Regional brain calcium changes in the rat middle cerebral artery occlusion model of ischemia

Host-Guest Chemistry for Simultaneous Imaging of Endogenous Alkali Metals and Metabolites with Mass Spectrometry

Sodium and potassium are biological alkali metal ions that are essential for the physiological processes of cells and organisms. In combination with small-molecule metabolite information, disturbances in sodium and potassium tissue distributions can provide a further understanding of the biological processes in diseases. However, methods using mass spectrometry are generally tailored toward either elemental or molecular detection, which limits simultaneous quantitative mass spectrometry imaging of alkali metal ions and molecular ions. Here, we provide a new method by including crown ether molecules in the solvent for nanospray desorption electrospray ionization mass spectrometry imaging (nano-DESI MSI) that combines host-guest chemistry targeting sodium and potassium ions and quantitative imaging of endogenous lipids and metabolites. After evaluation and optimization, the method was applied to an ischemic stroke model, which has highly dynamic tissue sodium and potassium concentrations, and we report 2 times relative increase in the detected sodium concentration in the ischemic region compared to healthy tissue. Further, in the same experiment, we showed the accumulation and depletion of lipids, neurotransmitters, and amino acids using relative quantitation with internal standards spiked in the nano-DESI solvent. Overall, we demonstrate a new method that with a simple modification in liquid extraction MSI techniques using host-guest chemistry provides the added dimension of alkali metal ion imaging to provide unique insights into biological processes.

CpG preconditioning reduces accumulation of lysophosphatidylcholine in ischemic brain tissue after middle cerebral artery occlusion

Ischemic stroke is one of the major causes of death and permanent disability in the world. However, the molecular mechanisms surrounding tissue damage are complex and further studies are needed to gain insights necessary for development of treatment. Prophylactic treatment by administration of cytosine-guanine (CpG) oligodeoxynucleotides has been shown to provide neuroprotection against anticipated ischemic injury. CpG binds to Toll-like receptor 9 (TLR9) causing initialization of an inflammatory response that limits visible ischemic damages upon subsequent stroke. Here, we use nanospray desorption electrospray ionization (nano-DESI) mass spectrometry imaging (MSI) to characterize molecular effects of CpG preconditioning prior to middle cerebral artery occlusion (MCAO) and reperfusion. By doping the nano-DESI solvent with appropriate internal standards, we can study and compare distributions of phosphatidylcholine (PC) and lysophosphatidylcholine (LPC) in the ischemic hemisphere of the brain despite the large changes in alkali metal abundances. Our results show that CpG preconditioning not only reduces the infarct size but it also decreases the degradation of PC and accumulation of LPC species, which indicates reduced cell membrane breakdown and overall ischemic damage. Our findings show that molecular mechanisms of PC degradation are intact despite CpG preconditioning but that these are limited due to the initialized inflammatory response.

Animal models of cerebral ischemia: A review

Stroke seriously threatens human health because of its characteristics of high morbidity, disability, recurrence, and mortality, thus representing a heavy financial and mental burden to affected families and society. Many preclinical effective drugs end in clinical-translation failure. Animal models are an important approach for studying diseases and drug effects, and play a central role in biomedical research. Some details about animal models of cerebral ischemia have not been published, such as left-/right-sided lesions or permanent cerebral ischemia/cerebral ischemia-reperfusion. In this review, ischemia in the left- and right-hemisphere in patients with clinical stroke and preclinical studies were compared for the first time, as were the mechanisms of permanent cerebral ischemia and cerebral ischemia-reperfusion in different phases of the disease. The results showed that stroke in the left hemisphere was more common in clinical patients, and that most patients with stroke failed to achieve successful recanalization. Significant differences were detected between permanent cerebral ischemia and cerebral ischemia-reperfusion models in the early, subacute, and recovery phases. Therefore, it is recommended that, with the exception of the determined experimental purpose or drug mechanism, left-sided permanent cerebral ischemia animal models should be prioritized, as they would be more in line with the clinical scenario and would promote clinical translation. In addition, other details regarding the preoperative management, surgical procedures, and postoperative care of these animals are provided, to help establish a precise, effective, and reproducible model of cerebral ischemia model and establish a reference for researchers in this field.

Measurement of cations, anions, and acetate in serum, urine, cerebrospinal fluid, and tissue by ion chromatography

Accurate quantification of cations and anions remains a major diagnostic tool in understanding diseased states. The current technologies used for these analyses are either unable to quantify all ions due to sample size/volume, instrument setup/method, or are only able to measure ion concentrations from one physiological sample (liquid or solid). Herein, we adapted a common analytical chemistry technique, ion chromatography and applied it to measure the concentration of cations; sodium, potassium, calcium, and magnesium (Na⁺, K⁺, Ca²⁺, and Mg²⁺) and anions; chloride, and acetate (Cl⁻, ⁻OAc) from physiological samples. Specifically, cations and anions were measured in liquid samples: serum, urine, and cerebrospinal fluid, as well as tissue samples: liver, cortex, hypothalamus, and amygdala. Serum concentrations of Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, and ⁻OAc (mmol/L): 138.8 ± 4.56, 4.05 ± 0.21, 4.07 ± 0.26, 0.98 ± 0.05, 97.7 ± 3.42, and 0.23 ± 0.04, respectively. Cerebrospinal fluid concentrations of Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, and ⁻OAc (mmol/L): 145.1 ± 2.81, 2.41 ± 0.26, 2.18 ± 0.38, 1.04 ± 0.11, 120.2 ± 3.75, 0.21 ± 0.05, respectively. Tissue Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, and ⁻OAc were also measured. Validation of the ion chromatography method was established by comparing chloride concentration between ion chromatography with a known method using an ion selective chloride electrode. These results indicate that ion chromatography is a suitable method for the measurement of cations and anions, including acetate from various physiological samples.

Acrolein: An Effective Biomarker for Tissue Damage Produced from Polyamines

It is thought that the major factor responsible for cell damage is reactive oxygen species (ROS), but our recent studies have shown that acrolein (CH₂=CH-CHO) produced from spermine and spermidine is more toxic than ROS. Thus, (1) the mechanism of acrolein production during brain stroke, (2) one of the mechanisms of acrolein toxicity, and (3) the role of glutathione in acrolein detoxification are described in this chapter.

A Novel Ligustrazine Derivative T-VA Prevents Neurotoxicity in Differentiated PC12 Cells and Protects the Brain against Ischemia Injury in MCAO Rats

Broad-spectrum drugs appear to be more promising for the treatment of acute ischemic stroke. In our previous work, a new ligustrazine derivative (3,5,6-trimethylpyrazin-2-yl) methyl 3-methoxy-4-[(3,5,6-trimethylpyrazin-2-yl)methoxy]benzoate (T-VA) showed neuroprotective effect on injured PC12 cells (EC₅₀ = 4.249 µM). In the current study, we show that this beneficial effect was due to the modulation of nuclear transcription factor-κB/p65 (NF-κB/p65) and cyclooxygenase-2 (COX-2) expressions. We also show that T-VA exhibited neuroprotective effect in a rat model of ischemic stroke with concomitant improvement of motor functions. We propose that the protective effect observed in vivo is owing to increased vascular endothelial growth factor (VEGF) expression, decreased oxidative stress, and up-regulation of Ca²⁺–Mg²⁺ ATP enzyme activity. Altogether, our results warrant further studies on the utility of T-VA for the potential treatment of ischemic brain injuries, such as stroke.

