Elsevier

Brain Research

Volume 877, Issue 2, 22 September 2000, Pages 281-287
Brain Research

Research report
Effect of hypotension severity on hippocampal CA1 neurons in a rat global ischemia model

https://doi.org/10.1016/S0006-8993(00)02684-6Get rights and content

Abstract

Neuronal death in the hippocampal CA1 subregion has been shown to occur in a delayed manner after transient global ischemia. The 2-vessel occlusion model is one of the most frequently used global ischemia paradigms in rodents. Although researchers often fail to induce bilateral delayed CA1 neuronal death, the importance of hypotension severity has not been fully discussed. We induced 10 min of global ischemia with 2-vessel occlusion and various severities of hypotension in rats, and the subsequent neuronal damage and neurogenesis in the hippocampal CA1 pyramidal cell layer were immunohistochemically studied. Neuronal apoptosis after global ischemia was also characterized by terminal deoxynucleotidyl transferase-mediated uridine 5′-triphosphate-biotin nick end labeling (TUNEL). The mean arterial blood pressure of 31-35 mmHg was the most appropriate range of hypotension in this model because of low mortality and consistent bilateral CA1 injury. Most of the neurons in the CA1 pyramidal cell layer lost neuron specific nuclear protein and became TUNEL-positive 3 days after ischemia. There was no evidence of apoptosis or neurogenesis at 7-28 days. There were ischemia-tolerant neurons in the CA1 pyramidal cell layer that survived delayed neurodegeneration, however, further studies are necessary to characterize the property of these neurons.

Introduction

The global ischemia model has been used to analyze selective vulnerability in the hippocampal CA1 subregion. Neuronal death in the CA1 subregion has been shown to occur 2–3 days after ischemia [1], [9], [16]. The 2-vessel occlusion model, first described by Smith et al. [15], is one of the most frequently used global ischemia paradigms in rodents [17], [18], [19]. Although researchers often fail to induce bilateral CA1 neuronal death using Smith’s or a modified 2-vessel occlusion model [5], [13], improvement in the technical aspects of the ‘‘success rate’’ has not been fully discussed. On the other hand, the effect of hypotension severity on neuronal death has not been thoroughly studied. We induced 10 min of global ischemia using a 2-vessel occlusion and hypotension model with various severities of hypotension. Subsequent neuronal damage in the hippocampal CA1 pyramidal cell layer was immunohistochemically studied. The neuronal proliferation was examined by administration of a thymidine analog, bromodeoxyuridine (BrdU). Neuronal apoptosis after global ischemia was also characterized by terminal deoxynucleotidyl transferase-mediated uridine 5′-triphosphate-biotin nick end labeling (TUNEL) staining.

Section snippets

Surgery

Transient global ischemia was induced by bilateral common carotid artery occlusion and bleeding to lower the mean arterial blood pressure (MABP) to 26-30 mmHg (severe hypotension group), 31-35 mmHg (moderate hypotension group) and 36-40 mmHg (mild hypotension group) using the method originally described by Smith et al. [15] with some modifications [1]. Male Sprague-Dawley rats (225–275 g, Charles River Laboratories, Wilmington, MA) were anesthetized with 5% isoflurane and maintained during

Results

The physiological data before and 10 min after ischemia were not significantly different among the three groups (Table 1). As shown in Table 2, severe hypotension caused more than 50% mortality, however, moderate and mild hypotension caused substantially lower mortality. A majority of the postoperative deaths occurred within 3 days of ischemia. The percentage of the damaged area in the mild hypotension group was significantly lower than in the moderate and severe groups (Fig. 1A). In the mild

Discussion

Several studies have described the fact that unilateral CA1 neuronal cell death often occurs using the model of bilateral carotid occlusion combined with systemic hypotension [5], [13]. Smith et al. [15] originally designed this model to lower the MABP to 50 mmHg, and this severity of hypotension was used as a standard MABP during ischemia [17], [18], [19]. However, it has been reported that the MABP of 50 mmHg did not induce consistent bilateral hippocampal injury [5]. In their model, the

Acknowledgements

This study was supported by National Institutes of Health grants NS14543, NS25372, NS36147, NS37530, NS38653 and NO1 NS82386. P.H.C. is a recipient of the Jacob Javits Neuroscience Investigator Award. We thank Bernard Calagui, Liza Reola and Jane O. Kim for technical assistance.

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