Laser doppler flowmetry in CA1 sector of hippocampus and cortex after transient forebrain ischemia in gerbils

Bilateral Common Carotid Artery Occlusion in the Rat as a Model of Retinal Ischaemia

Ocular ischaemic syndrome is a devastating eye disease caused by severe carotid artery stenosis. The purpose of the study was to develop a reliable rat model for this syndrome by means of common carotid artery occlusion and a controllable needle suture method. Adult Wistar rats were subjected to common carotid artery occlusion and sham surgery. The common carotid artery was ligated unilaterally or bilaterally with needles of different diameters, and ocular arterial filling time was examined by fluorescein fundus angiography at different time points. Haematoxylin-eosin staining of vessels and degree of stenosis were considered outcome measures. The ocular blood flow was monitored and measured by laser doppler flowmetry. Needles with a diameter of 0.4 mm were more effective in developing severe stenosis of the common carotid arteries compared with needles of other diameters. Bilateral common carotid artery occlusion was a more effective model than unilateral occlusion. The arterial filling time was significantly increased at 14 and 21 days after ligation (5.75 ± 0.45 and 6.27 ± 0.95 s, respectively) compared with arterial filling time before surgery (5.22 ± 0.64 s). The total blood flow in the sham surgery group was significantly higher than in the bilateral common carotid artery occlusion group. The fundus blood flow was statistically different between the two groups, whereas that of the anterior segment was not. In conclusion, the authors have established a rat model of ocular ischaemic syndrome via a controllable needle suture method, which was reliable up to 2-3 weeks after surgery.

Mouse models of global cerebral ischemia

Use of rodent models of hippocampal neurodegeneration are recommended for use in studies to understand the pathophysiology and molecular mechanisms involved. This unit includes protocols for two-vessel occlusion, three-vessel occlusion, and permanent bilateral vertebral artery occlusion plus methods for histological techniques for preparation of brain tissue and analysis of hippocampal injury.

Transition of areas of eosinophilic neurons and reactive astrocytes to delayed cortical infarcts after transient unilateral forebrain ischemia in Mongolian gerbils

The fate of postischemic tissues containing eosinophilic neurons (ENs), whether they remain viable or evolve into infarction, is largely unknown. We analyzed the time profile and distribution of ENs, reactive astrocytes (RAs), and infarction after transient cerebral ischemia. Unilateral forebrain ischemia was induced in Mongolian gerbils by two 10-min unilateral common carotid artery occlusions with a 5-h interval, and the brains at 24 h, 4 days, and 2, 4, and 16 weeks were prepared for morphometric analysis. Intra-ischemic laser Doppler flowmetry revealed significant ischemia, deeper in the anterior cortex, during carotid occlusion. Here, ENs appeared in the middle and deep layers at 24 h postischemia, and EN areas had extended to all cortical layers by 4 days. Large areas of high EN density turned into infarcts between 4 days and 4 weeks. In the posterior cortex, middle and deep cortical layers evolved low EN density areas without subsequent transformation into infarcts. RAs were consistently observed in areas with ENs, and RA areas with high EN density were largely transformed into infarcts between 4 days and 4 weeks postischemia. Areas of high, but not low, EN density were slowly transformed into infarcts after transient cerebral ischemia. Delayed astrocytic death took place in the RA areas with high EN density. In conclusion, density of ENs is an important indicator of delayed astrocytic death and infarction in postischemic tissue.

Extrapyramidal motor symptoms versus striatal infarction volume after focal ischemia in mongolian gerbils

Few behavioral tests are available to evaluate extrapyramidal dysfunctions after focal cerebral ischemia in rodents, although extrapyramidal motor dysfunctions are often observed clinically in patients with cerebral infarction. We evaluated the methamphetamine (MP)-induced rotation test for the detection and quantification of extrapyramidal motor dysfunction induced by striatal infarction in gerbils after focal cerebral ischemia. Mongolian gerbils (n=79) underwent the left common carotid artery occlusion (CCAO) for 10, 15, or 20 min. Spontaneous and MP-induced rotation tests were repeated postischemia, and the results compared with the extent of ischemic tissue injury. The density of dopaminergic neurons immunostained with a tyrosine hydroxylase antibody in the substantia nigra pars compacta (SNpc) also was measured. Histological examination revealed selective neuronal death of the hippocampal cornu ammonis 1 (CA1) sector in 10-min CCAO animals, infarction confined to the striatum and hippocampal neuronal death in 15-min CCAO animals, and widespread hemispheric infarction in 20-min CCAO animals. Dopaminergic neurons in the SNpc were preserved in 10- and 15-min CCAO animals but were significantly reduced in 20-min CCAO animals. In MP-induced rotation tests, 15-min CCAO animals showed biased rotation ipsilateral to the lesioned side. Biased rotation persisted 4 weeks postischemia, and the number of rotations significantly correlated with the regional infarction volume of the striatum. Twenty-minute CCAO animals showed biased rotation contralateral to the lesioned side; rotation number was not correlated with the infarction volume. Our results show that biased rotation behavior is a sensitive parameter of the extent of striatal injury after focal cerebral ischemia provided the lesion is not extended to the ipsilateral cortex. MP-induced rotation in rodents probably coordinates with the extrapyramidal motor dysfunction after striatal infarction in patients with vascular Parkinsonism.

