An incomplete cerebral ischemia produced a delayed dysfunction in the rat hippocampal system

Neuroprotective Effects of Chrysin Mediated by Estrogenic Receptors Following Cerebral Ischemia and Reperfusion in Male Rats

Introduction

Ischemic stroke is one of the leading causes of morbidity and mortality worldwide. Neuroprotective strategies were reported to attenuate cognitive deficits after ischemic incidents. Here we studied the neuroprotective potential of chrysin in a rat model of cerebral Ischemia/Reperfusion (I/R) in the presence or absence of Estrogen Receptors (ERs).

Methods

Adult male Wistar rats were pretreated with chrysin (CH) (CH; 30 mg/kg; gavage; for 21 consecutive days) alone or with selective ERs antagonists (ERα antagonist MPP; ERβ antagonist PHTPP; IP) or nonselective ERs antagonist (ICI182780; IP). Then, the bilateral common carotid arteries were occluded for 20 min, which was followed by 72 h reperfusion. Subsequently, cognitive performance was evaluated by Morris Water Maze (MWM) and shuttle box tasks, and afterward, their hippocampi were removed for ELISA assays and H&E staining. Oxidative indicators Malondialdehyde (MDA) and Glutathione Peroxidase (GPx), as well as inflammation mediators interleukin (IL)-1β and tumor necrosis factor-alpha (TNFα), were measured using commercial kits.

Results

Results of the current study showed that the anti-oxidative and anti-inflammatory properties of CH are possible mechanisms that could improve cognitive deficits and prevent neuronal cell death following I/R (P<0.001). These effects were reversed by ICI182780 (P>0.05). Furthermore, when chrysin was co-treated with ERβ antagonist, PHTPP showed a weak neuroprotective effect in I/R rats. However, these parameters were not significantly different when chrysin was combined with ERα antagonist MPP.

Conclusion

Our data confirm that chrysin could potentially serve as a neuroprotective agent against devastating effects of cerebral I/R injury, which may be mediated via its interaction with ERs, especially ERβ.

Protective effects of Chrysin against memory impairment, cerebral hyperemia and oxidative stress after cerebral hypoperfusion and reperfusion in rats

Stroke is devastating and a leading cause of morbidity and mortality worldwide. Cerebral ischemia-reperfusion and its subsequent reactive hyperemia lead to neuronal damage in the hippocampus and cognitive decline. Chrysin (5, 7-dihydroxyflavone) is a well-known member of the flavonoid family with antioxidant and neuroprotective effects. Therefore, in the present study, the aim was to investigate whether chrysin will be able to recover the brain function caused by ischemia-reperfusion (I/R) in rats. Adult male Wistar rats (250-300 g) were randomly divided into five groups: and submitted to cerebral I/R or a sham surgery after three-weeks of pretreatment with chrysin (CH; 10, 30 and 100 mg/kg; P.O.) and/or normal saline containing %5 DMSO. Subsequently, sensorimotor scores, cognition, local cerebral blood flow, extracellular single unit, and histological parameters were evaluated following I/R. Hippocampus was used to evaluate biomarkers including: oxidative stress parameters and prostaglandin E2 (PGE2) using ELISA kits. Data showed that pretreatment with chrysin significantly improved sensorimotor signs, passive avoidance memory, and attenuated reactive hyperemia, and increased the average number of spikes/bin (p < 0.001). Furthermore, chrysin pre-treatment significantly decreased the levels of MDA, NO, and PGE2 (p < 0. 001), while increased the levels of GPX and the number of surviving cells in the hippocampal CA1 region (p < 0.01, p < 0.001; respectively). This study demonstrates that chrysin may have beneficial effects in the treatment of cognitive impairment and help recover the brain dysfunction induced by I/R.

