociceptive afferent synaptic transmission in the spinal cord is believed to underlie central sensitization after inflammation or nerve injury. This glial NO-mediated control of presynaptic excitation may contribute to the induction at least in part.

An S-nitrosylated hemoglobin derivative protects the rat hippocampus from ischemia-induced long-term potentiation impairment with a time window

Evidence suggests that S-nitrosylation is a biological process involved in cerebral ischemia. The aim of the present study was to elucidate the effects of S-nitrosylated (SNO) polyethylene glycol-conjugated (PEG) hemoglobin (Hb) developed as an artificial oxygen carrier, which can absorb free NO and translocate NO to a sulfhydryl (SH) moiety, on ischemic cerebral dysfunction. Long-term potentiation (LTP) in the perforant path-dentate gyrus synapses of the rat hippocampus was evaluated as functional outcome 4 days after transient incomplete cerebral ischemia (2-vessel occlusion: 2VO, 10 min). SNO-PEG-Hb (250 mg/kg, i.v.) administered on Day 0, 1, 2, or 4 (immediately, 24 h, 48 h, or 96 h after reperfusion, respectively) alleviated 2VO-induced LTP impairment with a therapeutic time window. The effect was significant when SNO-PEG-Hb was administered on Day 1 or 2. SNO-PEG-Hb altered NOS features observed in the vehicle-treated 2VO rat, upregulation of eNOS, nNOS, and iNOS expressions at mRNA and protein levels; SNO-PEG-Hb further upregulated eNOS and nNOS and downregulated iNOS expressions. These findings suggest that SNO-PEG-Hb might have protective effects on the rat hippocampus from ischemia/reperfusion-induced functional damages, thereby increasing the therapeutic potential as an artificial oxygen carrier for use in the area of oxygen therapy.

Neuroprotection of catalpol in transient global ischemia in gerbils

The neuroprotection of catalpol and its mechanism was evaluated in cerebral ischemic model in gerbils. Three groups were designed as sham-operated, ischemia-treated, respectively, with catalpol and saline. Catalpol was injected intraperitoneally immediately after reperfusion and repeatedly at 12, 24, 48 and 72 h with the dose of 5.0 mg/kg. The neuroprotection was estimated by the indexes of behavior and histology. Behavioral testing was performed in Y-maze and the survival neurons in CA1 subfield were counted under a microscope after behavioral testing. In addition, apoptosis induced by ischemia was also examined by using the terminal deoxynucleotidyl transferase-mediated UTP nick end labeling method. It was shown that catalpol significantly attenuated apoptosis, rescued hippocampal CA1 neurons and reduced cognitive impairment. In order to make clear the mechanism of catalpol's neuroprotection, the activities of endogenous antioxidants and nitric oxide synthase together with the content of lipid peroxide in cortex and hippocampus were assayed. The results proved that catalpol significantly reduced the content of lipid peroxide, increased the activity of glutathione peroxidase and decreased the activity of nitric oxide synthase. All these suggested that catalpol was a potential neuroprotective agent and its neuroprotective effects were achieved at least partly by promoting endogenous antioxidant enzymatic activities and reducing the formation of nitric oxide.

Impact of enriched-environment housing on brain-derived neurotrophic factor and on cognitive performance after a transient global ischemia

Environmental enrichment promotes structural and functional changes in the brain, including enhanced learning and memory performance in rodents. Transient global cerebral ischemia (15 min) causes specific damage to dorsal hippocampal area CA1 pyramidal cells of the rat concomitantly with cognitive deficits. Thus, we investigated if environmental enrichment can protect rats against the cognitive and neurological consequences of transient ischemia. We evaluated the impairment of learning and memory with three tasks: odour discrimination, object exploration and spatial learning. Contrary to expectation, we found that the enriched environment improved performances for both ischemic and sham rats in odour discrimination and object exploration tasks compared with standard condition housed rats. After exposure to an enriched environment, ischemic rats performed better in the water maze than those in the standard housing conditions. However, exposure to an enriched environment does not protect against actual loss of CA1 pyramidal cells. Brain-derived neurotrophic factor (BDNF) levels were increased in environmental enrichment animals compared to those housed in standard conditions. We conclude that environmental enrichment has positive effects that are independent of the effects of ischemic brain lesions.