Hypoxia-induced retinal ganglion cell damage through activation of AMPA receptors and the neuroprotective effects of DNQX

Hypoxia-induced glutamate accumulation in neural tissues results in damage to neurons through excitotoxic mechanisms via activation of glutamate receptors (GluRs). Here we examine whether hypoxia in the developing retina would cause activation of the ionotropic α-amino-3-hydroxy-5-methylisoxazole-4-propioate (AMPA) GluRs and increase in Ca(2+) influx into retinal ganglion cells (RGCs) that might ultimately lead to their death. Neonatal Wistar rats were subjected to hypoxia for 2h and then sacrificed at various time points after the exposure together with normal age matched control rats. Primary cultures of RGCs were also prepared and subjected to hypoxia. Expression of AMPA glutamate receptor (GluR) 1-4 was examined in the retina. Additionally, expression of GluRs, intracellular Ca(2+) influx, reactive oxygen species (ROS) generation and cell death were investigated in cultured RGCs. GluR1-4 mRNA and protein expression showed a significant increase (P < 0.01) over control values after the hypoxic exposure both in vivo and in vitro. Cells expressing GluR1-4 in the retina were identified as RGCs by double immunofluorescence labeling with Thy1.1. Increased intracellular Ca(2+) in cultured RGCs following hypoxic exposure was reduced (P < 0.01) by 10 μM AMPA antagonist 6, 7-dinitroquinoxaline-2,3-dione (DNQX). Our results suggest that following a hypoxic insult, an increased amount of glutamate accumulates in the neonatal retina. This would then activate AMPA receptors which may damage RGCs through increased Ca(2+) accumulation and ROS generation. The involvement of AMPA receptors in damaging the RGCs is evidenced by suppression of intracellular Ca(2+) influx by DNQX which also decreased ROS generation and cell death by 50%.

Two region-dependent pathways of eosinophilic neuronal death after transient cerebral ischemia

Various types of eosinophilic neurons (ENs) are found in the post-ischemic brain. We examined the temporal profile of ENs in the core and peripheral regions of the ischemic cortex, and analyzed the relationship to the expression of various cell death-related factors. Unilateral forebrain ischemia was induced in Mongolian gerbils by transient common carotid artery occlusions, and the brains from 3 h to 2 weeks post-ischemia were prepared for morphometric and immunohistochemical analysis of ENs. ENs with minimally abnormal nuclei and swollen cell bodies appeared at 3 h in the ischemic core and at 12 h in the periphery. In both locations multiple cell death-related factors including calcium, micro-calpain, cathepsin D, 78 kDa glucose-regulated protein (GRP78) and ubiquitin were activated. In the ischemic core, pyknosis and irregularly atrophic cytoplasm peaked at 12 h, which was associated with significant increases in staining for calcium and micro-calpain. ENs with pyknosis and scant cytoplasm peaked at 4 days and were positive for TUNEL and calcium staining. In the ischemic periphery, ENs had slightly atrophic cytoplasm and sequentially developed pyknosis, karyorrhexis and karyolysis over 1 week. These cells were positive for TUNEL and calcium staining. All types of EN were negative for caspase 3. There may be two region-dependent pathways of EN changes in the post-ischemic brain: pyknosis with cytoplasmic shrinkage in the core, and nuclear disintegration with slightly atrophic cytoplasm in the periphery. This difference coordinates different activation patterns of cell death-related factors in ENs.

Phosphorylation of Calcium Calmodulin—Dependent Protein Kinase II following Lateral Fluid Percussion Brain Injury in Rats

Traumatic brain injury (TBI) can dramatically increase levels of intracellular calcium ([Ca(2+)](i)). One consequence of increased [Ca(2+)](i) would be altered activity and function of calcium-regulated proteins, including calcium-calmodulin-dependent protein kinase II (CaMKII), which is autophosphorylated on Thr(286)(pCaMKII(286)) in the presence of calcium and calmodulin. Therefore, we hypothesized that TBI would result in increased levels of pCaMKII(286), and that such increases would occur early after injury in brain regions known to be damaged following lateral fluid percussion TBI (i.e., hippocampus and cortex). In order to test this hypothesis, immunostaining of CaMKII was examined in rat hippocampus and cortex after lateral fluid percussion (LFP) injury using an antibody directed against pCaMKII(286). LFP injury produced a marked increase in pCaMKII(286) immunostaining in the hippocampus and overlying cortex 30 min after TBI. The pattern of increased immunostaining was uneven, and unexpectedly absent in some hippocampal CA3 pyramidal neurons. This suggests that phosphatase activity may also increase following TBI, resulting in dephosphorylation of pCaMKII(286) in subpopulations of CA3 pyramidal neurons. Western blotting confirmed a rapid increase in levels of pCaMKII(286) at 10 and 30 min after brain injury, and that it was transient and no longer significantly elevated when examined at 3, 8, and 24 h. These results demonstrate that TBI alters the autophosphorylation state of CaMKII, an important neuronal regulator of critical cell functions, including enzyme activities, cell structure, gene expression, and neuronal plasticity, and provide a molecular mechanism that is likely to contribute to cell injury and impaired plasticity after TBI.

Delayed changes in T1-weighted signal intensity in a rat model of 15-minute transient focal ischemia studied by magnetic resonance imaging/spectroscopy and synchrotron radiation X-ray fluorescence

Previous studies have found that rats subjected to 15-min transient middle cerebral artery occlusion (MCAO) show neurodegeneration in the dorsolateral striatum only, and the resulting striatal lesion is associated with increased T1-weighted (T1W) signal intensity (SI) and decreased T2-weighted (T2W) SI at 2-8 weeks after the initial ischemia. It has been shown that the delayed increase in T1W SI in the ischemic region is associated with deposition of paramagnetic manganese ions. However, it has been suggested that other mechanisms, such as tissue calcification and lipid accumulation, also contribute to the relaxation time changes. To clarify this issue, we measured changes in relaxation times, lipid accumulation, and elemental distributions in the brain of rats subjected to 15-min MCAO using MRI, in vivo 1H MR spectroscopy (MRS), and synchrotron radiation X-ray fluorescence (SRXRF). The results show that a delayed (2 weeks after ischemia) increase in T1W SI in the ischemic striatum is associated with significant increases in manganese, calcium, and iron, but without evident accumulation of MRS-visible lipids or hydroxyapatite precipitation. It was also found that 15-min MCAO results in acutely reduced N-acetylaspartate (NAA)/creatine (Cr) ratio in the ipsilateral striatum, which recovers to the control level at 2 weeks after ischemia.

Lack of iNOS induction in a severe model of transient focal cerebral ischemia in rats

Calcium-independent nitric oxide synthase (NOS) activity has been reported in ischemic brains and usually attributed to the inducible isoform, iNOS. Because calcium-independent mechanisms have recently been shown to regulate the constitutive calcium-dependent NOS, we proposed to confirm the presence of iNOS activity in our model of transient focal cerebral ischemia in rats. Our initial results showed that, in our model, ischemia induced an important increase in brain calcium concentration. Consequently, the determination of calcium-independent NOS activity required a higher concentration of calcium chelator than classically used in the NOS assay. In these conditions, calcium-independent NOS activity was not observed after ischemia. Moreover, our ischemia was associated with neither iNOS protein expression, measured by Western blotting, nor increased NO production, evaluated by its metabolites (nitrate/nitrite). Our results demonstrate that iNOS activity may be overestimated due to increased brain calcium concentration in ischemic conditions and also that iNOS is not systematically induced after cerebral ischemia.