Cardiac Arrest Induces Ischemic Long-Term Potentiation of Hippocampal CA1 Neurons That Occludes Physiological Long-Term Potentiation

Ischemic long-term potentiation (iLTP) is a form of synaptic plasticity that occurs in acute brain slices following oxygen-glucose deprivation. In vitro, iLTP can occlude physiological LTP (pLTP) through saturation of plasticity mechanisms. We used our murine cardiac arrest and cardiopulmonary resuscitation (CA/CPR) model to produce global brain ischemia and assess whether iLTP is induced in vivo, contributing to the functionally relevant impairment of pLTP. Adult male mice were subjected to CA/CPR, and slice electrophysiology was performed in the hippocampal CA1 region 7 or 30 days later. We observed increased miniature excitatory postsynaptic current amplitudes, suggesting a potentiation of postsynaptic AMPA receptor function after CA/CPR. We also observed increased phosphorylated GluR1 in the postsynaptic density of hippocampi after CA/CPR. These data support the in vivo induction of ischemia-induced plasticity. Application of a low-frequency stimulus (LFS) to CA1 inputs reduced excitatory postsynaptic potentials in slices from mice subjected to CA/CPR, while having no effects in sham controls. These results are consistent with a reversal, or depotentiation, of iLTP. Further, depotentiation with LFS partially restored induction of pLTP with theta burst stimulation. These data provide evidence for iLTP following in vivo ischemia, which occludes pLTP and likely contributes to network disruptions that underlie memory impairments.

Protective Effects of Enriched Environment Against Transient Cerebral Ischemia-Induced Impairment of Passive Avoidance Memory and Long-Term Potentiation in Rats

Introduction

Enriched Environment (EE), a complex novel environment, has been demonstrated to improve synaptic plasticity in both injured and intact animals. The present study investigated the capacity of an early environmental intervention to normalize the impairment of passive avoidance memory and Long-Term Potentiation (LTP) induced by transient bilateral common carotid artery occlusion (2-vessel occlusion, 2VO) in rats.

Methods

After weaning, young Wistar rats (22 days old) were housed in EE or Standard Environment (SE) for 40 days. Transient (30-min) incomplete forebrain ischemia was induced 4 days before the passive avoidance memory test and LTP induction.

Results

The transient forebrain ischemia led to impairment of passive avoidance memory and LTP induction in the Perforant Path-Dentate Gyrus (PP-DG) synapses. Interestingly, housing and growing in EE prior to 2VO was found to significantly reverse 2VO-induced cognitive and LTP impairments.

Conclusion

Our results suggest that early housing and growing in EE exhibits therapeutic potential to normalize cognitive and LTP abnormalities induced by 2VO ischemic model in rats.

Long-term depression in Purkinje neurons is persistently impaired following cardiac arrest and cardiopulmonary resuscitation in mice

Cardiac arrest and cardiopulmonary resuscitation (CA/CPR) produce brain ischemia that results in cognitive and motor coordination impairments subsequent to injury of vulnerable populations of neurons, including cerebellar Purkinje neurons. To determine the effects of CA/CPR on plasticity in the cerebellum, we used whole cell recordings from Purkinje neurons to examine long-term depression (LTD) at parallel fiber (PF) synapses. Acute slices were prepared from adult male mice subjected to 8 min cardiac arrest at 1, 7, and 30 days after resuscitation. Concurrent stimulation of PF and climbing fibers (CFs) resulted in robust LTD of PF-evoked excitatory postsynaptic currents (EPSCs) in controls. LTD was absent in recordings obtained from mice subjected to CA/CPR, with no change in EPSC amplitude from baseline at any time point tested. AMPA and mGluR-mediated responses at the PF were not altered by CA/CPR. In contrast, CF-evoked NMDA currents were reduced following CA/CPR, which could account for the loss of LTD observed. A loss of GluN1 protein was observed following CA/CPR that was surprisingly not associated with changes in mRNA expression. These data demonstrate sustained impairments in synaptic plasticity in Purkinje neurons that survive the initial injury and which likely contribute to motor coordination impairments observed after CA/CPR.

