Degeneration of neurons in the thalamic reticular nucleus following transient ischemia due to raised intracranial pressure: excitotoxic degeneration mediated via non-NMDA receptors?

Abolished perineuronal nets and altered parvalbumin-immunoreactivity in the nucleus reticularis thalami of wildtype and 3xTg mice after experimental stroke

Treatment strategies for ischemic stroke are still limited, since numerous attempts were successful only in preclinical research but failed under clinical condition. To overcome this translational roadblock, clinical relevant stroke models should consider co-morbidities, age-related effects and the complex neurovascular unit (NVU) concept. The NVU includes neurons, vessels and glial cells with astrocytic endfeet in close relation to the extracellular matrix (ECM). However, the role of the ECM after stroke-related tissue damage is poorly understood and mostly neglected for treatment strategies. This study is focused on alterations of perineuronal nets (PNs) as ECM constituents and parvalbumin-containing GABAergic neurons in mice with emphasis on the nucleus reticularis thalami (NRT) in close proximity to the ischemic lesion as induced by a filament-based stroke model. One day after ischemia onset, immunofluorescence-based quantitative analyses revealed drastically declined PNs in the ischemia-affected NRT from 3- and 12-month-old wildtype and co-morbid triple-transgenic (3xTg) mice with Alzheimer-like alterations. Parvalbumin-positive cells decreased numerically in the ischemia-affected NRT, while staining intensity did not differ between the affected and non-affected hemisphere. Additional qualitative analyses demonstrated ischemia-induced loss of PNs and allocated neuropil ECM immunoreactive for aggrecan and neurocan, and impaired immunoreactivity for calbindin, the potassium channel subunit Kv3.1b and the glutamate decarboxylase isoforms GAD65 and GAD67 in the NRT. In conclusion, these data confirm PNs as highly sensitive constituents of the ECM along with impaired neuronal integrity of GABAergic neurons. Therefore, specific targeting of ECM components might appear as a promising strategy for future treatment strategies in stroke.

Microrecording and image-guided stereotactic biopsy of deep-seated brain tumors

OBJECT

Image-guided stereotactic brain tumor biopsy cannot easily obtain samples of small deep-seated tumor or selectively sample the most viable region of malignant tumor. Image-guided stereotactic biopsy in combination with depth microrecording was evaluated to solve such problems.

METHODS

Operative records, MRI findings, and pathological specimens were evaluated in 12 patients with small deep-seated brain tumor, in which image-guided stereotactic biopsy was performed with the aid of depth microrecording. The tumors were located in the caudate nucleus (1 patient), thalamus (7 patients), midbrain (2 patients), and cortex (2 patients). Surgery was performed with a frameless stereotactic system in 3 patients and with a frame-based stereotactic system in 9 patients. Microrecording was performed to study the electrical activities along the trajectory in the deep brain structures and the tumor. The correlations were studied between the electrophysiological, MRI, and pathological findings. Thirty-two patients with surface or large brain tumor were also studied, in whom image-guided stereotactic biopsy without microrecording was performed.

RESULTS

The diagnostic yield in the group with microrecording was 100% (low-grade glioma 4, high-grade glioma 4, diffuse large B-cell lymphoma 3, and germinoma 1), which was comparable to 93.8% in the group without microrecording. The postoperative complication rate was as low as that of the conventional image-guided method without using microelectrode recording, and the mortality rate was 0%, although the target lesions were small and deep-seated in all cases. Depth microrecording revealed disappearance of neural activity in the tumor regardless of the tumor type. Neural activity began to decrease from 6.3 ± 4.5 mm (mean ± SD) above the point of complete disappearance along the trajectory. Burst discharges were observed in 6 of the 12 cases, from 3 ± 1.4 mm above the point of decrease of neural activity. Injury discharges were often found at 0.5-1 mm along the trajectory between the area of decreased and disappeared neural activity. Close correlations between electrophysiological, MRI, and histological findings could be found in some cases.

CONCLUSIONS

Image-guided stereotactic biopsy performed using depth microrecording was safe, it provided accurate positional information in real time, and it could distinguish the tumor from brain structures during surgery. Moreover, this technique has potential for studying the epileptogenicity of the brain tumor.