Injury-induced alterations in N-methyl-D-aspartate receptor subunit composition contribute to prolonged 45calcium accumulation following lateral fluid percussion

Cells that survive traumatic brain injury are exposed to changes in their neurochemical environment. One of these changes is a prolonged (48 h) uptake of calcium which, by itself, is not lethal. The N-methyl-D-aspartate receptor (NMDAR) is responsible for the acute membrane flux of calcium following trauma; however, it is unclear if it is involved in a flux lasting 2 days. We proposed that traumatic brain injury induced a molecular change in the NMDAR by modifying the concentrations of its corresponding subunits (NR1 and NR2). Changing these subunits could result in a receptor being more sensitive to glutamate and prolong its opening, thereby exposing cells to a sustained flux of calcium. To test this hypothesis, adult rats were subjected to a lateral fluid percussion brain injury and the NR1, NR2A and NR2B subunits measured within different regions. Although little change was seen in NR1, both NR2 subunits decreased nearly 50% compared with controls, particularly within the ipsilateral cerebral cortex. This decrease was sustained for 4 days with levels returning to control values by 2 weeks. However, this decrease was not the same for both subunits, resulting in a decrease (over 30%) in the NR2A:NR2B ratio indicating that the NMDAR had temporarily become more sensitive to glutamate and would remain open longer once activated. Combining these regional and temporal findings with 45calcium autoradiographic studies revealed that the degree of change in the subunit ratio corresponded to the extent of calcium accumulation. Finally, utilizing a combination of NMDAR and NR2B-specific antagonists it was determined that as much at 85% of the long term NMDAR-mediated calcium flux occurs through receptors whose subunits favor the NR2B subunit. These data indicate that TBI induces molecular changes within the NMDAR, contributing to the cells' post-injury vulnerability to glutamatergic stimulation.

In, out, shake it all about: elevation of [Ca2+]i during acute cerebral ischaemia

Because of the extensive second messenger role played by calcium, free intracellular calcium levels are strictly regulated. Under normal physiological conditions, this is achieved through a combination of restricted calcium entry, efficient efflux and restricted intracellular mobility. Overall, the process of regulating free calcium is dependent on ATP derived from oxidative metabolism. Under conditions of cerebral ischaemia, ATP levels fall rapidly and calcium homeostasis becomes significantly disturbed resulting in the initiation of calcium-dependent neurodegenerative processes. In this review, the mechanisms underlying physiological calcium homeostasis and the links between calcium disregulation and neurodegeneration will be discussed.

Relationship between the neuroprotective effect of Na+/H+ exchanger inhibitor SM-20220 and the timing of its administration in a transient middle cerebral artery occlusion model of rats

The aim of this study was to determine the relationship between the neuroprotective effect of SM-20220 (N(aminoiminomethyl)-1-methyl-1H-indole-2-carboxamide methanesulfonate) and the timing of its administration in an experimental stroke model. Two hours of occlusion followed by 22 h of perfusion of the left middle cerebral artery (MCA) was performed by inserting a nylon thread into the MCA to occlude it, and pulling the thread to initiate reperfusion. Intravenous infusion of SM-20220 for 1 h reduced the infarct volume at doses of 0.2-0.8 mg/kg in a dose-dependent manner without causing changes in the systemic arterial blood pressure or blood gases, when SM-20220 administration was started 1 h after the onset of occlusion. Administration of SM-20220 at a dose of 0.4 mg/kg also reduced the edema formation induced by ischemia. In contrast, SM-20220 failed to reduce the infarction, even at 1.6 mg/kg, when administration was started 2 h after the onset of occlusion. Thus, the therapeutic time window of SM-20220 for this transient MCA occlusion model is 1 h. Daily administration of SM-20220 (0.4 mg/kg) for the 7 d following 1.5 h of middle cerebral artery occlusion reduced the infarct volume with statistical significance (p<0.05), showing that SM-20220 did not merely delay but prevented ischemic damage.

Age-dependency of 45calcium accumulation following lateral fluid percussion: acute and delayed patterns

This study was designed to determine the regional and temporal profile of 45calcium (45Ca2+) accumulation following mild lateral fluid percussion (LFP) injury and how this profile differs when traumatic brain injury occurs early in life. Thirty-six postnatal day (P) 17, thirty-four P28, and 17 adult rats were subjected to a mild (approximately 2.75 atm) LFP or sham injury and processed for 45Ca2+ autoradiography immediately, 6 h, and 1, 2, 4, 7, and 14 days after injury. Optical densities were measured bilaterally within 16 regions of interest. 45Ca2+ accumulation was evident diffusely within the ipsilateral cerebral cortex immediately after injury (18-64% increase) in all ages, returning to sham levels by 2-4 days in P17s, 1 day in P28s, and 4 days in adults. While P17s showed no further 45Ca2+ accumulation, P28 and adult rats showed an additional delayed, focal accumulation in the ipsilateral thalamus beginning 2-4 days postinjury (12-49% increase) and progressing out to 14 days (26-64% increase). Histological analysis of cresyl violet-stained, fresh frozen tissue indicated little evidence of neuronal loss acutely (in all ages), but considerable delayed cell death in the ipsilateral thalamus of the P28 and adult animals. These data suggest that two temporal patterns of 45Ca2+ accumulation exist following LFP: acute, diffuse calcium flux associated with the injury-induced ionic cascade and blood brain barrier breakdown and delayed, focal calcium accumulation associated with secondary cell death. The age-dependency of posttraumatic 45Ca2+ accumulation may be attributed to differential biomechanical consequences of the LFP injury and/or the presence or lack of secondary cell death.

Determination of the spatial distribution of major elements in the rat brain with X-ray fluorescence analysis

An energy dispersive X-ray fluorescence analysis was applied for determining the spatial (two-dimensional) distribution of elemental concentrations in rat brain sections. Freeze-dried brain sections prepared from normal and ischemic rats with middle cerebral artery occlusion were scanned with a collimated X-ray beam (0.18 mm in diameter, 50-kV acceleration voltage). The fluorescent Kalpha X-rays of P, S, Cl, and K were detectable, so that the two-dimensional distribution of fluorescent X-ray intensities could be determined for these elements. Furthermore, quantitative determination was possible for P and K by using the fundamental parameter technique. However, the accurate determination of Na and Ca was difficult, because of the low energy of Kalpha X-ray of Na, and the interference of K-Kbeta with Ca-Kalpha. The change in elemental concentrations in ischemic tissue, including the decrease in K concentration and increase in Cl concentration, was demonstrated by this method as a two-dimensional contour map. Since it is possible to obtain a pictorial representation of the elemental concentration in tissue sections, this method may be useful to evaluate the ionic changes in injured brain tissue in relation to histological or autoradiographical observations.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

Novel pharmacologic strategies in the treatment of experimental traumatic brain injury: 1998

The mechanisms underlying secondary or delayed cell death following traumatic brain injury are poorly understood. Recent evidence from experimental models suggests that widespread neuronal loss is progressive and continues in selectively vulnerable brain regions for months to years after the initial insult. The mechanisms underlying delayed cell death are believed to result, in part, from the release or activation of endogenous "autodestructive" pathways induced by the traumatic injury. The development of sophisticated neurochemical, histopathological and molecular techniques to study animal models of TBI have enabled researchers to begin to explore the cellular and genomic pathways that mediate cell damage and death. This new knowledge has stimulated the development of novel therapeutic agents designed to modify gene expression, synthesis, release, receptor or functional activity of these pathological factors with subsequent attenuation of cellular damage and improvement in behavioral function. This article represents a compendium of recent studies suggesting that modification of post-traumatic neurochemical and cellular events with targeted pharmacotherapy can promote functional recovery following traumatic injury to the central nervous system.

