Increase of hypoxic tolerance in rat hippocampal slices following 3-nitropropionic acid is not mediated by endogenous nerve growth factor

Study the effect of crocin in three maternal hypoxia protocols with different oxygen intensities on motor activity and balance in rat offspring

Hypoxia as one of the most common clinical disturbances in pregnancy period can cause destructive changes in motor sensory cortex and can lead to imperfect organization in motor reactions. Crocin, a water-soluble carotenoid, is the most active ingredients of saffron and a lot of studies declare its positive effectiveness on improving motor activity. Since the hypoxia intensity affects its malicious amount on movement, in this paper, we have studied the effect of crocin in three maternal hypoxia protocols with different oxygen intensities on motor activity and balance in rat offspring. In this experiment, female rats (Wistar) were used on the 20th day of pregnancy. The rats were randomly divided into eight experimental groups: sham, crocin, hypoxia with three different intensities: 10% oxygen and 90% nitrogen for 1 h (hypoxia-ɪ), 7% oxygen and 93% nitrogen for 1 h (hypoxia-ɪɪ), 7% oxygen and 93% nitrogen for 3 h (hypoxia-ɪɪɪ) and treated-crocin hypoxia groups. To produce hypoxia, pregnant rats were placed in a hypoxia box. In crocin group, rat offspring received 30 mg/kg crocin via IP injection at P14-28. Control group also received saline injection at the same time. Finally, balance and motor activity in offspring were measured respectively by rotarod and open-field devices. Results showed that motor activity significantly decreased in hypoxia-ɪɪɪ group as compared with sham group (p < 0.01). Balance in hypoxia-ɪɪɪ group significantly decreased as compared with sham group (p < 0.05). As a result, crocin treatment improved all these changes. The results of this study implied that both hypoxia duration and intensity have profound effects on motor activities impairments.

Delayed Onset and Reduced Cognitive Deficits through Pre-Conditioning with 3-Nitropropionic Acid is Dependent on Sex and CAG Repeat Length in the R6/2 Mouse Model of Huntington's Disease

BACKGROUND

Impairments in energy metabolism are implicated in Huntington's disease (HD) pathogenesis. Reduced levels of the mitochondrial enzyme succinate dehydrogenase (SDH), the main element of complex II, are observed post mortem in the brains of HD patients, and energy metabolism defects have been identified in both presymptomatic and symptomatic HD patients.

OBJECTIVE

Chemical preconditioning with 3-nitropropionic acid (3-NP), an irreversible inhibitor of SDH, has been shown to increase tolerance against experimental hypoxia in both heart and brain. Here we studied the effect of chronic preconditioning in the R6/2 mouse model of HD using mice carrying CAG repeat lengths of either 250 or 400 repeats. Both are transgenic fragment models, with 250CAG mice having a more rapid disease progression than 400CAG mice.

METHODS

Low doses of 3-NP (24 mg/kg) were administered via the drinking water and the effect on phenotype progression and cognition function assessed.

RESULTS

After 3-NP treatment there were significant improvements in all aspects of the behavioural phenotype, apart from body weight, with timing and magnitude of improvements dependent on both CAG repeat length and sex. Specifically, a delay in the deterioration of general health (as shown by delayed onset of glycosuria and increased survival) was seen in both male and female 400CAG mice and in female 250CAG mice and was consistent with improved appearance of 3-NP treated R6/2 mice. Male 250CAG mice showed improvements but these were short term, and 3-NP treatment eventually had deleterious effects on their survival rate. When cognitive performance of 250CAG mice was assessed using a two-choice discrimination touchscreen task, we found that female mice showed significant improvements.

DISCUSSION

Together, our results support the idea that energy metabolism contributes to the pathogenesis of HD, and suggest that improving energy deficits might be a therapeutically useful target.

