Quantitative effects of cerebral infarction on spatial learning in rats

Quantification of hypoxic regions distant from occlusions in cerebral penetrating arteriole trees

The microvasculature plays a key role in oxygen transport in the mammalian brain. Despite the close coupling between cerebral vascular geometry and local oxygen demand, recent experiments have reported that microvascular occlusions can lead to unexpected distant tissue hypoxia and infarction. To better understand the spatial correlation between the hypoxic regions and the occlusion sites, we used both in vivo experiments and in silico simulations to investigate the effects of occlusions in cerebral penetrating arteriole trees on tissue hypoxia. In a rat model of microembolisation, 25 μm microspheres were injected through the carotid artery to occlude penetrating arterioles. In representative models of human cortical columns, the penetrating arterioles were occluded by simulating the transport of microspheres of the same size and the oxygen transport was simulated using a Green’s function method. The locations of microspheres and hypoxic regions were segmented, and two novel distance analyses were implemented to study their spatial correlation. The distant hypoxic regions were found to be present in both experiments and simulations, and mainly due to the hypoperfusion in the region downstream of the occlusion site. Furthermore, a reasonable agreement for the spatial correlation between hypoxic regions and occlusion sites is shown between experiments and simulations, which indicates the good applicability of in silico models in understanding the response of cerebral blood flow and oxygen transport to microemboli.

The brain function depends on the continuous oxygen supply through the bloodstream inside the microvasculature. Occlusions in the microvascular network will disturb the oxygen delivery in the brain and result in hypoxic tissues that can lead to infarction and cognitive dysfunction. To aid in understanding the formation of hypoxic tissues caused by micro-occlusions in the penetrating arteriole trees, we use rodent experiments and simulations of human vascular networks to study the spatial correlations between the hypoxic regions and the occlusion locations. Our results suggest that hypoxic regions can form distally from the occlusion site, which agrees with the previous observations in the rat brain. These distant hypoxic regions are primarily due to the lack of blood flow in the brain tissues downstream of the occlusion. Moreover, a reasonable agreement of the spatial relationship is found between the experiments and the simulations, which indicates the applicability of in silico models to study the effects of microemboli on the brain tissue.

ROCK and PDE-5 Inhibitors for the Treatment of Dementia: Literature Review and Meta-Analysis

Dementia is a disease in which memory, thought, and behavior-related disorders progress gradually due to brain damage caused by injury or disease. It is mainly caused by Alzheimer’s disease or vascular dementia and several other risk factors, including genetic factors. It is difficult to treat as its incidence continues to increase worldwide. Many studies have been performed concerning the treatment of this condition. Rho-associated kinase (ROCK) and phosphodiesterase-5 (PDE-5) are attracting attention as pharmacological treatments to improve the symptoms. This review discusses how ROCK and PDE-5 affect Alzheimer’s disease, vascular restructuring, and exacerbation of neuroinflammation, and how their inhibition helps improve cognitive function. In addition, the results of the animal behavior analysis experiments utilizing the Morris water maze were compared through meta-analysis to analyze the effects of ROCK inhibitors and PDE-5 inhibitors on cognitive function. According to the selection criteria, 997 publications on ROCK and 1772 publications on PDE-5 were screened, and conclusions were drawn through meta-analysis. Both inhibitors showed good improvement in cognitive function tests, and what is expected of the synergy effect of the two drugs was confirmed in this review.

Involvement of Progranulin and Granulin Expression in Inflammatory Responses after Cerebral Ischemia

Progranulin (PGRN) plays a crucial role in diverse biological processes, including cell proliferation and embryonic development. PGRN can be cleaved by neutrophil elastase to release granulin (GRN). PGRN has been found to inhibit inflammation. Whereas, GRN plays a role as a pro-inflammatory factor. However, the pathophysiological roles of PGRN and GRN, at early stages after cerebral ischemia, have not yet been fully understood. The aim of this study was to obtain further insight into the pathologic roles of PGRN and GRN. We demonstrated that the amount of PGRN was significantly increased in microglial cells after cerebral ischemia in rats and that neutrophil elastase activity was also increased at an early stage after cerebral ischemia, resulting in the production of GRN. The inhibition of neutrophil elastase activity suppressed PGRN cleavage and GRN production, as well as the increase in pro-inflammatory cytokines, after cerebral ischemia. The administration of an elastase inhibitor decreased the number of injured cells and improved the neurological deficits test scores. Our findings suggest that an increase in the activity of elastase to cleave PGRN, and to produce GRN, was involved in an inflammatory response at the early stages after cerebral ischemia, and that inhibition of elastase activity could suppress the progression of cerebral ischemic injury.

Neurological function following cerebral ischemia/reperfusion is improved by the Ruyi Zhenbao pill in a rats

The present study aimed to investigate the effect and underlying mechanisms of the Ruyi Zhenbao pill on neurological function following cerebral ischemia/reperfusion in rats. Male Sprague-Dawley rats underwent middle cerebral artery occlusion following reperfusion. The rats received intragastrically either sodium carboxymethyl cellulose (control and model groups) or Ruyi Zhenbao pill at doses of 0.2, 0.4 or 0.8 g/kg. Neurological function was assessed by cylinder, adhesive and beam-walking tests after 14-day Ruyi Zhenbao pill treatment. Neurogenesis and angiogenesis were detected using immunofluorescence staining. The expression levels of brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF) and vascular endothelial growth factor (VEGF) were determined by enzyme-linked immunosorbent assays. Treatment with 0.4 and 0.8 g/kg Ruyi Zhenbao for 14 days significantly improved neurological function, and increased the number of von Willebrand Factor- and neuronal nuclear antigen-positive cells in the ischemic hemisphere of rats. Ruyi Zhenbao pill treatment also significantly enhanced the expression levels of BDNF, NGF and VEGF in the ischemic hemisphere. The results demonstrated that the Ruyi Zhenbao pill improved neurological function following ischemia in rats. The mechanisms of the Ruyi Zhenbao pill are associated with increasing the expression levels of BDNF, NGF and VEGF, and subsequently promoting neurogenesis and angiogenesis in the ischemic zone.

Intravenous injection of neural progenitor cells facilitates angiogenesis after cerebral ischemia

Earlier we demonstrated that the injection of neural progenitor cells (NPCs) has therapeutic potential for the improvement of learning dysfunction after cerebral ischemia. However, it remained to be clarified how transplantation of NPCs can improve ischemia-induced dysfunction. In this study, we examined whether intravenous injection of NPCs after cerebral ischemia could enhance angiogenesis by affecting the expression of angiogenic factors. The injection of NPCs on day 7 after cerebral ischemia enhanced angiogenesis on day 28. Vascular endothelial growth factor (VEGF) and its receptor VEGFR2 were increased in expression by the NPC injection. The level of angiopoietin-1 (Ang-1), an angiogenic factor, but not that of Ang-2, which acts as an antagonist for the Ang-1 receptor, was also increased on day 28. In addition, the expression of Ang-1 receptor Tie2 was enhanced in brain capillaries. Furthermore, the amounts of tight junctional proteins, which are in the blood-brain barrier and whose expression occurs downstream of Ang-1/Tie2 signaling, were increased by the NPC injection. These results suggest that the NPC injection promoted angiogenesis through Ang-1/Tie2 and/or VEGF/VEGFR2 signaling in brain capillaries after cerebral ischemia. Such signaling might have the potential for causing vascular stabilization and maturation for a long period after cerebral ischemia.

