NEUROINFORMATICS: THE INTEGRATION OF SHARED DATABASES AND TOOLS TOWARDS INTEGRATIVE NEUROSCIENCE

There is significant interest amongst neuroscientists in sharing neuroscience data and analytical tools. The exchange of neuroscience data and tools between groups affords the opportunity to differently re-analyze previously collected data, encourage new neuroscience interpretations and foster otherwise uninitiated collaborations, and provide a framework for the further development of theoretically based models of brain function. Data sharing will ultimately reduce experimental and analytical error. Many small Internet accessible database initiatives have been developed and specialized analytical software and modeling tools are distributed within different fields of neuroscience. However, in addition large-scale international collaborations are required which involve new mechanisms of coordination and funding. Provided sufficient government support is given to such international initiatives, sharing of neuroscience data and tools can play a pivotal role in human brain research and lead to innovations in neuroscience, informatics and treatment of brain disorders. These innovations will enable application of theoretical modeling techniques to enhance our understanding of the integrative aspects of neuroscience. This article, authored by a multinational working group on neuroinformatics established by the Organization for Economic Co-operation and Development (OECD), articulates some of the challenges and lessons learned to date in efforts to achieve international collaborative neuroscience.

Transcorneal stimulation of trigeminal nerve afferents to increase cerebral blood flow in rats with cerebral vasospasm: a noninvasive method to activate the trigeminovascular reflex

OBJECT

The goal of this study was to investigate whether stimulation of trigeminal afferents in the cornea could enhance cerebral blood flow (CBF) in rats after they have been subjected to experimental subarachnoid hemorrhage (SAH). Cerebral vasospasm following SAH may compromise CBF and increase the risks of morbidity and mortality. Currently, there is no effective treatment for SAH-induced vasospasm. Direct stimulation of the trigeminal nerve has been shown to dilate constricted cerebral arteries after SAH; however, a noninvasive method to activate this nerve would be preferable for human applications. The authors hypothesized that stimulation of free nerve endings of trigeminal sensory fibers in the face might be as effective as direct stimulation of the trigeminal nerve.

METHODS

Autologous blood obtained from the tail artery was injected into the cisterna magna of 10 rats. Forty-eight and 96 hours later (five rats each) trigeminal afferents were stimulated selectively by applying transcorneal biphasic pulses (1 msec, 3 mA, and 30 Hz), and CBF enhancements were detected using laser Doppler flowmetry in the territory of the middle cerebral artery. Stimulation-induced changes in cerebrovascular parameters were compared with similar parameters in sham-operated controls (six rats). Development of vasospasm was histologically verified in every rat with SAH. Corneal stimulation caused an increase in CBF and blood pressure and a net decrease in cerebrovascular resistance. There were no significant differences between groups for these changes.

CONCLUSIONS

Data from the present study demonstrate that transcorneal stimulation of trigeminal nerve endings induces vasodilation and a robust increase in CBF. The vasodilatory response of cerebral vessels to trigeminal activation is retained after SAH-induced vasospasm.

Persistent defect in transmitter release and synapsin phosphorylation in cerebral cortex after transient moderate ischemic injury

BACKGROUND AND PURPOSE

Synaptic transmission is highly vulnerable to metabolic perturbations. However, the long-term consequences of transient metabolic perturbations on synapses are not clear. We studied the long-lasting changes in synaptic transmission and phosphorylation of presynaptic proteins in penumbral cortical neurons after transient moderate ischemia.

METHODS

Rats were subjected to 1 hour of middle cerebral artery occlusion. After reperfusion, electric activity of neurons in the peri-infarct region was recorded intracellularly and extracellularly in situ. Phosphorylation of synapsin-I and tyrosine residues was studied by immunohistochemistry.

RESULTS

Neurons in the penumbra displayed no postsynaptic potentials 1 to 3 hours after recirculation. However, these cells were able to generate action potentials and were responsive to glutamate, suggesting that postsynaptic excitability was preserved but the synaptic transmission was blocked because of a presynaptic defect. The synaptic transmission was still depressed 24 hours after recirculation in neurons in the peri-infarct area that survived ischemia. The amount of immunoreactive synapsin-I, synaptophysin, and synaptotagmin was not appreciably changed for 72 hours after reperfusion. However, phosphorylation of synapsin-l was significantly decreased, whereas phosphotyrosine immunoreactivity was increased, suggesting a selective defect in synapsin-I phosphorylation.