Electroacupuncture Ameliorates Learning and Memory and Improves Synaptic Plasticity via Activation of the PKA/CREB Signaling Pathway in Cerebral Hypoperfusion

Electroacupuncture (EA) has shown protective effects on cognitive decline. However, the underlying molecular mechanisms are ill-understood. The present study was undertaken to determine whether the cognitive function was ameliorated in cerebral hypoperfusion rats following EA and to investigate the role of PKA/CREB pathway. We used a rat 2-vessel occlusion (2VO) model and delivered EA at Baihui (GV20) and Dazhui (GV14) acupoints. Morris water maze (MWM) task, electrophysiological recording, Golgi silver stain, Nissl stain, Western blot, and real-time PCR were employed. EA significantly (1) ameliorated the spatial learning and memory deficits, (2) alleviated long-term potentiation (LTP) impairment and the reduction of dendritic spine density, (3) suppressed the decline of phospho-CREB (pCREB) protein, brain-derived neurotrophic factor (BDNF) protein, and microRNA132 (miR132), and (4) reduced the increase of p250GAP protein of 2VO rats. These changes were partially blocked by a selective protein kinase A (PKA) inhibitor, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinoline-sulfonamide (H89), suggesting that the PKA/CREB pathway is potentially involved in the effects of EA. Moreover, any significant damage to the pyramidal cell layer of CA1 subregion was absent. These results demonstrated that EA could ameliorate learning and memory deficits and alleviate hippocampal synaptic plasticity impairment of cerebral hypoperfusion rats, potentially mediated by PKA/CREB signaling pathway.

Therapeutic hypothermia protects against ischemia-induced impairment of synaptic plasticity following juvenile cardiac arrest in sex-dependent manner

Pediatric cardiac arrest (CA) often leads to poor neurologic outcomes, including deficits in learning and memory. The only approved treatment for CA is therapeutic hypothermia, although its utility in the pediatric population remains unclear. This study analyzed the effect of mild therapeutic hypothermia after CA in juvenile mice on hippocampal neuronal injury and the cellular model of learning and memory, termed long-term potentiation (LTP). Juvenile mice were subjected to cardiac arrest and cardiopulmonary resuscitation (CA/CPR) followed by normothermia (37°C) and hypothermia (30°C, 32°C). Histological injury of hippocampal CA1 neurons was performed 3days after resuscitation using hematoxylin and eosin (H&E) staining. Field excitatory post-synaptic potentials (fEPSPs) were recorded from acute hippocampal slices 7days after CA/CPR to determine LTP. Synaptic function was impaired 7days after CA/CPR. Mice exposed to hypothermia showed equivalent neuroprotection, but exhibited sexually dimorphic protection against ischemia-induced impairment of LTP. Hypothermia (32°C) protects synaptic plasticity more effectively in females, with males requiring a deeper level of hypothermia (30°C) for equivalent protection. In conclusion, male and female juvenile mice exhibit equivalent neuronal injury following CA/CPR and hypothermia protects both males and females. We made the surprising finding that juvenile mice have a sexually dimorphic response to mild therapeutic hypothermia protection of synaptic function, where males may need a deeper level of hypothermia for equivalent synaptic protection.

Increasing small conductance Ca2+-activated potassium channel activity reverses ischemia-induced impairment of long-term potentiation

Global cerebral ischemia following cardiac arrest and cardiopulmonary resuscitation (CA/CPR) causes injury to hippocampal CA1 pyramidal neurons and impairs cognition. Small conductance Ca(2+)-activated potassium channels type 2 (SK2), expressed in CA1 pyramidal neurons, have been implicated as potential protective targets. Here we showed that, in mice, hippocampal long-term potentiation (LTP) was impaired as early as 3 h after recovery from CA/CPR and LTP remained impaired for at least 30 days. Treatment with the SK2 channel agonist 1-Ethyl-2-benzimidazolinone (1-EBIO) at 30 min after CA provided sustained protection from plasticity deficits, with LTP being maintained at control levels at 30 days after recovery from CA/CPR. Minimal changes in glutamate release probability were observed at delayed times after CA/CPR, implicating post-synaptic mechanisms. Real-time quantitative reverse transcriptase-polymerase chain reaction indicated that CA/CPR did not cause a loss of N-methyl-D-aspartate (NMDA) receptor mRNA at 7 or 30 days after CA/CPR. Similarly, no change in synaptic NMDA receptor protein levels was observed at 7 or 30 days after CA/CPR. Further, patch-clamp experiments demonstrated no change in functional synaptic NMDA receptors at 7 or 30 days after CA/CPR. Electrophysiology recordings showed that synaptic SK channel activity was reduced for the duration of experiments performed (up to 30 days) and that, surprisingly, treatment with 1-EBIO did not prevent the CA/CPR-induced loss of synaptic SK channel function. We concluded that CA/CPR caused alterations in post-synaptic signaling that were prevented by treatment with the SK2 agonist 1-EBIO, indicating that activators of SK2 channels may be useful therapeutic agents to prevent ischemic injury and cognitive impairments.