Thrombin activity associated with neuronal damage during acute focal ischemia

Mechanisms of ischemic neuronal and vascular injury remain obscure. Here we test the hypothesis that thrombin, a blood-borne coagulation factor, contributes to neurovascular injury during acute focal ischemia. Stroke was induced in adult Sprague Dawley rats by occluding the middle cerebral artery. Intra-arterial thrombin infusion during ischemia significantly increased vascular disruption and cellular injury. Intravenous infusion of argatroban, a direct thrombin inhibitor, alleviated neurovascular injury. Immunostaining showed thrombin on neurons in the ischemic core. Using an activatable cell-penetrating peptide engineered to detect thrombin activity, we discovered that thrombin proteolytic activity was specifically associated with neuronal damage during ischemia. Protease activated receptor-1, the presumptive thrombin receptor, appeared to mediate ischemic neurovascular injury. Furthermore, rats receiving thrombin during ischemia showed cognitive deficit, whereas rats receiving argatroban retained intact learning and memory. These results suggest a potential role for thrombin contributing to neurovascular injury and several potential avenues for neuroprotection.

Intravenous injection of neural progenitor cells improves cerebral ischemia-induced learning dysfunction

The ability of stem cells to enhance neurological recovery seen after cerebral ischemia has been reported. However, it remains to be clarified whether neural progenitor cells (NPCs) improve cerebral ischemia-induced learning dysfunction. We found in an earlier study that the direct injection of NPCs into the hippocampus prevents spatial learning dysfunction after cerebral ischemia. As the intravascular injection of cells represents a minimally invasive therapeutic approach, we sought to determine whether the intravenous injection of NPCs also would improve ischemia-induced spatial learning dysfunction. Cerebral ischemia was produced by the injection of 700 microspheres into the right hemisphere of rats. The injection of NPCs via a femoral vein on day 7 after the induction of ischemia improved the modified neurological severity score and reduced the prolongation of the escape latency seen in the water maze task on days 12-28 after cerebral ischemia. The intravenous injection of NPCs on day 7 did not affect the viable area of the ipsilateral hemisphere on day 28 compared with that of the non-treated ischemic rats. Furthermore, the NPCs injected via the vein were detected in the ipsilateral hemisphere; and they expressed brain-derived neurotrophic factor (BDNF) on day 28. The decrease in the BDNF level in the ipsilateral hemisphere was also inhibited by the injection of NPCs. These results suggest that the NPCs injected via the vein after cerebral ischemia improved spatial learning dysfunction, but without having any restorative effect on the damaged areas, possibly by acting as a source of neurotrophic factors.

Injection of neural progenitor cells improved learning and memory dysfunction after cerebral ischemia

Accumulating evidence indicates that stem cells have the ability to improve neurological deficits seen after cerebral ischemia. However, the effects of neural progenitor cells (NPCs) on cerebral ischemia-induced learning and memory dysfunction remain to be clarified. The purpose of the present study was to determine whether the injection of exogenous NPCs could prevent learning and memory dysfunction after cerebral ischemia. Sustained cerebral ischemia was produced by the injection of 700 microspheres into the right hemisphere of each rat. We demonstrated that injection of NPCs into the hippocampus at 10 min after the induction of cerebral ischemia reduced prolongation of the escape latency seen in acquisition and retention tests of the water maze task on Days 12-28 after cerebral ischemia. Injection of NPCs partially attenuated the decrease in viable areas of the ipsilateral hemisphere on Day 28 after the cerebral ischemia. We also demonstrated that injection of NPCs prevented the decrease in the level of BDNF seen at the early period after cerebral ischemia. These results suggest that the injection of exogenous NPCs into the hippocampus can prevent cerebral ischemia-induced learning and memory dysfunction, possibly through maintenance of the BDNF level.

Quantitative effects of nefiracetam on spatial learning of rats after cerebral embolism

Recent studies have shown that nefiracetam ameliorates cognitive dysfunction because of ischemia when behavioral testing occurs during treatment. We sought to determine if there was a persistent effect after treatment, by testing spatial learning of embolized rats after nefiracetam therapy.

METHODS

Male Sprague Dawley rats (250 to 300 g) were divided into 3 categories. The control group (n = 5) underwent no surgery or cerebral embolism. The vehicle group (n = 12) was anesthetized with halothane, underwent surgery, injected with intracarotid microspheres, and given orally 5 mL/kg of the vehicle (0.5% aqueous sodium carboxymethyl cellulose) for 21 days. The nefiracetam group (n = 12) was embolized and treated orally with 30 mg/kg nefiracetam (6 mg/mL in vehicle) for 21 days. Outcome was determined with visual spatial learning after the end of treatment.

RESULTS

Embolization caused a significant impairment in visual spatial learning, which nefiracetam completely ameliorated (group main effect, F(2,444) = 6.4, P = .002). Mean latency to the escape was 35 +/- 6 seconds for the vehicle group versus 18 +/- 4 seconds for the nefiracetam group, after 4 days of testing. This effect persisted after a further interval of 10 days (retention test). A reversal test (to assess working memory for new information) yielded mean latencies of 26 +/- 6 seconds for the control group, 49 +/- 5 seconds for vehicle, and 25 +/- 4 seconds for nefiracetam (group main effect, F(2,109) = 8.0, P = .0005, Newman-Keuls, P < .05), showing that both the control and nefiracetam groups were different from the vehicle group.

CONCLUSION

Nefiracetam therapy improves the learning behavior of embolized rats. The results are not caused by an activating effect of the drug because the animals are tested after the treatment period is over and because the beneficial effect is seen using the delayed retention test. Finally, working memory is markedly preserved by nefiracetam, an effect observed several weeks after treatment.

Reovirus as an experimental therapeutic for brain and leptomeningeal metastases from breast cancer

Brain and leptomeningeal metastases are common in breast cancer patients and our current treatments are ineffective. Reovirus type 3 is a replication competent, naturally occurring virus that usurps the activated Ras-signaling pathway (or an element thereof) of tumor cells and lyses them but leaves normal cells relatively unaffected. In this study we evaluated reovirus as an experimental therapeutic in models of central nervous system (CNS) metastasis from breast cancer. We found all breast cancer cell lines tested were susceptible to reovirus, with > 50% of these cells lysed within 72 h of infection. In vivo neurotoxicity studies showed only mild local inflammation at the injection site and mild communicating hydrocephalus with neither diffuse encephalitis nor behavioral abnormalities at the therapeutically effective dose of reovirus (intracranial) (ie 10(7) plaque-forming units) or one dose level higher. In vivo, a single intratumoral administration of reovirus significantly reduced the size of tumors established from two human breast cancer cell lines and significantly prolonged survival. Intrathecal administration of reovirus also remarkably prolonged survival in an immunocompetent racine model of leptomeningeal metastases. These data suggest that the evaluation of reovirus as an experimental therapeutic for CNS metastases from breast cancer is warranted.

