Evaluation of neuronal cell death after a new global ischemia model in infant mice

Impact of cerebral hypoperfusion-reperfusion on optic nerve integrity and visual function in the DBA/2J mouse model of glaucoma

Objective

One of the most important risk factors for developing a glaucomatous optic neuropathy is elevated intraocular pressure. Moreover, mechanisms such as altered perfusion have been postulated to injure the optical path. In a mouse model, we compare first negative effects of cerebral perfusion/reperfusion on the optic nerve structure versus alterations by elevated intraocular pressure. Second, we compare the alterations by isolated hypoperfusion-reperfusion and isolated intraocular pressure to the combination of both.

Methods and analysis

Mice were divided in four groups: (1) controls; (2) perfusion altered mice that underwent transient bi-common carotid artery occlusion (BCCAO) for 40 min; (3) glaucoma group (DBA/2J mice); (4) combined glaucoma and altered perfusion (DBA/2J mice with transient BCCAO). Optic nerve sections were stereologically examined 10–12 weeks after intervention.

Results

All experimental groups showed a decreased total axon number per optic nerve compared with controls. In DBA/2J and combined DBA/2J & BCCAO mice the significant decrease was roughly 50%, while BCCAO leaded to a 23% reduction of axon number, however reaching significance only in the direct t-test. The difference in axon number between BCCAO and both DBA/2J mice was almost 30%, lacking statistical significance due to a remarkably high variation in both DBA/2J groups.

Conclusion

Elevated intraocular pressure in the DBA/2J mouse model of glaucoma leads to a much more pronounced optic nerve atrophy compared with transient forebrain hypoperfusion and reperfusion by BCCAO. A supposed worsening effect of an altered perfusion added to the pressure-related damage could not be detected.

Transcranial Direct Current Stimulation Ameliorates Cognitive Impairment via Modulating Oxidative Stress, Inflammation, and Autophagy in a Rat Model of Vascular Dementia

To investigate the potential applications and the molecular mechanisms of transcranial direct current stimulation (tDCS) on cognitive impairment in a vascular dementia (VD) animal model. Sprague-Dawley rats were used in this study. VD rat model was induced by modified permanent bilateral common carotid artery occlusion (2-VO) approach. Anodal tDCS was applied to the animals. Morris water maze was used to analyze spatial memory and navigation ability. The pathological changes in the hippocampal CA1 region and cerebral cortex were examined via Hematoxylin-Eosin staining. The rats were sacrificed for the measurement of the level of superoxide (SOD), glutathione (GSH), reactive oxidative species (ROS), malondialdehyd (MDA), Interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α level in the hippocampus. Western blot was carried out to measure the hippocampal expression of microtubule-associated protein 1 light chain 3 (LC-3) and p62. Rats with VD have decreased number of neurons in the hippocampus and cerebral cortex, as well as worse cognitive impairment. The proliferation of activated microglia and astroglia, accompanied with attenuation of myelination were observed in the white matter about 1 month after 2-VO operation. These abnormalities were significantly ameliorated by tDCS treatment. Further study revealed that anodal tDCS could suppress the MDA and ROS level, while enhance the SOD and GSH level to reduce the oxidative stress. Anodal tDCS could inhibit hypoperfusion-induced IL-1β, IL-6, and TNF-α expression to attenuate inflammatory response in hippocampus. Moreover, anodal tDCS treatment could alleviate autophagy level. The study has demonstrated a possible therapeutic role of tDCS in the treatment of cognitive impairment in VD.