Effect of nicardipine, a Ca2+ channel blocker, on pyruvate dehydrogenase activity and energy metabolites during cerebral ischemia and reperfusion in gerbil brain

The purpose of this study was to determine if nicardipine, a calcium ion channel blocker, affects pyruvate dehydrogenase (PDH) activity and improves energy metabolism during cerebral ischemia and reperfusion. Cerebral ischemia was induced, using the bilateral carotid artery occlusion method, for 60 min followed by reperfusion up to 120 min in gerbils. Nicardipine (1 mg/kg) or saline (vehicle-treated) was given to gerbils 30 min prior to the occlusion of the common carotid arteries. PDH activity and metabolites (ATP, PCr, and lactate) were measured in cortex prior to ischemia, immediately following ischemia, and after each reperfusion period. After 60 min ischemia, PDH activity increased in both groups, and was significantly higher in the nicardipine-treated group. After 20 min reperfusion, PDH activity in the nicardipine-treated group recovered to control levels, whereas, the PDH activity in the vehicle-treated group remained elevated, and was higher than the nicardipine-treated animals. At 60 and 120 min reperfusion, the activities in the vehicle-treated group were significantly below control levels, there were no differences, however, between the two groups. ATP and PCr concentrations were markedly depleted immediately after ischemia in both groups. ATP levels at 20 min reperfusion and PCr levels at 60 min reperfusion were significantly higher in the nicardipine-treated group. Lactate concentrations in both groups increased 7-8 fold, similarly, immediately after ischemia. During reperfusion, the lactate remained elevated in both groups, though the levels in the nicardipine-treated group were lower than those in the vehicle-treated group, but not significantly. Nicardipine treatment normalized PDH activity quickly and improved energy metabolism after reperfusion.

Nimodipine prevents early loss of hippocampal CA1 parvalbumin immunoreactivity after focal cerebral ischemia in the rat

The effect of focal cerebral ischemia induced by middle cerebral artery occlusion on hippocampal interneurons containing the calcium-binding protein parvalbumin (PV) was studied in rats. Four hours after the onset of ischemia, a reduced number of PV-immunoreactive (-ir) neurons was observed in the lateral part of the CA1 region, while PV-ir was not altered in the CA2 and CA3 areas. Pretreatment with the L-type Ca2+ channel blocker nimodipine prevented the ischemia-induced loss of PV-ir in the CA1, suggesting a role for L-type voltage sensitive calcium channels in the mechanism of early neuronal alterations in the hippocampus CA1 region after focal cerebral ischemia.

Dynamics of extracellular calcium activity following contusion of the rat spinal cord

The role of Ca2+ in cellular injury has received particular attention in studies of acute spinal cord trauma. In this context, the spatial and temporal distribution of extracellular Ca2+ ([Ca2+]e) may have an important bearing on the development of secondary tissue injury. We therefore studied the spatial-temporal distribution of [Ca2+]e following moderate (25 g-cm) contusive injury to the rat thoracic (T9-T11) spinal cord. Double-barreled, Ca(2+)-selective microelectrodes were used to measure the magnitude and time course of [Ca2+]e at increasing depths from the dorsal spinal cord surface. After 2 h, the tissue was frozen and later analyzed for total Ca concentration using atomic absorption spectroscopy. [Ca2+]e fell at all depths, but the decrease was maximal at 250 and 500 microns from the dorsal surface, where, at 0-10 min after injury, [Ca2+]e averaged 0.09 +/- 0.03 and 0.06 +/- 0.03 mM respectively. By 2 h postinjury, [Ca2+]e recovered to nearly 1 mM across all depths. Over this time, total tissue calcium concentration ([Ca]t) was 4.54 +/- 0.16 mumol/g in injured cords vs 2.75 +/- 0.1 mumol/g in sham-operated controls. These data place emphasis on the dorsal gray matter as a principal site of ionic derangement in acute spinal cord injury. The implications of these findings are discussed with reference to secondary injury processes.

Ketamine alters calcium and magnesium in brain tissue following experimental head trauma in rats

We previously reported that the N-methyl-D-aspartate receptor antagonists dizocilpine maleate and ketamine improved the neurological severity score (NSS) after head trauma in rats. Other investigators have reported increased calcium and decreased magnesium following head trauma in untreated rats. The present study was designed to determine whether ketamine influences the concentrations of calcium and magnesium in brain tissue following head trauma. Eighty-six male Sprague-Dawley rats (180 +/- 15 g) were divided into eight groups. Groups A (no head injury) and C (head injury) received no treatment. Groups B (no head injury) and D-H (head injury) received ketamine. In groups D, E, and F, ketamine, 180 mg/kg i.p., was given 1, 2, and 4 h after head trauma, respectively. In groups G and H, ketamine, 120 and 60 mg/kg, respectively, was given 1 h after head trauma. After we killed the rats at 48 h, cortical slices were taken to measure tissue calcium and magnesium content by the inductively coupled plasma atomic emission spectroscopy method. In the contused hemispheres, calcium increased and magnesium decreased (p < 0.0001). Among the head-injured groups, the increase in brain tissue calcium was smaller in groups receiving 60 mg/kg of ketamine at 1 h or 180 mg/kg of ketamine at 1, 2, or 4 h than in the group not receiving ketamine. The decrease in brain tissue magnesium was smaller in the groups receiving 180 mg/kg of ketamine at 1 and 2 h than in the group not receiving ketamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Concussive brain injury is associated with a prolonged accumulation of calcium: a 45Ca autoradiographic study

In order to determine the extent and duration of calcium (Ca2+) flux following a lateral fluid percussion brain injury in the rat, 45Ca autoradiography was used to study animals immediately, 6, 24 and 96 h after the insult. In addition, cell suspension studies were conducted to determine the extent of cellular flux of 45Ca. Optical density and/or scintillation counting was utilized to provide a relative measure of 45Ca accumulation within 20 different structures. The results indicated that in animals who exhibited no gross morphological damage, 45Ca accumulation following injury was exhibited primarily within the ipsilateral cerebral cortex, dorsal hippocampus and striatum. This accumulation continued for several days returning to control levels by the 4th day after injury. In animals who sustained morphological damage, the contusion site exhibited a marked accumulation of 45Ca which did not resolve spontaneously over the course of 4 days. We conclude from this work that Ca2+ flux is a major component of this experimental model of traumatic injury. Furthermore, that depending on the extent of cell damage, the accumulation of Ca2+ is regionally different. Finally, that even in an injury which by itself does not produce gross morphological tissue damage, accumulation of Ca2+ can continue for at least 48 h.