Hepatocyte growth factor improved learning and memory dysfunction of microsphere-embolized rats

Hepatocyte growth factor (HGF), an organotropic factor for regeneration and protection in various organs, has the ability to attenuate cerebral ischemia-induced cell death. The effect of HGF on learning and memory function after cerebral ischemia, however, remains unknown. We have demonstrated that administration of human recombinant HGF (hrHGF) into the ventricle reduced prolongation of the escape latency in acquisition and retention tests of the water maze task on Days 12-28 after microsphere embolism-induced cerebral ischemia. Treatment with hrHGF also attenuated the decrease in viable area and the density and number of perfused cerebral vessels, particularly those with a diameter smaller than 10 microm, of the ipsilateral hemisphere on Day 28 after the cerebral ischemia. We observed that treatment with hrHGF reduced the number of TUNEL-positive cerebral endothelial cells at the early stage after the ischemia. These results suggest that hrHGF prevents learning and memory dysfunction seen after sustained cerebral ischemia by protecting against injury to the endothelial cells. HGF treatment may be a potent therapeutic strategy for cerebrovascular diseases, including cerebral infarct and vascular dementia.

Microsphere-induced embolic stroke: an MRI study

Despite the many studies of the middle cerebral artery occlusion (MCAO) model, efficient therapy for stroke is still lacking, emphasizing the need for further development and characterization of experimental stroke models. In the present study, the rather unexplored multifocal microsphere-induced stroke model in rats was characterized by multiparametric MRI. We induced microembolic infarction in a group of Sprague-Dawley rats by injecting a dose of about 1000 50-microm polyethylene microspheres intracranially from the external carotid artery. Diffusion-, perfusion-, and T(2)-weighted MRI were used to evaluate the infarct development during and following the first 3 hr after microsphere injection (N = 20). The animals were also imaged at 12-hr (N = 8), 24-hr (N = 17), and 48-hr (N = 5) time points. After the final imaging time point, the brains were removed and sectioned into 2-mm-thick slices, and infarct volumes were measured by 2,3,4-triphenyltetrazolium chloride (TTC) staining. From calculated apparent diffusion coefficient (ADC) maps, a volume of reduced ADC appeared 0.5-1.0 hr postinjection, and by the 3-hr time point the volume of ADC reduction had increased to a size of 5% +/- 1% (mean +/- SEM) of the brain hemisphere. The lesion volume increased significantly (P < 0.01) to 16% +/- 2% of the hemisphere volume at the 12-hr time point, while at 24 hr the lesion (15% +/- 2% of the hemisphere) was also significantly larger (P < 0.001) than at 3 hr. The perfusion deficit resulting from the microsphere injection was immediate, going from a cerebral blood flow index (CBF(i)) of 74% +/- 3% at the time of microsphere injection to 68% +/- 2% of the contralateral mean at 3 hr (P < 0.05), to 55% +/- 4% of the contralateral values at 12 hr (P < 0.05), and to 57% +/- 2% of the contralateral mean at 24 hr (P < 0.001). The lesion development in the microsphere-induced stroke model was found to be slower than in the MCAO model, and continued up to the 24-48-hr time point.

Hepatocyte growth factor attenuates cerebral ischemia-induced learning dysfunction

Hepatocyte growth factor (HGF) acts as an organotropic factor for regeneration and protection in various organs and has the ability to attenuate cerebral ischemia-induced cell death. However, the effect of HGF on learning and memory function after a cerebral ischemic event is unknown. We demonstrate here that administration of human recombinant HGF (hrHGF) into the ventricle reduced the prolongation of the escape latency in the acquisition and retention tests in the water maze task on days 12-28 after microsphere embolism-induced cerebral ischemia. In addition, disruption of the blood-brain barrier at the early stage after microsphere embolism, which was determined by FITC-albumin leakage, was markedly reduced by treatment with hrHGF. We demonstrated that this effect of hrHGF on the blood-brain barrier was associated with protection against the apoptotic death of the cerebral endothelial cells at the early stage after the ischemia. These results suggest that hrHGF can prevent the learning and memory dysfunction soon after sustained cerebral ischemia by protecting against injury to the endothelial cells. The use of HGF may be a potent strategy for the treatment of cerebrovascular diseases, including cerebral infarct and vascular dementia.

Experimental models in focal cerebral ischemia: are we there yet?

Therapeutic options available for acute stroke management are sparse and inadequate. Therefore, new insights into stroke pathophysiology leading to new therapeutic targets are needed. In order to attain these goals, adequate animal models for cerebral ischemia are needed. In the following paper the authors will review the various animal models for stroke and emphasize their potential strengths and weaknesses.

A possible mechanism for improvement by a cognition-enhancer nefiracetam of spatial memory function and cAMP-mediated signal transduction system in sustained cerebral ischaemia in rats

1. Accumulated evidence indicates that the adenylyl cyclase (AC)/cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)/cAMP-responsive element binding protein (CREB) signal transduction system may be linked to learning and memory function. 2. The effects of nefiracetam, which has been developed as a cognition enhancer, on spatial memory function and the AC/cAMP/PKA/CREB signal transduction system in rats with sustained cerebral ischaemia were examined. 3. Microsphere embolism (ME)-induced sustained cerebral ischaemia was produced by injection of 700 microspheres (48 micro m in diameter) into the right hemisphere of rats. Daily oral administration of nefiracetam (10 mg kg(-1) day(-1)) was started from 15 h after the operation. 4. The delayed treatment with nefiracetam attenuated the ME-induced prolongation of the escape latency in the water maze task that was examined on day 7 to 9 after ME, but it did not reduce the infarct size. 5. ME decreased Ca(2+)/calmodulin (CaM)-stimulated AC (AC-I) activity, cAMP content, cytosolic PKA Cbeta level, nuclear PKA Calpha and Cbeta levels, and reduced the phosphorylation and DNA-binding activity of CREB in the nucleus in the right parietal cortex and hippocampus on day 3 after ME. The ME-induced changes in these variables did not occur by the delayed treatment with nefiracetam. 6. These results suggest that nefiracetam preserved cognitive function, or prevented cognitive dysfunction, after sustained cerebral ischaemia and that the effect is, in part, attributable to the prevention of the ischaemia-induced impairment of the AC/cAMP/PKA/CREB signal transduction pathway.