CONCLUSIONS

These data demonstrate that synaptic transmission may be permanently impaired after transient moderate brain injury. Since postsynaptic excitability is preserved, the transmission failure is likely to be caused by presynaptic mechanisms, one of which may be impaired phosphorylation of presynaptic proteins.

Spleen damage in endotoxaemic mice: the involvement of nitric oxide

The association between Escherichia coli endotoxin-induced organ damage and nitric oxide-related mechanisms was investigated in the spleen of male Swiss albino mice (20-40 g) by using (1) Pt/Ir electrochemical sensor connected to an amperometric detection system (NO-501, InterMedical Co., Japan), (2) nitrotyrosine immunohistochemistry, (3) conventional light microscopy and (4) immunoblotting techniques in parallel. 1 h before endotoxin injection, animals were pretreated with either nitric oxide synthase inhibitor, L-N(G)-nitroarginine methyl ester (L-NAME, 20 mg kg(-1), i.p.) or inducible nitric oxide synthase expression inhibitor, dexamethasone (5 mg kg(-1), i.p.) or the inhibitor of murine inducible nitric oxide synthase in vivo, 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT, 1 mg kg(-1), i.p.). 5 h after endotoxin treatment, electrochemically detected concentration of nitric oxide was significantly elevated (nM, endotoxin: 716.6 +/- 178.2, n = 10 vs saline: 209.4 +/- 127.8, n = 9, P = 0.0312, unpaired Student's t-test) and remained so throughout the 30 min monitorization period. Neither dexamethasone nor AMT blocked the endotoxin-induced overproduction of nitric oxide indicating that the enhanced inducible nitric oxide synthase activity cannot be the only explanation. When dexamethasone and L-NAME combination was used to block both the constitutive and the inducible isoforms, nitric oxide production was virtually abolished, indicating a significant contribution from the constitutive isoform of nitric oxide synthase. The results of nitrotyrosine immunohistochemistry and the conventional light microscopy were also in agreement with the amperometric method while immunoblotting revealed the expression of both the endothelial and the inducible isoforms of nitric oxide synthase were induced endotoxaemic animals. Thus, conclude that endotoxin-induced splenic damage in endotoxaemia can be explained by enhanced production of nitric oxide due to the induction of both endothelial and inducible nitric oxide synthases while causal relationship and the roles of other deleterious mediators such as oxygen-derived free radicals are yet to be established.

Chronic daily administration of selegiline and EGb 761 increases brain's resistance to ischemia in mice

Brief cerebral ischemia is reported to cause selective neuronal necrosis, apoptotic cell death, silent infarcts and, when recurrent, cognitive decline. Acute administration of selegiline and EGb 761 have been shown to have anti-apoptotic and neuroprotective effects in experimental ischemia. Their daily use is currently advised to slow down cognitive decline in patients with vascular dementia. Hence, unlike previous studies, we studied the neuroprotective action of chronic daily administration of these drugs in Swiss mice subjected to 30-min middle cerebral artery occlusion and 72 h of reperfusion since this model was reported to induce a slowly evolving infarct with profuse apoptotic cell death. Infarct area was evaluated by H&E staining on coronal brain sections and, apoptotic cells were identified by histological criteria, terminal transferase-mediated d-UTP nick-end labeling (TUNEL) and by immunohistochemical detection of caspase-cleaved actin fragments (fractin). Fifty-one mice received daily intraperitoneal injections of 10 mg/kg selegiline (n=18) or 50 mg/kg EGb 761 (n=17) or equal volume of saline (n=16) for 10-14 days before but not on the day of insult. The infarct volume, number of TUNEL- and fractin-positive cells were significantly reduced in treatment groups by 30, 42 and 51% (selegiline) and, 27, 27 and 29% (EGb 761), respectively. These data suggest that prophylactic use of selegiline and EGb 761 could increase the brain's resistance to mild ischemic injury.

