Anoxic-ischaemic cell change in rat brain light microscopic and fine-structural observations

Local cerebral glucose utilization in chronic middle cerebral artery occlusion in the cat

This study examines the correlation between local CMRglc (LCMRglc) alterations and clinicopathological changes in a chronic middle cerebral artery (MCA) occlusion model in the cat. The left MCA was occluded for a period of 2 h. The animals were grouped into mild, moderate, and severe ischemia based on the depression of the EEG 30 min after the MCA occlusion. Following release of the clip, the animals were allowed to recover for a week during which time daily neurological examinations were performed. On the seventh day [14C]2-deoxyglucose was injected for the determination of LCMRglc. Alternative blocks were processed for histological evaluation in which both neuronal and phagocytic changes were graded into four categories (0 = normal to 3 = severe). LCMRglc (mumol/100 g/min) in the ischemic hemisphere (all histological grades) was significantly lower than the metabolic rate in comparable regions of the sham MCA occlusion group. Regions with significant phagocytosis (grade 2 and 3) invariably exhibited activated glucose metabolism (57.4 +/- 8.4 and 105.9 +/- 6.8 mumol/100 g/min, respectively), which was significantly higher than in regions without phagocytosis (30.4 +/- 0.8 mumol/100 g/min). There was a significant gradient of metabolism in the central, peripheral, and boundary zone and the non-MCA territory in the animals with severe ischemic lesions. LCMRglc in the central MCA territory was well correlated with the EEG amplitude changes (r = 0.82, p less than 0.05) and the morphological score (r = -0.89, p less than 0.05). The metabolic rate was significantly depressed in both the ipsilateral and the contralateral central MCA territories in comparison with the sham occlusion animals. The depression in LCMRglc in the contralateral hemisphere correlated well with the concomitant depression in the contralateral EEG amplitude. These studies demonstrate that local heterogeneous metabolic alterations and contralateral cortical diaschisis exist chronically following temporary MCA occlusion and that the increases in local cerebral glucose metabolism seen in chronic stroke may be due to phagocytotic activity.

Improvement of energy state and basic modifications of neuropathological damage in rabbits as a result of graded postischemic spinal cord reoxygenation

The role of graded postischemic reoxygenation applied at the end of 20 min of spinal cord ischemia was studied with respect to the intraspinal pO2 tension, energy state, and histopathological sequelae. Graded postischemic reoxygenation can induce a positive shift in the intraspinal pO2 tension, but normal postischemic reoxygenation with normotensive pO2 blood tension inevitably causes the postischemic intraspinal pO2 overshoot. Graded postischemic reoxygenation significantly improves the energy state expressed by higher adenosine triphosphate (ATP), phosphocreatine (PCr) and glucose levels. Using the Nauta impregnating degenerating method, clear histopathological differences were found in the L3-S3 segments after 20 min of ischemia. Apparently divergent damage was observed when normal reoxygenation or graded postischemic reoxygenation was used. Diametrically different histopathological outcomes were obtained with normal reoxygenation and graded postischemic reoxygenation 2 and 4 days postoperatively.

Morphological consequences of early reperfusion following thrombotic or mechanical occlusion of the rat middle cerebral artery

The early morphological consequences of recirculation following middle cerebral artery (MCA) occlusion were studied in two rat models. The proximal MCA was occluded for 1 h by either a surgical clip or platelet thrombus; subsequently, 1 h of recirculation was facilitated. Following clip occlusion and recirculation, mild astrocytic swelling, especially around blood vessels, was detected in reperfused cortical and striatal areas. Neuronal changes included slight chromatin clumping and dilation of the rough endoplasmic reticulum. In contrast, severe structural abnormalities were detected following recanalization of the thrombosed MCA segment. Marked astrocytic swelling of cell bodies and perivascular processes with neuropil vacuolation were commonly seen. A heterogeneous pattern of neuronal alterations, including a high frequency of dense shrunken neurons surrounded by swollen astrocytic processes was documented in cortical and striatal regions. Severe neuronal changes were documented in brain regions exhibiting a well-perfused microcirculation. Vascular endothelial cells contained large numbers of pinocytotic vesicles associated with luminal and abluminal surfaces. Pronounced and rapid morphological changes evolve with reperfusion when thrombotic and ischemic events occur simultaneously. The basis for these rapid parenchymal changes following vascular thrombosis may involve acute alterations in cerebral microvascular permeability which exacerbate ischemic consequences.

Substantia nigra lesions in mercaptopropionic acid induced status epilepticus: a light and electron microscopic study

Light microscopic and ultrastructural changes of substantia nigra were studied in paralyzed ventilated rats with status epilepticus induced by mercaptopropionic acid. Some rats were killed at the end of seizure activity and others were examined in varying intervals after the arrest of seizure. The earliest changes were reduction in the size of the neuronal nuclei and chromatin clumping followed by simultaneous distention of axons and dendrites. There was also enlargement of the neuronal perikarya associated with microvacuolation. This neuronal microvacuolation corresponded ultrastructurally to swollen mitochondria with disrupted cristae. These changes were followed by progressive neuronal shrinkage and astrocytic swelling. The swollen astrocytic processes together with swollen neurites gave a spongy appearance to the involved area. The lesion thereafter progressively enlarged and evolved into an area of frank necrosis containing abundant macrophages. This lesion is morphologically different from that produced in cortex and hippocampus by seizure activity or due to the direct effect of excitotoxins. The significance of substantia nigra pars reticularis changes and their pathogenesis are discussed.

Acute ultrastructural response of hypoxic hypoxia with relative ischemia in the isolated brain

The acute cortical response to surgical brain isolation and subsequent extracorporal normoxic or 30 min hypoxic (PaO2 = 20 mm Hg) perfusions (hypoxic hypoxia with relative ischemia) was evaluated. Cerebral blood flow, arterial pH and CO2 were maintained constant during both perfusions; only the arterial oxygen content was changed. The isolated brain model used in this and previous investigations produces no qualitative ultrastructural changes in the neocortex following brain isolation and normoxic perfusion. However, the acute cortical structural response to 30 min of hypoxic hypoxia with relative ischemia demonstrated a number of important observations. Hypoxic hypoxia produced ultrastructural responses common to cerebral ischemia such as nuclear chromatin clumping, nucleolar condensation and cytoskeletal breakdown. Although neuronal abnormalities seen after 30 min of hypoxic hypoxia were similar to those acute neuronal changes observed following complete cerebral ischemia without recirculation, they differed three ways: (a) mitochondrial swelling and microvacuolation were observed in many cortical pyramidal neurons. (b) Glycogen particles within astroglial processes were observed even after a 30-min period of hypoxic hypoxia. (c) Perivascular astroglial swelling was minimal despite considerable perineuronal swelling. In contrast, incomplete cerebral ischemia produces mitochondrial changes similar to those in hypoxic hypoxia but also causes the depletion of tissue glycogen and perivascular glial swelling. Thus, hypoxic hypoxia with relative ischemia produces a unique acute ultrastructural response compared to either complete or incomplete cerebral ischemia.

