Dexmedetomidine and Phosphocreatine Post-treatment Provides Protection against Focal Cerebral Ischemia-reperfusion Injury in Rats

In this study we investigated the neuroprotective efficacy of dexmedetomidine (Dex) and phosphocreatine (PCr) alone or in combination in a rat model of focal cerebral ischemia-reperfusion injury (I/R). I/R was induced by intraluminal middle cerebral artery occlusion (MCAO) and reperfusion. Male Sprague-Dawley rats were randomly allocated to the Sham group and I/R group, and the I/R group was further divided into three subgroups: Dex (9 μg.kg⁻¹ Dex), PCr (180 mg.kg⁻¹ PCr) and Dex + PCr (9 μg.kg⁻¹ Dex + 180 mg.kg⁻¹ PCr). All treatments were given intravenously at the onset of reperfusion. After 24 hr of reperfusion, the neurological deficit score (NDS) was determined and a magnetic resonance imaging (MRI) scan was performed. Serum concentrations of malonaldehyde (MDA) and 4-hydroxynonenal (4-HNE) were measured and cerebral infarct volume was estimated by triphenyl tetrazolium chloride (TTC) staining. Blood brain barrier, neuronal and mitochondrial damage was assessed by optical and electron microscopy. Neuronal injury was further assessed using double cleaved caspase-3 and NeuN immunofluorescent staining. Compared with group I/R, Dex and PCr significantly reduced the neurological deficit score (P < 0.01), infarct volume (P < 0.01), and brain blood barrier, neuronal and mitochondrial damage. The level of oxidative stress (P < 0.001) and neuronal injury (P < 0.001) also decreased and surviving neurons increased (P < 0.001). Compared with Dex or PCr alone, the combination treatment had overall greater effects (P < 0.05). These results indicate that posttreatment with Dex or PCr decreases focal cerebral I/R injury and that these agents in combination have greater protective effects than each alone.

Homeostatic changes in neuronal network oscillations in response to continuous hypoperfusion in the mouse forebrain

Neuronal activity is highly sensitive to changes in oxygen tension. In this study, we examined the impact of hypoxic/ischemic conditions on neuronal ensemble activity patterns in the mouse brain using in vivo extracellular electrophysiological recordings from up to 8 sites in the thalamus, dorsal hippocampus, and neocortex, while cerebral hypoperfusion was induced by unilateral carotid artery occlusion. After a few minutes, the occlusion triggered a rapid change in the power of the local field oscillations. In the hippocampus, but not in the neocortex, the absolute power changes at all frequency ranges (relative to the baseline) became less pronounced with time, and no significant changes were observed 30min after the occlusion-induced hypoperfusion. We also tested whether continuous hypoperfusion induced by the occlusion for up to 1 week alters neuronal activity. In the hippocampus and the thalamus, the chronic occlusion did not lead to a reduction in the power of the local field oscillations. These results indicate that certain neuronal populations have the ability to maintain internal neurophysiological homeostasis against continuous hypoperfusion.

PACAP as a neuroprotective factor in ischemic neuronal injuries

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 27- or 38-amino acid neuropeptide, which belongs to the vasoactive intestinal polypeptide/glucagon/secretin family. PACAP and its three receptor subtypes are expressed in neural tissues, with PACAP known to exert pleiotropic effects on the nervous system. This review provides an overview of current knowledge regarding the neuroprotective effects, mechanisms of action, and therapeutic potential of PACAP in response to ischemic brain injuries.

Direct experimental occlusion of the distal middle cerebral artery induces high reproducibility of brain ischemia in mice

