Hippocampal neuronal damage after transient forebrain ischemia in monkeys

Central and Peripheral Secondary Cell Death Processes after Transient Global Ischemia in Nonhuman Primate Cerebellum and Heart

Cerebral ischemia and its pathological sequelae are responsible for severe neurological deficits generally attributed to the neural death within the infarcted tissue and adjacent regions. Distal brain regions, and even peripheral organs, may be subject to more subtle consequences of the primary ischemic event which can initiate parallel disease processes and promote comorbid symptomology. In order to characterize the susceptibility of cerebellar brain regions and the heart to transient global ischemia (TGI) in nonhuman primates (NHP), brain and heart tissues were harvested 6 months post-TGI injury. Immunostaining analysis with unbiased stereology revealed significant cell death in lobule III and IX of the TGI cerebellum when compared to sham cerebellum, coinciding with an increase in inflammatory and apoptotic markers. Cardiac tissue analysis showed similar increases in inflammatory and apoptotic cells within TGI hearts. A progressive inflammatory response and cell death within the cerebellum and heart of chronic TGI NHPs indicate secondary injury processes manifesting both centrally and peripherally. This understanding of distal disease processes of cerebral ischemia underscores the importance of the chronic aberrant inflammatory response and emphasizes the needs for therapeutic options tailored to target these pathways. Here, we discuss the protocols for characterizing the histopathological effects of transient global ischemia in nonhuman primate cerebellum and heart, with an emphasis on the inflammatory and apoptotic cell death processes.

Atrophy of the Posterior Subiculum Is Associated with Memory Impairment, Tau- and Aβ Pathology in Non-demented Individuals

Alzheimer’s disease (AD) is associated with atrophy of the cornu ammonis (CA) 1 and the subiculum subfield of the hippocampus (HC), and with deficits in episodic memory and spatial orientation. These deficits are mainly associated with the functionality of the posterior HC. We therefore hypothesized that key AD pathologies, i.e., β-amyloid and tau pathology would be particularly associated with the volume of the posterior subiculum in non-demented individuals. In our study we included 302 cognitively normal elderly participants (CN), 183 patients with subjective cognitive decline (SCD) and 171 patients with amnestic mild cognitive impairment (MCI), all of whom underwent 3T magnetic resonance images (MRI). The subicular subfield was segmented using Freesurfer 5.3 and divided into 10 volumetric segments moving from the most posterior (segment 1) to the most anterior part along the axis of the hippocampal head and body (segment 10). Cerebrospinal fluid (CSF) Aβ₄₂ and phosphorylated tau (P-tau) were quantified using ELISA and were used as biomarkers for β-amyloid and tau pathology, respectively. In the total sample, tau-pathology and Aβ-pathology and (measured by elevated P-tau and low Aβ₄₂ levels in CSF) and mild memory dysfunction were mostly associated with the volume changes of the posterior subiculum. Both SCD and MCI patients with elevated P-tau or low Aβ₄₂ levels displayed predominantly posterior subicular atrophy in comparisons to control subjects with normal CSF biomarker levels. Finally, there was no main effect of Aβ₄₂ or P-tau when comparing SCD with abnormal P-tau or Aβ₄₂ with SCD with normal levels of these CSF-biomarkers. However, in the left subiculum there was a significant interaction revealing atrophy in the left posterior but not the anterior subiculum in participants with low Aβ₄₂ levels. The same pattern was observed on the contralateral side in participants with elevated P-tau levels. In conclusion, AD pathologies and mild memory dysfunction are mainly associated with atrophy of the posterior parts of the subicular subfields of the HC in non-demented individuals. In light of these findings we suggest that segmentation of the HC subfields may benefit from considering the volume of the different anterior-posterior subsections of each subfield.

Chronic inflammation and apoptosis propagate in ischemic cerebellum and heart of non-human primates

The major pathological consequences of cerebral ischemia are characterized by neurological deficits commonly ascribed to the infarcted tissue and its surrounding region, however, brain areas, as well as peripheral organs, distal from the original injury may manifest as subtle disease sequelae that can increase the risks of co-morbidities complicating the disease symptoms. To evaluate the vulnerability of the cerebellum and the heart to secondary injuries in the late stage of transient global ischemia (TGI) model in non-human primates (NHP), brain and heart tissues were collected at six months post-TGI. Unbiased stereological analyses of immunostained tissues showed significant Purkinje cells loss in lobule III and lobule IX of the TGI cerebellum relative to sham cerebellum, with corresponding upregulation of inflammatory and apoptotic cells. Similarly, TGI hearts revealed significant activation of inflammatory and apoptotic cells relative to sham hearts. Aberrant inflammation and apoptosis in the cerebellum and the heart of chronic TGI-exposed NHPs suggest distal secondary injuries manifesting both centrally and peripherally. These results advance our understanding on the sustained propagation of chronic secondary injuries after TGI, highlighting the need to develop therapeutic interventions targeting the brain, as well as the heart, in order to abrogate cerebral ischemia and its related co-morbidities.