Reperfusion does not improve impaired rapid-onset cortical plasticity in patients with severe stenosis of the internal carotid artery

Background

Severe stenosis of the internal carotid artery (ICA) has been associated with impaired cognition in patients, but its effect on rapid-onset cortical plasticity is not known. Carotid endarterectomy (CEA) in patients with severe ICA stenosis reduces stroke risk, but the impact on cognition or physiology of the respective hemisphere remains controversial.

Methods/Results

16 patients with severe stenosis of the ICA and 16 age and sex matched controls were included. Rapid-onset cortical plasticity was assessed using the paired-associative stimulation (PAS) protocol. PAS models long-term synaptic potentiation in human motor cortex, combining repetitive stimulation of the peripheral ulnar nerve with transcranial magnetic stimulation of the contralateral motor cortex. Cognitive status was assessed with a neuropsychological test battery. In patients, verbal learning and rapid-onset cortical plasticity were significantly reduced as compared to controls. Identical follow-up tests in 9 of the 16 patients six months after CEA revealed no improvement of cognitive parameters or cortical plasticity.

Conclusions

Decreased rapid-onset cortical plasticity in patients with severe stenosis of the ICA was not improved by reperfusion. Thus, other strategies known to increase plasticity should be tested for their potential to improve cortical plasticity and subsequently cognition in these patients.

Effects of birth asphyxia on neonatal hippocampal structure and function in the spiny mouse

Studies of human neonates, and in animal experiments, suggest that birth asphyxia results in functional compromise of the hippocampus, even when structural damage is not observable or resolves in early postnatal life. The aim of this study was to determine if changes in hippocampal function occur in a model of birth asphyxia in the precocial spiny mouse where it is reported there is no major lesion or infarct. Further, to assess if, as in human infants, this functional deficit has a sex-dependent component. At 37 days gestation (term=39 days) spiny mice fetuses were either delivered immediately by caesarean section (control group) or exposed to 7.5min of in utero asphyxia causing systemic acidosis and hypoxia. At 5 days of age hippocampal function was assessed ex vivo in brain slices, or brains were collected for examination of structure or protein expression. This model of birth asphyxia did not cause infarct or cystic lesion in the postnatal day 5 (P5) hippocampus, and the number of proliferating or pyknotic cells in the hippocampus was unchanged, although neuronal density in the CA1 and CA3 was increased. Protein expression of synaptophysin, brain-derived neurotrophic factor (BDNF), and the inositol trisphosphate receptor 1 (IP(3)R1) were all significantly increased after birth asphyxia, while long-term potentiation (LTP), paired pulse facilitation (PPF), and post-tetanic potentiation (PTP) were all reduced at P5 by birth asphyxia. In control P5 pups, PPF and synaptic fatigue were greater in female compared to male pups, and after birth asphyxia PPF and synaptic fatigue were reduced to a greater extent in female vs. male pups. In contrast, the asphyxia-induced increase in synaptophysin expression and neuronal density were greater in male pups. Thus, birth asphyxia in this precocial species causes functional deficits without major structural damage, and there is a sex-dependent effect on the hippocampus. This may be a clinically relevant model for assessing treatments delivered either before or after birth to protect this vulnerable region of the developing brain.