Lack of protracted behavioral abnormalities following intermittent or continuous chronic mild hypoxia in perinatal C57BL/6 mice

Several prospective studies indicated perinatal hypoxia as risk factor for psychiatric disorders like schizophrenia. It is thought that hypoxia prior to or during birth may contribute to alterations leading to the protracted clinical manifestation during young adulthood. However, only a small fraction of children with a history of perinatal hypoxia develop later psychotic symptoms, therefore it is not known if hypoxia alone is sufficient to trigger long-term behavioral changes. Here we exposed C57BL/6 mice from postnatal day 3-7 (P3-P7) to two established paradigms of chronic mild hypoxia (10% ambient O2), intermittent and continuous. Subsequently, mice were analysed during young adult stages using several basic behavioral tests. Previous studies demonstrated severe, but only transient, cortical damage in these paradigms; it is not clear, if these reversible morphological changes are accompanied by long-term behavioral effects. We found that neither intermittent nor continuous perinatal hypoxia induced long-term behavioral alterations. This may be due to the high regenerative capacity of the perinatal brain. Other possibilities include a potential resistance to perinatal hypoxia of the mouse strain used here or a level of hypoxia that was insufficient to trigger significant behavioral changes. Therefore, our data do not exclude a role of perinatal hypoxia as risk factor for psychiatric disorders. They rather suggest that either other, more severe hypoxic conditions like anoxia, or the presence of additional factors (as genetic risk factors) are necessary for generating long-term behavioral abnormalities.

Increased serum brain-derived neurotrophic factor protein upon hypoxia in healthy young men

Exposing animals to brief hypoxic periods leads to neuroprotective ischemic tolerance termed preconditioning. This phenomenon is well documented in the brain, but the underlying mechanisms require further elucidation. As nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are important mediators of maintaining homeostatic conditions in the adult nervous system in terms of physiological and pathophysiological processes, we hypothesized that hypoxic preconditioning might modulate serum neurotrophin concentrations. Hypoxia was induced for 30 min in 14 healthy young men resulting in a constant blood oxygen saturation of 75%. Hyperinsulinemic euglycemic clamps were performed and serum concentrations of BDNF and NGF were measured at baseline, directly after the intervention, and at the end of the session. Overall, serum BDNF concentrations decreased over time by maximally 35% (P = 0.001) while in contrast NGF concentrations remained unchanged. Acute hypoxia alleviated the decrease of BDNF resulting in higher BDNF concentrations as compared to normoxic control (P < 0.01). Our findings show that acute hypoxia results in significantly higher serum BDNF concentrations pointing to a potential role of BDNF in the underlying mechanism of hypoxic preconditioning. Based on its neuroprotective properties, BDNF may be of high clinical relevance for therapeutic options in ischemic neurovascular diseases.

Metabolic downregulation: a key to successful neuroprotection?

BACKGROUND AND PURPOSE

The search for effective neuroprotectants remains frustrating, particularly with regard to specific pharmaceuticals. However, laboratory studies have consistently shown remarkable neuroprotection with 2 nonpharmacological strategies-therapeutic hypothermia and ischemic preconditioning. Recent studies have shown that the mechanism of protection underlying both of these treatments is correlated to downregulation of cellular and tissue metabolism. Thus, understanding the mechanisms underlying such robust protective effects could lead to appropriate translation at the clinical level. In fact, hypothermia is already being used at many centers to improve neurological outcome from cardiac arrest.

METHODS

A systematic review of both topics is presented in terms of underlying pathophysiological mechanisms and application at the clinical level.

RESULTS

Although the mechanisms of protection for both therapeutic strategies are multifold, both share features of downregulating metabolism. Both therapeutic strategies are robust neuroprotectants, but translating them to the clinical arena is challenging, though not impossible, and clinical studies have shown or suggest benefits of both treatments.

CONCLUSIONS

The strategy of metabolic downregulation should be further explored to identify effective neuroprotectants that can be easily applied clinically.