The thalamic reticular nucleus: a functional hub for thalamocortical network dysfunction in schizophrenia and a target for drug discovery

The thalamus (comprising many distinct nuclei) plays a key role in facilitating sensory discrimination and cognitive processes through connections with the cortex. Impaired thalamocortical processing has long been considered to be involved in schizophrenia. In this review we focus on the thalamic reticular nucleus (TRN) providing evidence for it being an important communication hub between the thalamus and cortex and how it may play a key role in the pathophysiology of schizophrenia. We first highlight the functional neuroanatomy, neurotransmitter localisation and physiology of the TRN. We then present evidence of the physiological roles of the TRN in relation to oscillatory activity, cognition and behaviour. Next we discuss the role of the TRN in rodent models of risk factors for schizophrenia (genetic and pharmacological) and provide evidence for TRN deficits in schizophrenia. Finally we discuss new drug targets for schizophrenia in relation to restoring TRN circuitry dysfunction.

Multiscale entropy analysis of EEG for assessment of post-cardiac arrest neurological recovery under hypothermia in rats

Neurological complications after cardiac arrest (CA) can be fatal. Although hypothermia has been shown to be beneficial, understanding the mechanism and establishing neurological outcomes remains challenging because effects of CA and hypothermia are not well characterized. This paper aims to analyze EEG (and the alpha-rhythms) using multiscale entropy (MSE) to demonstrate the ability of MSE in tracking changes due to hypothermia and compare MSE during early recovery with long-term neurological examinations. Ten Wistar rats, upon post-CA resuscitation, were randomly subjected to hypothermia (32 degrees C-34 degrees C, N = 5) or normothermia (36.5 degrees C-37.5 degrees C, N = 5). EEG was recorded and analyzed using MSE during seven recovery phases for each experiment: baseline, CA, and five early recovery phases (R1-R5). Postresuscitation neurological examination was performed at 6, 24, 48, and 72 h to obtain neurological deficit scores (NDSs). Results showed MSE to be a sensitive marker of changes in alpha-rhythms. Significant difference (p < 0.05) was found between the MSE for two groups during recovery, suggesting that MSE can successfully reflect temperature modulation. A comparison of short-term MSE and long-term NDS suggested that MSE could be used for predicting favorability of long-term outcome. These experiments point to the role of cortical rhythms in reporting early neurological response to ischemia and therapeutic hypothermia.

Cellular and molecular pathways of ischemic neuronal death

Three routes have been identified triggering neuronal death under physiological and pathological conditions. Excess activation of ionotropic glutamate receptors cause influx and accumulation of Ca2+ and Na+ that result in rapid swelling and subsequent neuronal death within a few hours. The second route is caused by oxidative stress due to accumulation of reactive oxygen and nitrogen species. Apoptosis or programmed cell death that often occurs during developmental process has been coined as additional route to pathological neuronal death in the mature nervous system. Evidence is being accumulated that excitotoxicity, oxidative stress, and apoptosis propagate through distinctive and mutually exclusive signal transduction pathway and contribute to neuronal loss following hypoxic-ischemic brain injury. Thus, the therapeutic intervention of hypoxic-ischemic neuronal injury should be aimed to prevent excitotoxicity, oxidative stress, and apoptosis in a concerted way.

Neuronal stress response and neuronal cell damage after cardiocirculatory arrest in rats