Nonhuman primate model in clinical modeling of diseases for stem cell therapy

Nonhuman primates (NHPs) are alike humans in size, behavior, physiology, biochemistry, and immunology. Given close similarities to humans, the NHP model offers exceptional opportunities to understand the biological mechanisms and translational applications with direct relevance to human conditions. Here, we evaluate the opportunities and limitations of NHPs as animal models for translational regenerative medicine. NHP models of human disease propose exceptional opportunities to advance stem cell-based therapy by addressing pertinent translational concerns related to this research. Nonetheless, the value of these primates must be carefully assessed, taking into account the expense of specialized equipment and requirement of highly specialized staff. Well-designed initial fundamental studies in small animal models are essential before translating research into NHP models and eventually into human trials. In addition, we suggest that applying a directed and collaborative approach, as seen in the evolution of stroke NHP models, will greatly benefit the translation of stem cell therapy in other NHP disease models.

Organization and Detailed Parcellation of Human Hippocampal Head and Body Regions Based on a Combined Analysis of Cyto- and Chemoarchitecture

The hippocampal formation (HF) is one of the hottest regions in neuroscience because it is critical to learning, memory, and cognition, while being vulnerable to many neurological and mental disorders. With increasing high-resolution imaging techniques, many scientists have started to use distinct landmarks along the anterior-posterior axis of HF to allow segmentation into individual subfields in order to identify specific functions in both normal and diseased conditions. These studies urgently call for more reliable and accurate segmentation of the HF subfields DG, CA3, CA2, CA1, prosubiculum, subiculum, presubiculum, and parasubiculum. Unfortunately, very limited data are available on detailed parcellation of the HF subfields, especially in the complex, curved hippocampal head region. In this study we revealed detailed organization and parcellation of all subfields of the hippocampal head and body regions on the base of a combined analysis of multiple cyto- and chemoarchitectural stains and dense sequential section sampling. We also correlated these subfields to macro-anatomical landmarks, which are visible on magnetic resonance imaging (MRI) scans. Furthermore, we created three versions of the detailed anatomic atlas for the hippocampal head region to account for brains with four, three, or two hippocampal digitations. These results will provide a fundamental basis for understanding the organization, parcellation, and anterior-posterior difference of human HF, facilitating accurate segmentation and measurement of HF subfields in the human brain on MRI scans.

In vivo animal stroke models: a rationale for rodent and non-human primate models

On average, every four minutes an individual dies from a stroke, accounting for 1 out of every 18 deaths in the United States. Approximately 795,000 Americans have a new or recurrent stroke each year, with just over 600,000 of these being first attack [1]. There have been multiple animal models of stroke demonstrating that novel therapeutics can help improve the clinical outcome. However, these results have failed to show the same outcomes when tested in human clinical trials. This review will discuss the current in vivo animal models of stroke, advantages and limitations, and the rationale for employing these animal models to satisfy translational gating items for examination of neuroprotective, as well as neurorestorative strategies in stroke patients. An emphasis in the present discussion of therapeutics development is given to stem cell therapy for stroke.

Anomaly in aortic arch alters pathological outcome of transient global ischemia in Rhesus macaques

We investigated a non-human primate (NHP) transient global ischemia (TGI) model which was induced by clipping the arteries originating from the aortic arch. Previously we demonstrated that our TGI model in adult Rhesus macaques (Macaca mulatta) results in marked neuronal cell loss in the hippocampal region, specifically the cornu Ammonis (CA1) region. However, we observed varying degrees of hippocampal cell loss among animals. Here, we report for the first time an anomaly of the aortic arch in some Rhesus macaques that appears as a key surgical factor in ensuring the success of the TGI model in this particular NHP. Eleven adult Rhesus macaques underwent the TGI surgery, which involved 10-15-minute clipping of both innominate and subclavian arteries. Animals were allowed to survive between 1 day and 28 days after TGI. Because of our experience and knowledge that Japanese macaques exhibited only innominate and subclavian arteries arising from the aortic arch, macroscopic visualization of these two arteries alone in the Rhesus macaques initially assured us that clipping both arteries was sufficient to produce TGI. During the course of one TGI operation, however, we detected 3 arterial branches arising from the aortic arch, which prompted us to subsequently search for 3 branches in succeeding TGI surgeries. In addition, we performed post-mortem examination of the heart to confirm the number of arterial branches in the aortic arch. Finally, in order to reveal the pathological effect of the aortic arch anomaly, we compared the hippocampal cell loss between animals found to have 3 arterial branches but had all or only two branches clipped during TGI operation. Post-mortem examination revealed that eight NHPs had the typical two arterial aortic branches, but three NHPs displayed an extra arterial aortic branch, indicating that about 30% of Rhesus macaques had 3 arterial branches arising from the aorta. Histological analyses using Nissl staining showed that in NHPs with the aortic arch anomaly clipping only two of three arterial branches led to a partial cell loss and minimal alteration in number of cell layers in the hippocampal region when compared with clipping all three branches, with the hippocampal cell death in the latter resembling the pathological outcome achieved by clipping the two arterial branches in NHPs displaying the typical two-artery aortic arch. The finding that 3 of 11 NHPs exhibited an extra arterial aortic branch recognizes this aortic arch anomaly in Rhesus macaques that warrants a critical surgical maneuver in order to successfully produce consistent TGI-induced hippocampal cell loss.