Nitric oxide is involved in ischemia-induced apoptosis in brain: a study in neuronal nitric oxide synthase null mice

Nitric oxide can promote or inhibit apoptosis depending on the cell type and coexisting metabolic or experimental conditions. We examined the impact of nitric oxide on development of apoptosis 6, 24, and 72 h after permanent middle cerebral artery occlusion in mutant mice that lack the ability to generate nitric oxide from neuronal nitric oxide synthase. Adjacent coronal sections passing through the anterior commissure were stained with hematoxylin and eosin or terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL). Immunoblotting was used to identify changes in the anti- and proapoptotic proteins Bcl-2 and Bax, respectively. Activation of caspases was assessed by appearance of actin cleavage products using a novel antiserum directed against 32-kDa actin fragment (fractin). In the neuronal nitric oxide synthase mutant mouse, infarct size and TUNEL positive apoptotic neurons were reduced compared to the wild-type controls. At 6 h, Bcl-2 levels in the ischemic hemisphere were increased in mutants but decreased in the wild-type strain. Bax levels did not change significantly. Caspase-mediated actin cleavage appeared in the ischemic hemisphere at this time point, and was significantly less in mutant brains at 72 h compared to the wild-type. The reduction in the number of TUNEL and fractin positive apoptotic cells appears far greater than anticipated based on the smaller lesion size in mutant mice.Hence, from these data we suggest that a deficiency in neuronal nitric oxide production slows the development of apoptotic cell death after ischemic injury and is associated with preserved Bcl-2 levels and delayed activation of effector caspases.

Synergistic protective effect of caspase inhibitors and bFGF against brain injury induced by transient focal ischaemia

We tested the hypothesis that combined use of trophic factors and caspase inhibitors increases brain resistance to ischaemia in mice. Intracerebroventricular administration of bFGF (>10 ng) 30 min after MCA occlusion decreased infarct size and neurological deficit in a dose-dependent manner following 2 h ischemia and reperfusion (20 h). Combined administration of the subthreshold doses of bFGF (3 ng) and caspase inhibitors (z-VAD.FMK, 27 ng or z-DEVD.FMK, 80 mg) reduced infarct volume by 60%, and reduced neurological deficit. Treatment with a subthreshold dose of bFGF (3 ng) extended the therapeutic window for z-DEVD.FMK (480 ng) from 1 to 3 h after reperfusion. Caspase-3 activity in the ischaemic brain was increased 30 min and 2 h after reperfusion but, was significantly reduced in bFGF-treated animals by 29 and 16%, respectively. Caspase-3 activity was not reduced by a direct bFGF effect because addition of bFGF (10 nM - 2 microM) did not decrease recombinant caspase-3 activity, in vitro. Our data show that combining caspase inhibitors and bFGF lengthens the treatment window for the second treatment, plus lowers the dosage requirements for neuroprotection. These findings are important because low doses of caspase inhibitors or bFGF reduce the possibility of side effects plus extend the short treatment window for ischaemic stroke.

Association of nitric oxide production and apoptosis in a model of experimental nephropathy

BACKGROUND

In recent studies increased amounts of nitric oxide (NO) and apoptosis have been implicated in various pathological conditions in the kidney. We have studied the role of NO and its association with apoptosis in an experimental model of nephrotic syndrome induced by a single injection of adriamycin (ADR).

METHODS

The alteration in the NO pathway was assessed by measuring nitrite levels in serum/urine and by evaluating the changes in vascular reactivity of the isolated perfused rat kidney (IPRK) system. Rats were stratified into control groups and ADR-induced nephropathy groups. These two groups were then divided into: group 1, animals receiving saline; and group 2, animals receiving aminoguanidine (AG) which is a specific inhibitor of inducible-NO synthase. On day 21, rats were sacrificed after obtaining material for biochemical analysis.

RESULTS

Histopathological examination of the kidneys of rats treated with ADR revealed focal areas of mesangial proliferation and mild tubulointerstitial inflammation. They also had significantly higher levels of proteinuria compared with control and treatment groups (P < 0.05). Urine nitrite levels were significantly increased in the ADR-nephropathy group (P < 0.05). In the IPRK phenylephrine and acetylcholine related responses were significantly impaired in the ADR-nephropathy group. Apoptosis was not detected in controls. However, in the ADR-nephropathy group, numerous apoptotic cells were identified in the tubulointerstitial areas. Double staining revealed numerous interstitial apoptotic cells to stain for ED1, a marker for monocytes/macrophages. Treatment with AG prevented the impairment of renal vascular bed responses and reduced both urine nitrite levels and apoptosis to control levels.