Cardiocirculatory arrest is the most common clinical cause of global cerebral ischemia. We studied neuronal cell damage and neuronal stress response after cardiocirculatory arrest and subsequent cardiopulmonary resuscitation in rats. The temporospatial cellular reactions were assessed by terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end-labeling (TUNEL) staining of DNA fragments, in situ hybridization (heat shock protein hsp70; immediate early genes c-fos and c-jun), and immunocytochemical (HSP70; and myeloperoxidase, specific marker of polymorphonuclear leukocytes [PMNL]) techniques. Cardiac arrest of 10 minutes' duration was induced in mechanically ventilated male Sprague-Dawley rats anesthetized with nitrous oxide and halothane. After cardiopulmonary resuscitation, animals were allowed to reperfuse spontaneously for 6 hours, 24 hours, 3 days, and 7 days (n = 6 per group). Five sham-operated animals were controls. The TUNEL staining revealed an early onset degeneration in the thalamic reticular nucleus (TRN) at 6 hours that peaked at 3 days. In contrast, degeneration was delayed in the hippocampal CA1 sector, showing an onset at 3 days and a further increase in the number of TUNEL-positive cells at 7 days. A minor portion of TUNEL-positive nuclei in the CA1 sector showed condensed chromatin and apoptotic bodies, whereas all nuclei in the TRN revealed more diffuse staining. After 6 hours of reperfusion, levels of mRNA for hsp70 and c-jun were elevated in circumscribed areas of cortex, in all hippocampal areas, and in most nuclei of thalamus, but not in the TRN. After 24 hours, a strong expression of mRNA for hsp70 and c-jun could be observed in the second layer of the cortex and in hippocampal CA1 sector; hsp70 also was observed in hippocampal CA3 sector. Some animals showed expression of hsp70 and c-jun in the dentate gyrus. After 3 days, hsp70 and c-jun were detected mainly in the CA1 sector of hippocampus. At 7 days, mRNA for both returned to control values. Therefore, delayed cell degeneration in the CA1 sector corresponds to a prolonged expression of hsp70 and c-jun in this area. In situ hybridization studies for c-fos revealed a strong signal in CA3 and dentate gyrus and a less prominent signal in TRN at 6 hours. At 24 hours, CA4 and amygdalae were positive, whereas at 3 and 7 days, the signal reached control levels; no prolonged or secondary expression was observed in the CA1 sector. Immunohistochemical study confirmed translation of HSP70 in various areas corresponding to the detection of mRNA, including the CA1 sector. The number of PMNL increased significantly at 6 hours and 7 days after cardiac arrest; PMNL were distributed disseminately and were not regionally associated with neuronal cell damage. The current data support the view that CA1 neurons might undergo an apoptosis-associated death after cardiac arrest, but PMNL are not directly involved in this process. The marked differences in the time course and the characteristics of TUNEL staining and the neuronal stress response in CA1 sector and TRN point to different mechanisms of neuronal injury in the two selectively vulnerable areas.

Correlation between potentiation of AP1 DNA binding and expression of c-Fos in association with phosphorylation of CREB at serine133 in thalamus of gerbils with ischemia

Protein biosynthesis is mainly under the control at the level of gene transcription in eukaryotes. Transcription factors are nuclear proteins with abilities to modulate the activity of RNA polymerase II which is responsible for the formation of messenger RNA from double stranded DNA in the cell nuclei. Binding of a radiolabeled oligonucleotide probe for the transcription factor activator protein-1 (AP1) was transiently potentiated 1 to 6 h after the recirculation of blood supply in the thalamus and striatum, but not in the entorhinal cortex, olfactory bulb, frontal cortex, cerebellar cortex and medulla-pons, in gerbils with transient global forebrain ischemia for 5 min, in addition to the hippocampal subregions. The ischemic insult not only increased the immunoreactivity with an antibody against cyclic AMP response element binding protein (CREB) phosphorylated at serine133, but also induced the expression of both c-Jun and c-Fos family proteins 3 h after the recirculation in the thalamus. Limited proteolysis by Staphylococcus aureus (S. aureus) V8 protease revealed the expression of different partner proteins of AP1 in response to ischemic signals in the thalamus. Moreover, ischemia for 2 min led to more prolonged elevation of AP1 binding in the thalamus at least up to 12 h after the reperfusion than that seen with ischemia for 5 min. These results suggest that potentiation of AP1 DNA binding may at least in part involve mechanisms associated with the expression of c-Fos protein through phosphorylation of CREB at serine133 in the thalamus of gerbils with ischemia.

Audiogenic seizures after neck tourniquet-induced cerebral ischemia in the rat

Development of audiogenic seizures (AGS) and their correlation with neurodegeneration were studied after 7.5 min of whole-brain ischemia. One day post-ischemia, all animals became hyperreactive and responded to auditory stimulation by generalized seizures. Neuronal necrosis developed already 6 h post-ischemia in inferior colliculi, reticular thalamic nucleus and hippocampal hilar region. Repeated ischemia did not induce any neurological changes, suggesting that the neurological effects are consequences of selective neuronal injury.

