Rhythmic light flicker rescues hippocampal low gamma and protects ischemic neurons by enhancing presynaptic plasticity

The complex relationship between specific hippocampal oscillation frequency deficit and cognitive dysfunction in the ischemic brain is unclear. Here, using a mouse two-vessel occlusion (2VO) cerebral ischemia model, we show that visual stimulation with a 40 Hz light flicker drove hippocampal CA1 slow gamma and restored 2VO-induced reduction in CA1 slow gamma power and theta-low gamma phase-amplitude coupling, but not those of the high gamma. Low gamma frequency lights at 30 Hz, 40 Hz, and 50 Hz, but not 10 Hz, 80 Hz, and arrhythmic frequency light, were protective against degenerating CA1 neurons after 2VO, demonstrating the importance of slow gamma in cognitive functions after cerebral ischemia. Mechanistically, 40 Hz light flicker enhanced RGS12-regulated CA3-CA1 presynaptic N-type calcium channel-dependent short-term synaptic plasticity and associated postsynaptic long term potentiation (LTP) after 2VO. These results support a causal relationship between CA1 slow gamma and cognitive dysfunctions in the ischemic brain.

Hippocampal microvasculature changes in association with oxidative stress in Alzheimer's disease

Vascular endothelial dysfunction is a primary phenotype of aging, and microvascular (MV) lesion is mainly associated with Alzheimer's disease (AD). Here we have studied the correlation of MV wall thickness and CA1 pyramidal neuronal pathology in autopsy-confirmed AD brains. Both hyaline (h-MV) and increased cell number (c-MV) associated MV wall thickening was found in age-matched control (AC) hippocampus without significant change in Aβ level (Braak stages 0-III). AC neurons neighboring the h-MV showed lower levels of oxidative DNA/RNA damage and Aβ precursor protein (APP), while the neurons around c-MV showed higher oxidative DNA/RNA damage with increased APP expression. Neurons in AC hippocampus without MV wall thickening (thin wall) showed increased DNA/RNA damage and APP levels compared to AC cases with h-MV and c-MV walls. In the AD hippocampus neurons neighboring h-MV walls showed increased levels of Aβ and decreased number of dendritic spines (at Braak stages IV-VI). C-MV neighboring neurons in the AD cases showed higher levels of DNA/RNA damage with increased APP at stages II - III, followed by lower levels of oxidative DNA/RNA damage, decreased APP and increased Aβ levels with loss of dendritic spines at stages IV-VI. Prolonged treatment of primary human fetal hippocampal neurons with tert-butyl hydroperoxide (TBHP) induced oxidative DNA damage with a sustained increase in APP. Aβ increased rapidly and then decreased overtime. Short-term TBHP treated neurons showed lower levels of superoxide (O₂^{• -}) without significant DNA damage. Short-term TBHP treatment induced a gradual decrease in APP but an increase in Aβ levels over time. In conclusion this study indicates that AD hippocampus at Braak stages II-III are characterized by strong oxidative DNA/RNA damage with increased APP in neurons associated with c-MV, while stages IV-VI are characterized by a slow increase in Aβ in neurons neighboring both h-MV and c-MV.

Monitoring of cerebral blood flow during hypoxia-ischemia and resuscitation in the neonatal rat using laser speckle imaging

Neonatal hypoxic-ischemic encephalopathy (HIE) is associated with alterations in cerebral blood flow (CBF) as a result of perinatal asphyxia. The extent to whichCBFchanges contribute to injury, and whether treatments that ameliorate these changes might be neuroprotective, is still unknown. Higher throughput techniques to monitorCBFchanges in rodent models ofHIEcan help elucidate the underlying pathophysiology. We developed a laser speckle imaging (LSI) technique to continuously monitorCBFin six postnatal-day 10 (P10) rats simultaneously before, during, and after unilateral hypoxia-ischemia (HI, ligation of the left carotid artery followed by hypoxia in 8% oxygen). After ligation,CBFto the ligated side fell by 30% compared to the unligated side (P < 0.0001). Hypoxia induced a bilateral 55% reduction inCBF, which was partially restored by resuscitation. Compared to resuscitation in air, resuscitation in 100% oxygen increasedCBFto the ligated side by 45% (P = 0.033). Individual variability inCBFresponse to hypoxia between animals accounted for up to 24% of the variability in hemispheric area loss to the ligated side. In both P10 and P7 models of unilateralHI, resuscitation in 100% oxygen did not affect hemispheric area loss, or hippocampalCA1 pyramidal neuron counts, after 1-week survival. ContinuousCBFmonitoring usingLSIin multiple rodents simultaneously can screen potential treatment modalities that affectCBF, and provide insight into the pathophysiology ofHI.