Hindlimb paralytic effects of arginine vasopressin and related peptides following spinal subarachnoid injection in the rat

Intrathecal (IT) injection of arginine vasopressin (AVP) in rats caused a transient (less than 30 min), dose-related paralysis of the hindlimbs, loss of hindlimb and tail nociceptive responsiveness, and increased mean arterial pressure. Motor dysfunction was produced with comparable potency by lysine vasopressin (LVP) and arginine vasotocin (AVT); oxytocin (OXY) was approximately 1000 times less potent. Paralysis induced by these peptides was selectively blocked following IT pretreatment with 0.5 nmoles of the vasopressin V1 receptor antagonist [1-(beta-mercapto-beta,beta-cyclopentamethylene propionic acid), 2-(O-methyl)tyrosine] Arg8-vasopressin (d(CH2)5[Tyr(Me2)]AVP). Pressor and antinociceptive responses to AVP were also blocked by this compound. However, at higher doses (2-5 nmoles, IT), d(CH2)5[Tyr(Me2)]AVP produced hindlimb paralysis, antinociception, and pressor responses by itself. In contrast to the fiber degeneration, cell loss, and necrosis found in lumbosacral cords of rats persistently paralyzed by other peptides (dynorphin A, somatostatin, and ICI 174864), neuropathological changes were not evident in spinal cords of rats transiently paralyzed by IT AVP. These results indicate that AVP-related peptides affected diverse spinal cord functions through interactions with a V1-like receptor. The similar pattern of cardiovascular and antinociceptive responses to other peptides (dynorphin A, somatostatin, and ICI 174864), which also caused hindlimb paralysis, suggests that the former responses may actually reflect the nonselective consequences of a peptide-induced disruption of spinal cord function, rather than specific shared pharmacological effects.

Effects of D-(-)-aminophosphonovalerate on behavioral and histological changes induced by systemic kainic acid

In rats, the seizures induced by systemic kainic acid (KA) are followed by extensive neuronal damage, notably in the hippocampal region. We report that the specific N-methyl-D-aspartate (NMDA) receptor antagonist, D-(-)-aminophosphonovalerate (D(-)APV), given i.c.v. prior to or 2 h after i.p. KA injection markedly protected CA1 but not other hippocampal neurons against degeneration. In contrast, D(-)APV had no effect on KA-induced wet dog shakes or on behavioral seizures. We conclude that NMDA receptors participate in the neurotoxic but not in the behavioral effects of systemic KA.

Nerve cell injury in the brain of stroke-prone spontaneously hypertensive rats

The brain lesions in stroke-prone spontaneously hypertensive rats (SHRSP) are characterized by multifocal microvascular and spongy-cystic parenchymal alterations particularly in the gray matter. An essential feature of the lesions is the presence of edema with massive extravasation of plasma constituents as evidenced by specific gravity measurements, Evans blue technique and immunohistochemistry. The nerve cell injury occurring in the brain lesions in SHRSP is further characterized by light and electron microscopy in the present study. Two types of neuronal changes were seen within the blood-brain barrier (BBB) leakage sites. A small number of neurons with dark condensed nucleus and cytoplasm were found most often at the periphery of recent lesions. The majority of injured neurons were pale and showed intracellular edema confined to the dendrites and perikarya sparing axons and synapses. Their nuclei were well preserved with finely dispersed chromatin. The swollen and watery cell processes of neurons and astrocytes gave a spongy appearance to the neuropil. The intracellular edema seemed to result in cytolysis. The results suggest that primary anoxia-ischemia is not the major pathogenetic mechanism behind the nerve cell injury in severely hypertensive SHRSP, rather it is the massive BBB leakage and consequent brain edema that causes cytolytic destruction of neurons. Secondary focal ischemia as a consequence of occlusion in microvessels may, however, contribute to the nerve cell destruction.

Light and electron microscopic evaluation of hydrogen ion-induced brain necrosis

Excessive accumulation of hydrogen ions in the brain may play a pivotal role in initiating the necrosis seen in infarction and following hyperglycemic augmentation of ischemic brain damage. To examine possible mechanisms involved in hydrogen ion-induced necrosis, sequential structural changes in rat brain were examined following intracortical injection of sodium lactate solution (pH 4.5), as compared with injections at pH 7.3. Following pH 7.3 injection, neuronal swelling developed between 1 and 6 h, but only a needle track wound surrounded by a thin rim of necrotic neurons and vacuolated neuropil was present 24 h after injection. In contrast, pH 4.5 injection produced neuronal necrosis as soon as 1 h after injection, followed by necrosis of astrocytes and intravascular thrombi at 3 and 6 h. Alterations common to both groups included vascular permeability to horseradish peroxidase, dilation of extracellular spaces, astrocyte swelling, capillary compression, and vascular stasis. These data suggest that neurons, astrocytes, and endothelia can be directly damaged by increased acid in the interstitial space. Lethal injury initially appeared to affect neurons, while subsequent astrocyte necrosis and vascular occlusion may damage tissue by secondary ischemia.

Synaptic alterations in the acoustic cortex of the rat following insulin-induced hypoglycemia

Hypoglycemia was induced by intracarotid insulin infusions in adult Lewis rats. Electron microscopy of the acoustic cortices in these animals revealed that hypoglycemia provoked marked morphological and morphometric alterations in the pre- and postsynaptic terminals present, as well as in the astrocytic processes seen. The number of the synaptic vesicles in the "active zone" of the synapses was dramatically decreased, with most of the vesicles loosely dispersed in the entire presynaptic profile. Some of the pre- and postsynaptic terminals were enlarged and contained dilated cisternae of smooth endoplasmic reticulum, as well as mitochondria exhibiting a marked internal disorganization. The synaptic clefts in a large number of synapses were dilated and contained fibrillary material. The most striking morphological alterations seen involved a membrane discontinuity of the postsynaptic terminal and was found mostly in the synapses of the superficial layer of the acoustic cortex. Most of the morphological alterations observed in the acoustic cortex following uncomplicated hypoglycemia are seen in sensitive areas of the brain after ischemia or hypoxia.

Cerebral glucose metabolism during the recovery period after ischemia--its relationship to NADH-fluorescence, blood flow, EcoG and histology

Local cerebral glucose utilization (lCMRgl), NADH fluorescence, cerebral blood flow (CBF), electrocortical activity (ECoG) and histology were studied during a 4 hr recovery period following 2 hrs of left middle cerebral artery (MCA) occlusion in cats. Changes in relative reduced pyridine nucleotides and CBF were measured by fluororeflectometry, ECoG was obtained from the left middle ectosylvian gyrus (MEG), and lCMRgl was measured at the end of the recovery period autoradiographically with 14-C-2-deoxyglucose. A sham group was comprised of 4 cats. The ten animals subjected to the stroke were classified into 3 groups based on the mean amplitude of the ECoG at the end of the ischemic period. At the end of the recovery period, the relative reduced pyridine nucleotides showed a 22.5% oxidation (oxidation of NADH), a 66.2% reduction (reduction of NAD) and a 3.0% reduction compared to the sham group in the severe, moderate and mild groups, respectively. LCMRgl of the left MEG in the severe group was 64.2% of the corresponding sham value, whereas lCMRgl in the moderate and mild groups were 124.8% and 132.0% of the sham, respectively. CBF at the end of the recovery period ranged from 28.1% to 83.0% of the sham value, although there was no significant difference among these groups. Histologically, a large portion of the neurons in the left MEG in the severe group showed ischemic neuronal changes, while the damage was less severe in the moderate and mild groups. On the basis of these data, it is suggested that a relative substrate deficiency and/or a loss of mitochondrial enzymatic pool size may occur in the animals comprizing the severe group. Conversely, anaerobic glycolysis may be activated in the moderate group, while the mild group exhibits an increase in glucose metabolism that is most likely aerobic. A gradient in the magnitude of changes in lCMRgl was noted from the central MCA territory to the surrounding brain regions in the ischemic hemisphere. In addition, there was a mild, but statistically significant (p less than 0.05), depression in lCMRgl with no histological damage in the non-ischemic hemisphere of the severe group.