Monosialoganglioside (GM1) restores membrane fatty acid levels in ischemic tissue after cortical focal ischemia in rat

Using a consistent, reproducible and reliable cortical focal ischemia in rat (permanent unilateral occlusion of the left middle cerebral artery & the ipsilateral common carotid artery [MCAo + CCAo] with a 1 h temporary occlusion of the contralateral CCA), the levels of four major membrane fatty acids (palmitic, C16:0; stearic, C18:0; Oleic, C18:1 and arachidonic, C20:4) were analyzed at 3, 36 and 72 h, and 2 and 4 wk following ischemia to determine the critical point of irreversibility of the cellular plasma membrane disorganization in primary ischemic (Area 1, parietal cortex) and peri-ischemic (Area 2, tempero-occipital cortex) areas. The cortical focal ischemia resulted in time dependent differential loss in four of these major membrane fatty acids. The quantitative differences among primary and peri-ischemic areas reflected the different degree of ischemic injury inflicted to these regions. Acute treatment with ganglioside GM1 protected the further losses of all of these fatty acids and differentially restored their levels in these various injury sites over periods of time. The changes in levels of these membrane fatty acids indicate that the primary ischemic area suffers an irreversible injury and peri-ischemic area suffers reversible injury. After acute treatment (< 2 h) with ganglioside GM1, a partial recovery was observed in primary ischemic area and complete recovery was observed in peri-ischemic areas. These studies support the hypothesis that, ischemia leads to a irreversible plasma membrane disorganization which underlies the eventual cell death, and protection and restoration of these membrane changes by drugs, such as ganglioside GM1 leads to neuroprotection against ischemic injury.

Endonuclease activation following focal ischemic injury in the rat brain

The structural changes which occur in chromatin DNA after ischemic brain injury are poorly understood. This study examined the appearance of double-strand DNA breaks and the temporal profile of DNA degradation following focal ischemic injury in rat brain. Focal cerebral ischemia was produced by tandem occlusion of the common carotid and proximal middle cerebral arteries. The effects of decapitation ischemia were also studied by DNA analysis. DNA was extracted by standard methods from the ischemic brain tissues and electrophoresed on a 1.5% agarose gel. With decapitation ischemia, random DNA cleavage was observed as a dense "smear" on the gel electrophoresis beginning 6 h after the ischemic insult, and increasing in amount thereafter. Focal ischemia provided DNA fragmentation, which is specific DNA cleavage at the internucleosomal linker regions, particularly in the caudoputamen. Coexisting random degradation and specific fragmentation of DNA was observed in the cortex following focal ischemia. To determine whether an endonuclease responsible for DNA fragmentation was present, nuclear proteins were extracted from normal brain nuclei and the endonuclease activity was determined using plasmid DNA and a nuclear incubation system. This demonstrated that brain nuclear proteins have Ca(2+)-dependent endonuclease activity which is related to DNA fragmentation. Ischemic injury causes both random and specific DNA cleavage in the brain, which is probably mediated by Ca(2+)-dependent endonuclease.

Novel pharmacologic therapies in the treatment of experimental traumatic brain injury: a review

Delayed or secondary neuronal damage following traumatic injury to the central nervous system (CNS) may result from pathologic changes in the brain's endogenous neurochemical systems. Although the precise mechanisms mediating secondary damage are poorly understood, posttraumatic neurochemical changes may include overactivation of neurotransmitter release or re-uptake, changes in presynaptic or postsynaptic receptor binding, or the pathologic release or synthesis of endogenous "autodestructive" factors. The identification and characterization of these factors and the timing of the neurochemical cascade after CNS injury provides a window of opportunity for treatment with pharmacologic agents that modify synthesis, release, receptor binding, or physiologic activity with subsequent attenuation of neuronal damage and improvement in outcome. Over the past decade, a number of studies have suggested that modification of postinjury events through pharmacologic intervention can promote functional recovery in both a variety of animal models and clinical CNS injury. This article summarizes recent work suggesting that pharmacologic manipulation of endogenous systems by such diverse pharmacologic agents as anticholinergics, excitatory amino acid antagonists, endogenous opioid antagonists, catecholamines, serotonin antagonists, modulators of arachidonic acid, antioxidants and free radical scavengers, steroid and lipid peroxidation inhibitors, platelet activating factor antagonists, anion exchange inhibitors, magnesium, gangliosides, and calcium channel antagonists may improve functional outcome after brain injury.

Regional imaging of brain tissue calcium ions using aequorin

To investigate regional changes in calcium ion concentrations, we developed a new histochemical method using aequorin, a calcium ion-sensitive photoprotein. In this method, reagent film containing aequorin was made and an unfixed slice of frozen brain 16 microns thick was placed on it. Tissue calcium ions permeated the reagent layer and the bioluminescence of aequorin-calcium ions was recorded photographically with high spatial resolution. There was a close linear relationship (r = 0.903) between the optical density of the bioluminescent images and the logarithmic values of the tissue calcium ion concentration. Using this method, we could visualize the regional tissue calcium ion distribution in pathological states in rat brains.

Nicardipine reduces the levels of leukotriene C4 and prostaglandin E2, following different ischemic periods in rat brain tissue

Ischemic depolarization of nerve membranes is associated with a rapid influx of calcium into the cell, resulting in production of arachidonic acid (AA) metabolites. These metabolites, particularly leukotriene C4 (LTC4) have a very potent vasoconstrictor effect on cerebral arteries inducing vasogenic edema that may damage the ischemic penumbra. Calcium antagonists are assumed to prevent or reduce metabolic disturbances associated with ischemia. In this study, after developing an experimental animal model simulating the concept of the ischemic penumbra in the rat, the levels of LTC4 and prostaglandin E2 (PGE2) produced in the forebrain following different ischemic periods, such as 4th, 15th, 60th and 240th min were measured by a bioassay method, including 6 rats for each ischemic group. Then the effect of the 1-4 dihydropyridine nicardipine (1 mg/kg) on these mediators was investigated by giving it to the rat 30 min before the development of the ischemic model in each corresponding group (n = 6). We showed that nicardipine significantly reduced the high levels of LTC4 and PGE2 in the 4th min and 4th h of cerebral ischemia (p less than 0.005, p less than 0.0005). So it may be concluded that institution of nicardipine may be helpful in protecting the ischemic penumbra during the early hours of cerebral ischemia.

Blood-brain barrier permeability to micromolecules and edema formation in the early phase of incomplete continuous ischemia

The distribution patterns of ionic Lanthanum (La3+; mol. wt. 139) were evaluated after 15, 30 and 60 min of middle cerebral artery occlusion in perfused-fixed rats. Blood-brain barrier (BBB) permeability to Evans blue (EB) and horseradish peroxidase (HRP; mol. wt. 40,000) in vivo was also evaluated. Brain tissue specific gravity was measured. An increase in brain water content was found as early as 30 min following occlusion. HRP and EB extravasation was not observed. La3+ crossed the interendothelial clefts of venules and capillaries at 30 and 60 min and was seen in both extracellular and intracellular brain compartments at 60 min. La3+ extravasation was seen in nonedematous areas bordering the regions of water accumulation. Our findings suggest that the early phase of incomplete continuous ischemia is accompanied by changes in BBB permeability and the interendothelial clefts of venules and capillaries seem to represent one of the early sites of ischemic damage.

Effects of the calcium antagonist nilvadipine on focal cerebral ischemia in spontaneously hypertensive rats

We studied the efficacy of preischemic and postischemic systemic treatment with a new calcium antagonist nilvadipine in a permanent focal cerebral ischemia model of spontaneously hypertensive rats. Rats that underwent microsurgical middle cerebral artery occlusion were blindly assigned to a single intraperitoneal injection of nilvadipine (0.32 mg/kg) or the same amount of polyethylene glycol either 15 minutes before, immediately after, 1 hour after, or 3 hours after occlusion of the left middle cerebral artery. Neurologic conditions of rats were closely examined, and rats were killed 24 hours later. Removed brains were sliced coronally, stained with triphenyltetrazolium chloride, and the size of infarct was determined. Although no neurologic improvements were observed in the treated rats, the area of infarcts was significantly reduced in the groups treated before, immediately after, and 1 hour after occlusion of the middle cerebral artery. Treatment started 3 hours after occlusion was ineffective.