Persistent effects of delayed treatment with nefiracetam on the water maze task in rats with sustained cerebral ischemia

The present study was aimed at determining whether nefiracetam might have a persistent cognition-enhancing effect in animals with sustained cerebral ischemia. Sustained cerebral ischemia was induced by injecting 700 microspheres into the right internal carotid artery of rats [microsphere-embolized (ME) rats]. The ME and sham-operated rats were treated with 10 mg/kg/day nefiracetam p.o. from the first to the 9th day after the operation. The escape latency of the ME rat in the water maze test, when performed on days 7 to 9 after the operation, was lengthened. This effect was attenuated by the delayed treatment with nefiracetam. The nefiracetam-treated ME rat showed a shortened escape latency in the retention test on day 17 as well as in the contraposition test on day 18. These results indicate that a persistent improvement of the spatial memory function impaired by sustained cerebral ischemia was achieved even after cessation of treatment with nefiracetam. The functional damage to learning and memory was associated with decreases in the membranous adenylyl cyclase I and cytosolic protein kinase A (PKA) catalytic subunit and regulatory subunit proteins in the right hippocampus and cerebral cortex. The delayed treatment with nefiracetam appreciably prevented the decreases in these proteins. The present study suggests that nefiracetam may have an ability to cause persistent improvement of learning and memory function, possibly through protection against the ischemia-induced impairment to the adenylyl cyclase/cAMP/PKA signal transduction pathway.

Impairment of cerebral cAMP-mediated signal transduction system and of spatial memory function after microsphere embolism in rats

The transcription factor cAMP-responsive element binding protein (CREB) has been implicated in synaptic plasticity and memory. The purpose of the present study was to characterize alterations in the cAMP/protein kinase A (PKA)/CREB system after sustained cerebral ischemia. Sustained cerebral ischemia was induced by injection of 900 microspheres (48 microm in diameter) into the right (ipsilateral) hemisphere of rats. Alterations in the CREB, PKA, and cAMP levels in the cerebral cortex and hippocampus were examined up to 7 days after microsphere embolism. Immunoblotting analysis showed a decrease in the immunoreactivity of phosphorylated CREB (pCREB) in the ipsilateral hemisphere on the third day after microsphere embolism, whereas that of the total CREB was not altered. An electrophoretic gel mobility shift assay showed a decrease in the cAMP response element (CRE)-DNA binding activity of CREB in the ischemic region on the third day after the microsphere embolism. Cytosolic PKA C beta in the ipsilateral hemisphere was selectively decreased on the first day after the microsphere embolism, whereas the levels of another catalytic subunit, C alpha, and a regulatory subunit, RII alpha, were not altered. Immunoreactivity of the PKA catalytic subunit C alpha in the nucleus of the ipsilateral hemisphere was decreased on the third day after the embolism. The decreases in the pCREB, CRE-DNA binding activity, and PKA C alpha and C beta levels lasted at least up to 7 days after the operation. A decrease in the cAMP content was also seen in the ipsilateral hemisphere throughout the experiment. Furthermore, microsphere embolized rats showed prolongation of the escape latency in the water maze task determined on the seventh to ninth day after the operation. Our results suggest that sustained cerebral ischemia may impair the phosphorylation and CRE-DNA binding activity of CREB and that these effects may be one of the possible causes for learning and memory dysfunction.

Effects of nefiracetam on spatial memory function and acetylcholine and GABA metabolism in microsphere-embolized rats

The present study aimed to determine whether nefiracetam, N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide, a cognition enhancer, has an effect on learning and memory function in sustained cerebral ischemia, and whether the effect, if any, may accompany modification of the cholinergic or gamma-aminobutyric acid (GABA)ergic system, which are conceived to be involved in the learning and memory function, in the ischemic brain. Sustained cerebral ischemia was induced by the injection of 700 microspheres into the right hemisphere of the rat. The animals were treated once daily with 10 mg/kg nefiracetam p.o. from 15 h after the operation to either 10 days for the water maze study, or 3 or 5 days after the operation for neurochemical examination. Microsphere-embolized rats showed stroke-like symptoms 15 h after the operation and lengthened the escape latency in the water maze task on days 7-10, suggesting a spatial learning dysfunction. The delayed treatment did not reduce the stroke-like symptoms, but effectively shortened the escape latency. The animals at days 3 and 5 after the operation showed decreases in acetylcholine content and choline acetyltransferase activity, which were not prevented by nefiracetam. The microsphere-embolized rats showed decreases in GABA content and glutamic acid decarboxylase activity. The delayed treatment appreciably restored GABA content in the hippocampus on day 5 and reversed glutamic acid decarboxylase activity in both brain regions on day 5. These results suggest that the GABAergic activity rather than the cholinergic activity may be, at least in part, involved in the pharmacological effects of nefiracetam in the ischemic brain.

Effects of underwater sound exposure on neurological function and brain histology

To evaluate the safety of sonar exposure from a neurological perspective, the vulnerability of the central nervous system to underwater exposure with high-intensity, low-frequency sound (HI-LFS) was experimentally examined. Physiological, behavioral and histological parameters were measured in anesthetized, ventilated rats exposed to brief (5 min), underwater HI-LFS. Exposure to 180 dB sound pressure level (SPL) re 1 microPa at 150 Hz (n = 9) did not alter acute cardiovascular physiology (arterial blood pH, pO(2), pCO(2), heart rate, or mean arterial blood pressure) from that found in controls (n = 11). Rats exposed to either 180 dB SPL re 1 microPa at 150 Hz (n = 12) or 194 dB SPL re 1 microPa at 250 Hz (n = 12) exhibited normal cognitive function at 8 and 9 days after sound exposure. Evaluation of neurological motor function revealed a minor deficit 7 days after 180 dB SPL/150 Hz exposure that resolved by 14 days, and no deficits after 194 dB SPL/250 Hz exposure. No overt histological damage was detected in any group. These data suggest that underwater HI-LFS exposure may cause transient, mild motor dysfunction.

Alterations in hippocampal GAP-43, BDNF, and L1 following sustained cerebral ischemia

Alterations in factors involved in the regeneration of the neuronal network in the hippocampus of rats with microsphere embolism (ME) were examined. Nine hundred microspheres (48 microm in diameter) were injected into the right hemisphere, and immunochemical and immunohistochemical studies on the hippocampus were performed on the seventh day thereafter. Hematoxylin-eosin staining showed progressive and severe degeneration of the hippocampus after ME. The protein levels of brain-derived neurotrophic factor (BDNF), 43-kDa growth-associated protein (GAP-43), and adhesion protein L1 (L1) in the ipsilateral hippocampus of the ME animal, determined by Western blot analysis or enzyme immunoassay, were increased, unaltered, and decreased, respectively. In contrast, the immunohistochemical study showed increases in a marker of axonal sprouting GAP-43, and a neurotrophic factor BDNF, and a decrease in an adhesion molecule L1 in some areas of the hippocampal ischemic penumbra of such animals. These results suggest that some factors for regeneration of the neuronal network in the ischemic penumbra responded to sustained cerebral ischemia for a certain period, although functional network of the nerve cells in the microsphere-injected hemisphere would be unlikely established after ME.