Age-dependent cell death in the olfactory cortex: lack of transneuronal degeneration in neonates

Adult olfactory cortical neurons in layer IIa undergo fulminant transneuronal degeneration after removal of afferent olfactory bulb fibers (Price, '76, Neurosci Abst. 2:161; Heimer and Kalil, '78, J. Comp. Neurol. 178:559-609). This provides an unusual example of dependence of a mature population of neurons on axonal input. In order to investigate whether similar transneuronal degeneration occurs in immature animals, a series of rats were subjected to unilateral olfactory bulb removal at various ages during the first 3 postnatal weeks. The brains were examined for degeneration after short survivals by use of the de Olmos cupric silver method, which selectively stains degenerating neurons. In addition, animals with long survivals were examined with the HRP retrograde tracing method, in order to determine if cells that survive the acute effects of deafferentation develop normal patterns of connections. Young neurons are more resistant to the effects of olfactory bulb removal than more mature neurons. There was little degeneration of cortical neurons after bulb ablation during the first 2 postnatal weeks. Although layer IIa does not become distinct from layer IIb in these experimental animals, cells that have connections normally characteristic of the cells of layer IIa, and are situated at the superficial edge of layer II, were identified with the HRP method. The severity of transneuronal degeneration increases and becomes adultlike between the second and third postnatal weeks. This increase in transneuronal degeneration is temporally associated with a progressive reduction in axonal sprouting following deafferentation during the first 3 postnatal weeks, as described in the companion paper (Friedman and Price, '86). Thus, axon sprouting may "protect" the immature IIa neurons from the effects of removal of the fibers from the olfactory bulb. A period of normal cell death has also been identified in olfactory cortex by the use of the de Olmos cupric silver method. This cellular degeneration is much less severe and has a different time course and laminar distribution than the transneuronal degeneration produced by olfactory bulb ablation in adults. Although normal cell death appears to be potentiated by removal of the olfactory bulb on postnatal day 1, it is clearly a different process from the transneuronal reaction.

Ischemia, resuscitation, and reperfusion: mechanisms of tissue injury and prospects for protection

Since its introduction in 1960, CPR has evolved into a complex program involving not only the medical community but also the lay public. Currently, program activities include instruction of the lay public in basic life support techniques, development and deployment of emergency medical systems, recommendations for drug protocols for advanced cardiac life support and, most recently, introduction of new methods for tissue protection following resuscitation. After 25 years of experience, we are beginning to understand the pathophysiology of tissue ischemia during cardiac arrest and the interventions required to improve chances of survival and quality of life of the cardiac arrest victim. Recent data in the literature suggest that modification of certain interventions in the resuscitation program may be needed. The poor neurologic outcomes with prolonged standard CPR show that it is not protective after 4 to 6 minutes of cardiac arrest. Modifications to this technique, including SVC-CPR or IAC-CPR, have not been shown to increase resuscitability or hospital discharge rates. Human studies of open-chest cardiac massage are needed to evaluate this option. Defibrillation is the definitive treatment for ventricular fibrillation. Greater emphasis should be placed on the earliest possible delivery of this treatment modality. Computerized defibrillators may provide greater and earlier access to defibrillation in the homes of patients at high risk of ventricular fibrillation. They may also be applicable by untrained public service personnel (police and firemen), individuals in geographically inaccessible areas (aircraft), or emergency medical technicians in rural areas where skill retention is a significant problem. Calcium has no proved benefit in cardiac resuscitation. There is biochemical evidence that it may be harmful in brain resuscitation. Its use in resuscitation should be discontinued. The dose of epinephrine currently advocated in the ACLS protocols may be inadequate to increase aortic diastolic pressure and coronary and cerebral perfusion pressures and thus aid resuscitation. Animal studies indicate that substantial increases in the current dosage are needed to achieve these effects. Human studies are needed to verify these results. A role for calcium antagonists in the treatment of postarrest encephalopathy has been demonstrated in animals and is currently undergoing clinical trials. Iron-dependent lipid peroxidative cell membrane injury may be important in the pathogenesis of postarrest encephalopathy. Animal studies suggest that the iron chelator deferoxamine may have a significant therapeutic role in the treatment of postarrest encephalopathy.

The effect of nicardipine on neuronal function following ischemia

In cerebral ischemia, it has been proposed that calcium influx into neurons results in irreversible cellular injury during reperfusion. We administered nicardipine, a dihydropyridine calcium entry blocker, by continuous subcutaneous infusion to twenty five rats beginning before (PR) or following (PO) ischemia, and compared somatosensory evoked potentials (SEPs) to twenty eight ischemic control animals. Comparable ischemic cellular changes were seen in the hippocampi of all animals. SEP amplitude was higher in both the PR (p less than .005) and PO (p less than .0005) groups compared to controls. This effect was found in all three components (P1, N1, P2) of the evoked response. Plasma nicardipine levels of 6-10 ng/ml were associated with mild hypotension. We conclude that nicardipine improved neuronal function as measured by SEPs when administered before or after ischemia, most likely by interrupting the cytotoxic events occurring in cortical neurons during reperfusion.

Selective functional vulnerability of cortical neurons following transient MCA-occlusion in the cat

Simultaneous recordings of several cortical neurons were obtained before, during and after transient 15 min occlusion of the middle cerebral artery in cats. With the use of a multiple electrode array consisting of 4-7 platinum/iridium microelectrodes, the cortical pericellular blood flow was concurrently measured by means of the hydrogen clearance technique. Hydrogen clearance measurements revealed a homogeneous blood flow distribution throughout all phases of the experiment in the area covered by the different microelectrodes. Considering only the results of experiments with low residual blood flow during ischemia (less than 0.1 ml/g/min), single unit activity ceased immediately after occlusion and remained so during the ischemic period. The recovery time of action potentials after reperfusion ranged from 10 min to 3 hours depending on the examined neuron. Lower values for discharge rates of the individual cells were generally observed after reoccurrence, although some units exhibited temporarily an even higher spike frequency. Furthermore, the spike form usually changed in that the hyperpolarizing afterpotentials were enlarged after recirculation. However, some cells with a nearly unchanged spike form were found as well. The results indicate that the recovery of cell function largely depends on the individual neuron which supports the idea of a selective functional vulnerability of cortical neurons in response to ischemia.

A study of postmortem autolysis in the human organ of Corti

Forty-six human temporal bones from 24 individuals were removed at autopsy and prepared for electron microscopy. The adequacy of histologic preservation was evaluated by light and electron microscopy. Characteristic autolytic changes included vacuolization of afferent neurons and neural poles of inner and outer hair cells, lysis of limiting membranes of hair and supporting cells, swelling of endoplasmic reticulum, and dissolution of mitochondrial cristae. The rate of autolysis varied significantly within cellular components of the inner ear. The neural poles of hair cells demonstrated more rapid autolysis than apical poles and nerve terminals showed more autolysis than myelinated nerve fibers. Postmortem time and the cause of death affected the adequacy of histologic preservation. Fixation in patients dying of pneumonia, hypoxia, head injury, or malignancy tended to be poor, whereas the fixation achieved in patients dying of cardiac disease with postmortem time of under 140 minutes was generally good.

Kainic acid-induced seizures: dose-relationship of behavioural, neurochemical and histopathological changes

Behavioural, neurochemical and histopathological changes induced by systemic injection of kainic acid were investigated at various doses of the neurotoxin (3, 6 and 10 mg/kg s.c.). There was a positive correlation between the dose of kainic acid and the extent of both the acute neurochemical changes 3 h after the injection (increases of 3,4-dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid levels and a decrease in noradrenaline levels in all brain regions investigated), the acute histopathological changes (shrinkage and condensation of nerve cells and brain oedema in the entire forebrain) and the extent of behavioural alterations (immobility, 'wet dog shakes' and limbic seizures). However, the slope of the dose-response curves was very steep. Late and irreversible alterations included losses of the enzyme markers glutamic acid decarboxylase and choline acetyltransferase and, histopathologically, incomplete parenchymal necrosis and haemorrhages. These changes, however, were restricted to a few brain regions, the most important being the hippocampus, amygdala, entorhinal and pyriform cortex, and olfactory bulb, and they were seen only in animals which had undergone severe convulsions. It is suggested that the irreversible brain lesions in this animal model of limbic (temporal lobe) epilepsy are not solely induced by a direct action of kainic acid, but may be caused--at least in part--by additional, secondary pathogenetic mechanisms.