Acetylation of histones in neocortex and hippocampus of rats exposed to different modes of hypobaric hypoxia: Implications for brain hypoxic injury and tolerance

Acetylation of nucleosome histones results in relaxation of DNA and its availability for the transcriptional regulators, and is generally associated with the enhancement of gene expression. Although it is well known that activation of a variety of pro-adaptive genes represents a key event in the development of brain hypoxic/ischemic tolerance, the role of epigenetic mechanisms, in particular histone acetylation, in this process is still unexplored. The aim of the present study was to investigate changes in acetylation of histones in vulnerable brain neurons using original well-standardized model of hypobaric hypoxia and preconditioning-induced tolerance of the brain. Using quantitative immunohistochemistry and Western blot, effects of severe injurious hypobaric hypoxia (SH, 180mm Hg, 3h) and neuroprotective preconditioning mode (three episodes of 360mm Hg for 2h spaced at 24h) on the levels of the acetylated proteins and acetylated H3 Lys24 (H3K24ac) in the neocortex and hippocampus of rats were studied. SH caused global repression of the acetylation processes in the neocortex (layers II-III, V) and hippocampus (CA1, CA3) by 3-24h, and this effect was prevented by the preconditioning. Moreover, hypoxic preconditioning remarkably increased the acetylation of H3K24 in response to SH in the brain areas examined. The preconditioning hypoxia without subsequent SH also stimulated acetylation processes in the neocortex and hippocampus. The moderately enhanced expression of the acetylated proteins in the preconditioned rats was maintained for 24h, whereas acetylation of H3K24 was intense but transient, peaked at 3h. The novel data obtained in the present study indicate that large activation of the acetylation processes, in particular acetylation of histones might be essential for the development of brain hypoxic tolerance.

Acupuncture reduced apoptosis and up-regulated BDNF and GDNF expression in hippocampus following hypoxia-ischemia in neonatal rats

ETHNOPHARMACOLOGICAL RELEVANCE

Acupuncture attenuates neuronal damages following ischemia.

AIM OF THE STUDY

The purpose of the present study was to investigate the beneficial effects of acupuncture on hypoxia-ischemia induced brain damages in neonatal rats.

MATERIALS AND METHODS

Male postnatal 7 days rats were randomly divided into 3 groups: sham control (sham), hypoxia-ischemia (HI), and HI plus acupuncture treatment (HI+Acu). The rats in HI and HI+Acu groups were submitted to model of neonatal HI, established by occluding the left common carotid artery followed by a 3.5h period of hypoxia (8% O2-92% N2). At 24h after HI, animals were stimulated by acupuncture treatment once a day and the treatment continued during 4 weeks, 5days/week. Behavioral functions, learning and memory ability, and body weight were observed at different time-points after HI. DNA fragmentation assay were performed with TUNEL staining to evaluate apoptosis and expression levels of mitochondrial Bcl-2, mitochondrial Bax, Cleaved caspase 3, Cleaved caspase 9 in the damaged hippocampus were detected by western blotting 28 days following HI. GDNF, BDNF levels in hippocampus were also determined.

RESULTS

The results showed that acupuncture significantly promoted growth and development, improved neurobehavioral function, learning and memory ability after 20 days' treatment. Furthermore, we obtained one interesting finding that acupuncture attenuated cellular apoptosis and up-regulated GDNF and BDNF levels in hippocampus.

CONCLUSIONS

All of these results suggest that acupuncture as a potential treatment may exert neuroprotective effects via inhibiting cellular apoptosis, increased GDNF and BDNF expression levels in rat hippocampus experiencing HI.

Neuroprotective effects of Alpinia katsumadai against experimental ischemic damage via control of oxidative stress

CONTEXT

Alpinia katsumadai (Zingiberaceae) has been identified by the National Plant Quarantine Service in Korea. The extract of Alpinia katsumadai seed (EAKS) has antioxidant activities.

OBJECTIVE

We investigated the neuroprotective effects of EAKS on ischemic damage in the gerbil hippocampal CA1 region after transient cerebral ischemia.

MATERIALS AND METHODS

The ethanol extract of EAKS was obtained by organic solvent, collected in Kangwon province (South Korea) and orally administered using a feeding needle once a day for one week before transient cerebral ischemia in gerbils.