Hippocampal CA1 cell loss in a non-human primate model of transient global ischemia: a pilot study

We exposed adult Rhesus (Macaca mulatta) to a transient global ischemia, which was induced by clipping the innominate and subclavian arteries that originated from the aortic arch. NHP1 received 20-min, while NHP2 and NHP3, were exposed to a 15-min transient global ischemia and were euthanized at day 1 (NHP1), day 5 (NHP2) or day 30 (NHP3) after ischemia, respectively. NHP1 displayed severe paralysis and rigidity, and intermittent convulsions over the next 24 h. Although histological examination of the brain revealed no detectable gross brain damage (i.e., swelling) and only minimal cell loss in the hippocampus, the acute survival time after surgery likely prevented the cerebral ischemia to fully develop and to be morphologically manifested. Nonetheless, the 20-min ischemia might have been too severe and caused a systemic multiple organ collapse that produced the abnormal behavioral symptoms. On the other hand, NHP2 and NHP3 which received 15-min ischemia only exhibited minor hindlimb paralysis. Indeed, by 48 h after ischemia, both animals appeared fully recovered with only fine motor deficits. Immunohistochemical examination revealed that NHP2 and 3, but not NHP1, had a marked neuronal cell loss in the hippocampal region, specifically the cornu Ammonis (CA1) region. The cell loss in these two ischemic NHP hippocampi was further confirmed by direct comparison with a normal Rhesus brain. These findings replicate the brain pathology seen in Japanese macaques exposed to the same ischemia model [T. Tsukada, M. Watanabe, T. Yamashima, Implications of CAD and DNase II in ischemic neuronal necrosis specific for the primate hippocampus, J. Neurochem. 79 (2001) 1196-1206; T. Yamashima, Implication of cysteine proteases calpain, cathepsin and caspase in ischemic neuronal death of primates, Prog. Neurobiol. 62 (2000) 273-295; T. Yamashima, Y. Kohda, K. Tsuchiya, T. Ueno, J. Yamashita, T. Yoshioka, E. Kominami, Inhibition of ischemic hippocampal neuronal death in primates with cathepsin B inhibitor CA-074: a novel strategy for neuroprotection based on calpain-cathepsin hypothesis, Eur. J. Neurosci. 10 (1998) 1723-1733; T. Yamashima, T.C. Saido, M. Takita, A. Miyazawa, J. Yamano, A. Miyakawa, H. Nishijyo, J. Yamashita, S. Kawashima, T. Ono, T. Yoshioka, Transient brain ischemia provokes Ca2+, PIP2 and calpain responses prior to delayed neuronal death in monkeys, Eur. J. Neurosci. 8 (1996) 1932-1944; T. Yamashima, A.B. Tonchey, T. Tsukada, T.C. Saido, S. Imajoh-Ohmi, T. Momoi, E. Kominami, Sustained calpain activation associated with lysosomal rupture executes necrosis of the postischemic CA1 neurons in primates, Hippocampus 13 (2003) 791-800]. The present minimally invasive transient global ischemia model using Rhesus shows many histopathological symptoms seen in human patients who experienced global ischemia, and should allow translational validation of experimental therapeutics for ischemic injury. Additional studies are warranted to reveal behavioral deficits associated with this ischemia model.

Ameliorative effects of a neuroprotective agent, T-817MA, on place learning deficits induced by continuous infusion of amyloid-beta peptide (1-40) in rats

Alzheimer's disease (AD) is a neurodegenerative disease characterized by cognitive decline due to neuronal loss and neural network dysfunction. It has been postulated that progressive neuronal loss in AD is consequence of the neurotoxic properties of the amyloid-beta peptide (Abeta). In the present study, we investigated the effect of T-817MA (1-{3-[2-(1-benzothiophen-5-yl)ethoxy] propyl}-3-azetidinol maleate), a newly synthesized neurotrophic compound, on place learning deficits in rats with hippocampal damages. To induce granule cell loss in the dentate gyrus (DG) of the hippocampus, Abeta (1-40) was continuously infused (300 pmol/day) into the cerebral ventricle using a mini-osmotic pump for 5 weeks. Three weeks after the Abeta infusion, the rats were tested in a place learning task, which required them to alternatively visit two diametrically opposed areas in an open field to obtain intracranial self-stimulation reward. The results indicated that the Abeta-infused rats without treatment of T-817MA displayed learning impairment in the task; their performance level was significantly inferior to that of the vehicle rats. Treatment of T-817MA (8.4 mg/kg/day, p.o.) significantly improved the task performance of the Abeta-infused rats. Furthermore, T-817MA prevented granule cell loss due to Abeta-infusion, which was correlated to task performance of the rats. However, other cognitive enhancer, an acetylcholinesterase inhibitor, had no such effects. The results demonstrated that T-817MA ameliorated learning deficits induced by Abeta infusion, which might be attributed to neuroprotection in the hippocampus.