Secondary stroke prevention: inside the vessels and beyond

Cerebral ischaemic stroke is frequently a relapsing, if not chronic, disease. Its incidence is age-dependent, and with the ageing of society the need for effective therapies increases. This review considers current and alternative hypotheses underlying secondary prevention of stroke. Currently, secondary stroke prevention is widely practiced with aspirin (acetylsalicylic acid), a drug that has been in use for more than 100 years. Newer drugs such as ticlopidine and clopidogrel have subsequently been developed, but their efficacy barely surpasses that of aspirin. Other drugs used in secondary stroke prevention include HMG-CoA reductase inhibitors and antihypertensive agents. The endovascular paradigm has shaped the thinking of secondary stroke prevention, and aspirin, ticlopidine and clopidogrel are known as 'platelet inhibitors'; however, their pharmacological and clinical effects are not fully explained within the platelet paradigm. Moreover, in recent years, reduction of stroke incidence has also been observed with HMG-CoA reductase inhibitors, regardless of their lipid-lowering effects. Hence, current understanding needs to be supplemented by considering mechanisms beyond platelet inhibition. Evidence has shown that aspirin, ticlopidine and clopidogrel share neuroprotective properties not explained by the platelet paradigm and that are reminiscent of a preconditioning effect. This neuroprotective mechanism is also shared with HMG-CoA reductase inhibitors.

Neurotoxic effects of repetitive inhibition of oxidative phosphorylation in young adults surfacing with deficits of spatial learning in old age

Little is known about whether events in youth impact performance in old age. We examined spatial navigation in young (4.5 months) and middle-aged (9 months) CD-1 mice in a complex maze after treatment with 3-nitropropionate (3-np; 20 mg/kg body weight; 9 injections intraperitoneally [i.p.] every other day). Young mice treated with 3-np were examined in a mirror version of this maze in old age (22 months) and with a nonreference memory task of an eight-arm radial maze. The performance of young mice was affected to a small degree by treatment with 3-np. However, the performance of middle-aged mice severely declined on 3-np treatment. Animals treated at a young age with 3-np showed learning deficits in old age for both the complex maze and the radial maze. We conclude that exposure to repetitive inhibition of oxidative phosphorylation in youth leads to impairment of spatial learning surfacing in old age.

The stamp of ancestry: roots of behavioral and neuronal impairment in adulthood

Exposure of pregnant animals to noxious conditions affects neuronal function in the offspring. However, exposure or treatment of the maternal animal during pregnancy affects both ancestor and offspring. In the present study, female CD-1 mice were repetitively treated with 3-nitropropionate (3-np), a selective inhibitor of succinic dehydrogenase, exclusively prior to mating. Clinically, mice appeared normal during treatment. Five days after cessation of treatment animals were mated with control male animals. At 4 months of age spatial learning, LTP, NADH autofluorescence, and hypoxic tolerance were alike in controls and the offspring of treated female ancestors. However, an additional metabolic challenge in the offspring unmasks impairment of spatial learning, diminution of long-term potentiation (LTP), an altered protein microenvironment of mitochondrial enzymes, and reduced hypoxic tolerance. We conclude that the exposure of maternal ancestors to subclinical repetitive impairment of oxidative phosphorylation fosters impairment of behavior and neuronal function in the adult offspring, becoming apparent only on additional challenge. This finding may ultimately help to understand the causes of neuronal impairment or even neuropsychiatric disease in old age.

Ischaemic preconditioning: therapeutic implications for stroke?

Ischaemic preconditioning (IPC), also known as ischaemic tolerance (IT), is a phenomenon whereby tissue is exposed to a brief, sublethal period of ischaemia, which activates endogenous protective mechanisms, thereby reducing cellular injury that may be caused by subsequent lethal ischaemic events. The first description of this phenomenon was in the heart, which was reported by Murry and co-workers in 1986. Subsequent studies demonstrated IPC in lung, kidney and liver tissue, whereas more recent studies have concentrated on the brain. The cellular mechanisms underlying the beneficial effects of IPC remain largely unknown. This phenomenon, which has been demonstrated by using various injury paradigms in both cultured neurons and animal brain tissue, may be utilised to identify and characterise therapeutic targets for small-molecule, antibody, or protein intervention. This review will examine the experimental evidence demonstrating the phenomenon termed IPC in models of cerebral ischaemia, the cellular mechanisms that may be involved and the therapeutic implications of these findings.