Oxaloacetate restores the long-term potentiation impaired in rat hippocampus CA1 region by 2-vessel occlusion

Various acute brain pathological conditions are characterized by the presence of elevated glutamate concentrations in the brain interstitial fluids. It has been established that a decrease in the blood glutamate level enhances the brain-to-blood efflux of glutamate, removal of which from the brain may prevent glutamate excitotoxicity and its contribution to the long-lasting neurological deficits seen in stroke. A decrease in blood glutamate level can be achieved by exploiting the glutamate-scavenging properties of the blood-resident enzyme glutamate-oxaloacetate transaminase, which transforms glutamate into 2-ketoglutarate in the presence of the glutamate co-substrate oxaloacetate. The present study had the aim of an evaluation of the effects of the blood glutamate scavenger oxaloacetate on the impaired long-term potentiation (LTP) induced in the 2-vessel occlusion ischaemic model in rat. Transient (30-min) incomplete forebrain ischaemia was produced 72 h before LTP induction. Although the short transient brain hypoperfusion did not induce histologically identifiable injuries in the CA1 region (Fluoro-Jade B, S-100 and cresyl violet), it resulted in an impaired LTP function in the hippocampal CA1 region without damaging the basal synaptic transmission between the Schaffer collaterals and the pyramidal neurons. This impairment could be fended off in a dose-dependent manner by the intravenous administration of oxaloacetate in saline (at doses between 1.5 mmol and 0.1 mumol) immediately after the transient hypoperfusion. Our results suggest that oxaloacetate-mediated blood and brain glutamate scavenging contributes to the restoration of the LTP after its impairment by brain ischaemia.

Effects of propofol and halothane on long-term potentiation in the rat hippocampus after transient cerebral ischaemia

BACKGROUND

Propofol is reported to have protective effects on cerebral ischaemia-induced neuronal death. The aim of this study was to explore whether propofol and halothane can protect hippocampal neuronal function from ischaemic injury during general anaesthesia in rats.

METHODS

Rats were divided into 2-vessel occlusion (incomplete cerebral ischaemia) and 4-vessel occlusion (complete cerebral ischaemia) groups consisting of three subgroups each (sham-operated, propofol and halothane groups). One hour after starting propofol 1 mg kg(-1) min(-1) with 30% O2 and N2 or halothane 0.8% in 30% O2 and N2 rats with or without bilateral vertebral artery occlusion had bilateral common carotid arteries occluded by vessel clips for 10 min. Anaesthesia was maintained for another 1 h. Seven days after ischaemia-reperfusion, hippocampal long-term potentiation in the perforant path-dentate gyrus synapse was determined as an index of cerebral outcome.

RESULTS

In the propofol groups, the formation of long-term potentiation was significantly impaired in the 2-vessel and 4-vessel occlusion groups compared to the respective sham-operated groups (P < 0.01 and P < 0.05, respectively). Impaired formation of long-term potentiation in propofol groups was comparable to that in halothane groups. The formation of long-team potentiation in the propofol and halothane 2-vessel group was not significantly different from that in the awake 2-vessel group.

CONCLUSIONS

Propofol and halothane administered during ischaemia do not possess protective effects against hippocampal neuronal dysfunction induced by cerebral ischaemia-reperfusion as evaluated by our transient ischaemic rat models.

Dehydroepiandrosterone sulfate prevents ischemia-induced impairment of long-term potentiation in rat hippocampal CA1 by up-regulating tyrosine phosphorylation of NMDA receptor

We have reported that dehydroepiandrosterone sulfate (DHEAS) reduces the threshold for long-term potentiation (LTP) in Shaffer collateral-CA1 synapses through the amplification of Src-dependent NMDA receptor signaling. The present study is a follow-up of the above reports, aiming at evaluating the effects of DHEAS on the impaired LTP in reversible forebrain ischemic rats. Transient (20 min) incomplete forebrain ischemia led to an impaired LTP in the hippocampal CA1 region without damages to the basal synaptic transmission between the Shaffer collaterals and pyramidal neurons. Repetitive administrations of DHEAS (20 mg/kg for 3 days) from the first 3 h of reperfusion, but not acute DHEAS application (50 microM), prevent the impairment of LTP produced by ischemia. Co-administration of the specific sigma(1) receptor antagonist NE100 with DHEAS completely prevented the protective effect of DHEAS. In contrast, progesterone (PRGO) not only had no protective effect against the ischemic LTP impairment, but also attenuated the protective effect of DHEAS on the impaired LTP. Tyrosine phosphorylation of NMDA receptor subunit 2B (NR2B) significantly decreased after ischemia, whereas that of NR1 had no obvious change. Furthermore, the repetitive administration of DHEAS improved the reduction in tyrosine phosphorylation of NR2B. These findings suggest that the repetitive activation of sigma(1) receptor induced by DHEAS might prevent the ischemic LTP impairment through regulating the tyrosine phosphorylation of NR2B.