Effects of the anti-platelet aggregation drug dilazep on cognitive function in Dahl salt-sensitive rats

Among the consequences of the increasing prolongation of lifespan is a worldwide increase in the number of cases of dementia or impaired cognition. In the present study, to test the hypothesis that mechanisms independent of high blood pressure are involved in maintaining cognitive function, we assessed the effects of long-term dilazep treatment on cognitive dysfunction in normotensive Dahl salt-sensitive (Dahl S) rats fed a low-salt diet, using the standard passive avoidance test. Normotensive Dahl S rats fed a 0.3% NaCl diet were treated for 6 months with low-dose dilazep (2.5 microg/ml in drinking water) or high-dose dilazep (12.5 microg/ml). Systolic blood pressure was within normotensive range throughout the study and did not differ among the experimental groups. The results of the passive avoidance test revealed that dilazep treatment attenuated the decline of latency time relative to that in the untreated control rats (control latency time, 235 s; low-dilazep group, 389 s; high-dilazep group, 397 s), suggesting that the cognitive function of normotensive Dahl S rats was improved by dilazep treatment. This improvement of cognition was associated with significant increases in the number of neuronal cells in the hippocampal region and with an increase in capillary length in dilazep-treated Dahl rats. In addition, the dilazep treatments significantly attenuated arteriolar injury of glomeruli in the kidney. These data suggest that dilazep treatment, through vascular and non-vascular effects, maintains the brain function in Dahl S rats susceptible to vascular injury and organ dysfunction.

Sustained calpain activation associated with lysosomal rupture executes necrosis of the postischemic CA1 neurons in primates

Because of the paucity of primate experimental models, the precise molecular mechanism of ischemic neuronal death remains unknown in humans. This study focused on nonhuman primates to determine which cascade necrosis or apoptosis is predominantly involved in the development of delayed (day 5) neuronal death in the hippocampal CA1 sector undergoing 20 min ischemia. We investigated expression, activation, and/or translocation of micro-calpain, lysosome-associated membrane protein-1 (LAMP-1), caspase-3, and caspase-activated DNase (CAD), as well as morphology of the postischemic CA1 neurons and DNA electrophoresis pattern. Immunoblotting showed sustained (immediately after ischemia until day 5) and maximal (day 3) activation of micro-calpain. The immunoreactivity of activated micro-calpain became remarkable as coarse granules at lysosomes on day 2, while it translocated throughout the perikarya on day 3. The immunoreactivity of LAMP-1 also showed a dynamic and concomitant translocation that was maximal on days 2-3, indicating calpain-mediated disruption of the lysosomal membrane after ischemia. In contrast, immunoblotting demonstrated essentially no increase in the activated caspase-3 at any time points after ischemia, despite upregulation of pro-caspase-3. Although expression of CAD was slightly upregulated on day 1 or 2, or both, it was much less compared with lymph node or intestine tissues. Furthermore, light and electron microscopy showed eosinophilic coagulation necrosis and membrane disruption without apoptotic body formation, while DNA electrophoresis did not show a ladder pattern, but rather a smear pattern. Sustained calpain activation and the resultant lysosomal rupture, rather than CAD-mediated apoptosis, may cause ischemic neuronal necrosis in primates.

PET imaging of ischemic neuronal death in the hippocampus of living monkeys

The aim of the present study was to visualize postischemic hippocampal neuronal death in the living monkey brain, using a high-resolution positron emission tomography (PET) and novel radioligands. In preceding papers, we reported on postischemic hippocampal neuronal death in a model of Japanese monkeys (Macaca fuscata) undergoing a 20-min complete whole-brain ischemia. Using the same model here, we investigated the in vivo bindings of two radiotracers, [11C]Ro15-4513 (a type II benzodiazepine receptor ligand) and [11C](+)3-MPB (a muscarinic cholinergic receptor ligand), in the hippocampus on day 7 after ischemia, as compared to the normal hippocampus. A significant decrease in the in vivo binding of [11C]Ro154513 and [11C(+)3-MPB was observed in the postischemic monkey hippocampus on day 7 after ischemia compared to controls. Light and electron microscopic analyses of postischemic CA1 neurons showed typical features of coagulation necrosis, as associated with a marked reduction of postsynaptic densities and presynaptic vesicles. These results suggest that semiquantification of hippocampal neuronal death is possible in the living primate brain using PET, and that the same procedures can be applied for evaluating neuronal cell loss in patients with ischemic injuries and/or dementia.