Functional changes of glial glutamate transporter GLT-1 during ischemia: an in vivo study in the hippocampal CA1 of normal mice and mutant mice lacking GLT-1

Glutamate transporters remove glutamate from the extracellular space and maintain it below neurotoxic levels under normal conditions. However, the dynamics under ischemic conditions remain to be determined. In the present study, we evaluated the function of the glial glutamate transporter (GLT-1) during brain ischemia by using an in vivo brain microdialysis technique in GLT-1 mutant mice. A microdialysis probe was placed in the hippocampal CA1 of GLT-1 mutant and wild-type mice, and glutamate levels were measured during 5 and 20 min ischemia. The glutamate levels in mice lacking GLT-1 were significantly higher than the corresponding glutamate levels in wild-type mice during 5 min ischemia. Delayed neuronal death was induced in the CA1 of the mice lacking GLT-1 but not in the CA1 of the wild-type mice. When ischemia was elongated to the duration of 20 min, the glutamate levels in wild-type mice were significantly higher than the corresponding glutamate levels in mice lacking GLT-1 during the last 12.5 min of 20 min ischemia. Acute neuronal death was also observed in the CA1 of wild-type mice. These results suggest that GLT-1 takes up extracellular glutamate to protect neurons in the early stage of ischemia and then releases glutamate, triggering acute neuronal death, when ischemic conditions are elongated. The function of GLT-1 may change from neuroprotective to neurodegenerative during ischemia.

Brain damage in a mouse model of global cerebral ischemia. Effect of NMDA receptor blockade

The importance of particular genes in neuronal death following global cerebral ischemia can readily be studied in genetically modified mice provided a reliable model of ischemia is available. For that purpose, we developed a mouse model of global cerebral ischemia that induces consistent damage to different regions of the brain and with a low mortality rate. Twelve minutes of ischemia was induced in C57BL/6 mice by bilateral common carotid artery occlusion under halothane anesthesia and artificial ventilation. Body and brain temperature were monitored and cortical cerebral blood flow in each hemisphere was measured by laser Doppler flowmeter before, during, and for 5 min after ischemia. Extensive damage was found in the striatum and marked cell damage was observed in the CA1 and CA2 regions of hippocampus and in thalamus. Mild damage was seen in the CA3 region, dentate gyrus and cortex. Hippocampal damage in the CA1 region is delayed and developed over 48 h. Intraischemic hypothermia of 33 degrees C provided a robust neuroprotection. The non-competitive N-methyl-D-aspartate receptor blocker, MK-801, did not provide protection in the hippocampus, cortex, striatum or thalamus when administered 30 min prior to ischemia or 2 h after the end of ischemia, but selectively mitigated damage in the hippocampus, when administered immediately following ischemia. This model of global cerebral ischemia may be useful in pharmacological and genomic studies of ischemic brain damage.

Real-time cortical cerebral blood flow follow-up in conscious, freely moving rats by laser Doppler flowmetry

This article describes a laser Doppler flowmetry (LDF) system that enables repeated measurements and thereby long-term followup of cortical cerebral blood flow (CBF) in awake and freely moving rats. The system consists of a specially designed flow probe adapter, a flow probe connector, and a LDF flow probe, which may thereby rotate through its own axis. During the experiment, the flow adapter is permanently mounted onto the rat's skull bone. A thin layer of skull bone is left intact at the site for cortical CBF measurements. The probe connector and the flow probe may be repeatedly detached and remounted to the adapter, which allows for cortical cerebral blood flow recording from exactly the same anatomical location. The laser Doppler flowmetry system enables stable cortical CBF recordings in the conscious rat while it moves freely in a bowl cage.