Suppressive effect of E-64c on ischemic degradation of cerebral proteins following occlusion of the middle cerebral artery in rats

Microtubule-associated protein 2 (MAP2) levels in the left cerebral hemisphere decreased significantly 3 days after occlusion of the left middle cerebral artery in rats to 29 +/- 16.3% of control levels. Since MAP2 is one of the substrates of calpain, E-64c, a synthetic calpain inhibitor, was administered at a dose of 400 mg/kg twice a day for 3 days, with the first dose being given before the production of ischemia. This depletion was significantly inhibited in vivo by E-64c (P less than 0.05) to increase MAP2 levels to 55 +/- 25.7% of control levels. E-64c had no significant effect on the ischemia-induced depletion of myelin-associated glycoprotein. Sham-operated rats were used as controls. Our results suggest that calpain is partially involved in the degradation of MAP2, and that the use of calpain inhibitors can be a useful clinical approach to cerebral ischemia.

Changes in the concentrations of cerebral proteins following occlusion of the middle cerebral artery in rats

Using an immunoblotting technique, we investigated changes in the concentrations of microtubule-associated protein 2, 200-kDa neurofilament, tubulin, myelin-associated glycoprotein, and 2':3'-cyclic nucleotide 3'-phosphodiesterase in the brains of 40 rats following occlusion of the left middle cerebral artery or sham operation. Compared with those 4 hours after surgery, concentrations of all proteins decreased significantly in the left hemisphere 3 days after surgery (p less than 0.01). Microtubule-associated protein 2 was the most susceptible to ischemia, and its mean +/- SEM concentration decreased to 23 +/- 9.4% of that in concurrent sham-operated controls. Degradation products of microtubule-associated protein 2 and myelin-associated glycoprotein were detected on the blots. Furthermore, in the contralateral hemisphere (where calpain might be activated), concentrations of these two proteins decreased to 57 +/- 12.0% and 83 +/- 4.3% of those in concurrent sham-operated controls, respectively, 3 days after surgery. Changes in the concentrations of cerebral proteins in the contralateral hemisphere are important for understanding clinical symptoms not attributable solely to the ipsilateral lesion following a focal cerebral stroke.

The increase in local cerebral glucose utilization following fluid percussion brain injury is prevented with kynurenic acid and is associated with an increase in calcium

Immediately following a lateral fluid percussion brain injury, the cerebral cortex and hippocampus ipsilateral to the percussion show a marked accumulation of calcium and a pronounced increase in glucose metabolism. To determine if this increase in glucose metabolism was related to the indiscriminate release of the excitatory amino acid (EAA) glutamate, kynurenic acid (an EAA antagonist) was perfused into the cerebral cortex through a microdialysis probe for 30 min prior to injury. The results show that adding kynurenic acid to the extracellular space prior to trauma prevents the injury-induced increase in glucose utilization. These results indicate that calcium contributes to the ionic fluxes that are typically seen following brain injury and supports the concept of an increased energy demand upon cells to drive pumping mechanisms in order to restore membrane ionic balance.

Allosteric modulation of N-methyl-D-aspartate receptors

In this review we have attempted to describe the basis for current models of the NMDA receptor, and justify the need for the various binding sites that have been proposed. The NMDA receptor is clearly a complex molecule with a number of modulatory sites, any of which may have great functional significance. From the data presented above it is apparent that the NMDA recognition site is closely coupled with the glycine site, and can also be regulated by Zn2+. The glycine site is reciprocally coupled to the NMDA site, and may also be coupled to a divalent-cation site outside the channel. However, the glycine site is insensitive to Zn2+. The Zn2+ site is probably not inside the channel to any degree, but can profoundly affect the ability of NMDA site ligands to operate the channel. However, the determination of reciprocal effects at the Zn2+ site await the development of a suitably potent and selective ligand for this site. Several lines of evidence suggest that the phencyclidine and channel-blocking Mg2+ site are located within the NMDA-operated ion channel. Glutamate, glycine, and Zn2+ alter the binding of ligands to these sites. However, this is most likely to be due to alteration of access of the ligands to their sites rather than a direct allosteric coupling. It does appear that phencyclidine site drugs and Mg2+ bind to separate sites within the channel, and that these separate sites are allosterically coupled. This complex series of interactions, many of which are mediated by endogenous agents, may allow very fine control over the expression of NMDA receptor-mediated synaptic transmission. In addition to these ligand-produced modulatory effects, there may also be covalent modification of the channel by receptor phosphorylation. Furthermore, the voltage sensitivity of some of the effects allows control of NMDA receptor-mediated signaling by alteration of the membrane potential in the postsynaptic cell, which can be achieved in a wide variety of ways. The level of sophistication possible in adjusting the responsiveness of this receptor seems entirely appropriate given its central involvement in a wide variety of fundamental neurobiological events, and underscores the deleterious pathological sequelae of the system tilting out of balance. At the same time, the wide array of possible therapeutic targets raises hopes that it may soon be possible to treat effectively some severely debilitating and currently untreatable diseases.

Somatosensory evoked potentials in rat cerebral cortex before and after middle cerebral artery occlusion

We recorded somatosensory evoked potentials in pentobarbital-anesthetized rats before and after middle cerebral artery occlusion. Trigeminal (vibrissae), median (forelimb), and sciatic (hind limb) nerve stimuli produced consistent, robust, and sharply localized responses in the trigeminal, forelimb, and hind limb regions of the somatosensory cortex of 18 rats. These regions are situated at sequentially greater distances from the center of infarcts produced by middle cerebral artery occlusion. In eight rats, occlusion 1-2 mm below the rhinal fissure abolished somatosensory evoked potentials in all three cortical region within minutes. Positive wavelets preceding the primary cortical response were also diminished by the occlusion, suggesting that ischemia affected the thalamocortical white matter. Four of these eight rats did not show histologically apparent ischemic involvement of the hind limb cortical region at 3 hours after occlusion; sciatic nerve evoked potentials recovered substantially in all four rats, and the amplitudes exceeded baseline (129 +/- 30% at 1 hour, 173 +/- 33% at 3 hours) in three of the four rats. Three of the eight rats did not have gross ischemic involvement of the forelimb cortical region; median nerve evoked potentials recovered fully in all eight rats, but the amplitudes did not exceed baseline. All eight rats had evidence of ischemic damage in the trigeminal cortex; no rat showed full recovery in this region, and all but one had trigeminal evoked potentials that were less than 20% of baseline amplitudes by 3 hours after occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Accumulation of arachidonic acid cyclo- and lipoxygenase products in rat brain during ischemia and reperfusion: effects of treatment with GM1-lactone

The aim of our study was to investigate the changes of various biochemical parameters (concentrations of lactate, free arachidonate, cyclo- and lipoxygenase products) in rat brain after ischemia and reperfusion and the effects of pretreatment with the ganglioside derivative GM1-lactone on the same parameters. Ischemia was induced by reversible occlusion of common carotid arteries for 20 min, which included a final 5 min of respiration of 5% oxygen in nitrogen. Reperfusion was obtained by removing the occlusion. Pre-ischemic conditions were obtained on sham-operated animals. Animals were killed by microwave irradiation of their heads. Brain levels of lactate and of free arachidonate were markedly increased after ischemia and returned to normal values at 5 min of reperfusion. Levels of the cyclooxygenase metabolites prostaglandin F2 alpha, 6-keto-prostaglandin F1 alpha, and thromboxane B2 were increased after ischemia, whereas levels of the lipoxygenase metabolite leukotriene C4 (LTC4) did not change. After reperfusion, a very marked increase of the cyclooxygenase products occurred but not of LTC4. Treatment with GM1-lactone prevented the elevation of cyclo- and lipoxygenase metabolites especially during reperfusion, with limited effects on lactate and free arachidonate levels.