Neuroprotective effects of pyridoxal phosphate and pyridoxal against ischemia in monkeys

Previously, in monkeys undergoing 20 min whole brain ischemia we demonstrated that the activated calpain-induced lysosomal disruption with the resultant leakage of cathepsins B and L, causes neuronal death in the cornu Ammonis (CA) 1 sector on day 5. Selective cathepsin inhibitors significantly protected ischemic CA1 neurons from delayed necrosis. Recently, pyridoxal phosphate (PLP) and pyridoxal (hydrochloride) (PL) were demonstrated to inhibit cathepsins B and L in vitro, because the active aldehyde at position 4 of the pyridine ring has an affinity for the active site -SH of cysteine residues of cathepsins. Here, we studied whether PLP and PL can, in vivo, protect monkey CA1 neurons from ischemic insult. In monkeys undergoing 20 min whole brain ischemia, 15 mg/kg body weight/day of drugs were intravenously injected for 10 days before and after the ischemic insult. Histological analysis of the surviving CA1 neurons was done using the hippocampus resected on day 5 after ischemia. For PLP or PL, approximately 17% (P = 0.0639) or 54% (P < 0.0001) of the total population (100%) of control CA1 neurons were, respectively, saved from the ischemia-induced neuronal death, showing a remarkable contrast to the surviving neurons (approximately 3.9%) in non-treated monkeys. These data suggested that PL (perhaps PLP intracellularly) is useful as a novel neuroprotectant in primates.

Implications of CAD and DNase II in ischemic neuronal necrosis specific for the primate hippocampus

The exact molecular mechanism of ischemic neuronal death still remains unclear from rodents to primates. A number of studies using lower species animals have suggested implication of apoptosis cascade, while using monkeys the authors recently claimed necrosis cascade by calpain-induced leakage of lysosomal cathepsins (calpain-cathepsin hypothesis). This paper is to study implications of apoptotic versus necrotic cascades for the development of hippocampal CA1 neuronal death in the primate brain undergoing complete global ischemia. Here, we focused on two terminal cell death effectors; caspase-activated DNase (CAD) and lysosomal enzyme DNase II, in the monkey CA1 sector undergoing 18 min ischemia. The expressions of their mRNA and proteins, and the subcellular localizations as well as ultrastructure and specific DNA gel electrophoresis were examined. Expression of CAD was much less in the normal brain, compared with the lymph node or heart tissues. On day 1 after ischemia, however, CAD mRNA and protein were significantly increased in the CA1 sector, and then CAD protein immunohistochemically showed a translocation from the perikarya into the nucleus. Activated DNase II protein was significantly increased on days 2 and 3 after ischemia, and also showed a similar translocation indicating lysosomal leakage. Although the post-ischemic CA1 neurons showed positive terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) staining on days 3-5, they showed eosinophilic coagulation necrosis on light microscopy, and frank membrane disruption and mild chromatin condensation on electron microscopy. Furthermore, DNA smear pattern typical for necrosis was observed instead of DNA laddering. These data altogether suggest that the post-ischemic CA1 neuronal death of the monkey occurs not by apoptosis but by necrosis with participations of lysosomal enzymes DNase II and cathepsins as well as CAD. The interactions between apoptotic (caspase-3 and CAD) and necrotic (calpain, cathepsin and DNase II) cascades should be studied further.

Implication of cysteine proteases calpain, cathepsin and caspase in ischemic neuronal death of primates

Although more than 8000 papers of apoptosis are published annually, there are very few reports concerning necrosis in the past few years. A number of recent studies using lower species animals have suggested that the cornu Ammonis (CA) 1 neuronal death after brief global cerebral ischemia occurs by apoptosis, an active and genetically controlled cell suicide process. However, the studies of monkeys and humans rather support necrosis, the calpain-mediated release of lysosomal enzyme cathepsin after ischemia conceivably contributes to the cell degeneration of CA1 neurons. This paper provides an overview of recent developments in ischemic neuronal death, presents the cascade of the primate neuronal death with particular attentions to the cysteine proteases, and also indicates selective cathepsin inhibitors as a novel neuroprotectant. Furthermore, the possible interaction of calpain, cathepsin, and caspase in the cascade of ischemic neuronal death is discussed.