Limited but significant protective effect of hypothermia on ultra-early-type ischemic neuronal injury in the thalamus

We investigated the protective effect of hypothermia on ultra-early-type ischemic injury in the thalamic reticular nucleus of the rat. Cerebral ischemia was produced by 5 min of cardiac arrest followed by resuscitation. Rectal and cranial temperature during and after cardiac arrest was maintained at 37-38 degrees C in the normothermic group and at 32-33 degrees C in the hypothermic group. In the postischemic hypothermic group, temperature was maintained at 32-33 degrees C starting 15 min after normothermic ischemia. Histological damage was evaluated quantitatively. While after 5 min of recirculation there was no difference in morphological changes in terms of neuronal halo formation, intraischemic hypothermia reduced the severity of the degenerative changes represented by vacuolated or dark neurons by 15 min. Postischemic hypothermia failed to show any evidence of protection by 30 min. The protective effect of intraischemic hypothermia remained significant when evaluated at 14 days after ischemia by volumetry of the lesion and neuronal density analysis, whereas postischemic hypothermia had no clear protective effect. These results suggest that the protective effect of intraischemic hypothermia applies to neurons susceptible to ultra-early-type injury, but the effect of postischemic hypothermia is limited because normothermic ischemia results in extensive degeneration in these neurons by 15 min.

Ischemia-induced anxiety following cardiac arrest in the rat

Male Long-Evans rats were subjected to 7 min of chest compression (CC) to produce cardiac arrest and global ischemia resulting in damage to the brain. Timidity and motor activity were evaluated using the elevated plus maze, one of the most widely accepted methods for measuring anxiety in rats. Post-ischemic rats spent much less time in the open arms (3% at day 5) than handled (54%) or sham-compressed (30%) rats. This was interpreted as increased anxiety. Thus, post-ischemic rats developed more anxiety than normal handled rats or sham-operated rats. Anxiety increased markedly on post-ischemic day 2, suggesting a delayed effect. Anxiety gradually decreased after day 5 but recovery was still incomplete up to 115 days post-ischemia. Motor activity decreased gradually during days 2-5 post-ischemia and then recovered to the normal range after day 15. These results are inconsistent with damage limited to the hippocampus and suggest that less obvious histological changes may be occurring elsewhere in the brain.

Audiogenic seizures following global ischemia induced by chest compression in Long-Evans rats

Transient global ischemia was used to produce a rat model of generalized tonic-clonic epilepsy. Controlled chest compression in ketamine-anesthesized Long-Evans rats produced transient global ischemia by mechanically preventing the heart from pumping blood. Circulation was restored by standard cardiopulmonary resuscitation techniques. With a temporal muscle (skull) temperature of 35 +/- 0.4 degrees C, 75% (76/102) of the rats survived 7 min of chest compression. Generalized seizures could be evoked in 78% (59/76) of the surviving rats by a 60 s exposure to a loud sound (bell, 110 dB) beginning 24 h after the ischemic episode. The seizure patterns seen resembled those described by Maresceaux (1987) for genetically seizure-prone Wistar rats. Susceptibility to sound-induced seizures declined with time, with wide variations in recovery rate between individuals; one rat showed a daily sound-induced seizure for over 5 months. Seizures were attenuated or blocked by treatment with carbamazepine or sodium valproate. This model is similar to the great vessel occlusion model used by Kawai et al. (1995), but is less invasive. We believe it will be useful in the evaluation of therapies for acquired generalized (grand mal) seizures.

Neuroprotective efficacy of lifarizine (RS-87476) in a simplified rat survival model of 2 vessel occlusion