Several investigators have used murine models to investigate the pathophysiology of brain ischemia. The focal ischemic model is a closer approximation to human stroke which includes a necrotic core, penumbra, and undamaged tissue. Occlusion of a unilateral artery, especially the middle cerebral artery (MCA), is performed in this model, but collateral circulation often induces variation of ischemic lesions both qualitatively and quantitatively. It is likely that the more proximal the artery which is unilaterally occluded is, the more inconsistent the outcomes. The present study was designed to examine the reproducibility of infarct lesion by distal or proximal artery occlusion. Direct occlusion of the distal MCA was performed and compared with unilateral common carotid artery occlusion (CCAO) in C57BL/6 mice. Direct MCA occlusion (MCAO) consistently induced ischemic lesions in cortical areas. All model animals (n=14) survived 24 h after occlusion, and exhibited a maximum infarct volume (20.0 +/- 5.0%). In contrast, permanent and transient unilateral CCAO models had mortality rates of 62.5 and 25.0%, and showed severe to absent lesions with the infarct volumes of 29.0 +/- 20.8 and 33.2 +/- 24.2%, respectively. In conclusion, distal MCAO produces high reproducibility of ischemic insults and survivability compared to unilateral CCAO. Thus, distal MCAO is a useful method for the focal ischemic model.

CSF orexin A concentrations and expressions of the orexin-1 receptor in rat hippocampus after cardiac arrest

Orexins/hypocretins are neuropeptides that have various physiological effects, including the regulation of feeding behavior, neuroendocrine functions and sleep-wake cycles. Recent studies have suggested that the orexin system may also be involved in brain ischemic reactions. It is also known that changes in sleep patterns, energy homeostasis and neuroendocrine functions are often occur in neurological conditions associated brain ischemia. In the current study, we investigated the time-dependent changes in cerebrospinal fluid (CSF) orexin-A concentration and the expression of the orexin-1 receptor (OX1R) in the rat hippocampus after global ischemia-reperfusion (5 min cardiopulmonary arrest), which is known to induce delayed cell death in the CA1 region of the hippocampus. The CSF orexin-A concentration was elevated transiently at 24 h after ischemia. On days 2 and 4 after ischemia, CSF orexin concentrations were significantly reduced relative to the baseline, and returned to the baseline level by day 7. These changes were correlated with increased expression of OX1R in the CA1 on days 1 and 2 post-ischemia. These results suggest that dynamics of orexin signaling observed may have functional roles for neuronal damage associated with transient ischemia.

Progressive expression of vascular endothelial growth factor (VEGF) and angiogenesis after chronic ischemic hypoperfusion in rat

Cerebrovascular stenosis caused by arteriosclerosis induces failure of the cerebral circulation. Even if chronic cerebral hypoperfusion does not induce acute neuronal cell death, cerebral hypoperfusion may be a risk factor for neurodegenerative diseases. The purpose of this study was to determine if vasodilation, expression of VEGF, and neovascularization are homeostatic signs of cerebral circulation failure after permanent common carotid artery occlusion (CCAO) in the rat. Neuronal cell death in neocortex was observed 2 weeks after CCAO and gradually increased in a time-dependent manner. The diameter of capillaries and expression of VEGF also increased progressively after CCAO. Moreover, we observed unusual irregular angiogenic vasculature at 4 weeks. In conclusion, chronic hypoperfusion results in mechanisms to compensate for insufficiency in blood flow including vasodilation, VEGF expression, and neovascularization in the ischemic region. These results suggest that angiogenesis might be induced in adult brain through the support of growth factors and transplantation of vascular progenitor cells, and that neovascularization might be a therapeutic strategy for children and adults with diseases such as vascular dementia.

Controlled normothermia during ischemia is important for the induction of neuronal cell death after global ischemia in mouse

A stable model of neuronal damage after ischemia is needed in mice to enable progression of transgenic strategies. We performed transient global ischemia induced by common carotid artery occlusions with and without maintaining normal rectal temperature (Trec) in order to determine the importance of body temperature control during ischemia. We measured brain temperature (Tb) during ischemia/reperfusion. Mice with normothermia (Trec within +/- 1 degrees C) had increased mortality and neuronal cell death in the CA1 region of hippocampus, which did not occur in hypothermic animals. If the Trec was kept within +/- 1 degrees C, the Tb decreased during ischemia. After reperfusion, Tb in the normothermia group developed hyperthermia, which reached > 40 degrees C and was > 2 degrees C higher than Trec. We suggest that tightly controlled normothermia and prevention of hypothermia (Trec) during ischemia are important factors in the development of a stable neuronal damage model in mice.