Impairment of adenylyl cyclase and of spatial memory function after microsphere embolism in rats

The purpose of the present study was to characterize alterations in the adenylyl cyclase (AC), cyclic adenosine 3',5'-monophosphate (cAMP), and spatial memory function after sustained cerebral ischemia. Sustained cerebral ischemia was induced by injection of 900 microspheres (48 microm in diameter) into the right (ipsilateral) hemisphere of rats. Alterations in the AC and cAMP in the cerebral cortex and hippocampus were examined up to 7 days after the embolism. A decrease in the cAMP content was seen in the ipsilateral hemisphere throughout the experiment. Microsphere embolism (ME) decreased the activity of Ca(2+)/calmodulin (CaM)-sensitive AC in the ipsilateral hemisphere throughout the experiment, whereas the basal and 5'-guanylyl imidodiphosphate (Gpp(NH)p)-sensitive AC activities were not altered. Immunoblotting analysis of AC subtypes with specific antibodies showed a decrease in the immunoreactivity of AC-I in the ipsilateral hemisphere during these periods. No significant differences in the immunoreactivity of AC-V/VI and AC-VIII were observed after ME. The levels of GTP-binding proteins Galpha(s), Galpha(i), and Gbetawere unchanged. Furthermore, microsphere-embolized rats showed prolongation of the escape latency in the water maze task determined on the seventh to ninth day after the operation. These results suggest that sustained cerebral ischemia may induce the impairment of the AC, particularly a selective reduction in the AC-I level and activity, coupled with the decrease in cAMP content. This reduction may play an appreciable role in the disturbance in cAMP-mediated signal transduction system, possibly leading to learning and memory dysfunction.

Effects of a phosphodiesterase IV inhibitor rolipram on microsphere embolism-induced defects in memory function and cerebral cyclic AMP signal transduction system in rats

The effects of treatment with rolipram, a specific phosphodiesterase IV inhibitor, on learning and memory function and on the cyclic AMP/PKA/CREB signal transduction system were examined in rats with microsphere embolism (ME)-induced cerebral ischaemia. Sustained cerebral ischaemia was induced by the injection of 900 microspheres (48 microm in diameter) into the right hemisphere of the rat brain. The animals were treated once daily with 3 mg kg(-1) rolipram i.p. from 6 h after the onset of the operation for consecutive 10 days. Microsphere-embolized rats showed prolongation of the escape latency in the water maze task starting from day 7 after the operation and lasting for 3 consecutive days. Treatment with rolipram reduced the escape latency. ME decreased the cyclic AMP content, cytosolic PKA Cbeta level, and nuclear PKA Calpha and Cbeta levels, as well as reduced the pCREB level and the DNA-binding activity of CREB in the cerebral cortex and hippocampus on day 10 after the operation. These alterations were attenuated by treatment with rolipram. These results suggest that ME-induced failure in learning and memory function may be mediated by dysfunction of the cyclic AMP/PKA/CREB signal transduction system, that rolipram may ameliorate ME-induced impairment of learning and memory function, and that the drug effect may be partly attributed to activation of the cyclic AMP/PKA/CREB signal transduction system.

Selective reduction in type I adenylyl cyclase after microsphere embolism in rat brain

Alterations of adenylyl cyclase (AC) subtypes after cerebral ischemia remain unclear. The purpose of the present study was to characterize alterations in AC after sustained cerebral ischemia. Sustained cerebral ischemia was induced by injection of 900 microspheres into the right (ipsilateral) internal carotid artery of rats. Microsphere embolism (ME) decreased the Ca(2+)/calmodulin-sensitive AC activity in the ipsilateral hippocampus examined up to 7 days after the embolism, whereas basal and 5'-guanylyl imidodiphosphate-sensitive AC activities were not altered. An immunoreactivity of type I adenylyl cyclase (AC-I) was decreased in the ipsilateral hippocampus during these periods, whereas type V/VI AC and VIII AC immunoreactivities were not altered. These results suggest that a selective reduction in the AC-I level and activity is induced by ME, which may lead to dysfunction of AC signal transduction.

Applications of the Morris water maze in the study of learning and memory

The Morris water maze (MWM) was described 20 years ago as a device to investigate spatial learning and memory in laboratory rats. In the meanwhile, it has become one of the most frequently used laboratory tools in behavioral neuroscience. Many methodological variations of the MWM task have been and are being used by research groups in many different applications. However, researchers have become increasingly aware that MWM performance is influenced by factors such as apparatus or training procedure as well as by the characteristics of the experimental animals (sex, species/strain, age, nutritional state, exposure to stress or infection). Lesions in distinct brain regions like hippocampus, striatum, basal forebrain, cerebellum and cerebral cortex were shown to impair MWM performance, but disconnecting rather than destroying brain regions relevant for spatial learning may impair MWM performance as well. Spatial learning in general and MWM performance in particular appear to depend upon the coordinated action of different brain regions and neurotransmitter systems constituting a functionally integrated neural network. Finally, the MWM task has often been used in the validation of rodent models for neurocognitive disorders and the evaluation of possible neurocognitive treatments. Through its many applications, MWM testing gained a position at the very core of contemporary neuroscience research.

Comparison of calcium-binding proteins expressed in cultured hNT neurons and hNT neurons transplanted into the rat striatum

An alternative source of cells for neural transplantation and brain repair that has many characteristics of immature neurons is the hNT neuron, derived from an embryonal human teratocarcinoma (NTera2) cell line that is terminally differentiated in vitro with retinoic acid. The majority of hNT neurons are GABAergic in cell culture. We have determined the calcium-binding protein (CBP) phenotypes of hNT neurons for three CBPs, calretinin (CR), calbindin D-28K (CB), and parvalbumin (PV), in cell culture and after transplantation into the rat striatum. In cell culture, 95% of all cell profiles were human nuclear matrix antigen (NuMA) positive. PV-positive hNT neurons constituted 50% of all neuron-like profiles, with CB+ and CR+ constituting 14 and 6% of cells, respectively. In contrast, when the striatal grafts were examined after 30 days survival using confocal microscopy, only 10% of hNT neurons immunopositive for NuMA were PV+; 19% were CB+/NuMA+, approximately the same percentage as was seen in vitro, and 82% of grafted hNT neurons were CR+. These results suggest that hNT neurons can be subdivided into at least three subpopulations based on the CBP phenotype that they express and that there is a CBP phenotypic shift following transplantation. Three related hypotheses are proposed to account for this phenotypic shift of hNT neurons after transplantation: (a) selective survival of the CR+ subpopulation of hNT neurons, (b) selective transitory quiescence of the transplanted PV+ cells due to transplantation stress, or (c) dedifferentiation of the hNT neurons following transplantation, which may allow them to respond to local environmental cues during the engraftment process.