Temporal effects of edaravone, a free radical scavenger, on transient ischemia-induced neuronal dysfunction in the rat hippocampus

We examined the effect of a free radical scavenger edaravone on ischemia/reperfusion-induced impairment of long-term potentiation in the perforant path-dentate gyrus synapses of the rat hippocampus, as a measure of functional outcome 4 days after transient global ischemia (2-vessel occlusion, 10 min). Edaravone (3 and 10 mg/kg, i.v.) immediately after reperfusion (Day 0) alleviated ischemia-induced impairment of long-term potentiation in a dose-related manner, whereas treatment on Day 1 or 4 after reperfusion failed to rescue the impaired long-term potentiation. Edaravone administration on Day 0 also prevented the post-ischemic increase in hydroxyl radical formation and the expression of vascular endothelial growth factor, basic fibroblast growth factor and neuronal and inducible nitric oxide synthases of the hippocampus. Thus, edaravone protected the rat hippocampus from ischemia-induced long-term potentiation impairment with a therapeutic time window, suggesting that free radical formation after ischemia/reperfusion is a pivotal trigger of neurofunctional complications after global ischemic stroke.

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.

Effects of lactate/pyruvate on synaptic plasticity in the hippocampal dentate gyrus

The present study was undertaken to investigate whether monocarboxylates (lactate and pyruvate) can support synaptic plasticity. As an index of synaptic activity, population spikes (PS) were recorded in the hippocampal dentate gyrus. Replacement of glucose with monocarboxylates maintained PS after transient depression, and supported a similar degree of paired-pulse facilitation (PPF). Monocarboxylates-supported long-term potentiation (LTP), but the degree of enhancement was less than that of glucose-supported PS. Monocarboxylates failed to support long-term depression (LTD). These results indicate that monocarboxylates could serve as sufficient substrates for PPF, and that they could also support LTP but with less efficiency than glucose.

Effects of ibudilast on hippocampal long-term potentiation and passive avoidance responses in rats with transient cerebral ischemia

The present study evaluated the effects of ibudilast on impaired passive avoidance responses and hippocampal long-term potentiation (LTP) caused by transient cerebral ischemia in rats. The hippocampal nerve cell density was also measured. The latency determined in retention trials of passive avoidance shortened significantly in the 4-vessel occlusion (4VO) group (in which four blood vessels were occluded for 20 min to cause cerebral ischemia). A significant recovery in the latency was observed by administration of ibudilast (10 mg kg (-1)). The population spike amplitude in both the hippocampal CA1 region and perforant path-dentate gyrus synapses was potentiated by tetanus stimulation in the sham-operated group, while in the 4VO group, LTP was significantly inhibited. This inhibition was reversed by administration of ibudilast (10 mg kg (-1)). A marked reduction of cell densities in the CA1 region was observed in the 4VO group compared with the normal group. The nerve cell density in the hippocampal CA1 region was decreased by 20 min of cerebral ischemia. Ibudilast significantly inhibited the reduction of cell densities in a dose-dependent manner. In contrast, the cell density in the dentate gyrus was comparable in the 4VO and normal groups, and no significant changes were observed in the ibudilast groups. These findings suggest that ibudilast might possess neuronally protective properties, i.e. protecting neurons not only from deaths but also from functional damage due to certain cerebral ischemia.