Improved posthypoxic recovery in vitro on treatment with drugs used for secondary stroke prevention

Besides aspirin several new drugs for inhibition of platelet aggregation and 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibition are used in secondary stroke prevention. Pharmacology and clinical effects, however, are not fully explained by current understanding of underlying mechanisms. Population spike amplitude (PSAP), an established marker of slice integrity, was measured during hypoxia and recovery thereof in hippocampal slices from control CD1 mice (25-35 g) and animals pretreated in vivo with a single i.p. injection of clopidogrel, ticlopidine, or atorvastatine at different time intervals and dosages. Posthypoxic recovery of PSAP was 20 +/- 35% in control CD1 mice. Upon pretreatment with clopidogrel (1-24 h, 0.5-2 mg/kg body weight) an increase up to 81 +/- 20% (p < 0.01 to control) was observed at 1h interval and 1mg/kg. Application of ticlopidine (1-24 h, 1-4 mg/kg body weight) resulted in an improvement of posthypoxic recovery to 61 +/- 41% (p < 0.05 to control) while administration of atorvastatine (1-24 h, 1-4 mg/kg body weight) caused an increase up to 87 +/- 31% (p < 0.01 to control) at 1h interval and 2 mg/kg. On application of these substances in vitro the NADH autofluorescence spectrum in hippocampal slices is blue-shifted suggesting an alteration of oxidative metabolism. The present data demonstrate a shared neuroprotective effect of agents known to inhibit platelets (acetylsalicylic acid, clopidogrel, and ticlopidine) and HMG-CoA reductase (atorvastatine). The time course of this neuroprotective action in the current experimental study (onset within an hour, duration of several hours in contrast to several days) resembles clinical practice in dosing these substances. We hypothesize that an increase of hypoxic tolerance resulting from mild mitochondrial inhibition by these substances is a principal constituent of the effectiveness of these drugs.

Neurotrophic Factor Expression after Focal Brain Ischemia Preceded by Different Preconditioning Strategies

BACKGROUND

Both prolonged brain ischemia and preconditioning (PC) induce expression of neurotrophic factors. However, the influence of PC on their expression after a long-term ischemia remains vague. Previously, we have found various effects of PC on mRNA levels of different cytokines after focal brain ischemia. Thus, we investigated mRNA expression of nerve growth factor, brain-derived neurotrophic factor (BDNF) and ciliary neurotrophic factor after 90-min middle cerebral artery occlusion (MCAo) preceded by ischemic or chemical PC.

METHODS

MCAo was induced in rats using the suture method. PC had been carried out 3 days earlier. There were 4 experimental groups: MCAo alone; ischemic PC and MCAo; chemical PC and MCAo, and sham-operated rats. Expression of mRNAs in the ipsi- and contralateral cortex was studied by semiquantitative RT-PCR at 12 and 24 h after MCAo.

RESULTS

Despite clearly neuroprotective effects of both PC strategies, mRNA levels of neurotrophic factors were similar in tolerant and nontolerant rats. Only BDNF mRNA expression, 12 h after reperfusion, was lower when ischemic PC was applied prior to long-term ischemia.

CONCLUSIONS

These results suggest that PC generally does not change the expression of neurotrophic factor expression after a long-term focal brain ischemia compared to the nontolerant state.

A potential role for β- and γ-crystallins in the vascular remodeling of the eye

We demonstrate that expression of beta- and gamma-crystallins is associated with intraocular vessels during normal vascular development of the eye and also in the Nuc1 rat, a mutant in which the hyaloid vascular system fails to regress normally. Real-Time RT PCR, Western blot and metabolic labeling studies indicate an increased expression of beta- and gamma-crystallins in Nuc1 retina. The increased expression of crystallins was localized to the astrocytes surrounding the intraocular vessels. A similar pattern of crystallin expression was also observed in the retinal vessels during normal development. Cultured human astrocytes exposed to 3-nitropropionic acid, an established model of neuronal hypoxia, increased VEGF expression, as expected, but also increased expression of crystallins. Our data suggest that crystallins may function together with VEGF during vascular remodeling. Interestingly, in human PFV (persistent fetal vasculature) disease, where the hyaloid vasculature abnormally persists after birth, we show that astrocytes express both VEGF and crystallins.