Ameliorative effects of tamolarizine on place learning impairment induced by transient forebrain ischemia in rats

In the present study we investigated the effect of (+/-)-1-(3, 4-dimethoxyphenyl)-2-(4-diphenylmethylpiperazinyl) ethanol dihydrochloride (tamolarizine), a calcium entry blocker, on place learning impairment in rats with damage selective to the hippocampal CA1 subfield induced by transient forebrain ischemia. Tamolarizine was administered (40 mg/kg) immediately after 15-min brain ischemia. Place learning was tested in a task in which the rat was required to alternatively visit two places located diametrically opposite each other in an open field. The ischemia+saline group showed severe learning impairment in this task; their performance level was significantly inferior to that of the sham-operated group through the test period (30 days). Although the ischemia+tamolarizine group showed slight impairment of place learning during the course of this test, they later reached almost the same performance level as the sham-operated group. Selective neuronal loss in the CA1 subfield was much less in the ischemia+tamolarizine group than in the ischemia+saline group. These results indicate that tamolarizine treatment protects the hippocampus from ischemic brain damage and ameliorates place learning impairment.

Long-term inhibition of renin-angiotensin system sustains memory function in aged Dahl rats

The Dahl salt-sensitive (DS) rat, a genetic model of salt-induced hypertension in humans, is more likely to develop severe vascular injuries than a rat with spontaneous hypertension. We designed an experiment to scrutinize the effects of renin-angiotensin inhibition on cognitive dysfunction in the aged, normotensive DS with a passive avoidance test. Eighteen months of treatment with a very low dose of the angiotensin-converting enzyme (ACE) inhibitor cilazapril (2.5 microg/mL in drinking water) or the angiotensin II type 1 receptor antagonist E4177 did not reduce blood pressure throughout the experiment, although in the low dose cilazapril group (12.5 microg/mL in drinking water), blood pressure dropped within 6 months after treatment began. The cilazapril treatments dose-dependently improved memory function in the aged, normotensive DS fed a low-salt diet compared with the untreated, control rats. This improvement was associated with significant increases in hippocampal CA1 cells and capillary densities in the CA1 regions compared with those in the untreated DS. Similarly, E4177 slightly improved the memory dysfunction observed in the aged DS. The cells in the hippocampal CA1 region were restored slightly, but the capillary densities were not influenced by the receptor antagonist. On the other hand, the ACE inhibitor and receptor antagonist both attenuated urinary protein excretions with an improvement of glomerular sclerosis. These data suggest that long-term treatment with an ACE inhibitor improves memory dysfunction probably through restoration of capillary and hippocampal cells. The effects are due to the inhibition of the angiotensin II type 1 receptor and probably to the enhancement of the kallikrein-kinin system.

Inhibition of ischaemic hippocampal neuronal death in primates with cathepsin B inhibitor CA-074: a novel strategy for neuroprotection based on 'calpain-cathepsin hypothesis'

Although Cornu Ammonis (CA) 1 neurons of the hippocampus are known to be vulnerable to transient ischaemia, the mechanism of ischaemic neuronal death is still unknown, and there are very few strategies to prevent neuronal death at present. In a previous report we demonstrated micro-calpain activation at the disrupted lysosomal membrane of postischaemic CA1 neurons in the monkey undergoing a complete 20 min whole brain ischaemia. Using the same experimental paradigm, we observed that the enzyme activity of the lysosomal protease cathepsin B increased throughout the hippocampus on days 3-5 after the transient ischaemia. Furthermore, by immunocytochemistry cathepsin B showed presence of extralysosomal immunoreactivity with specific localization to the cytoplasm of CA1 neurons and the neuropil of the vulnerable CA1 sector. When a specific inhibitor of cathepsin B, the epoxysuccinyl peptide CA-074 (C18H29N3O6) was intravenously administered immediately after the ischaemic insult, approximately 67% of CA1 neurons were saved from delayed neuronal death on day 5 in eight monkeys undergoing 20 min brain ischaemia: the extent of inhibition was excellent in three of eight and good in five of eight monkeys. The surviving neurons rescued by blockade of lysosomal activity, showed mild central chromatolysis and were associated with the decreased immunoreactivity for cathepsin B. These observations indicate that calpain-induced cathepsin B release is crucial for the development of the ischaemic neuronal death, and that a specific inhibitor of cathepsin B is of potential therapeutic utility in ischaemic injuries to the human CNS.