RESULT

We adapted oral administration of 25 and 50 mg/kg EAKS because there are no data about the absorption and metabolism of EKAS. We found a significant neuroprotection in the 50 mg/kg EAKS-treated ischemia group, not in the 25 mg/kg EAKS-treated ischemia group, at 4 days ischemia-reperfusion (I-R). In the 50 mg/kg EAKS-treated ischemia group, about 68% of pyramidal neurons in the CA1 region were immunostained with neuronal nuclei (NeuN) 4 days after I-R, compared to the vehicle-treated ischemia group. 8-Hydroxy-2'-deoxyguanosine (a marker for DNA damage) and 4-hydroxy-2-nonenal (a marker for lipid peroxidation) immunoreactivity in the CA1 region of the EAKS-treated ischemia group were not markedly changed compared to the vehicle-treated ischemia group. In addition, Cu,Zn- and Mn-SOD immunoreactivity in the CA1 region of the EAKS-treated ischemia group were increased compared to the vehicle-treated ischemia group.

DISCUSSION

Repeated supplements of EAKS could protect neurons against ischemic damage, showing that DNA damage and lipid peroxidation are attenuated and SODs are increased in the ischemic CA1 region.

Disrupted iron metabolism and ensuing oxidative stress may mediate cognitive dysfunction induced by chronic cerebral hypoperfusion

Iron is a highly reactive free radical catalyst that has been shown to exacerbate oxidative stress and cell death in many neurodegenerative diseases. In this study, we produced a rat model of chronic cerebral hypoperfusion (CCH) by permanent bilateral carotid artery occlusion to investigate markers of iron and oxidative stress associated with it. We found CCH led to significant spatial memory impairment in the Morris water maze at 4 months after bilateral ligation. Iron deposition was observed in both the hippocampal CA1 area and cerebral cortex, and was correlated with localized neuronal death and increased lipid peroxidation. Western blotting revealed that the expression levels of ferritin heavy chain and the transferrin receptor were significantly elevated in hippocampus and cortex after CCH, whereas expression of iron regulatory protein 1 was significantly lower than in sham-treated rats. We conclude that localized neurodegeneration and concomitant cognitive impairments following CCH may result, at least in part, from local disruption of neuronal iron metabolism.

Distinct pattern separation related transfer functions in human CA3/dentate and CA1 revealed using high-resolution fMRI and variable mnemonic similarity

Producing and maintaining distinct (orthogonal) neural representations for similar events is critical to avoiding interference in long-term memory. Recently, our laboratory provided the first evidence for separation-like signals in the human CA3/dentate. Here, we extended this by parametrically varying the change in input (similarity) while monitoring CA1 and CA3/dentate for separation and completion-like signals using high-resolution fMRI. In the CA1, activity varied in a graded fashion in response to increases in the change in input. In contrast, the CA3/dentate showed a stepwise transfer function that was highly sensitive to small changes in input.

Involvement of Glutamate transporter-1 in neuroprotection against global brain ischemia-reperfusion injury induced by postconditioning in rats

Ischemic postconditioning refers to several transient reperfusion and ischemia cycles after an ischemic event and before a long duration of reperfusion. The procedure produces neuroprotective effects. The mechanisms underlying these neuroprotective effects are poorly understood. In this study, we found that most neurons in the CA1 region died after 10 minutes of ischemia and is followed by 72 hours of reperfusion. However, brain ischemic postconditioning (six cycles of 10 s/10 s reperfusion/re-occlusion) significantly reduced neuronal death. Significant up-regulation of Glutamate transporter-1 was found after 3, 6, 24, 72 hours of reperfusion. The present study showed that ischemic postconditioning decreases cell death and that upregulation of GLT-1 expression may play an important role on this effect.

[Role of Ca(2+)-activated potassium channels with high-conductivity in hypoxic preconditioning and posthypoxic hyperexcitability in CA1 hippocampal neurons in vitro]

The role of highly conductive Ca(2+)-activated potassium channels (BK(Ca)-channels) of rat hippocampal CA1 neurons in the processes induced by repeated episodes of brief hypoxia was investigated. A specific blocker of BK(Ca)-channels iberiotoxin (10-20 nM) tended to decrease the efficiency of hypoxia in depressing the amplitude of population spikes during hypoxic episode. Iberiotoxin significantly abolished both the preconditioning effect of hypoxic episodes and the posthypoxic hyperexcitability of pyramidal neurons. It is suggested that BK(Ca)-channels play an important role in the mechanisms of such forms of neuroplasticity as rapid hypoxic preconditioning and posthypoxic hyperexcitability in hippocampal CA1 neurons.