Differential regulation of 5' splice variants of the glutamate transporter EAAT2 in an in vivo model of chemical hypoxia induced by 3-nitropropionic acid

Defective glutamate uptake has been implicated as a pathogenic event of neuronal damage related to cerebral ischemia and hypoxia. In several models of ischemia-hypoxia, a reduced immunoreactivity and altered RNA expression of excitatory amino acid transporter 2 (EAAT2), the major excitatory amino acid transporter, have been reported. However, the gene regulation of EAAT2 under these conditions is incompletely understood. In this study, we investigated alternative splicing of EAAT2 in an in vivo mouse model of chemical hypoxia as induced by 3-nitropropionic acid (3-NP). The neurotoxin 3-NP is an inhibitor of mitochondrial energy production. Furthermore, it is known to inhibit glutamate reuptake directly, representing at least one of the mechanisms responsible for 3-NP-induced neurodegeneration. Here we report an expression analysis of five known (mEAAT2/5UT1-5) and two novel (mEAAT2/5UT6, -7) 5' splice variants of EAAT2 using semiquantitative PCR. The RNA expression was studied at 2, 12, 24, 48, and 72 hr and 7 days after 3-NP administration. mEAAT2/5UT4 and mEAAT2/5UT5 were up-regulated in the frontal cortex and down-regulated in the hippocampus 12-72 hr after chemical hypoxia. In the cerebellum, there was an increased expression of mEAAT2/5UT4 and a down-regulation of mEAAT2/5UT5. mEAAT2/5UT3 show a different regional expression pattern, being regulated in the cerebellum only. mEAAT2/5UT1-7 encoded distinct 5' regulatory sequences, including conserved elements of translational control. It is easily conceivable that expression alterations of 5' splice variants of EAAT2 are related to glutamate transporter malfunction after chemical hypoxia. Our findings contribute to the hypothesis that RNA splicing events can serve as a molecular mechanism of posthypoxic gene regulation.

Increased neuronal hypoxic tolerance induced by repetitive chemical hypoxia

To investigate the effects of time interval and cumulative dosage of repetitive mild cellular hypoxia on shape of neurodegeneration and neuroprotection in mice, population spike amplitude (PSA) was measured during hypoxia and posthypoxic recovery in hippocampal slices from untreated control and mice pretreated in vivo with a single or repeatedly intraperitoneal injection of 3-nitropropionate (3-NP). Posthypoxic recovery of PSA was dose-dependent in single pretreated slices, with maximal recovery on pretreatment attained with 20 mg/kg 3-NP (82 +/- 32%, P < 0.01). Upon 5 and 9 treatments with 20 mg/kg 3-NP (dosage interval 3 days), PSA recovered to (38 +/- 9)% with the difference being not significant vs control group and (72 +/- 45)% with the difference being significant (P < 0.05 to control, P < 0.05 to 5 treatments), respectively. In contrast, with 2 days time interval, recovery after 5 and 9 treatments was (30 +/- 25)% and (16 +/- 14)%, respectively (without significant difference from control). Continued neuroprotection was also observed upon increase of dosage interval to 4 and 5 days. It was suggested that repetitive chemical hypoxia is a model for neurodegenerative disease and continued neuroprotection depending on time interval between repetitive hypoxic episodes rather than cumulative dosage. At appropriate time intervals increased neuronal hypoxic tolerance could be induced with number of hypoxic episodes.

Protein binding of NADH on chemical preconditioning

Chemical preconditioning, an emerging neuroprotective strategy described in recent years, results in preserved energy metabolism during hypoxia via yet unknown mechanisms. The hypoxic increase of NADH content is attenuated by preconditioning. The goal of the present study was to investigate whether attenuation of the hypoxic NADH increase is due to a shift between free and protein-bound NADH. NADH in solution has a fluorescence maximum at 469.2 nm. In untreated mouse hippocampal slices, lambda(control onset) is 456.2 +/- 5.3 nm in CA1 (mean +/- SD; p < 0.01 vs. solution) and 454.6 +/- 6.1 nm in CA3 [p < 0.01 vs. solution, not significant (NS) to lambda(control onset) in CA1]. In slices prepared from animals pretreated in vivo with 20 mg/kg 3-nitropropionate, lambda(preconditioning onset) is 439.2 +/- 5.0 nm (p < 0.001 vs. control) in CA1 and 434.2 +/- 6.4 nm in CA3 (p < 0.001 vs. control; NS to lambda(preconditioning onset) in CA1). In controls, the fluorescence maximum shifts to lambda(control hypoxia) 458.2 +/- 1.3 nm in CA1 (NS vs. onset) and 456.0 +/- 3.6 nm in CA3 (NS vs. onset). On preconditioning with 3-nitropropionate, lambda(preconditioning hypoxia) shifts to 446.4 +/- 4.3 nm in CA1 (p < 0.03 vs. onset) and 438.6 +/- 6.9 nm in CA3 (p < 0.03 vs. onset). Posthypoxic decay of free and protein-bound NADH is diminished after preconditioning. We conclude that the free NADH level is reduced on an increase of hypoxic tolerance by chemical preconditioning. Reduction of free NADH content is maintained during hypoxia after preconditioning.