Neurologic and neuropathologic outcome after middle cerebral artery occlusion in rats

Focal cerebral ischemia was produced in 45 rats by occlusion of the left middle cerebral artery. Groups of rats were investigated over a long period after occlusion, that is, from a few hours to 42 days after the production of focal ischemia. Light microscopy showed infarcts in the frontoparietal cortex and the lateral caudoputamen. The ischemic changes closely resembled those found in ischemic infarcts in humans and followed a similar pattern over time. Measurements of the sizes of the infarct, the ipsilateral (operated) hemisphere, and the contralateral hemisphere from camera lucida drawings revealed that the infarct size changed with time after occlusion. Rats killed during the first 7 days (acute phase) had the largest infarcts; in rats killed thereafter, the infarct size diminished. The size of the ipsilateral hemisphere also changed with time; during the first 7 days after occlusion this hemisphere was swollen and larger than the contralateral hemisphere. We suggest that these acute changes are caused by cerebral edema. After the first 7 days, enlargement of the ipsilateral hemisphere gave way to a significant reduction in the size of both the ipsilateral hemisphere and the infarct. We believe that the major reasons for this shift in size are resorption of fluid together with diminished production of edema and elimination of dead cells by macrophages. We suggest that the amount of tissue loss (i.e., the degree of atrophy and the remaining infarct "scar") found 21-42 days after occlusion (during the late phase) is a measure of the total amount of tissue that succumbed as a consequence of ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Interrelationship of brain edema, motor deficits, and memory impairment in rats exposed to focal ischemia

We investigated the relations of brain edema, ion shifts, motor performance, and memory impairment using a focal ischemia model in rats. Cortical infarction was produced by ligation of the middle cerebral artery and the ipsilateral common carotid artery combined with temporary occlusion of the contralateral common carotid artery for 1 hour. Water content and sodium, potassium, and calcium concentrations were measured until Day 14 after the ischemic insult. Significant edema formation was observed; it peaked on Day 3 (p less than 0.001) and then declined. The tissue sodium concentration changed in a manner similar to that of water content, but the tissue potassium concentration changed in an opposite fashion. Massive accumulation of calcium was detected as early as Day 1 after ischemia (almost four times the normal level). The increased calcium concentration was sustained even up to Day 14. Motor performance examinations performed on Day 3, including inclined plane, balance beam, and prehensile tests, demonstrated significantly reduced (p less than 0.001) motor ability that did recover even by Day 7. Passive avoidance learning was carried out on Day 2, followed by a memory retention test on Day 3. Significant memory dysfunction was observed in ischemic compared with sham-operated rats (p less than 0.001). A high correlation coefficient (r = 0.91, p less than 0.01, n = 13) was obtained between water content and calcium concentration on Day 3. Both the total motor score and the degree of disturbance of the passive avoidance reaction also correlated well with water content.

Nicardipine reduces ischemic brain injury. Magnetic resonance imaging/spectroscopy study in cats

We investigated whether the calcium channel entry blocker nicardipine would reduce ischemic brain damage in barbiturate-anesthetized cats subjected to permanent unilateral occlusion of the middle cerebral artery. The evolution of cerebral injury was assessed in vivo in 24 cats by a combination of proton magnetic resonance imaging and phosphorus-31 magnetic resonance spectroscopy for 5 hours following occlusion. Immediately thereafter, the volume of histochemically ischemic brain tissue was determined planimetrically in triphenyl tetrazolium chloride-stained serial coronal sections. Nicardipine was initially administered as an intravenous bolus injection of 10 mg/kg/hr 15 minutes before or 15 minutes after occlusion, followed by continuous infusion at 8 mg/kg/hr for the 5 hours of the experiment. Compared with untreated controls, cats that received nicardipine before or after occlusion showed a significant reduction in the extent of edema in the ipsilateral cerebral cortex, internal capsule, and basal ganglia. The results of phosphorus-31 magnetic resonance spectroscopy studies suggest that nicardipine may protect against cerebral ischemic damage by an action on cellular metabolic processes that preserve high-energy phosphates during the ischemic period.

Nimodipine prevents hyperglycemia-induced cerebral acidosis in middle cerebral artery occluded rats

The effects of acute moderate hyperglycemia on local cerebral pH (LCpH) and local cerebral blood flow (LCBF) were studied in rats infused with glucose before middle cerebral artery (MCA) occlusion, and compared with findings in MCA occlusion alone. The effects of nimodipine infusion on LCBF and LCpH in MCA-occluded hyperglycemic rats were also studied. LCpH and LCBF were determined simultaneously by a double-label autoradiographic technique. Hyperglycemia was induced by an intraperitoneal injection of 2 g/kg D-glucose before MCA occlusion. Nimodipine-treated rats received the drug as an intravenous infusion of 0.5 micrograms/kg/min starting 15 min after occlusion, and ending at decapitation 4 h postocclusion. Cortical LCpH of five structures in the MCA territory of hyperglycemic rats varied between 6.64 +/- 0.04 and 6.72 +/- 0.02 (mean +/- SEM). These values were significantly lower than LCpH in the same ischemic structures in the control rats, which varied between 6.76 +/- 0.04 and 6.82 +/- 0.03 (p less than 0.05 for four of five structures). Cortical LCpH of hyperglycemic nimodipine-treated rats ranged between 6.94 +/- 0.02 and 7.05 +/- 0.02, indicating significant elevations in LCpH (p less than 0.001) compared with the untreated ischemic hyperglycemic animals. LCBF in the ischemic structures was not modified by hyperglycemia or nimodipine treatment. This suggests that nimodipine, by mechanisms other than improvement in blood flow, can prevent the enhanced cerebral tissue acidosis produced by hyperglycemia before incomplete focal ischemia.