Transient changes of brain-derived neurotrophic factor (BDNF) mRNA expression in hippocampus during moderate ischemia induced by chronic bilateral common carotid artery occlusions in the rat

Chronic bilateral common carotid artery occlusion (BCCAO) induces moderate ischemia (oligemia) in the rat forebrain in the absence of overt neuronal damage. In situ hybridization for brain-derived neurotrophic factor (BDNF) mRNA was used to search for a molecular response to moderate ischemia. BDNF mRNA was significantly increased in the hippocampal granule cells at 6 h of occlusion (ANOVA, Tukey test P<0.05). At 1, 7 and 14 days BDNF mRNA levels returned to control levels. The frequency of BDNF gene expression at 6 h was 83%, which was significantly higher than the 7% incidence of histological injury in the hippocampus (Fisher's exact test, P<0.002). Cerebral blood flow was reduced to 75% of control levels in the hippocampus after 1 week of BCCAO when measured with the autoradiographic method. Measurements of tissue flow with a microprobe for laser Doppler flow excluded decreases into the ischemic range during the period when elevated gene expression was observed. Prolonged moderate ischemia (oligemia) is a sufficient stimulus for BDNF gene expression in the hippocampus. These molecular studies provide direct evidence for an involvement of the hippocampus in the BCCAO model.

Different effects of anxiolytic agents, diazepam and 5-HT(1A) agonist tandospirone, on hippocampal long-term potentiation in vivo

Benzodiazepines and 5-HT(1A) agonists have been widely used as anxiolytic agents. Some clinical reports document that 5-HT(1A) agonists induce memory impairment to a lesser degree than diazepam. In the present study, we compared the effects of diazepam and 5-HT(1A) agonist, tandospirone, on hippocampal long-term potentiation (LTP) in Schaffer collateral-CA1, mossy fiber-CA3 and perforant path-dentate gyrus synapses. In the diazepam-injected group, the reduction in LTP was observed in all three types of synapses, although the effective dose differed among these. In the tandospirone-injected group, no reduction in LTP was observed except in Schaffer-CA1 synapses. In addition, population spike amplitude was potentiated by tandospirone in mossy fiber-CA3 synapses in a dose-dependent manner. Thus, there was a discrepancy in the effects on hippocampal LTP between diazepam and tandospirone, possibly reflecting the reported clinical properties of these drugs, in that 5-HT(1A) partial agonists do not affect learning and memory, whereas diazepam impairs memory function.

Functional differentiation of multiple perilesional zones after focal cerebral ischemia

Transient and permanent focal cerebral ischemia results in a series of typical pathophysiologic events. These consequences evolve in time and space and are not limited to the lesion itself, but they can be observed in perilesional (penumbra) and widespread ipsi- and sometimes contralateral remote areas (diaschisis). The extent of these areas is variable depending on factors such as the type of ischemia, the model, and the functional modality investigated. This review describes some typical alterations attributable to focal cerebral ischemia using the following classification scheme to separate different lesioned and perilesional areas: (1) The lesion core is the brain area with irreversible ischemic damage. (2) The penumbra is a brain region that suffers from ischemia, but in which the ischemic damage is potentially, or at least partially, reversible. (3) Remote brain areas are brain areas that are not directly affected by ischemia. With respect to the etiology, several broad categories of remote changes may be differentiated: (3a) remote changes caused by brain edema; (3b) remote changes caused by waves of spreading depression; (3c) remote changes in projection areas; and (3d) remote changes because of reactive plasticity and systemic effects. The various perilesional areas are not necessarily homogeneous; but a broad differentiation of separate topographic perilesional areas according to their functional state and sequelae allows segregation into several signaling cascades, and may help to understand the functional consequences and adaptive processes after focal brain ischemia.

Deficits in nitric oxide production after tetanic stimulation are related to the reduction of long-term potentiation in Schaffer-CA1 synapses in aged Fischer 344 rats

In the present study, we investigated whether nitric oxide (NO) production after tetanic stimulation is involved in long-term potentiation (LTP) in Schaffer-CA1 synapses in both young adult and aged rats. The changes in both the population spike amplitude and NO metabolites, nitrite (NO2-) and nitrate (NO3-), in the CA1 region were simultaneously determined before and after tetanic stimulation. Increases in NOx (NO2- plus NO3-) levels in the CA1 region were observed after tetanic stimulation in young adult rats as well as increase in the population spike amplitude. In aged rats, LTP was significantly inhibited compared with that in young adult rats. No increase in NOx level after tetanic stimulation was observed in aged rats. These findings directly demonstrated that NO production might be involved in the process of LTP formation in Schaffer-CA1 synapses of the rat hippocampus, and that the deficiency of hippocampal NO production might be responsible for reduction of LTP formation in aged rats.