Impaired tolerance to repetitive hypoxia in hippocampal slices of Cu,Zn superoxide dismutase transgenic mice

Energy metabolism is impaired in the Cu,Zn superoxide dismutase transgenic mouse model of amyotrophic lateral sclerosis. The goal was to investigate tolerance against single and repetitive hypoxia in C57B6SJL-TgN(SOD1-G93A)1GUR mice (G93A mice). Posthypoxic recovery (15 min hypoxia, 45 min recovery) of population spike amplitude in hippocampal region CA1 was 38 +/- 29% (mean +/- SD) in controls and 67 +/- 41% (ns) in G93A mice at day 40. Upon in vivo pretreatment with 20 mg/kg 3-nitropropionate posthypoxic recovery increased to 82 +/- 32% (P < 0.01) in controls and decreased to 35 +/- 33% in G93A mice (P < 0.05 to pretreated controls). Results at day 80 and 110 were similar. We conclude that G93A mice show a long-lasting impairment to sustain repetitive hypoxic episodes whereas tolerance to a single hypoxic episode is comparable to controls.

Induction of ischemic tolerance in rat cortical neurons by 3-nitropropionic acid: chemical preconditioning

Sublethal ischemia leads to increased tolerance against subsequent ischemia. We investigated whether tolerance could also be elicited by mild respiratory-chain inhibition (chemical hypoxia) in a rat neuronal-cell enriched culture system. 3-Nitropropionic acid (3-NPA) caused a concentration-dependent inhibition of succinate-dehydrogenase. Two hours preconditioning with 3-NPA 24-48 h before oxygen-glucose deprivation (OGD) reduced neuronal damage morphologically and reduced lactate deydrogenase (LDH) release up to 72% compared to sham-treated sister cultures without 3-NPA. In an attempt to elucidate transcriptional mechanisms, we found no rapid translocation of the hypoxia-sensitive transcription factors N F-KB or hypoxia-inducible factor-I (HIF-I) at 3-NPA concentrations sufficient to trigger tolerance against OGD. In accordance to previous in vivo and brain slice data, we conclude that 3-NPA chemically induces tolerance against oxygen-glucose deprivation in vitro. However, the underlying mechanisms remain elusive.

Primary hypoxic tolerance and chemical preconditioning during estrus cycle in mice

BACKGROUND AND PURPOSE

Exogenous application of estrogens or progesterone ameliorates hypoxic/ischemic cell damage. This study investigates whether values of primary and induced hypoxic tolerance vary endogenously during the estrus cycle in female mice.

METHODS

Population spike amplitude (PSA) and NADH were measured during hypoxic hypoxia and recovery in hippocampal slices from untreated control animals (C slices) and slices prepared from animals pretreated in vivo with a single intraperitoneal injection of 3-nitropropionate (3NP) (3NP slices) or acetylsalicylate (ASA) (ASA slices).

RESULTS

Posthypoxic recovery of PSA was dose dependent in 3NP slices from males, with maximal recovery on pretreatment attained with 20 mg/kg 3NP (82+/-32% [mean+/-SD]; C slices, 38+/-29%; P<0.01). PSA recovered to 17+/-12% in C slices during proestrus, 43+/-23% during estrus, and 63+/-44% during diestrus. In 3NP slices, recovery of PSA increased to 57+/-36% (P<0. 05) during proestrus. Hypoxic tolerance was not increased in other stages of the estrus cycle. Hypoxic NADH increase during proestrus declined from 212+/-76% in C slices to 133+/-11% in 3NP slices (P<0. 05). Recovery of PSA in ASA slices was 75+/-36% (P<0.01 versus control) in males and 48+/-34% during proestrus (P<0.05 versus ASA slices from males).