Increased vulnerability of hippocampal CA1 neurons to hypoperfusion in ataxia and male sterility (AMS) mouse

The nna1 gene mutation is associated with spontaneous degeneration of cerebellar Purkinje cells and germ cells in Ataxia and Male Sterility (AMS) mouse. Since nna1 is also expressed in hippocampal neurons, we investigated their vulnerability to hypoperfusion in AMS mouse. Eight-week-old male wild type (WT) and AMS mice were subjected to bilateral common carotid artery occlusion (BCCAO) for 10 min and sacrificed 1, 3, 7 and 28 days after BCCAO. Nissl staining revealed the neuronal cell loss and pyknotic change in the CA1 of AMS mice. TUNEL(+) apoptotic cells were found in the area at 7 days in AMS mice. Bcl-2 mRNA and protein in WT hippocampus were increased, while they were not increased in AMS. Bax mRNA was increased in AMS. Moreover, Bax activation was immunohistochemically demonstrated only in AMS at 3 and 7 days after BCCAO. An oxidative DNA damage marker, 8-hydroxydeoxyguanosine-positive cells were increased in both strains at 1 day; decreased in WT at 3 days but remained high in AMS. BCCAO increased glutathione, an antioxidant, in WT, but not in AMS at 3 days. The mRNA level of mitochondrial uncoupling protein 2, a regulator of oxidative stress, was increased only in WT at 1 day. Nna1 mRNA was similarly expressed in WT and AMS, but the protein was undetectable in AMS. Thus, our results indicate the increased vulnerability of hippocampal CA1 neurons of AMS mice to cerebral hypoperfusion could be due to an imbalance between oxidative stress and antioxidative defense system.

Aggravated chronic brain injury after focal cerebral ischemia in aquaporin-4-deficient mice

The water channel aquaporin-4 (AQP4) is important in brain water homeostasis, and is also involved in astrocyte growth and glial scar formation. It has been reported that AQP4 deficiency attenuates acute ischemic brain injury as a result of reducing cytotoxic edema. Here, we determined whether AQP4 deficiency influences chronic brain injury after focal cerebral ischemia induced by 30 min of middle cerebral artery occlusion (MCAO). AQP4(-/-) mice exhibited a lower survival rate and less body weight gain than wild-type mice, but their neurological deficits were similar to wild-type mice during 35 days after MCAO. At 35 days after MCAO, AQP4(-/-) mice showed more severe brain atrophy and cavity formation in the ischemic hemisphere as well as more neuronal loss in the hippocampus. Furthermore, astrocyte proliferation and glial scar formation were impaired in AQP4(-/-) mice. Therefore, AQP4 deficiency complicated by astrocyte dysfunction aggravates chronic brain injury after focal cerebral ischemia, suggesting that AQP4 may be important in the chronic phase of the post-ischemic recovery process.

Importance of normothermia control in investigating delayed neuronal injury in a mouse global ischemia model

This study aims to establish a mouse global cerebral ischemia model in which the physiological parameter measurements and neuronal injury evaluations are conducted in the same group of animals and to identify the effect of post-ischemic core temperature (CT) on the outcome of neuronal injury. Global ischemia was induced by 12-min bilateral common carotid artery occlusion followed by 7 days of reperfusion in C57BL/6 mice. Immediately after occlusion, mice were randomly assigned to be kept in environments of different temperatures [25 degrees C (room temperature, group 1), 33-34 degrees C for 2h (group 2), and 33-34 degrees C for 24h (group 3)] before being returned to their home cages. We found that in group 1, CT declined to approximately 32 degrees C after ischemia and then recovered at 24h post-ischemia; in group 2, CT remained at the pre-ischemia level during the first 2h, declined after the mice were returned to room temperature, and recovered at 24h post-ischemia; and in group 3, CT remained constant at the pre-ischemia level throughout the reperfusion period. The number of surviving neurons in a sector of the hippocampal CA1 region was significantly lower in all ischemic groups than in the sham controls, but the number was significantly higher in group 1 than that in groups 2 or 3 (P<0.05). We observed that CT declines initially but recovers spontaneously at 24h post-ischemia. Early post-ischemic hypothermia impacts the delayed neuronal injury, suggesting that tight temperature control immediately following ischemia is important to obtain the most reproducible neuronal damage in mouse models of cerebral global ischemia.