Antioxidant enzyme activities and oxidative stress in affective disorders

Recent data from several reports indicate that free radicals are involved in the biochemical mechanisms underlying neuropsychiatric disorders in human. The results of several reports suggest that lower antioxidant defences against lipid peroxidation exist in patients with depression and that there is a therapeutic benefit from antioxidant supplementation in unstable manic-depressive patients. We investigated the antioxidant enzyme status and the indices of oxidative stress and lipid peroxidation end products in erythrocytes from patients with affective disorder. For this purpose, we measured superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) activities, as well as malondialdehyde (MDA) and nitric oxide (NO) levels in patients with affective disorders (n=30) in both pre- and post-treatment periods, and in a control group (n=21). CAT activities were significantly decreased in both pre-, and post-treatment periods in patients compared to the control group. GSH-Px activity in the pre-treatment period in the patients was significantly lower than both post-treatment patient and control groups. MDA levels were increased in both pre-, and post-treatment patient groups compared to the control group. NO level was lower in the pre-treatment patient group than in the control group. There were statistically significant correlations between SOD and MDA, and SOD and NO in the pre-treatment patient and control groups. Because the overall study sample was small, and the post-treatment patient group was even smaller, it can tentatively be suggested that the antioxidant system is impaired during a mood episode in patients with affective disorders, normalizing at the end of the episode.

Hippocampal nitric oxide upregulation precedes memory loss and A beta 1-40 accumulation after chronic brain hypoperfusion in rats

Chronic brain hypoperfusion (CBH) using permanent occlusion of both common carotid arteries in an aging rat model, has been shown to mimic human mild cognitive impairment (MCI), an acknowledged high risk condition that often converts to Alzheimer's disease. An aging rat model was used to determine whether hippocampal nitric oxide (NO) is abnormally expressed following CBH for two or eight weeks. At each time point, spatial memory was measured with the Morris water maze and hippocampal A beta 1-40/1-42 concentrations were obtained using sandwich ELISA. Real-time amperometric measures of NO representing the constitutive isoforms of neuronal nitric oxide synthase (nNOS) and endothelial (e)NOS were also taken at each time point to ascertain whether NO levels changed as a result of CBH, and if so, whether such NO changes preceded or followed any memory or amyloid-beta pathology. We found that two weeks after CBH, NO hippocampal levels were upregulated nearly four-fold when compared to nonoccluded rats but no alteration in spatial memory of A beta products were observed at this time point. By contrast, NO concentration had declined to control levels by eight weeks but spatial memory was found significantly impaired and A beta 1-40 (but not A beta 1-42) had increased in the CBH group when compared to control rats. Since changes in shear stress are known to upregulate eNOS but generally not nNOS, these results suggest that shear stress induced by CBH hyperactivated vascular NO derived from eNOS in the first two weeks as a reaction by the capillary endothelium to maintain homeostasis of local cerebral blood flow. The return of vascular NO to basal levels after eight weeks of CBH may have triggered metabolic changes within hippocampal cells resulting in hippocampal dysfunction as reflected by spatial memory impairment and by accumulation of A beta 1-40 peptide. In conclusion, our study shows that CBH initiates spatial memory loss in aging rats thus mimicking human MCI and also increases A beta 1-40 in the hippocampus. The memory and amyloid changes are preceded by NO upregulation in the hippocampus. These preliminary findings may be important in understanding, at least in part, the molecular mechanisms that precede memory impairment during chronic brain ischemia and as such, the pre-clinical stage leading to Alzheimer's disease.

Expression of inducible nitric oxide synthase after focal cerebral ischemia stimulates neurogenesis in the adult rodent dentate gyrus

The generation of new neurons in the adult mammalian hippocampus is thought to play a role in repairing the brain after injury. Here, we show that 7 d after focal cerebral ischemia, newly divided cells in the dentate gyrus of adult rats increased to approximately sevenfold, compared with sham controls. In the same area, this enhanced dentate neurogenesis was associated with activation of inducible nitric oxide synthase (iNOS). Inhibition of iNOS by aminoguanidine prevented ischemia-induced neurogenesis in the dentate gyrus. In null mutant mice lacking the iNOS gene, increased neurogenesis was not observed after focal cerebral ischemia. This study demonstrates that expression of iNOS is necessary for ischemia-stimulated cell birth in the dentate gyrus and indicates that activation of iNOS may provide a possible strategy for functional recovery from cerebral ischemic insult.

Effects of aminoguanidine on cerebral ischemia in mice: comparison between mice with and without inducible nitric oxide synthase gene

The expression of inducible nitric oxide synthase (iNOS) is induced in the late stage of cerebral ischemia, and NO produced by iNOS contributes to delays in recovery from brain neuronal damage. To examine the importance of iNOS in the above process, we compared the effects of aminoguanidine (AG), selective iNOS inhibitor, on infarct volume and neurological deficit in iNOS null mice and normal mice subjected to brain ischemia. Neurological deficits in iNOS null mice at 24 h post-ischemia were mild compared with those of normal mice, and did not improve by AG treatment at 96 h post-ischemia. The mean infarct volume of iNOS null mice was smaller than that of normal mice at 96 h post-ischemia, and was not influenced by AG treatment. In contrast, AG reduced the infarct volume in normal mice to levels similar to those of saline-treated iNOS null mice at 96 h post-ischemia. Our results indicated that AG suppresses iNOS activity in mice with brain ischemia to level equivalent to those seen in iNOS knockout mice, confirming that this enzyme is involved in ischemic brain injury.