Cognitive deficits induced by global cerebral ischaemia: prospects for transplant therapy

Global ischaemia induced by interruption of cerebral blood flow results in damage to vulnerable cells, notably in the CA1 and hilar hippocampal fields, and is frequently associated with memory deficits. This review examines cognitive deficits that occur in animal models of global ischaemia in rats and monkeys, the extent to which these deficits are associated with CA1 cell loss, and the evidence for functional recovery following transplants of foetal CA1 cells and grafts of conditionally immortalised precursor cells. In rats, impairments are seen most consistently in tasks of spatial learning and spatial working memory dependent on use of allocentric environmental cues. In monkeys, ischaemic deficits have been shown to a moderate extent in delayed object recognition tasks, but animals with a selective excitotoxic CA1 lesion show a profound impairment in conditional discrimination tasks, suggesting that these may be a more sensitive measure of ischaemic impairments. Several studies have reported correlational links between the extent of CA1 cell loss following two or four vessel occlusion (2 VO, 4 VO) in rats and behavioural impairments, but recent findings indicate that at intermediate levels of damage these relationships are weak and variable, and emerge clearly only when animals with maximal CA1 cell loss are included, suggesting that the deficits involve more than damage to the CA1 field. Nevertheless, ischaemic rats and CA1-lesioned marmosets with grafts of foetal CA1 cells show substantial improvements; in rats these are not found with grafts from other hippocampal fields. Conditionally immortalised cell lines and trophic grafts are currently being assessed for their functional potential in animal models, because clinical use of foetal cells will not be practicable. Recent findings suggest that an expanded population of neuroepithelial cells derived from the conditionally immortalised H-2Kb-tsA58 transgenic mouse improve spatial learning as effectively as CA1 foetal grafts in rats subjected to 4 VO, and clonal lines from the same source show similar promise. Lines derived from precursor cells have the potential to develop into different types of cell (neuronal or glial) depending on signals from the host brain. These cell lines may therefore have the capacity to repair damaged host circuits more precisely than is possible with foetal grafts, and offer a promising, approach both to functional recovery and to elucidating graft-host interactions.

Ischemic neuronal damage specific to monkey hippocampus: histological investigation

We previously reported lesions confined specifically to the hippocampus when produced by occluding eight vessels (the bilateral vertebral, common, internal, and external carotid arteries), which supply blood to the brain. However, histopathological changes in the primate brain, caused by ischemic injury, have not previously been thoroughly investigated. In the present study, macaque monkeys were subjected to 5-18-min ischemia by occluding the eight vessels. After the brains were perfused and fixed 5 days after the occlusion, all regions were histologically investigated for ischemic cell changes. Ischemia for 5 min produced no ischemic cell change. Ischemia for 10-15 min produced cell death limited to the deeper portion of the pyramidal cell layer of the CA1 subfield in the hippocampus. In most monkeys, no cell death was observed in any brain region outside of the hippocampus after ischemia for up to 15 min. Ischemia for 18 min produced more widespread cell death in the CA1 subfield of the hippocampus, and cell death was no longer confined to the hippocampus, but was observed in layers III, V, and VI of the neocortices, the striatum, and some other regions. Brains that were perfused and fixed 1 year after 15-min ischemic insult revealed no ischemic cell morphological change in any region, but the number of pyramidal cells in the CA1 subfield was decreased to about half. The results indicate that the CA1 subfield of the monkey hippocampus is the precise region of the brain most susceptible to ischemic insult in the primate forebrain, and after a critical time (15-min ischemia in this procedure) ischemic cell changes occur suddenly and extensively. Ischemia due to occlusion of eight arteries for 10-15 min could produce a model of human amnesia caused by transient ischemic insult.

Physiological results of monkey brain ischemia, and protection by a calcium blocker

Physiological and histological investigation was undertaken to examine dynamic and metabolic changes due to transient ischemic insult of the monkey brain with and without postischemic treatment by the calcium entry blocker, NC-1100 (1 mg/kg, IV). Monkeys were subjected to temporary occlusion of the eight major arteries: bilateral common carotid, internal and external carotid, and vertebral arteries. Blood flow was restored after 5-, 10-, 13-, and 15-min ischemia in different monkeys. The amplitudes of extradural, cortical, and hippocampal electroencephalograms decreased severely within 1-6 min after beginning occlusion. Complete recovery of these electroencephalograms required more than 1 h. During ischemia, significant change was obvious in arterial glucose, and systolic, diastolic, and mean blood pressure, all of which increased. There were no significant physiological differences between the untreated and NC-1100-treated groups, except decreased diastolic blood pressure and slightly lower postischemic heart rate in the treated group. These small differences might be accounted for by the effect of the calcium blocker. Ten to 15 minutes ischemia caused cell changes, including cell death, which were confined almost exclusively to the CA1 subfield of untreated hippocampi examined the fifth day after occlusion. However, no ischemia-induced cell change was observed in the CA1 subfield of hippocampi subjected to 10 to 15 min ischemia in the NC-1100-treated group. It was concluded that a calcium entry blocker can protect neurons from mild ischemia-induced injury and might ameliorate morphological damage and functional impairment of the brain due to ischemia in patients who suffer transient anoxic or hypoxic injury. The present physiological data should contribute to their clinical treatment.