Synergistic combinatorial stroke therapy: A quantal bioassay of a GABA agonist and a glutamate antagonist

We sought to prolong the window for stroke treatment using synergistic combinatorial therapy. We used the intraluminal filament occlusion model in rats to cause focal cerebral ischemia and a quantal bioassay to measure efficacy. The GABA agonist muscimol and the glutamate antagonist MK-801 were used alone and in combination at various times after ischemia onset. At progressively longer treatment delay intervals (30, 60, 75, 120, 240, and 360 min), higher doses of the single drugs were required to achieve neuroprotection. In contrast, the combination 1.0 mg/kg muscimol plus 0.5 mg/kg MK-801 was effective at all delay intervals studied except the longest (P < 0.05 at each time). After 240 min from ischemia onset, the combination was more effective than either single agent (P < 0.05 for each drug dose), suggesting synergism. The neuroprotective effect could not be demonstrated using morphometry. The treatment effects were probably not due to hypothermia because brain temperatures recorded in awake, unregulated subjects remained normo- or slightly hyperthermic following all treatments. Awake subjects kept on a heating pad exhibited mild brain hyperthermia. The combination caused a drop and MK-801 caused a significant increase in mean arterial blood pressure (main effects F(5,172) = 29, P < 0.0001). The combination of a GABA agonist and glutamate antagonist appears to possess synergistic neuroprotective effects when treatment is delayed up to 240 min following the onset of cerebral ischemia. Temperature regulation causes hyperthermia in awake subjects. The quantal bioassay is one method suitable for studies of synergistic stroke therapy.

Why do neuroprotective drugs work in animals but not humans?

Many neuroprotective agents that seemed promising in animal studies of ischemic brain injury prove to have no effect when tested in clinical trials, suggesting that fundamental elements of translational research require better definition. A number of modifications have led to improvements in preclinical and human studies since the earliest controlled trials failed to confirm hypotheses suggested by animal data. Continued re-evaluation and sharing of information derived from the laboratory bench or the patient's bedside should eventually lead to effective neuroprotection in acute stroke. Experimental data should be carefully studied to improve the quality of agents coming to clinical trials and to design trial phasing that effectively determines drug safety and efficacy. This article will examine preclinical modeling and its translation to prospective studies of acute stroke therapy and will focus on some potential solutions directed at clinical trial design.

Long-term functional end points following middle cerebral artery occlusion in the rat

The purpose of the present study was to assess the magnitude and stability of a number of functional deficits in rats subjected to occlusion of the middle cerebral artery (MCAO). Three groups of rats, treated with 90-min, 120-min, or sham occlusion were used in functional studies for 22 weeks following surgery. The following tests were used: methamphetamine-induced rotation, the staircase test, acquisition of operant responding, running-wheel behavior, and performance of operant differential reinforcement of a low-rate responding (DRL) schedule of reinforcement. Histology performed at 23 weeks following infarct showed on average modest damage of a 19% reduction in hemispheric volume. Of the behavioral tests conducted, rotation, the staircase test, and the operant DRL were sensitive to ischemic damage, and were under some circumstances related to lesion size. These data show that long-term functional deficits following MCAO are demonstrable, and hence, assessment of long-term neuroprotection is feasible.

Effect of ganaxolone in a rodent model of cerebral hematoma

BACKGROUND AND PURPOSE

Therapy with gamma-aminobutyric acid (GABA) agonists appears to improve outcome after experimental hematoma but with unacceptable side effects. We looked to synthetic GABA agonists, or positive GABA modulators, widely developed as anticonvulsants and anxiolytics, to find compounds that may be effective. Ganaxolone is a synthetic neuroactive steroid that positively modulates GABA. We sought to determine whether ganaxolone was beneficial using a model of intracerebral hematoma.

METHODS

We stereotaxically injected varying doses of bacterial collagenase into the caudate nucleus of rats to induce blood-brain barrier failure and hematoma formation. Four hours later, we administered intravenously 15 or 30 mg/kg ganaxolone (n=23 each group), 20 mg/kg pregnanolone (n=21), or vehicle (n=30). Forty-eight hours after collagenase injection, we rated each animal using a standard rodent neurological examination. The ratings were compared with the amounts of injected collagenase using the quantal bioassay procedure. Other sets of animals were tested later for visuospatial learning. Brains were then prepared for histomorphometry, and brain volumes were estimated.

RESULTS

We found that ganaxolone 30 mg/kg significantly increased the ED(50) in the bioassay, for a potency ratio of 1.8+/-0.41 compared with vehicle (P<0.05). Ganaxolone 15 mg/kg and pregnanolone did not affect neurological outcome. Ganaxolone 30 mg/kg did not clearly improve visuospatial learning several weeks after hemorrhage. Ganaxolone exhibited a weak effect on cerebral volumes 48 hours after stroke, but 3 months after hemorrhage no such effect could be detected.

CONCLUSIONS

Ganaxolone improves neurological outcome 48 hours after intracerebral hematoma but not visuospatial learning several weeks after intracerebral hematoma. Histological evidence of damage was reduced at 48 hours but not at 3 months.

Correlation of sequential MR images of microsphere-induced cerebral ischemia with histologic changes in rats

OBJECTIVE

To determine the time course of changes in MRI findings of multiple cerebral microembolism, the authors induced experimental multiple microinfarctions in rats using microspheres and then examined sequential MRI and histopathologic findings. The authors also evaluated how the amount of injected embolic materials affected the findings.

METHODS

The authors injected 25-microm microspheres (range, 2000-8000 gm) into the unilateral internal carotid arteries of rats. The animals were assessed by MRI and histopathology at 1 day or 8 days after embolization.

RESULTS

One day after embolization, multiple high-intensity areas on T2-weighted images were related to the number of injected microspheres and were associated with regions of cerebral edema on histopathologic specimens. On day 8, the high-intensity areas on T2-weighted images observed on day 1 were markedly diminished in the groups receiving up to 6000 microspheres. In the group injected with 8000 microspheres, however, the high-intensity areas were less diminished, and these areas were significantly larger than in the other groups (P < 0.05).

CONCLUSIONS

The MRI features of cerebral ischemia or infarction induced by microsphere embolism vary depending on the number of injected microspheres. Recovery from acute cerebral embolism has a threshold based on ischemic cell volume.

Combined therapy affects outcomes differentially after mild traumatic brain injury and secondary forebrain ischemia in rats

Muscarinic and NMDA receptors contribute to post-traumatic hypersensitivity to secondary ischemia. However, the effect of these receptor antagonists on behavior and CA1 neuronal death after traumatic brain injury (TBI) with acute (1 h after TBI) forebrain ischemia has not been systematically assessed. We examined cognitive and motor dysfunction and the relationship of behavior deficits to neuronal death in this model using muscarinic and NMDA antagonists. Three behavioral groups (n=10/group) of Wistar rats were subjected to mild TBI and 6 min of forebrain ischemia imposed 1 h after TBI with 45 days survival. Motor and spatial memory performance were assessed using the rotarod task and Morris water maze. Seven additional groups (n=6/group) were evaluated only for CA1 death after 7 days survival following sham, individual or combined injury with and without drug treatments. Rats were given 0.3 mg/kg MK-801 (M) and 1.0 mg/kg scopolamine (S) alone or combined (M-S) before or 45 min after TBI. Rotarod performance was tested at days 1-5 and maze performance on days 11-15 and 40-44 after M-S treatment. The 7-day studies showed M-S treatment (p<0.01) reduced CA1 neuronal death better than either S or M alone. Behavioral groups had inadvertent post-ischemic hypothermia that decreased CA1 death and likely influenced behavioral morbidity. M-S given before TBI (p<0.01) decreased memory deficits on day 15, while M-S treatment given after TBI was ineffective. Unexpectedly, M-S treatment before or after TBI produced transient motor deficits (p<0. 01). Memory improvement occurred independent of CA1 death.