CONCLUSIONS

Primary and induced hypoxic tolerance are endogenously modulated during the estrus cycle. Differences in hypoxic oxidative energy metabolism mediate part of the differential tolerance. Experimental and clinical therapeutic strategies against cerebral ischemia/hypoxia need to consider sex-related dependence.

3-Nitropropionic acid induces ischemic tolerance in gerbil hippocampus in vivo

Systemic administration of high dose of 3-nitropropionic acid (3-NP), an irreversible inhibitor of succinate dehydrogenase, causes neurodegeneration within the striatum in vivo. However, it has been reported that pretreatment with low dose of 3-NP may increase tolerance to subsequent hypoxia in hippocampal slices. The present study investigated whether ischemic tolerance can be induced in gerbil hippocampus in vivo by low dose of 3-NP. After pretreatment with 3-NP (single i.p. injection of 3 mg/kg, body weight 2-4 days prior to forebrain ischemia), the number of surviving neurons in CA1 region of hippocampus against succeeding forebrain ischemia was significantly higher than in the ischemic control group. Our results show that chemical preconditioning with low dose of 3-NP induces ischemic tolerance in gerbil hippocampus in vivo.

Acetylsalicylic acid increases tolerance against hypoxic and chemical hypoxia

BACKGROUND AND PURPOSE

Treatment with acetylsalicylic acid (ASA) is established for secondary stroke prevention. Recent studies showed neuroprotection of ASA against glutamatergic excitants. The goal of this study was to investigate the time course of neuroprotection of ASA against indirect excitotoxicity by hypoxic hypoxia and chemical hypoxia.

METHODS

Population spike amplitude (PSA) and ATP content were measured in hippocampal slices from untreated control animals (c-slices) and slices prepared from animals pretreated in vivo with a single intraperitoneal injection of 20 mg/kg body wt ASA 1 to 48 hours before slice preparation (p-slices).

RESULTS

Posthypoxic recovery of PSA was 30% in c-slices (15 minutes of hypoxia, 45 minutes of recovery). When c-slices were treated in vitro for 15 minutes with 20 mg/L ASA 30 minutes before hypoxia, posthypoxic recovery improved to 82 +/- 4% (mean +/- SE, P < .01). In p-slices, posthypoxic recovery of PSA improved in a time-dependent manner. With a time interval of 1 hour between in vivo pretreatment with ASA and slice preparation, posthypoxic recovery of PSA was 64 +/- 16% (P < .05). With time intervals of 6 hours, 24 hours, and 48 hours, posthypoxic recovery of PSA was 87 +/- 19% (P < .01), 59 +/- 12%, and 40 +/- 9%, respectively. Pretreatment with ASA in vitro or in vivo decreased the decline of ATP content during hypoxic hypoxia and chemical hypoxia (inhibition of succinic dehydrogenase by 3-nitropropionic acid). When extracellular glucose was reduced to 4 mmol/L, no difference was observed between c-slices and p-slices.

CONCLUSIONS

We conclude that ASA is neuroprotective against hypoxic hypoxia and chemical hypoxia and delays the decline of intracellular ATP content.

NMDA-antagonists reverse increased hypoxic tolerance by preceding chemical hypoxia

Glutamate antagonists mitigate hypoxic damage upon acute inhibition of energy metabolism. The goal of this study was to investigate their effect on increased hypoxic tolerance induced by preceding chemical inhibition of energy metabolism. While recovery of population spike amplitude (psap) is 30% of onset in slices prepared from control animals (15 min hypoxia, 45 min recovery), recovery exceeds 90% in slices prepared from animals that underwent mild chemical hypoxia in vivo by treatment with 20 mg/kg 3-nitropropionic acid 1 h prior to slice preparation (p-slices). In p-slices perfused for 5 min with D(-)-2-amino-5-phosphonopentanoic acid (APV) (100 microM) 45 min prior to hypoxia, recovery declines to 42 +/- 13% (mean +/- SEM). In contrast, posthypoxic recovery after similar perfusion with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (10 microM) is 72 +/- 15% (P < 0.05). We conclude that increased hypoxic tolerance is abolished by N-methyl-D-aspartate (NMDA)-antagonists but not non-NMDA-antagonists.