Inducible nitric oxide synthase expression in the ischemic core and penumbra after transient focal cerebral ischemia in mice

The present observations examined the hypothesis that the iNOS expression in the ischemic penumbra after a transient focal ischemic insult is involved in the recruitment of penumbra into infarction. The middle cerebral artery in mice was occluded for 2 h by an intraluminal filament and then recirculated. The measurement of iNOS activity, iNOS protein formation and NO concentration in the ischemic core and penumbra, and the determination of infarct volume were performed at 6, 12, 24 and 48 h after reperfusion. iNOS protein and iNOS enzymatic activity appeared at 6 h, peaked at 24 h, and declined at 48 h in the penumbra after reperfusion. iNOS protein was not detectable in contralateral area and in sham-operated brains. The time course of iNOS protein, enzymatic activity and NO concentration in the penumbra but not in the core matched the process of infarct maturation. Treatment with iNOS inhibitor aminoguanidine (100 mg.kg(-1), i.p.) at 6 and 12 h after reperfusion inhibited iNOS activity by 88.0 +/- 10.4% and reduced NO concentration by 48.5 +/- 8.3% in the penumbra, and lessened infarct size by 48.8 +/- 7.2%. The iNOS activity and NO level in the core were not affected by the administration of aminoguanidine. These results suggest that iNOS expression in the ischemic penumbra is involved in the recruitment of penumbra into infarction and thereby contributing to the enlargement of infarct.

Involvement of interleukin-1beta/nitric oxide pathway in the postischemic impairment of long-term potentiation of the rat hippocampus

To investigate whether postischemic cerebral dysfunction occurs via the interleukin-1 beta/nitric oxide (IL-1beta/NO) pathway, we examined the effects of an IL-1beta antagonist on long-term potentiation (LTP) impairment and excessive NO production in the rat hippocampus after 10-min global ischemia. Intracerebroventricilar administration of the IL-1beta antagonist attenuated NO production and rescued LTP impairment in the perforant path-dentate gyrus synapses, observed 1 day and 4 days after ischemic insult, respectively. There was an inverse relationship between LTP in the dentate gyrus synapses and hippocampal NO production. Centrally applied IL-1beta mimicked the consequences of transient ischemia in LTP formation and hippocampal NO production in non-ischemic rats. These findings indicate that the IL-1beta/NO pathway is involved in the hippocampal LTP impairment observed in the postischemic brain.

Prolonged suppression of brain nitric oxide synthase activity by 7-nitroindazole protects against cerebral hypoxic-ischemic injury in neonatal rat

Nitric oxide mediates glutamate-induced excitotoxicity associated with cerebral hypoxia-ischemia through production in the brain by several isoforms of nitric oxide synthase (NOS). We examined the influence of the selective neuronal NOS inhibitor, 7-nitroindazole (7-NI), on brain NOS activity and its neuroprotective effects against cerebral hypoxic-ischemic injury in the postnatal day (PND) 7 rat. In the first set of experiments, 7-NI (50 mg/kg) administered intraperitoneally (i.p.) transiently inhibited NOS activity to 40% below the vehicle control level at 1 h after injection (P<0.001, analysis of variance (ANOVA)). In contrast, 7-NI (100 mg/kg, i.p.) inhibited NOS activity to 56% below the control level at 1 h with prolonged suppression of NOS activity at 3, 6, 9 and 12 h after injection. Two-factor ANOVA revealed an overall effect on NOS activity of 7-NI treatment (P<0.001) and time after injection (P<0.001). In the second set of experiments, 7-NI (50, 100 mg/kg) or an equal volume of vehicle was administered after unilateral carotid artery ligation, but 30 min before hypoxia in PND 7 rats. 7-NI (100 mg/kg) significantly protected against cerebral hypoxic-ischemic injury (100 mg/kg of 7-NI, 1.7+/-1.0% damage; control, 8.7+/-1.6%,P<0.05). 7-NI administered 15 min after cerebral hypoxia-ischemia was not neuroprotective. The data suggest that the protective effect of 7-NI is dose dependent, and is related to the duration of suppressed NOS activity.