Modelling recovery of cognitive function after traumatic brain injury: spatial navigation in the Morris water maze after complete or partial transections of the perforant path in rats

The Morris water maze (MWM) has been used to assess cognitive function in rats after a variety of lesions designed to model brain damage and to assess the effects of drugs, growth factors, and neural transplants on post-operative deficits. The present study examined recovery of spatial navigation in the MWM over time in order to model the spontaneous recovery of cognitive function seen in humans. Diffuse axonal injury, a neuropathology commonly associated with traumatic brain injury (TBI), was modelled by transecting the perforant path (PP) bilaterally, either caudal to the hippocampus or dorsal to it at the decussation of the dorsal hippocampal commissure. Both groups with PP cuts showed substantial deficits initially, but spatial performance recovered with time and training. Recovery of platform finding was nearly complete within 14 days of testing, but recovery of platform searching did not occur for 2 or 3 more weeks. When the platform was moved to a new location, a continuing deficit in learning rate was revealed. When the platform was moved to a new position every day, this deficit was even more evident. These results illustrate the multi-faceted nature of recovery after brain injury and provide a new model for assessing the effects of manipulations designed to modulate recovery.

To what extent have functional studies of ischaemia in animals been useful in the assessment of potential neuroprotective agents?

A general consensus is being reached on the use of a combination of mortality and functional end-points in clinical trials of neuroprotective agents. However, to date, few preclinical studies have examined the effects of putative neuroprotective agents on functional outcome after ischaemia. The data described in this review show the importance of combining both histopathological and neurobehavioural studies when evaluating the neuroprotective efficacy of anti-ischaemic agents in animal models of cerebral ischaemia. Here, Jackie Hunter, Ken Mackay and Derek Rogers argue that measures of functional improvement in models of ischaemia should be incorporated to characterize further the neuroprotection afforded by a compound that could aid the selection of doses and end-point measures in early clinical trials.

Effect of ischemic cerebral volume changes on behavior

Ischemia causes long-term effects on brain volume and neurologic function but the relationship between the two is poorly characterized. We studied the relationships between brain volume and three measures of rodent behavior after cerebral ischemia was induced by injecting several thousand microspheres into the internal carotid arteries of rats. Forty eight hours later, each subject was rated using a global neurologic rating scale. Several weeks later, the subjects were tested for open field activity and visual spatial learning. Post-mortem we measured the volume of the cerebral hemispheres and estimated the volume densities of cortex, white matter, hippocampus, basal ganglia, thalamus, ventricle, and visible infarction. Ischemia caused significant impairment, as measured by the global rating scale; the probability of an abnormal rating was correlated with the number of microspheres trapped in the brains. Visual spatial learning was significantly impaired by ischemia, but this deficit was independent of the count of microspheres, whether the subject was abnormal at 48 h, and whether the left or right hemisphere was embolized. Cerebral hemisphere volume was reduced from 430 mm3 to 376 mm3 (P < 0.05). The cortex was reduced from 22 to 19% of cerebrum (P < 0.05) and the white matter compartment was reduced to similar degree. The lesion volume was 6% of cerebrum, comparable to that seen with other ischemia methods. The global outcome rating was significantly related to total cerebral volume, but not to volume changes in any single compartment. On the other hand, visual spatial learning was significantly influenced by volume changes in the cortex and white matter, but not by the topography of the visible infarctions. Open field activity was not altered by infarction. Our data suggests that the total volume of brain tissue lost to infarction may partially determine global neurological rating independently of the topography of the volume loss. Integrative functions such as learning may depend more on the integrity of specific compartments and less on the total volume of intact brain. The volume of visible cystic infarction was not related to long term behavioral outcome. These results should be confirmed using another method of inducing ischemia.

Altered neuronal and microglial responses to excitotoxic and ischemic brain injury in mice lacking TNF receptors

Brain injury, as occurs in stroke or head trauma, induces a dramatic increase in levels of tumor necrosis factor-alpha (TNF), but its role in brain injury response is unknown. We generated mice genetically deficient in TNF receptors (TNFR-KO) to determine the role of TNF in brain cell injury responses. Damage to neurons caused by focal cerebral ischemia and epileptic seizures was exacerbated in TNFR-KO mice, indicating that TNF serves a neuroprotective function. Oxidative stress was increased and levels of an antioxidant enzyme reduced in brain cells of TNFR-KO mice, indicating that TNF protects neurons by stimulating antioxidant pathways. Injury-induced microglial activation was suppressed in TNFR-KO mice, demonstrating a key role for TNF in injury-induced immune response. Drugs that target TNF signaling pathways may prove beneficial in treating stroke and traumatic brain injury.

Nonocclusive common carotid artery thrombosis in the rat results in reversible sensorimotor and cognitive behavioral deficits

BACKGROUND AND PURPOSE

Microemboli released during transient ischemic attack, stroke, and cardiac surgery are thought to cause a variety of functional deficits in humans. The purpose of this study was to characterize the type and extent of neurobehavioral deficits present after photochemically induced common carotid artery thrombosis (CCAT), a thromboembolic model of stroke in the rat that results in a platelet emboli shower.

METHODS

Thirty-two male Wistar rats were assigned to four groups. Groups 1 (n = 8) and 3 (n = 8) were long-term (6-week survival) and short-term (2-week survival) experimental groups subjected to right CCAT with the use of the photochemical technique. Groups 2 (n = 8) and 4 (n = 8) served as sham-operated controls for each experimental group. A battery of behavioral tests was applied daily beginning 24 hours after thrombosis; this consisted of elicited forelimb placing, postural reflex, beam balance, beam walking, and open field activity. Cognitive testing with a water maze task was performed on post-CCAT days 30 to 33 for groups 1 and 2 and on post-CCAT day 2 for groups 3 and 4. Ten-micrometer coronal brain sections were stained with hematoxylin and eosin, and infarct location and frequency were determined.

RESULTS

Significant sensorimotor deficits were observed, which recovered within 2 weeks after CCAT. The data that follow are derived by combining the two experimental groups and comparing these with the two sham groups. The following tests showed significant effects after CCAT: contralateral elicited forelimb placing, ipsilateral elicited forelimb placing, beam balance, and beam walking score. Cognitive dysfunction was seen acutely (group 3 animals) at 2 days after CCAT; Morris water maze length and latency to target were significantly greater in the experimental group. No deficits were seen in postural reflex, open field activity, or delayed cognitive testing. Histopathological assessment revealed small infarcts in 11 of 16 thrombosed rats. However, a strong relationship between neurobehavioral deficits and infarct location was not consistently demonstrated.