Fibrinogen, blood viscosity, and cerebral ischemia

This study examines the effect of fibrinogen and consequent blood viscosity reduction on cerebral blood flow and cellular injury following severe cerebral ischemia for 30 minutes in 78 Wistar rats. In half of these rats 10 to 15 cc's of blood was removed and replaced with a mixture of 5% albumin and autologous red blood cells maintaining a constant hematocrit but resulting in a 30% decrease in fibrinogen and corresponding reduction in viscosity. Fibrinogen reduction in a slight increase in baseline CBF and the elimination of post-ischemic hyperemia at 24 hours. Both study and control animals showed a similar decrease in CBF at 30 minutes and 2 hours. There was no significant difference in the severity of ischemic cellular change between the fibrinogen reduction group and controls, although there was a significant inverse relationship between the amount of viscosity change and severity of cellular injury within the treatment group. Fibrinogen reduction alone cannot significantly ameliorate ischemic injury in this model. Viscosity reduction therapy should include reduction of hematocrit and alteration of red cell deformability.

Mitochondrial calcium sequestration in cortical and hippocampal neurons after prolonged ischemia of the cat brain

Adult normothermic cats were submitted to 1- h complete cerebrocirculatory arrest, followed by blood recirculation for 6-8 h. Two groups of animals could be distinguished: In one group electrocorticogram and somatically evoked primary cortical potentials steadily recovered after ischemia, and in another electrophysiologic recovery was absent. At the end of the recirculation period, calcium content was measured in tissue samples taken from cerebral cortex and hippocampus, and compared with mitochondrial calcium sequestration as assessed by electron-microscopic cytochemistry. Protein content of cortex and hippocampus was also determined for evaluation of tissue swelling. The two regions were selected because previous experiments had revealed that in animals with electrophysiologic recovery cerebral cortex remains intact although hippocampus is selectively injured, whereas in animals without electrophysiologic recovery both cerebral cortex and hippocampus are damaged. In animals with functional recovery, neither calcium content nor mitochondrial calcium sequestration were significantly increased in either cerebral cortex or hippocampal subfield CA1. Only in dentate gyrus a minor degree of mitochondrial calcium sequestration was present. Calculation of tissue swelling revealed no change in cerebral cortex, but a volume increase by 18% in hippocampus, indicating development of brain edema in this region. In animals without functional recovery tissue calcium significantly increased both in cortex and hippocampus (by 49% and 73% of control, respectively), and there was significant mitochondrial calcium accumulation in both regions. Calculated brain swelling in these animals amounted to 16% and 26% in cortex and hippocampus, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The temporal evolution of hypoglycemic brain damage. III. Light and electron microscopic findings in the rat caudoputamen

The caudate nucleus and putamen belong to the selectively vulnerable brain regions which incur neuronal damage in clinical and experimental settings of both hypoglycemia and ischemia. We have previously documented the density and distribution of the hypoglycemic damage in rat caudoputamen, but the evolution of the injury, i.e., the sequence of structural changes, has not been assessed. Therefore, in the present study we analyze the light and electron microscopic alterations in the caudoputamen of rats exposed to standardized, pure insults of severe hypoglycemia with isoelectric EEG for 10-60 min, or in rats which, following insults of 30 or 60 min, were allowed to recover for periods from 5 min to 6 months. The hypoglycemic insult produced severe nerve cell injury in the dorsolateral caudoputamen. Immediately after the insult abnormal light neurons with clearing of the peripheral cytoplasm were present. These cells disappeared early in the recovery period, as they do in the cerebral cortex. Dark neurons were also present, but unlike those in the cerebral cortex they did not appear until recovery was instituted. Their number increased for a couple of hours and they became acidophilic within 4-6 h. At this stage, electron microscopy revealed severe clumping of the nuclear chromatin and cytoplasm as well as incipient fragmentation of cell membranes, all these changes indicating an irreversible injury. Within 24 h flocculent densities appeared in the mitochondria and by day 2-3 of recovery the great majority of the medium-sized neurons had undergone karyorrhexis and cytorrhexis, their remnants being subsequently removed by macrophages. After some weeks only large and a few medium-sized neurons remained amidst reactive astrocytes and numerous macrophages. The delay in the appearance of dark, lethally injured medium-sized neurons until the recovery was instituted suggests an effect that does not become apparent until the substrate supply and energy production are restored. Furthermore, it points out again the selectivity of the hypoglycemic nerve cell injury with respect to the type (metabolic characteristics?) and topographic location of the neurons.

The distribution of ischaemic damage and cerebral blood flow after unilateral carotid occlusion and hypotension in the rat

We have developed a model of haemodynamic cerebral ischaemia by inducing haemorrhagic hypotension (40-50 mmHg mean blood pressure) following unilateral common carotid occlusion, with external carotid ligation, in anaesthetised rats. The neuropathological pattern of ischaemic brain damage was correlated with the distribution of change in cerebral blood flow using the 14C-iodoantypyrine autoradiographic technique. Whereas hypotension alone (40-50 mmHg) resulted in neither ischaemic brain damage nor significant alterations in cerebral blood flow, the combination of this degree of hypotension with unilateral carotid occlusion produced predominantly unilateral ischaemic brain damage which correlated with regions of reduced cerebral blood flow. With this type of haemodynamically induced oligaemia, the most vulnerable areas were the lateral neocortex, the caudate nucleus, the hippocampus and the thalamus. Within the cortex, the greatest reductions in blood flow occurred in the deeper cortical layers, and this was the most frequent site of ischaemic cell change. These data support the concept of a haemodynamic mechanism in the pathogenesis of some transient cerebral ischaemic attacks in man.

Delayed neuronal recovery and neuronal death in rat hippocampus following severe cerebral ischemia: possible relationship to abnormalities in neuronal processes

Mechanisms involved in the postischemic delay in neuronal recovery or death in rat hippocampus were evaluated by light and electron microscopy at 3, 15, 30, and 120 min and 24, 36, 48, and 72 h following severe cerebral ischemia that was produced by permanent occlusion of the vertebral arteries and 30-min occlusion of the common carotid arteries. During the early postischemic period, neurons in the Ca1 and Ca3 regions both showed transient mitochondrial swelling followed by the disaggregation of polyribosomes, decrease in rough endoplasmic reticulum (RER), loss of Golgi apparatus (GA) cisterns, and decrease in GA vesicles . Recovery of these organelles in Ca3 neurons was first noted between 24 and 36 h and was accompanied by a marked proliferation of smooth endoplasmic reticulum (SER). Many Ca1 neurons initially recovered between 24 and 36 h, but subsequent cell death at 48-72 h was often preceded by peripheral chromatolysis, constriction and shrinkage of the proximal dendrites, and cytoplasmic dilatation that was continuous with focal expansion of RER cisterns. Because SER accumulates in resistant Ca3 neurons and proximal neuronal processes are damaged in vulnerable Ca1 neurons, we hypothesize that delayed cell recovery or death in vulnerable and resistant postischemic hippocampal neurons is related to abnormalities in neuronal processes.