CONCLUSION

We suggest that interactions between NO and apoptosis are important in the pathogenesis of the ADR-induced nephrosis.

In vitro/in vivo studies on a buccal bioadhesive tablet formulation of carbamazepine

A buccoadhesive controlled-release system for delivery of carbamazepine (CBZ) was prepared by compression of hydroxypropyl methylcellulose (HPMC) and carbomer, incorporating a penetration enhancer, sodium glycodeoxycholate (GDC). The release behaviour of systems containing CBZ and various amounts of the two polymers with and without GDC was found to be non-Fickian. Formation of an interpolymer complex between HPMC and carbomer was confirmed in acidic medium by turbidity, viscosity and FT-IR measurements. Addition of the drug to the buccoadhesive formulation reduced the adhesion force significantly (p < 0.1). GDC did not have any effect on bioadhesion. Permeability of bovine buccal mucosa to CBZ was determined using Ussing diffusion chambers [1]. In vivo interaction between the tablet and tissue was examined histologically as well as by scoring mucosal irritation. Histological changes observed in the buccal epithelium after 4 h contact with the tablets containing GDC recovered completely within 24 h after removal. No measurable plasma level of CBZ was obtained either in the absence or presence of GDC.

Altered mechanisms of motor-evoked potential generation after transient focal cerebral ischemia in the rat: implications for transcranial magnetic stimulation

We recently demonstrated that a long-lasting transmission defect in cortical synapses caused motor dysfunction after brief middle cerebral artery (MCA) occlusion in the rat despite rapid recovery of axons. In this experimental study, we have examined the impact of differential recovery of synapses and axons on generation of motor-evoked potentials (MEP) recorded from contralateral paralyzed and ipsilateral unaffected muscles, to gain insight into mechanisms of MEPs recorded from stroke patients by transcranial magnetic stimulation (TMS). MEPs generated by focal electrical stimulation of the forelimb area of motor cortex were simultaneously recorded from the brain stem, contra- and ipsilateral forelimb and contralateral hindlimb muscles in rats subjected to transient MCA occlusion. The effect of ischemia on cortical activity and axonal conduction was differentially studied by proximal or distal occlusion of the MCA. Regional cerebral blood flow changes in the forelimb area were monitored by laser-Doppler flowmetry during ischemia and reperfusion. In addition, synaptic transmission within the forelimb area of motor cortex was examined by intracellular and extracellular recording of potentials generated by stimulation of the premotor area. No MEP response was recorded during ischemia. Upon reperfusion: (i) motor axons readily regained their excitability and cortical stimulation caused successive pyramidal volleys (recorded as D waves from the brain stem) and a MEP from contralateral paralytic muscles although synaptic activation of motor pathways was not feasible; (ii) the amplitude of pyramidal volley was increased; (iii) MEPs with a longer latency were recorded from the ipsilateral forelimb. In conclusion, differential recovery of synapses and axons after ischemia may account for some previously unexplained findings (such as preserved MEPs in paralysed muscles) observed in cortical stimulation studies of stroke patients.

Role of endothelial nitric oxide generation and peroxynitrite formation in reperfusion injury after focal cerebral ischemia

BACKGROUND AND PURPOSE

Reperfusion injury is one of the factors that unfavorably affects stroke outcome and shortens the window of opportunity for thrombolysis. Surges of nitric oxide (NO) and superoxide generation on reperfusion have been demonstrated. Concomitant generation of these radicals can lead to formation of the strong oxidant peroxynitrite during reperfusion.

METHODS

We have examined the role of NO generation and peroxynitrite formation on reperfusion injury in a mouse model of middle cerebral artery occlusion (2 hours) and reperfusion (22 hours). The infarct volume was assessed by 2,3,5-triphenyl tetrazolium chloride staining; blood-brain barrier permeability was evaluated by Evans blue extravasation. Nitrotyrosine formation and matrix metalloproteinase-9 expression were detected by immunohistochemistry.