CONCLUSIONS

CCAT produces consistent sensorimotor and cognitive behavioral deficits that recover within 2 weeks of injury. Behavioral outcome was not necessarily associated with overt histopathological damage, suggesting that reversible injury mechanisms, both vascular and neuronal, may be partly responsible for the temporary loss of function. These data strengthen the role of CCAT as a clinically relevant model of thromboembolic stroke.

Combination chemotherapy extends the therapeutic window to 60 minutes after stroke

We sought to extend the therapeutic window for acute stroke therapy using the combination of a glutamate antagonist and a GABA agonist, which in prior studies was effective if given 5 min after stroke. We used a quantal bioassay to measure neuroprotective potency after injection of several thousand microspheres into the cerebral circulation of rats. The GABA-A agonist muscimol, but not MK-801, was effective if given 30, 45, or 60 min after embolization (potency ratio compared with saline of 3.0, 2.3, 1.8, respectively). If muscimol was combined with MK-801 at lower doses of each drug, the combination was neuroprotective (potency ratio of 4.2). Agonists of GABA-A, but not GABA-B, receptors blocked the toxic vacuolization seen in the cingulate and retrosplenial cortex after MK-801 treatment. Combination chemotherapy appears to extend the time window for acute stroke therapy in rats to 1 h and to result in fewer side effects.

YM796, a novel muscarinic agonist, improves the impairment of learning behavior in a rat model of chronic focal cerebral ischemia

We studied effects of YM796, a novel muscarinic agonist, on behavioral, histological and regional cerebral blood flow changes in the chronic phase after focal cerebral ischemia in rats. YM796 (0.03, 0.1, 0.3 and 1 mg/kg) was administered orally once a day from the 7th to the 13th day after the permanent occlusion of left middle cerebral artery. On the 7th day, rats were trained in one-trial step-through passive avoidance task 45 min after drug administration. Test trials were carried out on the 8th and 14th days. Neurological deficits, including hemiplegia and abnormal posture, were observed on the 7th and 14th days. After the completion of behavioral studies, the rats were decapitated and cerebral infarction was measured. Regional cerebral blood flow was also measured by the hydrogen clearance technique 7 days after MCA occlusion. YM796 (0.1-1 mg/kg) significantly (P < 0.05) attenuated the impairment of learning behavior in a dose-dependent manner without affecting spontaneous locomotor activity. The ameliorating effect of YM796 (0.3 mg/kg) on the impaired learning behavior was significantly (P < 0.05) suppressed by intracerebroventricular injection of pirenzepine (10 micrograms/rat), an M1 antagonist. No significant difference in either neurological deficits or cerebral infarction was found between the vehicle- and YM796-treated groups. Further, YM796 (0.3 mg/kg) had little effect on the reduced blood flow in the ipsilateral frontal cortex 7 days after occlusion. These results suggest that YM796 improves the impaired learning behavior probably by activating central M1 receptors in a rat model of chronic focal cerebral ischemia.

Combination therapy protects ischemic brain in rats. A glutamate antagonist plus a gamma-aminobutyric acid agonist

BACKGROUND AND PURPOSE

The excitotoxic effects of glutamate can be blocked almost completely with gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter, in cell culture, tissue slices, and in some animal models. After stroke in rats, we showed previously that an agonist of GABA, muscimol, was as neuroprotective as MK-801, an antagonist of glutamate. To obtain further neuroprotection and to avoid the side effects associated with high doses of MK-801, we wanted to assess the efficacy of the two agents in combination.

METHODS

Treatment was administered 5 minutes after embolic cerebral ischemia in Sprague-Dawley rats. The subjects were rated using a neurological evaluation 48 hours later. Visual-spatial learning was measured 8 to 10 weeks after stroke, after which we measured the volume of each cerebral hemisphere and several large cerebral compartments. Treatment groups included saline (n = 27), MK-801 1.0 mg/kg (n = 23), muscimol 1.0 mg/kg (n = 17), and both agents together using a dose of 0.5 mg/kg each (n = 25).

RESULTS

A probit analysis of the neurological ratings revealed a protective effect of muscimol used alone (MK-801 potency ratio, 2.0; P = NS; muscimol potency ratio, 4.0; P < .05) and a protective effect of the combination (potency ratio, 5.0; P < .05). Focal ischemia caused a moderate to severe delay in the acquisition of visual-spatial information, which was completely eliminated by the combination treatment but only partially ameliorated with MK-801 or muscimol alone. Ischemia reduced the cerebral hemisphere volume from 0.42 mm3 to 0.34 mm3 (P < .0001), the volume density of cortex from 22% to 17% of total cerebral volume (P < .01), and that of hippocampus from 4.3% to 3.0% (P < .05). Only the combination was neuroprotective, as measured by the ratio of the lesioned to the contralateral hemisphere volume (P = .013). The combination treatment and MK-801 protected the hemisphere volume, the cortex, and the hippocampus and reduced the size of visible infarction.

CONCLUSIONS

Combination therapy, using a glutamate antagonist and a GABA-A agonist, appeared to protect the brain and ameliorate a defect in learning behavior after stroke. The combination may have been more effective than either agent used alone, although further study of higher doses is needed.

Protective effect of synaptic inhibition during cerebral ischemia in rats and rabbits

BACKGROUND

Excitatory neurotransmitters appear to cause cell death during ischemia by inducing depolarization, influx of ions, and metabolic failure in the postsynaptic neuron. If this hypothesis is correct, then postsynaptic membrane hyperpolarization and inhibition of metabolism may be protective. Antagonists of the excitotoxic amino acid glutamate protect neurons in culture and in animal models of stroke but appear to cause unacceptable side effects in humans. We propose an alternative strategy of protection using agonists of the inhibitory neurotransmitter gamma-aminobutyric acid.

METHODS

We caused multifocal cerebral ischemia in rats and rabbits by injecting microspheres into the carotid circulation. We administered saline, muscimol, or MK-801 within 5 minutes of stroke onset. We used a bioassay to measure outcome. In rats, we also used learning to assess cortical function, and we performed detailed quantitative brain morphometry 3 months after infarction.

RESULTS

Using the bioassay, we found that muscimol exerted a protective effect in rats (p less than 0.01). There was a dose-response effect seen in muscimol-treated rabbits. Rats treated with muscimol or MK-801 exhibited significantly better visual-spatial learning compared with saline-treated subjects (p less than 0.001). Hemisphere volume after ischemia was comparable in all groups.

CONCLUSIONS

Agonists of gamma-aminobutyric acid and antagonists of glutamate appear to protect brain during ischemia. Since agonists of gamma-aminobutyric acid are known to have fewer side effects in humans, they may prove more useful in the clinical setting as neuroprotective agents.