Prostacyclin receptor deletion aggravates hippocampal neuronal loss after bilateral common carotid artery occlusion in mouse

Transient global cerebral ischemia causes delayed neuronal death in the hippocampal CA1 region. It also induces an increase in cyclooxygenase 2 (COX-2), which generates several metabolites of arachidonic acid, known as prostanoids, including prostacyclin (PGI(2)). To determine the role of the PGI(2) receptor (IP) in post-ischemic delayed cell death, wild-type and IP knockout (IP(-/-)) C57Bl/6 mice were subjected to 12-min bilateral common carotid artery occlusion or sham surgery, followed by 7 days of reperfusion. In the sham-operated mice, no statistical difference in CA1 hippocampal neuronal density was observed between the wild-type (2836+/-18/mm(2)) and IP(-/-) (2793+/-43/mm(2)) mice. Interestingly, in animals subjected to ischemia, surviving neuronal density in wild-type mice decreased to 50.5+/-7.9% and that of IP(-/-) mice decreased to 23.0+/-4.5% of their respective sham-operated controls (P<0.05). The results establish a role for the IP receptor in protecting pyramidal hippocampal neurons after this global ischemic model and suggest that IP receptor agonists could be developed to prevent delayed pyramidal neuronal cell death.

Postischemic hyperoxia reduces hippocampal pyruvate dehydrogenase activity

The pyruvate dehydrogenase complex (PDHC) is a mitochondrial matrix enzyme that catalyzes the oxidative decarboxylation of pyruvate and represents the sole bridge between anaerobic and aerobic cerebral energy metabolism. Previous studies demonstrating loss of PDHC enzyme activity and immunoreactivity during reperfusion after cerebral ischemia suggest that oxidative modifications are involved. This study tested the hypothesis that hyperoxic reperfusion exacerbates loss of PDHC enzyme activity, possibly due to tyrosine nitration or S-nitrosation. We used a clinically relevant canine ventricular fibrillation cardiac arrest model in which, after resuscitation and ventilation on either 100% O2 (hyperoxic) or 21-30% O2 (normoxic), animals were sacrificed at 2 h reperfusion and the brains removed for enzyme activity and immunoreactivity measurements. Animals resuscitated under hyperoxic conditions exhibited decreased PDHC activity and elevated 3-nitrotyrosine immunoreactivity in the hippocampus but not the cortex, compared to nonischemic controls. These measures were unchanged in normoxic animals. In vitro exposure of purified PDHC to peroxynitrite resulted in a dose-dependent loss of activity and increased nitrotyrosine immunoreactivity. These results support the hypothesis that oxidative stress contributes to loss of hippocampal PDHC activity during cerebral ischemia and reperfusion and suggest that PDHC is a target of peroxynitrite.

Orexin-1 receptor expression after global ischemia in mice

Orexins are neuropeptides that have a range of physiological effects including the regulation of feeding behavior and the sleep-wakefulness cycle. Recently, we reported that level of orexin A in spinal fluid was decreased in the patients of some neurodegenerative diseases and it is considered that orexin A and the receptors might be related to central nervous system disorders. However, the expression and localization of orexin receptors is not elicited well. Therefore, the purpose of this study is to investigate the time-dependent changes and the cellular localization of orexin receptor focusing on orexin-1 receptor (OX1R) in the mouse brain after transient common carotid artery occlusion (tCCAO) model by using immunohistochemical techniques. OX1R immunoreactivity dramatically increased and peaked in the hippocampus and cortex 2 days after tCCAO, but remained unchanged in the hypothalamus. Using double-immunohistochemistry, the OX1R immunopositive cells at 2 days after tCCAO were co-localized not only with neuronal marker, NeuN-immunoreactivity but also with astroglial and oligodendroglial markers, GFAP- and CNPase-immunoreactivities, respectively. These results suggested that OX1R is induced other cells in addition to the neurons during stress such as ischemia and orexins and its receptor might play an important role for ischemic insult.