RESULTS

Infarct volume was significantly decreased (47%) in animals treated with the nonselective nitric oxide synthase (NOS) inhibitor N(omega)-nitro-L-arginine (L-NA) at reperfusion. The specific inhibitor of neuronal NOS, 7-nitroindazole (7-NI), given at reperfusion, showed no protection, although preischemic treatment with 7-NI decreased infarct volume by 40%. Interestingly, prereperfusion administration of both NOS inhibitors decreased tyrosine nitration (a marker of peroxynitrite toxicity) in the ischemic area. L-NA treatment also significantly reduced vascular damage, as indicated by decreased Evans blue extravasation and matrix metalloproteinase-9 expression.

CONCLUSIONS

These data support the hypothesis that in addition to the detrimental action of NO formed by neuronal NOS during ischemia, NO generation at reperfusion plays a significant role in reperfusion injury, possibly through peroxynitrite formation. Contrary to L-NA, failure of 7-NI to protect against reperfusion injury suggests that the source of NO is the cerebrovascular compartment.

Endothelial nitric oxide synthase-dependent cerebral blood flow augmentation by L-arginine after chronic statin treatment

Nitric oxide, a product of nitric oxide synthase activity, relaxes vascular smooth muscle and elevates brain blood flow. We evaluated the importance of eNOS to cerebral blood flow augmentation after L-arginine infusion and increases in flow after eNOS upregulation in SV-129 mice. Blood flow was measured by laser-Doppler flowmetry before and after L-arginine infusion (450 mg/kg during a 15-minute period) or measured by 14C-iodoamphetamine indicator fractionation or 14C-iodoantipyrine tissue equilibration techniques. rCBF increased by 26% (laser Doppler flowmetry) after L-arginine infusion but did not change in mutant mice deficient in eNOS expression. After eNOS upregulation by chronic simvastatin treatment (2 mg/kg subcutaneously, daily for 14 days), L-arginine amplified and sustained the hyperemia (38%) and increased absolute brain blood flow from 86 +/- 7 to 119 +/- 10 mL/100 g per minute. Furthermore, pretreatment with simvastatin enhanced blood flow within ischemic brain tissue after middle cerebral artery occlusion. Together, these findings suggest that eNOS activity is critical for blood flow augmentation during acute L-arginine infusion, and chronic eNOS upregulation combined with L-arginine administration provides a novel strategy to elevate cerebral blood flow in the normal and ischemic brain.

Apoptosis in brain biopsies of subacute sclerosing panencephalitis patients

Subacute sclerosing panencephalitis (SSPE) is associated with inflammatory infiltration, neuronal loss, and demyelination. The pathogenesis of these changes is unclear. We examined DNA fragmentation and Bcl-2 expression in brain biopsies of nineteen SSPE patients to investigate the role of apoptosis in tissue damage. DNA fragmentation was present in oligodendroglia, and, in tissues with neuronal loss, in neurons. Reactive astrocytes had no DNA fragmentation, but strong Bcl-2 expression. These results suggest apoptosis as one of the mechanisms for oligodendroglial and neuronal death in SSPE.

Pinealectomy aggravates and melatonin administration attenuates brain damage in focal ischemia

Large infarcts develop in pinealectomized rats subjected to middle cerebral artery occlusion, which was attributed to loss of antioxidant action of melatonin. However, melatonin also has vascular actions, and pinealectomy may induce hypertension. The authors investigated (1) whether hemodynamic factors contribute to infarct development in pinealectomized rats, (2) whether melatonin administration can reverse the unfavorable effect of pinealectomy on infarct formation, and (3) whether melatonin can reduce the infarct volume in nonpinealectomized rats subjected to focal transient ischemia (2 hours middle cerebral artery occlusion, 22 hours reperfusion). Rats were pinealectomized 3 months before ischemia to eliminate any possible action of pinealectomy-induced hypertension on stroke. Blood pressure and regional CBF values during ischemia and reperfusion were not significantly different between pinealectomized and sham-operated rats, suggesting that pinealectomy-induced increase in infarct was not related to hemodynamic factors. The infarct volume resumed to the level of sham-operated rats on melatonin administration. Injection of melatonin (4 mg/kg) before both ischemia and reperfusion reduced infarct volume by 40% and significantly improved neurologic deficit scores in pinealectomized as well as sham-operated rats subjected to middle cerebral artery occlusion. These data suggest that physiologic melatonin release as well as exogenously given melatonin has a neuroprotective action in focal cerebral ischemia.