1. A new, modified rat two vessel occlusion model (with hypotension) was established and the neuroprotective efficacy of the novel agent lifarizine (RS-87476) was examined. 2. The two vessel occlusion model used in the study was a modification of the model described in the literature, whereby we have obviated the need to use a muscle relaxant and intubate the trachea to provide ventilatory support by providing a tight fitting face mask attached to the ventilator. Furthermore, the need to combine exsanguination and additional pharmacological means of inducing the mandatory hypotension (50 mmHg), required to decrease brain blood perfusion pressure, has been removed by simply manipulating the concentration of the already present halothane anaesthetic. 3. The appropriate level of hypotension having been reached, microvascular clips were applied to bilaterally occlude the common carotid arteries for 12 min. This resulted in a loss of the cortical EEG activity. Local cerebral blood flow was measured 6 min into the occlusion period, using the fully quantitative [14C]-iodoantipyrine autoradiographic technique, in a separate group of rats (n = 5). This illustrated the lack of any blood flow, in the areas under study, during the period when there was an isoelectric cortical EEG pattern. 4. The high grade global ischaemic lesion which occurred gave quantifiable neuronal damage in several vulnerable regions of the brain, namely, the hippocampal CA1 sub-field, cortex, thalamus, striatum, and cerebellar brain stem (Purkinje cells). 5. Following the global ischaemic insult the rats were allowed to recover for 72 h before assessment of the damage, during which time one group of rats (n = 11) received 100 micrograms kg-1 lifarizine i.a. 5 min post-occlusion, 500 micrograms kg-1 lifarizine i.p. 15 min post-occlusion, and 500 micrograms kg-1 lifarizine i.p. twice daily for 72 h. A second group of rats (n = 12) was treated with appropriate volumes of vehicle (0.4 ml kg-1 i.a. and 2 ml kg-1 i.p.) at identical time points. 6. Histopathological damage was assessed, from cresyl violet and haematoxyline/eosin stained sections, using a scoring system of 0-6 (no damage-complete neuronal death). The dosing regimen of lifarizine gave reduced damage in the hippocampal CA1 sub-field (4.1 +/- 0.3 to 2.8 +/- 0.6) and striatum (1.7 +/- 0.3 to 1.2 +/- 0.3) and significant neuroprotection in the anterior cortex (2.0 +/- 0.2 to 1.2 +/- 0.2; p < 0.05), thalamus (1.5 +/- 0.2 to 0.8 +/- 0.2; p < 0.01), posterior cortex (1.5 +/- 0.2 to 1.0 +/- 0.2; p < 0.05) and cerebellar brain stem (0.9 +/- 0.2 to 0.4 +/- 0.1; p < 0.01). The overall mean brain score was significantly reduced (from 1.5 +/- 0.1 to 0.9 +/- 0.2). 7. These data show that the newly modified 2 vessel occlusion model produced a quantifiable level of ischaemic damage and that the novel agent lifarizine is neuroprotective in the model.

The AMPA antagonist NBQX protects thalamic reticular neurons from degeneration following cardiac arrest in rats

Thalamic reticular (RT) neurons are selectively vulnerable to degeneration following global ischemia. The degenerative mechanism is thought to involve an excitotoxic component, mediated in part by sustained post-ischemic activation of AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate) type excitatory amino acid (EAA) receptors. In order to test this hypothesis, the selective competitive AMPA type EAA antagonist NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F) quinoxalinedione) was administered at 30 mg/kg to rats 1, 3, and 6 h after resuscitation from 10 min cardiac arrest. NBQX treatment resulted in a 2-fold increase of spared RT neurons, from a mean density of 3.6 +/- 0.8 x 10(3) neurons/mm3 in cardiac arrest cases to 7.4 +/- 1.1 x 10(3) neurons/mm3 in the NBQX treated group, which represents sparing of 41.7% of the normal population of RT neurons, and protection of 26.9% of vulnerable RT neurons. Neurons within the central core of the RT manifest both a higher degree of vulnerability to ischemic degeneration, > 92% loss, and a higher sensitivity to sparing following NBQX administration, 460% increased sparing, than neuronal sub-populations in the medial or lateral 1/3 of the RT. Protection by post-arrest administration of NBQX suggests that sustained post-arrest stimulation of AMPA receptors is an important component in the process of ischemic degeneration of RT neurons.

Loss of parvalbumin immunoreactivity defines selectively vulnerable thalamic reticular nucleus neurons following cardiac arrest in the rat

The thalamic reticular nucleus (NRT) is one of the most vulnerable structures to selective neuronal damage both in human cardiac arrest patients and in experimental rodent global cerebral ischemia models. The detailed distribution of neuronal injury within the NRT was examined following 10-min cardiac arrest in the rat with conventional Nissl staining, 45Ca autoradiography and immunocytochemistry of the calcium binding proteins parvalbumin (PV) and calretinin (CR). While Nissl staining was almost unable to show the exact boundary of the nucleus and of the lesion, immunocytochemistry of PV proved to be the most useful index of the exact location and extent of neuronal loss in the NRT after ischemia. Calcium autoradiography was a sensitive method for detecting the lesion, and showed a similar distribution to the loss of PV staining, but did not give optimal spatial resolution. Quantitative analysis of PV staining at 7 days of recirculation demonstrated cell loss restricted to the lateral aspect of the middle segment of the NRT, identical with the distribution of large fusiform neurons in the somatosensory component of the nucleus. CR-positive neurons in the NRT were completely spared, although not all surviving neurons contained CR. These studies provide the first detailed characterization of the distribution of vulnerable neurons within the NRT after experimental ischemia and suggest that immunocytochemistry of PV is a useful tool for quantitative analysis of the lesion for use in further experiments to elucidate the mechanisms of selective vulnerability of the NRT.