Effects of stimulating the nucleus basalis of Meynert on blood flow and delayed neuronal death following transient ischemia in the rat cerebral cortex

An increase in cortical cerebral blood flow (CBF), independent of metabolic vasodilation, via the activation of cholinergic neurons originating in the nucleus basalis of Meynert (NBM) in the basal forebrain and projecting to the widespread cortices was recently demonstrated. In the present study, we aimed to clarify whether the increase in CBF following a stimulation of the NBM can improve delayed death of the cortical neurons following transient ischemia in rats. CBF was measured with a laser Doppler flowmeter, and the delayed neuronal death of the cerebral cortex produced by intermittent (every 5 s) occlusions of the unilateral common carotid artery for 60 min was measured histologically in the cortical hemisphere at 3 different coronal levels (6 microm thickness). In control rats without occlusion there were 6000-8000 intact neurons and 9-19 damaged neurons in the cortical hemisphere at each coronal level. During the occlusions, CBF ipsilateral to the occluded artery decreased by 13-32% of the preocclusion level. Five days after the occlusions, the numbers of damaged neurons were increased to 75-181. Repetitive electrical stimulation was delivered to the NBM, ipsilateral to the occluded artery, starting 5 min before the occlusions and finishing around the end of them. The increase in CBF induced by NBM stimulation prevented the occlusion-induced decrease in CBF in all 3 of the cortices. The delayed death of the cortical neurons previously observed after the occlusions was scarcely observable in all the cortices when NBM was stimulated. The present results suggest that NBM-originating vasodilative activation can protect the ischemia-induced delayed death of cortical neurons by preventing a blood flow decrease in widespread cortices.

Intraischemic mild hypothermia increases hippocampal CA1 blood flow during forebrain ischemia

The hippocampal CA1 sector is selectively vulnerable to forebrain ischemia but protected by mild hypothermia. However, the consequence of intraischemic hypothermia on CA1 blood flow during the insult has not been adequately characterized. The effects of mild intraischemic hypothermia on relative changes in regional hippocampal CA1 blood flow were recorded continuously using laser Doppler flowmetry (LDF) during and 30 min after 6 min of forebrain ischemia. Six experimental groups (n=6/group) of fasted male Wistar rats were compared. Groups 1, 3 and 5 consisted of normothermic rats that underwent either 6 (for CBF measurements) and 6 or 10 (for 7 day survival-CA1 neuronal death measurements) min of transient forebrain ischemia using bilateral carotid clamping and hemorrhagic hypotension. Groups 2, 4 and 6 rats were subjected to mild hypothermia (34 degrees C) before, during, and 30 min after 6 (for CBF measurements) and 6 or 10 (for 7 day survival-CA1 neuronal death measurements) min of transient forebrain ischemia. CA1 blood flow and electroencephalogram (EEG) were continuously recorded. During the ischemic insult there were intergroup differences in the magnitude of CBF decreases in the CA1 region. In both groups 1 and 2, CBF returned to preischemic values within 1 min of reperfusion but hypothermic rats had more sustained hyperemia. Hypothermic rats had a quicker recovery of EEG activity and less delayed CA1 neuronal death (group 2 versus 4). These data suggest ischemic blood flow to the CA1 sector was altered by intraischemic mild hypothermia which may contribute to the greater benefit of intraischemic hypothermic neuroprotection.

Effects of nicotine on blood flow and delayed neuronal death following intermittent transient ischemia in rat hippocampus

A cholinergic neural vasodilative response in the cerebral cortex and hippocampus, independent of metabolic vasodilation, was recently demonstrated by activating the nicotinic acetylcholine receptors (nAChRs) via activation of cholinergic neurons originating in the nucleus basalis of Meynert and septal complex in the basal forebrain and projecting to the cortex and hippocampus (see reviews by Sato A and Sato Y: Neurosci Res 14: 242--274, 1992; Sato A and Sato Y: Alzheimer Dis Assoc Disord 9: 28--38, 1995). In the present study, we aimed to examine whether an increase in regional blood flow in the hippocampus (Hpc-BF) following stimulation of the nAChRs by i.v. injection of nicotine could improve the delayed death of the hippocampal neurons following transient ischemia in rats. Hpc-BF was measured by using a laser Doppler flowmeter. During intermittent (every 2 min) transient occlusion for a total of 6 min of bilateral carotid arteries besides permanent ligation of bilateral vertebral arteries, Hpc-BF decreased to about 16% of the preocclusion level, and 5 or 7 d later, after the occlusion, delayed neuronal death occurred in approximately 70% of the CA1 hippocampal neurons. Hpc-BF was increased dose-dependently by injection of nicotine (30--100 microg/kg, i.v.), independent of mean arterial pressure. Nicotine (30--100 microg/kg) administered 5 min before occlusion slightly but significantly attenuated the occlusion-induced decrease in Hpc-BF. The delayed death of the CA1 hippocampal neurons occurring after transient occlusion was attenuated by pretreatment with nicotine (30--100 microg/kg) to approximately 50% of the total neurons. The results indicate that nAChR stimulation-induced increases in Hpc-BF can protect against ischemia-induced delayed death of hippocampal neurons.