Compartmental changes in expression of c-Fos and FosB proteins in intact and dopamine-depleted striatum after chronic apomorphine treatment

Chronic administration of dopaminergic agonists to rats with unilateral 6-OH-dopamine (6-OHDA) lesions of nigrostriatal pathway produces behavioral sensitization to subsequent agonist challenges and may serve as a model for DOPA-induced dyskinesias. In order to understand striatal mechanisms behind this long-term behavioral change we examined striatal c-Fos and FosB immunoreactivity induced by apomorphine challenge (5 mg/kg, s.c.) after 3 days of withdrawal following a 2-week administration (5 mg/kg, b.i.d., s.c.) both in intact and 6-OHDA-lesioned animals. In intact rats, c-Fos induction by acute apomorphine exposure showed a striosomal pattern, whereas FosB immunopositivity was diffusely distributed. Following chronic administration, FosB induction turned to a clear striosome dominant pattern similar to c-Fos expression. In denervated striatum, expression of both proteins was profoundly augmented in a homogeneous pattern after a single dose of apomorphine. A distinct striosomal patterning appeared after chronic apomorphine administration in ventromedial part of the denervated striatum with a down-regulation in the matrix and relative enhancement in striosomes. These results suggest that compartmental reorganization of striatal neuronal activity may play a role in long-term behavioral changes induced by chronic dopaminergic treatments both under normal and dopamine-depleted conditions.

Occlusion of the MCA by an intraluminal filament may cause disturbances in the hippocampal blood flow due to anomalies of circle of Willis and filament thickness

We examined blood flow changes and histology in the hippocampus induced by occlusion of the middle cerebral artery (MCA) by a filament in Swiss albino and SV-129 mice (n=67) and in Wistar rats (n=64). Filling cerebral arteries with carbon black revealed that one or both posterior communicating arteries were hypoplastic in 50% of Swiss mice. Ischemic changes were detected in the ipsilateral hippocampus with 2,3,5-triphenyl tetrazolium chloride or hematoxylin and eosin staining when these mice were subjected to 2-h MCA occlusion and 22-h reperfusion. No such abnormalities were found in SV-129 mice and Wistar rats (except one). The hippocampal blood flow dropped to 60+/-2.3% of the baseline in mice with a normal circle of Willis but to 37+/-4.2% in those with an incomplete circle when the MCA was occluded with a 6/0 nylon filament. When an 8/0 filament was used, no flow change in mice with a normal circle but a decrease to 60+/-2% in those with an incomplete circle was observed. A flow drop to 63+/-4% was also seen in Wistar rats when a 3/0 filament used. These data demonstrate that occlusion of the MCA by a thick filament may cause flow reduction in the hippocampus, which may be severe enough to lead to infarction if the circle of Willis is anomalous.

Formulation and in vitro/in vivo investigation of carbamazepine controlled-release matrix tablets

Carbamazepine controlled-release tablet formulations containing hydroxypropyl methylcellulose (HPMC) as matrix material at different concentrations were developed and evaluated in vitro and in vivo. The formulation containing 10% HPMC (HPMC-10) showed a controlled-release profile comparable to that of a commercially available, controlled-release carbamazepine preparation (Tegretol CR 200). The kinetics of controlled-release carbamazepine tablets was examined in eight healthy volunteers. The peak plasma concentration of 1.99 +/- 0.56 micrograms.ml-1 was obtained for HPMC-10 at 15.0 +/- 9.0 h, and 1.33 +/- 0.35 micrograms.ml-1 for Tegretol CR 200 at 15.2 +/- 8.9 h, and AUC0-infinity values of 85.2 +/- 30.8 micrograms.h.ml-1 and 76.9 +/- 20.7 micrograms.h.ml-1, respectively. Developed formulation (HPMC-10) was found to be bioequivalent to Tegretol CR 200 and, controlled release was obtained with smoother concentration-time curve resulting in less fluctuations.