Spinal cord sodium, potassium, calcium, and water concentration changes in rats after graded contusion injury

Spinal cord Na, K, Ca, and H2O changes were measured 6 h after graded contusion injuries in 40 Sprague-Dawley rats. A 10 g weight was dropped 1.25 cm (n = 6), 2.5 cm (n = 7), 5.0 cm (n = 6), or 7.5 cm (n = 7) onto the thoracic spinal cord of 26 rats. An additional 10 rats served as laminectomy controls and 4 rats were unoperated controls. At 6 h after surgery or injury, the spinal cords were rapidly cut into 4 mm segments, weighed to obtain tissue wet weights (W), dried for 14-16 h at 97 degrees C in a vacuum oven (30 mmHg), and reweighed for tissue dry weights (D). Water concentrations ([H2O]d) were estimated from (W-D)/D in units of ml/g D. Ionic concentrations ([Na]d, [K]d, and [Ca]d) of the tissue samples were measured by atomic absorption spectroscopy with units of mumol/g D. Ionic shifts (delta [Na]d, delta [K]d, delta [Ca]d) were calculated by subtracting laminectomy control values from those measured in injured cords. Laminectomy alone significantly increased [Na]d and [H2O]d compared to unoperated controls. Mean +/- standard deviations of [H2O]d, [Na]d, [K]d, and [Ca]d were, respectively, 1.95 +/- 0.07, 182.6 +/- 5.9, 277.2 +/- 11.8, and 12.1 +/- 1.4 in unoperated controls; 2.12 +/- 0.08, 238.6 +/- 9.2, 277.8 +/- 9.2, and 11.7 +/- 1.1 in laminectomy controls. At the impact site, [K]d fell by 14-37% and [H2O]d rose by 14-24%, [Na]d by 13-64%, and [Ca]d by 65-137% of laminectomy control values. delta [Na]d, delta [K]d, and delta [Ca]d correlated linearly with impact velocities; [Ca]d increased by 1.0% per cm/sec (r = 0.995, p less than 0.005), [Na]d increased 0.67% per cm/sec (r = 0.950, p less than 0.01), and [K]d decreased 0.34% per cm/sec (r = 0.964, p less than 0.01). Neither delta [H2O] nor delta [Na]d + delta [K]d consistently predicted impact velocity. [Na]d + [K]d correlated with [H2O]d with a slope of 177.4 mumol/ml (r = 0.697, p less than 0.005). Since Na and K constitute greater than 95% of tissue inorganic ions, the slope approximates net ionic shift per ml of water entry or the ionic osmolarity of edema fluid. These results indicate that increasing contusions produce graded ionic shifts and that edema does not predict contusion severity. These data support our hypothesis that net ionic shifts cause edema in injured spinal cords.

Focal ischemia enhances choline output and decreases acetylcholine output from rat cerebral cortex

Choline concentration is rate limiting in the synthesis of acetylcholine. There is a negative arteriovenous difference for choline concentration across the brain, indicating the steady output of choline from this organ. Cerebral ischemia may increase extracellular choline concentration by interfering with its removal by the circulation and by enhancing its net production from phospholipids. We tested this hypothesis in six rats subjected to middle cerebral artery occlusion. We determined choline and acetylcholine output from the ischemic cerebral cortex by analyzing their concentrations in the fluid contained in cortical cups by gas chromatography-mass spectrometry. Mean +/- SEM choline output over 40 minutes before ischemia (baseline value) was 31.1 +/- 1.6 pmol/min/cm2. During ischemia, mean +/- SEM choline output rose to 100.8 +/- 13, 97.3 +/- 12.7, 100 +/- 22.4, and 93.1 +/- 16.9 pmol/min/cm2 in four consecutive 10-minute periods, respectively. Mean +/- SEM acetylcholine output was 15.6 +/- 1.1 before and 5.9 +/- 1.2, 8.3 +/- 2.6, 8.6 +/- 2.1, and 13.7 +/- 4.6 pmol/min/cm2 in the four 10-minute collection periods during ischemia. All four choline values and the first acetylcholine value during ischemia were significantly different from their respective baseline values. We conclude that ischemia induces an increase in extracellular choline concentration with possible implications for acetylcholine metabolism. The attending transient decline in acetylcholine output may be due to impaired release due to local hypoxia or to decreased acetylcholine synthesis.

The potential use of nicardipine in cerebrovascular disease

The efficacy of intravenous nicardipine in the prevention of vasospasm after subarachnoid hemorrhage has been investigated in a dose escalation study in 67 patients admitted within 1 week of subarachnoid hemorrhage. Favorable outcomes were noted in 52 patients (78%). Vasospasm was found by arteriography in 31 patients (46%). A dose-related trend was noted. At the lower dose levels, angiographic spasm was observed in 68% and symptomatic vasospasm in 27% of 34 patients. Only eight of 33 patients (24%) treated at the highest dose level (approximately 10 mg/hr) developed arteriographic evidence of vasospasm. Symptomatic vasospasm was diagnosed in only two of 33 patients (6%) treated with this dose. No deaths from vasospasm occurred. Verification of changes in tissue calcium has been obtained from the rat middle cerebral artery occlusion model, and we concluded that nicardipine administered after permanent occlusion may offer protection against cerebral ischemia in this animal model. Nicardipine uptake was greater at the infarct site than in surrounding tissue, with the highest concentration in the area of maximal ischemia. Nicardipine appears to affect changes in Ca2+ more than other ions: it significantly reduced Ca2+ accumulation in the territory of the middle cerebral artery by 60% at 6 hours, and significantly reduced Na+ and K+ shifts in the same territory by 40% and 50%, respectively, at 6 hours. Although much research remains to be done, a wide role for the dihydropyridines in a number of cerebrovascular conditions is emerging.

Calcium channel blockers correct acidosis in ischemic rat brain without altering cerebral blood flow

We compared the effects of intravenous infusions of 40 micrograms/kg/min verapamil (n = 5), 0.5 microgram/kg/min nimodipine (n = 5), and 5 ng/kg/min prostacyclin (n = 6) and no treatment (n = 6) on local cerebral pH and local cerebral blood flow in middle cerebral artery-occluded rats 90 minutes after the ischemic insult. Local cerebral pH and local cerebral blood flow were determined simultaneously by a double-label autoradiographic technique. The infusions were started 15 minutes after completion of the occlusion and ended at decapitation 90 minutes after completion of the occlusion. Cortical pH for four regions in the ischemic middle cerebral artery territory of rats receiving verapamil or nimodipine was normalized (mean +/- SEM 6.90 +/- 0.02 and 7.01 +/- 0.01, respectively, for the parietal, sensorimotor, frontal, and auditory cortexes), while mean +/- SEM pH in rats receiving prostacyclin was 6.79 +/- 0.01; in untreated rats, mean +/- SEM pH in the same brain regions was 6.72 +/- 0.01. Local cerebral pH in the verapamil- or nimodipine-treated rats was thus significantly different from that in untreated rats (p less than 0.05). Local cerebral blood flow in treated rats was not different from that in untreated ones. Our findings suggest that calcium channel blockers correct ischemic cerebral acidosis by metabolic mechanisms rather than by changes in blood flow.

Nicardipine reduces calcium accumulation and electrolyte derangements in regional cerebral ischemia in rats

We studied the effects of the calcium channel blocker nicardipine on regional tissue Ca2+, Na+, K+, and water shifts in the brains of seven Sprague-Dawley rats after permanent occlusions of the middle cerebral artery. We also assessed the entry of [14C]nicardipine into the brains of five rats; the highest concentrations of [14C]nicardipine were in the infarcted area. Nicardipine treatment significantly reduced Ca2+ accumulation in the middle cerebral artery territory by 60% compared with six untreated rats 6 hours after arterial occlusion. Eight 125-micrograms/kg boluses of nicardipine given every 30 minutes starting 5 minutes after arterial occlusion also significantly reduced the Na+ and K+ shifts in the middle cerebral artery territory by 40% and 50%, respectively, 6 hours after arterial occlusion. Nicardipine appears to reduce Ca2+ accumulation more than it reduces Na+ and water accumulation and K+ loss. Our results suggest that a calcium channel blocker can protect brain tissues in a model of focal cerebral infarction by directly reducing Ca2+ entry into ischemic cells.