Chronic antihypertensive treatment in the rat reverses hypertension-induced changes in cerebral blood flow autoregulation

Cerebral blood flow (CBF) autoregulation was studied in renal hypertensive rats receiving chronic antihypertensive treatment. Young Wistar Kyoto rats (WKY) were made hypertensive by the Loomis procedure i.e. partial infarction of one kidney with contralateral nephrectomy. Systolic tail blood pressure was measured at 2-week intervals throughout the study. After two months, by which time the rats had been severely hypertensive for 5-6 weeks, antihypertensive treatment was begun; reserpine, dihydralazine and hydrochlorothiazide were administered in the drinking water. Blood pressure fell rapidly to normotensive levels and remained so. Following two months of antihypertensive treatment, the lower blood pressure limit of CBF autoregulation was studied during controlled bleeding. In age-matched untreated renal hypertensive WKY, the lower limit of autoregulation was in the mean arterial pressure range 90-109 mm Hg, as compared to 50-69 mm Hg in age-matched normotensive WKY. In contradistinction to the untreated rats, the treated rats had a normal lower limit of autoregulation, i.e. 50-69 mm Hg. It was inferred that the reversal of the functional change in CBF autoregulation reflected reversal of hypertension-induced cerebrovascular hypertrophy/hyperplasia.

Experimental acute hypoxia. Brain preservation by phenobarbital pretreatment. Histological study in guinea pigs

Acute hypoxia was induced by keeping guinea pigs in an atmosphere of 5% O2/95% N2 for 20 min. Four groups of 10 guinea pigs each were used: (A) control; (B) after 20 min of hypoxia; (C) after 20 min of hypoxia and 20 min of oxygen therapy (100%); (D) pretreatment with phenobarbital (100 mg/kg body wt) and 20 min of hypoxia, followed by 20 min of oxygen therapy. The histological study did not show significant differences between barbiturate-treated and untreated hypoxic brains. In fact, the severity of ischemic-hypoxic damage as well as its distribution were similar in all the experimental groups of animals. Lesions predominated in the regions which are known to be more sensitive to hypoxia (3rd and 4th layers of parieto-occipital cortex, Sommer's fields, cerebellum). It is considered that in the experimental conditions barbiturates did not act as a protective agent--at least as assessed morphologically.

Fine structural nature of delayed neuronal death following ischemia in the gerbil hippocampus

An unusual, delayed neuronal death (DND) has been noticed in the hippocampus of the Mongolian gerbil following brief ischemia (Kirino 1982). On day 1 following 5--10 min of ischemia, light microscopy showed the CA1 pyramidal cells unchanged. On day 2, the cells showed massive growth of membranous cytoplasmic organelles instead of overt cellular disintegration. These neurons were destroyed extensively by day 4 after ischemic insult. Following longer ischemia (20--30 min), however, the changes in the CA1 pyramidal cells appeared faster and resembled the well-characterized ischemic cell change (ICC). To further clarify the differences between ICC and DND, gerbils were submitted to transient 5--30 min ischemia. They were perfusion-fixed following a given survival period and then processed for electron microscopy. Following transient ischemia, specimens showed slow cell changes with growth of cisterns of the endoplasmic reticulum (ER). In some CA1 neurons, the cytoplasm was shrunken and darkly stained, but they also displayed accumulation of ER cisterns. Occasionally, the CA1 cells demonstrated highly shrunken dark perikarya, no different than in ICC. These results indicate that DND seems to be the typical disease process of the CA1 sector and that a severer insult makes the change faster and more similar to ICC. ICC seems to occur when the CA1 pyramidal cells are damaged so severely that they cannot react with proliferous activity.

Significance of fluid flow for morphology of acute hypoxic-ischaemic brain cell injury

It has been suggested that the presence or absence of hypoxic fluid flow during ischaemia determines the structural character of the ischaemic nerve cell injury. It is hypothesised that if a flow of fluid irrigates the injured neurons, there will be major shifts of ions and water, with consequent volumetric changes in the tissue and the 'dark' type of neuronal injury will result; otherwise, the structural changes are less striking and are designated as the 'pale' type. To test this hypothesis, rats were subjected to a global cerebral insult by filling the vasculature with a plasma substitute, which was either left stagnant or was flowing, and was either oxygenated (hypoxic flow) or nitrogenated (anoxic flow). Light and electron microscopy of the brain following 10 to 60 min of hypoxic or anoxic ischaemia disclosed that, under all three circumstances, the predominant nerve cell injury was of the pale type. The results indicate that some additional factors present in whole blood (but not in the plasma substitute) are needed during or after the insult to induce in quantity the dark type of ischaemic nerve cell injury.

Limitations of tetrazolium salts in delineating infarcted brain

Tetrazolium salts, histochemical indicators of mitochondrial respiratory enzymes, have been used by some pathologists to detect infarcts in myocardium. We explored the utility of this technique in detecting experimental brain infarcts and report our findings. Infarcts were produced in cats, gerbils, and rats by unilateral temporal and permanent cerebral vessel occlusion. After various time periods the animals were killed, and their brains were reacted with 2,3,5, triphenyl, 2H-tetrazolium chloride (TTC). The experimental and contralateral hemispheres were examined by light and electron microscopy. The TTC-stained tissue was correlated with histology. In some situations the histological condition of the tissue correlated well with the TTC staining results. Brain regions supplied by temporarily occluded vessels and judged infarcted by light and electron microscopy did not stain. In these regions less than 6% of the mitochondria were intact. In brain tissue from animals with permanent vessel occlusion (no reflow) mitochondria were intact despite the fact that other cellular organelles, such as nuclei, were destroyed. TTC stained such mitochondria and as a result could not distinguish infarcted brain in complete ischemia situations (no reflow). Another draw back to this staining procedure was 36 h after infarction macrophages with intact mitochondria would replace damage neurons and be stained. Under ideal conditions though this technique can detect irreversibly damaged brain as early as 2.5 h after artery occlusion.

Brain lactic acidosis and ischemic cell damage: a topographic study with high-resolution light microscopy of early recovery in a rat model of severe incomplete ischemia

Transient severe incomplete ischemia was induced in rats by a combination of bilateral carotid artery clamping and hypovolemic hypotension. Production of lactic acid in the ischemic brain was modified by preischemic administration of glucose or saline. After 30 min of ischemia and 5 or 90 min of recirculation, the animals were fixed by perfusion. High-resolution light microscopy based on whole hemisphere plastic sections revealed that the model produces a highly predictable ischemia in the telencephalon, with a more inconstant injury in the diencephalon, rostral brain stem, and cerebellum. The extent of injury correlates well with studies of local cerebral blood flow in the same model. The present study largely confirmed the opinion, based on the earlier study of the frontoparietal cortex, that the neuronal injury is predominantly of the 'pale' type, although fair amounts of 'dark' injury also appeared with predilection to the pyriform cortex, hippocampus, and occasionally the cerebellum. Excessive tissue lactic acidosis due to glucose pretreatment aggravated both types of neuronal injury. It was also accompanied by marked astrocytic edema as well as capillary obstruction in the group with long recirculation. A novel type of ischemic tissue change emerged, consisting of osmiophilic granules and whorls probably derived from damaged cell membranes.