Cognitive deficits induced by global cerebral ischaemia: relationship to brain damage and reversal by transplants

The CA1 and hilar fields of the hippocampus are highly vulnerable to lack of oxygen after interruption of blood flow to the brain. Severe anterograde memory loss, seen in a significant proportion of heart attack survivors, has been attributed to selective bilateral ischaemic damage to the hippocampus. Animal models of global ischaemia, induced by extracranial occlusion of the major ascending arteries, enable assessment of the neuropathological and functional consequences of transient interruption of cerebral blood flow, and can inform strategies to reduce or alleviate ischaemic brain damage. This review focuses firstly on the nature of cognitive deficits induced by global ischaemia, how far they are consistent with lesion-based accounts of hippocampal function, and the extent to which these deficits can be correlated with CA1 cell loss. The second focus of the review is to examine the limited evidence for graft-induced recovery of cognitive function in animals subjected to global ischaemia. Recent findings that grafted foetal cells from discrete hippocampal fields follow appropriate laminar routes to form functional connections with host neurons, and that growth factors protect cells from ischaemic damage, have suggested that CA1 or trophic grafts placed in the region of ischaemic CA1 cell loss might restore or protect this vulnerable sector, and reduce cognitive deficits.

Distribution, morphological features, and synaptic connections of parvalbumin- and calbindin D28k-immunoreactive neurons in the human hippocampal formation

Calcium binding proteins calbindin D28k (CaBP) and parvalbumin (PV) are known to form distinct subpopulations of gamma-aminobutyric acid (GABA)ergic neurons in the rodent hippocampal formation. Light and electron microscopic morphology and connections of these protein-containing neurons are only partly known in the primate hippocampus. In this study, CaBP and PV were localized in neurons of the human hippocampal formation including the subicular complex (prosubiculum, subiculum, and presubiculum) in order to explore to what extent these subpopulations of hippocampal neurons differ in phylogenetically distant species. CaBP immunoreactivity was present in virtually all granule cells of the dentate gyrus and population of in a proportion of pyramidal neurons in the CA1 and CA2 regions. A distinct population of CaBP-positive local circuit neurons was found in all layers of the dentate gyrus and Ammon's horn. Most frequently they were located in the molecular layer of the dentate gyrus and the pyramidal layer of Ammon's horn. In the subicular complex pyramidal neurons were not immunoreactive for CaBP. In the prosubiculum and subiculum immunoreactive nonpyramidal neurons were equally distributed in all layers, whereas in the presubiculum they occurred mainly in the superficial layers. Electron microscopy showed typical somatic and dendritic features of the granule, pyramidal, and local circuit neurons. CaBP-positive mossy fiber terminals in the hilus of the dentate gyrus and terminals of presumed pyramidal neurons of Ammon's horn formed asymmetric synapses with dendrites and spines. CaBP-positive terminals of nonprincipal neurons formed symmetric synapses with dendrites and dendritic spines, but never with somata or axon initial segments. PV was exclusively present in local circuit neurons in both the hippocampal formation and subicular complex. Most of the PV-positive cell bodies were located among or close to the principal cell layers. However, large numbers of immunoreactive neurons were also found in the molecular layer of the dentate gyrus and in strata oriens of Ammon's horn. PV-positive cells were equally distributed in all layers of the subicular complex. Electron microscopy showed the characteristic somatic and dendritic features of local circuit neurons. PV-positive axon terminals formed exclusively symmetric synapses with somata, axon initial segments and dendritic shafts, and in a few cases with dendritic spines. The CaBP- and PV-containing neurons formed similar subpopulations in rodents, monkeys, and humans, although the human hippocampus displayed the largest variability of these immunoreactive neurons in their morphology and location. Calcium binding protein-containing neurons frequently occurred in the molecular layer of the human dentate gyrus and in the stratum lacunosum-moleculare of Ammon's horn.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium entry blocker ameliorates ischemic neuronal damage in monkey hippocampus

Effects of treatment with (+/-)-1-(3,4-dimethoxyphenyl)-2-(4- diphenylmethylpiperazinyl)ethanol dihydrochloride (NC-1100), a calcium entry blocker, on ischemic neuronal damage were investigated. Monkeys were subjected to temporary occlusion of eight (bilateral common carotid, internal and external carotid, and vertebral arteries) major arteries. Blood flow was restored after 5, 10, 13, and 15 min occlusion, and NC-1100 (1 mg/kg) was then immediately infused intravenously. Monkeys were killed by perfusion fixation 5 days after occlusion. All brain regions were then histologically investigated for ischemic neuronal changes. Physiological data of NC-1100-treated subjects were not significantly different than those of untreated subjects. Heart rate tended to decrease after ischemia in treated subjects. Occlusion of 8 arteries for 10 to 15 min produced ischemic neuronal damage confined exclusively to the CA1 subfield of the hippocampus. Treatment with NC-1100 markedly reduced ischemic neuronal damage in the CA1 subfield of the hippocampus. It is suggested that postischemic treatment with the calcium entry blocker, NC-1100, might protect the brain from the ischemic damage produced in patients suffering from transient ischemia.