Development of susceptibility to audiogenic seizures following cardiac arrest cerebral ischemia in rats

Susceptibility to audiogenic seizures (AGS) was investigated in Sprague-Dawley rats subjected to cardiac arrest cerebral ischemia (CACI), produced by compression of the major cardiac vessels. The onset of AGS was regularly observed 1 day after CACI of > 5 min duration. The duration of postischemic susceptibility to AGS was directly related to the density of cerebral ischemia, with 50% of more severely ischemic animals still showing AGS susceptibility 8 weeks after CACI. Lesioning of the inferior colliculi (IC) abolished the onset of AGS; no such effect was observed after lesioning the medial geniculate (MG). Glutamic acid decarboxylase (GAD) immunochemistry revealed approximately 50% loss of GAD-positive neurons in the IC, which was similar in animals with various durations of AGS susceptibility. Otherwise, there was a conspicuous sprouting of gamma-aminobutyric acid (GABA)-ergic terminals in the ventral thalamic nuclei, which peaked approximately 1 month after the CACI. Evaluation of GABA-A inhibitory function in the hippocampus by the paired pulse stimulation revealed changes indicating loss of GABA-A inhibition coinciding with the onset of AGS, and its return in animals tested 2 months after CACI. Our observations suggest a potential role of GABA-ergic dysfunction in the postischemic development of AGS.

The partial mu opiate agonist buprenorphine protects a sub-population of thalamic reticular neurons following cardiac arrest in rats

Extensive loss of neurons occurs from the middle region of the thalamic reticular nucleus (RT) in rats resuscitated after 10 min of cardiac arrest. Administration of the partial mu opiate agonist buprenorphine 45 min after resuscitation produces a small but significant increase in spared neurons along the medial and lateral margins of the middle RT, regions where mu receptors have been localized. Systemic administration of mu agonists may augment endogenous opiate mechanisms that contribute to the relative ischemic resistance of subpopulations of RT neurons.

Diencephalic changes in traumatic brain injury: relationship to sensory perceptual function

Magnetic resonance (MR) imaging scans of 33 traumatically brain-injured (TBI) patients were compared quantitatively to MR scans of controls matched for age and gender. Quantitative estimates of thalamic, internal capsule, and third ventricle morphology were obtained in each TBI patient. Comparisons were made to normal control subjects and revealed significant reduction in thalamic volume with corresponding increase in third ventricle. Measurements of internal capsule reflected nonsignificant changes. Significant correlations were observed between sensory-perceptual functioning, as measured by the Reitan-Kløve Sensory-Perceptual Exam, and thalamic volume in TBI patients. A decrease in thalamic volume was associated with an increase in sensory-perceptual errors.

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

BACKGROUND AND PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Pathophysiological process after transient ischemia of the middle cerebral artery in the rat

For the understanding of pathophysiology of the cerebral ischemia, we made a transient intraluminal occlusion of the middle cerebral artery in the rat and investigated the appearance of collapsed dark neurons and the extravasation of serum proteins using argyrophil III method and immunohistochemistry. In the acute stage (minutes to 3 days), dark neurons appeared in the lateral half of the ipsilateral striatum and adjacent cortex which formed the ischemic core of this model. Dark neurons also appeared in the ipsilateral reticular thalamic nucleus, hippocampus, and amygdala. The extravasation of serum proteins, albumin, leucocyte common antigen, immunoglobulin G, complement factor C3, as well as heat shock protein 70, was observed not only in the ischemic but sometimes also in the contralateral hemisphere. Among these, the expression of IgG and C3 was most prominent in the ischemic core. In the chronic stage (1 to 3 months), the ischemic core changed into the porencephaly, and the ventrobasal nucleus of the thalamus got also involved in the necrosis. A strong microgliosis was observed in the substantia nigra pars reticulata. Data suggest, that among many mechanisms that contribute to ischemic neuronal death, the activation of immune response, due to the damage of blood-brain barrier and the extravasation of serum proteins could promote the ischemic cell death in the brain.