Selective vulnerability in the gerbil hippocampus following transient ischemia

Following brief ischemia, the Mongolian gerbil is reported to develop unusual hippocampal cell injury (Brain Res 239:57--69, 1982). To further clarify this hippocampal vulnerability, gerbils were subjected to ischemia for 3, 5, 10, 20, and 30 min by bilateral occlusion of the common carotid arteries. They were perfusion-fixed after varying intervals of survival time ranging from 3 h up to 7 days. Following brief ischemia (5--10 min), about 90% of the animals developed typical hippocampal damage. The lesion was present throughout the extent of the dorsal hippocampus, whereas damage outside the hippocampus was not observed. Each sector of the hippocampus showed different types of cell reaction to ischemia. Ischemia cell change was seen in scattered CA4 neurons , and reactive change was found in CA2, whereas CA1 pyramidal cells developed a strikingly slow cell death process. Ischemia for 3 min did not produce hippocampal lesion in most cases. Following prolonged ischemia (20--30 min), brain injury had a wide variety in its extent and distribution. These results revealed that the gerbil brief ischemia model can serve as an excellent, reliable model to study the long-known hippocampal selective vulnerability to ischemia. Delayed neuronal death in CA1 pyramidal cells was confirmed after varying degrees of ischemic insult. These findings demonstrated that the pathology of neuronal injury following brief ischemia was by no means uniform nor simple.

Delayed neuronal death in the rat hippocampus following transient forebrain ischemia

An unusual, slowly progressing neuronal damage has been reported to occur in the gerbil hippocampus following ischemia (Kirino 1982). Delayed neuronal death following ischemia has also been noticed in the rat four-vessel occlusion model (Pulsinelli et al. 1982). By light microscopy this slow neuronal injury in the rat was not different from the previously known neuronal ischemic cell change. This report lead us to the question as to whether neurons in the rat hippocampus are damaged rapidly following an initial latent period or deteriorate slowly and progressively until they display overt changes. To clarify this point, observation was done on the hippocampal CA1 sector of the rat following ischemia. Rats were subjected to four-vessel occlusion, and those which developed ischemic symptoms were perfusion-fixed. Although the change appeared very slowly and lacked microvacuolation of the cytoplasm, neuronal alteration was practically not different from classical ischemic cell change. By electron microscopy, however, the change was detectable when the neurons still appeared intact by light microscopy. An increase in the membranous organelles and deposition of dark substances were the initial manifestations. It seemed that the CA1 neurons deteriorated very slowly and progressively, and that they retained partial viability in the initial phase of the change. In spite of the difference in light-microscopic findings, the mechanisms underlying delayed neuronal death in the rat and gerbil hippocampus seemed to be identical.

Cerebral blood flow during dihydralazine-induced hypotension in hypertensive rats

The cerebrovascular effects of graded, controlled dihydralazine-induced hypotension were studied in rats with renal hypertension (RHR) and spontaneous hypertension (SHR). Repeated measurements of cerebral blood flow (CBF) were made using the intraarterial 133Xenon injection technique in anaesthetised normocapnic animals. Dihydralazine was administered in single increasing i.v. doses (0.1 to 2 mg/kg), and CBF measured after each dose when a stable blood pressure had been reached. From a resting level of 145 +/- 7 mm Hg in RHR and 138 +/- 11 mm Hg in SHR, mean arterial pressure (MAP) fell stepwise to a minimum of around 50 mm Hg. CBF was preserved during dihydralazine induced hypotension, and remained at the resting level of 79 +/- 13 ml/100 g . min in RHR and 88 +/- 16 ml/100 g . min in SHR. Following 2 hours hypotension at the lowest pressure reached, the rats were sacrificed by perfusion fixation and the brains processed for light microscopy. Evidence of regional ischaemic brain damage was found in 4 of 11 animals: in 2 cases the damage appeared to be accentuated in the arterial boundary zones. Although the lower limit of CBF autoregulation in these rats is around 100 mm Hg during haemorrhagic hypotension, dihydralazine brought MAP to around 50 mm Hg without any concomitant fall in CBF. This was interpreted as being due to direct dilatation of cerebral resistance vessels. The combination of low pressure and direct dilatation may have resulted in uneven perfusion, thus accounting for the regional ischaemic lesions.

Kainic acid induced seizures: neurochemical and histopathological changes

Behavioural, histopathological and neurochemical changes induced by systemic injection of kainic acid (10 mg/kg, s.c.) were investigated in rats. The most pronounced behavioural changes were strong immobility ("catatonia"), increased incidence of "wet dog shakes", and long-lasting generalized tonic-clonic convulsions. The behavioural symptoms were fast in their onset and lasted for several hours. Two distinct phases of histopathological and neurochemical changes were observed. (1) Early partially reversible changes were seen up to 3 h after kainic acid injection. They consisted of shrinkage and pyknosis of neuronal perikarya together with swelling of dendrites and axon terminals. These changes were accompanied by generalized signs of edema throughout the whole brain. Neurochemically, there was a marked decrease in noradrenaline levels (up to 70%) and an increase in levels of 5-hydroxyindoleacetic acid, 3,4-dihydroxyphenylacetic acid and homovanillic acid (up to 200%) in all analysed brain regions, suggesting a strongly increased firing rate of aminergic neurones during the period of generalized seizures. These histological and neurochemical changes were found in all the brain regions examined; they were greatly reduced or only sporadically seen after 1-3 days, when the animals had recovered from the seizures. (2) Late irreversible changes developed 24 h and later following kainic acid injection. They consisted of incomplete tissue necrosis with loss of nerve cells and oligodendrocytes, demyelination, astroglial scar formation, small perivenous hemorrhages and extensive vascular sprouting. The changes were restricted to the pyriform cortex, amygdala, hippocampus (most pronounced in the CA1 sector), gyrus olfactorius lateralis, bulbus olfactorius and tuberculum olfactorium. Neurochemically, a selective decrease was seen in choline acetyltransferase activity (40%) of the amygdala/pyriform cortex area, and of glutamate decarboxylase activity in the dorsal hippocampus (45%) and amygdala/pyriform cortex (55%). No such changes were found in the frontal cortex and the striatum/pallidum. Since at these later time periods the widespread early changes in monoamine metabolism were mostly normalized, loss of acetylcholine and gamma-aminobutyric acid neurons in the affected brain regions represented a selective neurochemical change typical for this stage of kainic acid action. The observed neurochemical and histopathological changes may be directly related to the excitotoxic and convulsive properties of kainic acid. However, brain edema resulting in herniation damage of the basal portions of the brain in addition to disturbances of microcirculation and +

Cerebral ischaemia in the rat: increased permeability of post-synaptic membranes to horseradish peroxidase in the early post-ischaemic period

An earlier study of the rat hippocampal stratum radiatum after transient cerebral ischaemia has shown cell membrane breaks, mainly post-synaptically, occurring as early as 20 min after an ischaemic episode. In the present study HRP was injected into the lateral ventricle 10-15 min after ischaemia and allowed to diffuse until 60 min post-ischaemia. Ultrastructural examination in the control animals, showed that HRP was localized exclusively in the extracellular space. After 10 min of transient ischaemia, HRP was not confined to the extracellular space, but was also seen in about 10% of apical dendrites. Only a very few pre-synaptic terminals showed the presence of HRP. Thus, there is evidence of early post-ischaemic membrane damage occurring in vivo in the apical dendrites of the CA-1 pyramidal cells.

Effect of diazoxide-induced hypotension on cerebral blood flow in hypertensive rats

The effect on cerebral blood flow of acute diazoxide-induced hypotension was studied in rats with renal and spontaneous hypertension. Diazoxide (5 mg/kg, i.v. bolus), caused arterial pressure to fall rapidly to that of normotensive rats, i.e. c. 75 mmHg. There was a concomitant fall in cerebral blood flow of about 35% (P less than 0.01) in renal hypertensive rats and 25% (P less than 0.05) in spontaneously hypertensive rats; the greater fall in flow in the former corresponded to a greater drop in pressure. Flow remained at these reduced levels during a 2 h observation period. Histological examination revealed small areas of ischaemic damage in the brains of five of the twelve animals. In control hypertensive rats not given diazoxide, cerebral blood flow and blood pressure were stable during a 2 1/2 h period and there was no evidence of ischaemic damage to the brains. The diazoxide-induced reduction in cerebral blood flow was interpreted as being secondary to a blood pressure fall to below the lower limit of cerebral blood flow autoregulation. No evidence was found of direct effects on the cerebral circulation such as seen with ganglionic blockers, alpha-blockers and cerebral vasodilators.