Mild traumatic brain injury does not modify the cerebral blood flow profile of secondary forebrain ischemia in Wistar rats

The rat hippocampus is hypersensitive to secondary cerebral ischemia after mild traumatic brain injury (TBI). An unconfirmed assumption in previous studies of mild TBI followed by forebrain ischemia has been that antecedent TBI did not alter cerebral blood flow (CBF) dynamics in response to secondary ischemia. Using laser Doppler flowmetry (LDF), relative changes in regional hippocampal CA1 blood flow (hCBF) were recorded continuously to quantitatively characterize hCBF before, during, and after 6 min of forebrain ischemia in either normal or mildly traumatized rats. Two experimental groups of fasted male Wistar rats were compared. Group 1 (n = 6) rats were given 6 minutes of transient forebrain ischemia using bilateral carotid clamping and hemorrhagic hypotension. Group 2 (n = 6) rats were subjected to mild (0.8 atm) fluid percussion TBI followed 1 h after trauma by 6 min of transient forebrain ischemia. The laser Doppler flow probe was inserted stereotactically to measure CA1 blood flow. The electroencephalogram (EEG) was continuously recorded. During the forebrain ischemic insult there were no intergroup differences in the magnitude or duration of the decrease in CBF in CA1. In both groups, CBF returned to preischemic values within one minute of reperfusion but traumatized rats had no initial hyperemia. There were no intergroup differences in the CBF threshold when the EEG became isoelectric. These data suggest that the ischemic insult was comparable either with or without antecedent TBI in this model. This confirms that this model of TBI followed by forebrain ischemia is well suited for evaluating changes in the sensitivity of CA1 neurons to cerebral ischemia rather than assessing differences in relative ischemia.

Hippocampal and striatal blood flow during behavior in rats: chronic laser Doppler flowmetry study

A technique is described for the chronic measurement of cerebral blood flow in conscious, unrestrained rodents, utilizing laser doppler flowmetry (LDF) removably coupled to an optical fiber permanently implanted into brain tissue by established stereotaxic procedures. Changes in relative blood flow in response to a range of pharmacological and behavioral challenges were measured in the hippocampus (HBF) and striatum (StBF) 24-72 h and up to 28-32 days after surgical implantation of the optical fiber. Intraseptal microinfusion of L-glutamate in artificial cerebrospinal fluid 48-96 h and 28-32 days after surgery increased HBF. Pentobarbital (Nembutal) and urethane anesthesia decreased HBF. On the day of euthanasia under urethane anesthesia, HBF was demonstrated to be responsive to alteration of blood CO2 via hyper/hypocapnia, and autoregulation was demonstrated in response to hypovolemic hypotension. In behavioral experiments, blood flow was found to increase with activity and locomotion, as well as during paradoxical (PS) and slow-wave sleep (SWS). The greatest increase in CBF was measured during PS. Although basal levels of blood flow were similar between regions, the increase in blood flow during PS was greater in the hippocampus. This simple procedure enables real-time measurement of qualitative changes in regional cerebral blood flow during behaviors in conscious, unrestrained animals. The observation that constancy of measurements was obtained for 1 month enables within-subject analysis in longitudinal studies and reduces the number of animals required for investigations.

Attenuated hippocampal damage after global cerebral ischemia in mice mutant in neuronal nitric oxide synthase

To address the importance of nitric oxide or its reaction products as mediators of neurotoxicity in brain, tissue injury was assessed after transient global ischemia in mice rendered mutant in the gene for neuronal nitric oxide synthase. Halothane-anesthetized wild type and mutant mice were subjected to temporary occlusion of the basilar plus both carotid arteries for 5 or 10 min followed by three days of reperfusion. Hippocampal injury, assessed both by qualitative grading and by cell counting in the CA1 subregion, was significantly less in the mutant mice group after 5 or 10 min of ischemia. Mutant mice exhibited a lower mortality (P < 0.01), less weight loss, more normal grooming and spontaneous motor activity and better grasping in the 10 min group. There were no obvious differences in cerebrovascular anatomy or hemodynamics between wild type and mutant mice. The data suggest that a deficiency of neuronal nitric oxide synthase confers increased resistance to transient global cerebral ischemia, and support the suggestion that selective neuronal nitric oxide synthase inhibitors might reduce tissue injury associated with global cerebral ischemia.

Neuropathology of cerebral ischemia and hypoxia: recent advances in experimental studies on its pathogenesis

Cerebral hypoxia and ischemia are two of the most common disorders of the central nervous system. The pathomechanism has been a focus of interest in neuroscience for many years not only because of the clinical significance but also because of the peculiar distribution of the lesion (selective vulnerability) depending on the type of injury. This article reviews recent advances in the study of hypoxia-induced tissue injury of the central nervous system.