'Collapsed' (argyrophilic, dark) neurons in rat model of transient focal cerebral ischemia

To elucidate the early histopathological changes after transient focal cerebral ischemia, we made 1 h intraluminal occlusion of the middle cerebral artery on rats. After different reperfusion time, from minutes to 3 days, argyrophil III method was used for the demonstration of 'collapsed' (argyrophilic, dark) neurons. We could demonstrate the appearance of collapsed neurons in the lateral striatum and adjacent cortex where the dark neuron groups gave columnar patterns. These structures represent the ischemic core in this model. The collapsed neurons were detected also in the reticular thalamic nucleus, amygdala and hippocampus that are distant from the ischemic core. Data show that the early neuronal changes, demonstrated by this silver staining method, have a characteristic appearance in this model and involve more brain areas than were previously thought. These results could open more insight into the early pathophysiological processes triggered by the transient focal cerebral ischemia.

Selective loss and selective sparing of neurons in the thalamic reticular nucleus following human cardiac arrest

Neurons in the portion of the human thalamic reticular nucleus (RT) associated with the prefrontal cortex and mediodorsal thalamic nuclei were found to be selectively vulnerable to ischemic neuronal damage following relatively short (< or = 5-min) duration cardiac arrest. In contrast, selective sparing of these RT neurons occurred in cases with longer (> 10-min) duration of arrest that was sufficient to produce extensive ischemic neuronal damage throughout the cerebral cortex and thalamic relay nuclei. The selective degeneration of RT neurons appears to require the sustained activity of corticothalamic or thalamocortical projections to the RT following the ischemic insult. Loss of RT neurons associated with the frontal cortex and mediodorsal thalamus may be the biological basis of some types of persisting cognitive deficits in attentional processing experienced by patients following cardiac arrest, open heart surgery, or other forms of brief global cerebral ischemia.

Degeneration of rat thalamic reticular neurons following intrathalamic domoic acid injection

Domoic acid (DA), an analog of kainic acid, produces attentional deficits in humans who have ingested shell fish contaminated with this excitotoxin. The thalamic reticular nucleus (RT), by virtue of its location, connections and intrinsic properties, has been implicated in attentional processes. This study demonstrated the vulnerability of RT neurons following intrathalamic DA injections in rats. Lesions were characterized by almost total neuronal loss throughout the RT and sparing of adjacent populations of relay neurons in the VL and VPL. Los of RT neurons may underlie some types of attentional deficits observed in humans following DA poisoning.

Selective loss of neurons from the thalamic reticular nucleus following severe human head injury

The GABAergic neurons of the thalamic reticular nucleus, or nucleus reticularis thalami (RT), have been implicated as important components in attentional processing systems. Neurons in the RT are exquisitely sensitive to degeneration following kainic and domoic acid toxicity, experimental global ischemia, human cardiac arrest, and experimental closed head injury in nonhuman primates. The present study was performed to establish whether the selective loss of human RT neurons occurred following severe head injury. Brains from 37 human nonsurvivors of head injury were examined for evidence of RT neuronal loss. RT lesions in were found in 36 of 37 cases, representing 65 of 73 (89%) of the reticular nuclei examined. The incidence of RT lesions was similar in all age groups: 13 of 14 cases (92.9%) in the pediatric (< or = 16 years) group, 33 of 37 (89.2%) in the young adult (18-45 years) group, and 19 of 22 (86.4%) in the older adult (> 45 years) group. RT lesions were characterized by loss of one fourth to three fourths of the neurons from the region of the nucleus associated with the frontal cortex and thalamic mediodorsal (MD) and ventrolateral (VL) nuclei. Sparing of RT neurons correlated highly with the presence of extensive frontal cortical lesions, suggesting that an intact corticothalamic projection was necessary for RT degeneration following head injury. A pathologic cascade with a prominent excitotoxic component is proposed. The loss of these inhibitory thalamic reticular neurons and the resultant thalamic and neocortical neuronal dysfunctions may underlie some forms of attentional deficits that persist following head injury.