Modification of focal cerebral ischemia by prostacyclin and indomethacin

✓ The object of this investigation was to study the effects of prostacyclin (PGI2), with and without indomethacin, upon the evolution of cerebral infarction in the cat. Thirty-five fasted adult cats, lightly anesthetized with nitrous oxide, underwent right middle cerebral artery (MCA) occlusion. Eleven cats received an intracarotid infusion of 10 mg/ml PGI2 in buffered saline, pH 10.5, at a rate of 0.01 ml/kg/min (100 ng/kg/min), 10 cats received the same infusion plus a single dose of intravenous indomethacin (4 mg/kg) in buffered saline, and 11 cats received intracarotid buffered saline, pH 10.5, at a rate of 0.01 ml/kg/min, without therapeutic agents. Treatment with PGI2 was started upon MCA occlusion and continued for 6 hours, whereas indomethacin was given immediately prior to occlusion. Thirty minutes before perfusion, the animals were given fluorescein and Evans blue by intravenous injection. The cats were perfusion-fixed in vivo with carbon and buffered formalin 6 hours after MCA occlusion. Another five cats received tritium-labeled PGI2, and peripheral venous samples were collected and assayed for PGI2 and its alpha-keto metabolite. Mean arterial pressure was stable in treated animals during 6 hours of MCA occlusion, while untreated cats had significant (α = 0.05) progressive hypertension during that period. The regional cerebral blood flow (rCBF), measured by the intracarotid xenon-133 clearance method, decreased markedly in all animals immediately upon MCA occlusion. Untreated animals had a significant progressive improvement in rCBF during the occlusion period (α = 0.005), while treated animals had no such improvement. Quantitative electroencephalographic changes, gross edema, areas of fluorescein extravasation, and microscopic morphology (edema and infarct size) were not significantly different in the three groups. Prostacyclin appeared to reduce the extravasation of Evans blue dye. Systemic PGI2 levels were significant despite intracarotid administration. The authors conclude that 1) intracarotid PGI2 has a protective effect against the breakdown of the blood-brain barrier to protein-bound dyes seen in ischemic edema; 2) the systemic hemodynamic influence of PGI2, in the presence of impaired autoregulation, may compromise rCBF in the ischemic zone and offset any direct beneficial effects; and 3) indomethacin fails to modify the effects of PGI2.

Treatment of acute focal cerebral ischemia with prostacyclin

The object of this investigation was to study the effects of prostacyclin (PGI2) upon the evolution of acute focal cerebral ischemia in the cat. Twenty-five fasted adult cats, lightly anesthetized with nitrous oxide, underwent right middle cerebral artery (MCA) occlusion. Eleven cats received an intracarotid infusion of PGI2 in buffered saline pH 10.5 (100 ng/kg/min at 0.01 ml/kg/min), and 11 cats received intracarotid buffered saline pH 10.5 (0.01 ml/kg/min) without therapeutic agents. Treatment with PGI2 was started upon MCA occlusion and continued for 6 hours. Thirty minutes prior to perfusion, the animals were given fluorescein and Evans blue by intravenous injection. The cats were perfused-fixed in vivo with carbon and buffered formalin 6 hours after MCA occlusion. Another 3 cats received tritium labeled intracarotid PGI2, and peripheral venous samples were collected and assayed for PGI2 plasma levels. Mean arterial pressure was stable in PGI2 treated animals during 6 hours of MCA occlusion, while untreated cats had significant progressive hypertension during that period. The rCBF (measured by the intracarotid 133Xe method) decreased markedly in all animals immediately upon MCA occlusion. However, untreated animals had a significant progressive improvement in rCBF during the occlusion period, while PGI2 treated animals had no such improvement. Quantitative EEG changes, gross edema, areas of fluorescein extravasation, patterns of carbon perfusion, and infarct size were not significantly different in the two groups. While most untreated animals had marked Evans blue extravasation after 6 hours of MCA occlusion, most PGI2 treated animals had no such extravasation, indicating some protection of the blood-brain barrier in these animals.

Early changes in the rat hippocampus following seizures induced by bicuculline or L-allylglycine: a light and electron microscope study

Status epilepticus was induced in thirteen paralysed and ventilated rats by the injection of either bicuculline or L-allylglycine. After 1-2 h of seizure activity the animals were intracardially perfused with a 2% glutaraldehyde/3% paraformaldehyde solution. Hippocampal blocks from each rat were processed for light and electron microscopy. The effects of L-allylglycine were more severe than those of bicuculline. Changes include perivascular and perineuronal swelling of astrocytic processes, and neuronal alterations which were graded as follows: Grade I (least severe), neuronal cytoplasm appears slightly darker than usual; Grade II, condensed or dark neurons, usually with microvacuoles; and Grade III classical 'ischaemic cell change'--the cytoplasm and karyoplasm is dark and shrunken, with or without microvacuoles. Many of the microvacuoles originate from mitochondria. In a few cases swollen and disrupted mitochondria are also seen is distended basal dendrites of the CA3 and CA1 pyramidal neurons. Dentate granule cells appear unaffected. The hippocampal neuronal alterations induced by seizure activity include those of 'ischaemic cell change'. The pathogenetic factors common to hypoxia/ischaemia and status epilepticus remain to be identified.

The origin of lipid phagocytes in the central nervous system: I. The intrinsic microglia

The potential for the transformation of the normal microglial cell to a lipid phagocyte was studied by light and electron microscopy in the brains of rodents and by light microscopy only in primates. All were subjected to some form of hypoxia-ischemia and the microglial response was examined in regions of selective neuronal destruction (SND) so that infarction was deliberately excluded. In vivo perfusion-fixation was employed in all animals and light microscopic examination was carried out on paraffin- and sometimes celloidin-embedded material. Semithin plastic sections from several regions of the rodent brains were used for light microscopy but ultrastructural studies were confined to the hippocampus. In all animals the microglia were activated and transformed into rod cells exhibiting phagocytic properties but only a minority gave rise to lipid phagocytes. Blood vessels were normal in all animals and no hematogenous elements were identifed in the the parenchyma. As neuronal ghosts could be identified for up to 3 weeks it was concluded that the capacity of the microglia for phagocytic activity was limited.

Cerebral blood flow in rats with renal and spontaneous hypertension: resetting of the lower limit of autoregulation

The effect of chronic hypertension on cerebral blood flow (CBF) was studied in anaesthetised rats. CBF was measured with the intracarotid 133Xe injection method. Rats with spontaneous and renal hypertension were compared with normotensive controls. The lower limit of autoregulation was determined during controlled haemorrhage. In the normotensive rats, CBF remained constant until mean arterial pressure (MAP) had decreased to the range of 50-69 mm Hg. Thereafter, CBF decreased with each further decrease in MAP. In both types of hypertensive rats, CBF remained constant until MAP had decreased to the range of 70-89 mm Hg. Thus, a 20-mm Hg shift of the lower limit of CBF autoregulation was found in both spontaneous and renal hypertensive rats. A neuropathological study revealed ischaemic brains lesions in half of the hypertensive rats following hypotension, whereas only a single lesion was found in one of six normotensive rats. No ischaemic brain lesions were found in a control study in which CBF was shown to be stable over a 21/2-h period. In conclusion, hypertensive rats showed a shift of the lower limit of CBF autoregulation as well as an increased susceptibility to ischaemic brain damage during hypotension. These findings presumably reflect hypertensive structural changes in the cerebral circulation.