Effects of bifemelane on incomplete cerebral ischaemia-induced reduction of long-term potentiation in rat hippocampal neurones in vivo

In the present study, we investigated the effects of bifemelane on the reduction of hippocampal long-term potentiation after transient ischaemia. Bilateral common carotid arteries were clamped for 10 min. in halothane-anaesthetized rats. Thirty min. before occlusion, bifemelane (25 mg/kg, intraperitoneally) or saline was administered to the rats. Four days after occlusion, we measured long-term potentiation in Schaffer collateral-CA1 synapses and perforant path-dentate gyrus synapses in vivo. Long-term potentiation was significantly reduced in both the Schaffer collateral-CA1 and perforant path-dentate gyrus synapses in the saline-injected group. However bifemelane decreased the ischaemia-induced reduction of long-term potentiation in perforant path-dentate gyrus synapses, but not in Schaffer collateral-CA1 synapses. The findings suggest that bifemelane deserves further attention with regard to possible protective role in ischaemia.

Effects of an interleukin-1beta analogue [Lys-D-Pro-Thr], on incomplete cerebral ischemia-induced inhibition of long-term potentiation in rat hippocampal neurons in vivo

Although interleukin-1beta (IL-1beta) has recently been implicated in neuronal cell death in vitro and in vivo after global forebrain ischemia, the role of IL-1beta in the functional injuries, i.e. impairment of synaptic transmission, after cerebral ischemia that does not cause neuronal death in the nervous system remains unknown. To address this question, we investigated the effect of short-term incomplete ischemia without apparent neural death on hippocampal long-term potentiation (LTP) in anesthetized rats, and examined the possible role of IL-1beta as an intermediary in this effect. Short-term incomplete cerebral ischemia (10 min) was induced in halothane-anesthetized rats by bilaterally clamping the common carotid arteries. Four days after ischemia, functional injuries in neuronal transmission in the hippocampal formation were observed without significant changes in pathological studies such as neuronal cell death. The LTP elicited in both Shaffer-CA1 synapses and perforant path-dentate gyrus synapses was significantly inhibited by the short-term incomplete ischemia. This inhibition of LTP was blocked by IL-1beta tripeptide antagonist (Lys-D-Pro-Thr), suggesting that the inhibitory effect of mild ischemia on synaptic potentials and LTP may be mediated by the generation of IL-1beta. These findings have important implications for the role of IL-1beta in not only neuronal cell death but also functional injuries without cell loss, perhaps elicited by transient cerebral ischemia.

Effects of experimental hypercapnia on hippocampal long-term potentiation in anesthetized rats

The effects of hypercapnia, which has been reported to impair consciousness, on the long-term potentiation of the population spike in the CA1 pyramidal cell of the hippocampus in anesthetized rats were studied. Experimental hypercapnemia was induced by inspired 13% CO2 with 21% O2. Arterial blood gas analysis after 80 min inspired 13% CO2 showed pH 7.08+/-0.05, PCO2 = 104.09+/-12.86 mmHg, PO2 = 90.71+/-18.89 mmHg, BE -4.64+/-2.97 (mean +/- SD, n = 18). Inspired 13% CO2 reduced the amplitude of the population spike to 50% of the baseline. After delivery of tetanic stimulation (400 Hz, five bursts of eight pulses, inter-burst interval 1 s) population spike height was enhanced to pre-tetanic levels. Withdrawal of inspired CO2 unmasked an increase in population spike amplitude. These findings suggest that acute retention of carbon dioxide, which is designated as pure hypercapnemia without hypoxemia, may suppress hippocampal synaptic transmission but not its plasticity.