Prolonged therapeutic window for ischemic brain damage caused by delayed caspase activation

Apoptotic cell death is prominent in neurodegenerative disorders, such as Alzheimer's disease and Huntington's disease, and is found in cerebral ischemia. Using a murine model of delayed cell death, we determined that cleavage of zDEVD-amino-4-trifluoromethyl coumarin (zDEVD-afc) in brain homogenate, a measure of caspase activation, increased initially 9 hours after brief (30 minutes) middle cerebral artery occlusion along with caspase-3p20 immunoreactive cleavage product as determined by immunoblotting. zDEVD-afc cleavage activity was blocked by pretreatment or posttreatment with the caspase-inhibitor N-benzyloxycarbonyl-Asp(OMe)-Glu(OMe)-Val-Asp(OMe)-fluoromethyl-ketone (zDEVD-fmk), and ischemic damage was reduced when the drug was injected up to 9 hours after reperfusion. The protection was long lasting (21 days). Hence, the period before caspase activation defined the therapeutic opportunity for this neuroprotective agent after mild ischemic brain injury. Prolonged protection after caspase inhibition plus the extended treatment window may be especially relevant to the treatment of neurodegenerative disorders.

Mechanisms of motor dysfunction after transient MCA occlusion: persistent transmission failure in cortical synapses is a major determinant

BACKGROUND AND PURPOSE

Failure of prompt motor recovery after spontaneous recirculation or thrombolytic therapy may be due to an unsatisfactory restoration of synaptic activity within cortex and/or blockade of electrical impulses at the severely ischemic subcortical region.

METHODS

Afferent, efferent, and synaptic activities were focally examined within the rat sensorimotor cortex by recording the somatosensory-evoked potential (SEP) and motor area response evoked by stimulation of premotor afferents (PmEP) intracortically and the motor-evoked potential (MEP) generated by stimulation of the forelimb area from the brain stem. The effect of ischemia on electrical activity in the cortex and on axonal conduction in the subcortical region was studied differentially by proximal or distal occlusion of the MCA.

RESULTS

MEP consisted of direct and indirect waves generated by direct activation of pyramidal axons and indirect excitation of pyramidal neurons via cortical synapses, respectively. MEP, PmEP, and SEP disappeared on proximal occlusion. Following reperfusion after 1 to 3 hours of ischemia, the direct wave of MEP readily recovered but the indirect wave showed no improvement, suggesting a restored axonal conduction but impaired cortical synaptic transmission. The synaptic defect, which also caused a poor recovery in PmEP and SEP and on electrocorticogram, was persistent and detected 24 hours after 1 hour of proximal occlusion.

CONCLUSIONS

Our data suggest that motor dysfunction is caused by loss of cortical excitability and blockade of motor action potentials at the subcortical level during ischemia. After brief transient ischemia, axonal conduction readily recovers; however, a persistent transmission failure at cortical synapses leads to motor dysfunction.

Monitoring cellular edema at single-neuron level by electrical resistance measurements

Electrical resistance measurements have been used for investigating extracellular volume fraction (EVF) of brain tissue. Conventional techniques using multiple metal electrodes are limited in their spatial resolution, and thus not suitable for detecting local EVF changes at cellular level. We used a multibarrelled glass microelectrode to monitor cellular swelling locally at single-neuron level. The microelectrode was placed in CA1 region of the rat hippocampus, in situ. A constant current pulse was applied between one of the barrels and a reference electrode placed in the neck. The resultant voltage drop, which was directly proportional to the resistance of the immediate environment surrounding the tip of the microelectrode, was recorded through another barrel. A third barrel was used for iontophoretic injection of N-methyl-D-aspartate (NMDA) for inducing local cellular edema. The effect of diffuse edema induced by bilateral carotid artery ligation on EVF was also investigated. NMDA application increased the local tissue resistance by 2.0-, and ischemia, by 3.4-folds. We conclude that the method described can detect changes in EVF of minute volumes of brain tissue, and is suitable for monitoring very local effects of drugs or changes in the metabolism on cell volume.

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

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