Post cardiac arrest hyperoxic resuscitation enhances neuronal vulnerability of the respiratory rhythm generator and some brainstem and spinal cord neuronal pools in the dog

Selective neuronal vulnerability of the motor cortex, basal ganglia, brainstem, medulla, cerebellum, C6 and L6 segments of the spinal cord were studied after 15 min of cardiac arrest followed by 1 h of normoxic or hyperoxic resuscitation using the suppressive Nauta method in dogs. Hyperoxic resuscitation causes characteristic somatodendritic argyrophilia of the interneuronal pool in the spinal cord and lower medulla. Cuneate, lateral reticular, supraspinal, and caudal trigeminal nuclei as well as the dorsal and ventral respiratory neuronal groups were heavily involved. Similarly, the Purkinje cells, neurons in the middle and deep portions of the mesencephalic tectum, perirubral, pretectal, posterior commissure, middle-sized striatal and giant pyramidal (Betz's) neurons in the motor cortex became argyrophilic. Hyperoxic resuscitation versus normoxic resuscitation causes statistically significant somatodendritic argyrophilia of the dorsal respiratory group, cuneate, dorsal lateral geniculate and thalamic reticular nuclei.

Evaluation of a novel calcium channel blocker, (S)-emopamil, on regional cerebral edema and neurobehavioral function after experimental brain injury

The authors investigated the effects of a novel calcium channel blocker, (S)-emopamil, on cerebral edema and neurobehavioral and memory function following experimental fluid-percussion brain injury in the rat. Two independent experiments were performed to evaluate the effects of this compound on cardiovascular variables and postinjury cerebral edema (increases in tissue water content), and on cognitive deficits and neurological motor function following brain injury. Treatment with (S)-emopamil significantly reduced focal brain edema at 48 hours after brain injury. Profound memory dysfunction induced by brain injury was significantly attenuated following (S)-emopamil treatment. In addition, (S)-emopamil also attenuated the deficits in motor function that were observed over a 2-week period following brain injury. These results suggest that changes in calcium homeostasis may play an important role in the pathogenesis of trauma to the central nervous system and that the calcium channel blocker (S)-emopamil might be a useful compound for the treatment of traumatic brain injury.

Global cerebral ischemia associated with cardiac arrest in the rat: I. Dynamics of early neuronal changes

Light microscopic neuronal changes were studied in rats subjected to 10 min of global ischemia produced by compression of the major cardiac vessels. Observations of cresyl violet-stained sections revealed early changes involving predominantly GABAergic neurons in various locations. In rats killed 15 min after recirculation, the changes were characterized by the appearance of a clear peripheral zone with condensation of the remaining neuronal cytoplasm. After 1 h, these zones appeared to be compartmentalized into individual pearl-like vacuoles, especially prominent in the nucleus reticularis thalami. After 3 h, the cytoplasmic vacuoles disappeared and the neuronal changes, particularly in the cerebral cortex, striatum, hippocampus, and pars reticulata of the substantia nigra, consisted mainly of hyperchromasia or loss of Nissl substance. After 2 days, the cerebral cortex and thalamus contained occasional neurons with conspicuously large nucleoli. After 7 days, the hippocampus revealed an approximately 50% loss of CA1 pyramidal neurons, associated with intense microglial reactivity in the stratum radiatum, whereas the neuronal destruction was more complete in the nucleus reticularis thalami. Our observations suggest a possibility that early changes in GABAergic neurons may provide a period of neuronal disinhibition and thus contribute to an excitatory ischemic damage in regions connected by GABAergic circuitry.

Immunohistochemical localization of the alpha 1, alpha 2 and alpha 3 subunit of the GABAA receptor in the rat brain

The immunohistochemical distribution of the alpha 1, alpha 2 and alpha 3 subunit of the gamma-aminobutyric acid-A (GABAA) receptor was investigated in the rat brain using affinity-purified antibodies against unique parts of the amino acid sequence of the respective subunits. The distribution of the 3 subunits differed markedly from each other indicating heterogeneity of the GABAA-receptor composition in different brain regions and at various receptive compartments (dendrites or somata) of neuronal cells.

Degeneration of hippocampal CA1 neurons following transient ischemia due to raised intracranial pressure: evidence for a temperature-dependent excitotoxic process

Degeneration of hippocampal CA1 neurons occurs following transient complete ischemia produced by raised intracranial pressure. Both systemic injection of MK-801 and profound cerebral hypothermia produced by cisternal infusion of room temperature (22-25 degrees C) fluids protect vulnerable CA1 neurons from degeneration. Hypothermia appears to decrease hippocampal extracellular levels of glutamate during and after ischemia but provides only relative protection from ischemia as CA1 degeneration does occur with prolonged (30 min) periods of ischemia. Elevated intracranial pressure appears to produce ischemic degeneration in the hippocampus via an NMDA receptor mediated excitotoxic process which is highly temperature dependent.