The response of GABAergic and cholinergic neurons to transient cerebral ischemia

The vulnerability of striatal and hippocampal neurons to ischemia was studied by measuring the activity of neurotransmitter-related enzymes after transient forebrain ischemia in rats. Activities of glutamic acid decarboxylase (GAD) and choline acetyltransferase (CAT) were measured 6 h to 8 days after 20, 30 or 40 min of forebrain ischemia, as markers for GABAergic and cholinergic neurons respectively. Transient forebrain ischemia resulted in depression of striatal GAD activity while striatal CAT and hippocampal GAD activities were unaffected. Striatal GAD activity progressively decreased during the first 24 h postischemia and remained depressed 5--8 days later, suggesting irreversible damage to this population of neurons. The stability of striatal CAT and hippocampal GAD activity indicates that these cells were resistant to the present ischemic conditions.

Delayed neuronal death in the gerbil hippocampus following ischemia

In the CA1 subfield of the gerbil hippocampus, an unusual series of changes were noticed after ischemia. Mongolian gerbils were subjected to bilateral carotid occlusion for 5 min. Perfusion fixation was performed 3, 6 and 12 h or 1, 2, 4, 7 and 21 days afterwards. Specimens obtained from the dorsal hippocampus were processed for light and electron microscopy. Three different types of changes were observed in the CA4, CA2 and CA1 subfields. In CA4, the change was rapid and corresponded to ischemic cell change. The alteration in CA2 was relatively slow, and identical to what has been called reactive change. On the contrary, the change in the CA1 pyramidal cells was very slow, only becoming apparent by light microscopy 2 days following ischemia. The CA1 subfield was selected for electron microscopic observation. The lamellar alignment of proliferated cisterns of the endoplasmic reticulum was the most conspicuous finding in these cells. Four days following ischemia, almost all of the pyramidal cells in CA1 were destroyed. In the CA1 neuropil, numerous presynaptic terminals remained without being apposed to normal postsynaptic sites. These changes in CA1, called here 'delayed neuronal death', may differ from those thought to be typical of ischemic neuronal damage. It was unlikely that the disturbance of local blood vessels was the cause of these changes.

Complete cerebral ischaemia in the rat: an ultrastructural and stereological analysis of the distal stratum radiatum in the hippocampal CA-1 region

An ultrastructural study and a stereological analysis of the distal stratum radiatum in the hippocampal CA-1 region of the rat were performed after 10 min of complete cerebral ischaemia followed by 10, 20 and 60 min of blood reflow periods. Post-ischaemic changes were mainly limited to the region of synaptic terminals which showed either clumping or dispersion of the synaptic vesicle pools and damage to synaptic membranes. Presynaptic terminals and astrocytes were swollen after 10 and 20 min of reflow, but this abated after 60 min. Mitochondria in neurons showed varying degrees of swelling, but in astrocytes their structure was normal. There were no changes in capillaries. After 20 and 60 min of blood reflow, disruption of cell membranes was observed, mainly in the vicinity of the synaptic terminals. The size of the extracellular space diminished by approximately 30% in all three ischaemic groups. The data show that synaptic terminals are a primary and early target in the development of postischaemic nerve cell damage.

Effect of different conditions of acute exposure to carbon monoxide on the cerebral high-energy phosphates and ultrastructure of brain mitochondria in rats

Rats were exposed to carbon monoxide (CO) in different conditions: 4 min at 1.3% CO, 40 min at 0.5% CO or 12 h at 0.13--0.15% CO. After 4 min exposure to 1.3% CO the brain content of ATP and PC was substantially reduced; after 40 min exposure to 0.5% CO the cerebral ATP level was slightly increased, whereas the content of both ATP and PC in the brain of rats exposed to CO for 12 h was significantly higher than in the controls. The decrease in the brain level of ATP and PC after 4 min exposure to 1.3% CO was accompanied by ultrastructural changes of mitochondria. No evident differences in the level of cerebral high-energy phosphates were found between rats intoxicated with CO and rats subjected to experimental hypoxemia.

Treatment of acute focal cerebral ischemia with propranolol

Propranolol has been found to have a protective effect in experimental myocardial ischemia. Protection of ischemic kidneys was subsequently demonstrated following treatment with propranolol and its weaker beta blocking isomer, d-propranolol. The objective of the present investigation was to study the effects of propranolol (i.e., racemic d,1 mixture) and d-propranolol upon regional cerebral blood flow (rCBF) and early ischemic changes following experimental middle cerebral artery (MCA) occlusion. Thirty adult cats, lightly anesthetized with ketamine hydrochloride, underwent 3 hours or right MCA occlusion. Ten cats were untreated. Ten cats were given a continuous infusion of propranolol (1 mg/kg/hr) for 4 hours beginning 1 hour before MCA occlusion and a 4 mg/kg bolus immediately before occlusion. Ten cats were given a continuous infusion of d-propranolol (0.5 mg/kg/hr) for 4 hours beginning 1 hour before MCA occlusion and a 2 mg/kg bolus immediately before occlusion. The therapeutic agents were injected directly into the right carotid artery. The rCBF in the right Sylvian region was not significantly different in the 3 groups. EEG changes also were similar. Carbon filling defects were found to be smallest in the d-propranolol-treated group. Light microscopic studies demonstrated a reduction in infarct size in the propranolol and d-propranolol groups. The findings of the investigation indicated that propranolol and d-propranolol do not have a deleterious effect on rCBF after MCA occlusion and suggested that these agents have a protective effect upon ischemic cerebral tissue.

Early proliferative changes in astrocytes in postischemic noninfarcted rat brain

Transient cerebral ischemia in rats was produced by permanent occlusion of the vertebral arteries and 30-minute occlusion of the common carotid arteries. This model produces ischemic necrosis of neurons in the corpus striatum, cerebral cortex, and hippocampus; infarcts, with necrosis of neuropil, astrocytes, and blood vessels, are rare. Changes in striatal astrocytes at 40 minutes and 3 hours of reperfusion were evaluated by electron microscopy, and quantitative estimates of increases in cytoplasmic and mitochondrial area were performed. In areas of corpus striatum with moderate ischemic cell change, the percentage of astrocytic nuclei increased from 10.79% in controls to 17.76% at 40 minutes after ischemia (p less than 0.01) and 19.86% at 3 hours (p less than 0.01). Astrocytic cytoplasm was expanded and contained increased numbers of mitochondria, many of which were pleomorphic and had dilated intracristal spaces and condensed matrix. Rough endoplasmic reticulum was increased. Total mitochondrial area and number of mitochondrial profiles rose significantly in the astrocytic perikarya and foot processes at 3 hours postischemia. The greater number of astrocytes, the increases in mitochondria and rough endoplasmic reticulum and the configurational changes in the mitochondria suggest increased metabolic activity of astrocytes in postischemic, noninfarcted brain.

Experimental canine distemper encephalomyelitis in neonatal gnotobiotic dogs. A sequential ultrastructural study

The ultrastructural morphogenesis of neuronal degeneration and necrosis and patterns of associated myelin and axonal degeneration were studied in gnotobiotic dogs neonatally infected with neurovirulent R252 strain of canine distemper virus (CDV-R252). Distemper virus-infected neurons underwent a distinct sequence of ultrastructural changes culminating in direct viral-induced necrosis beginning after 21 days post inoculation (DPI). Viral-induced neuronal cytolysis occurs apparently independently of anti-viral immune mechanisms of immunologic destruction. Viral nucleocapsid aggregates in postsynaptic axosomatic and axodendritic complexes and in structurally intact axons provided morphologic evidence for viral-induced functional modulation of synaptic transmission and possible trans-synaptic interneuronal viral spread. There were secondary degenerative axonal and myelin changes, particularly in heavily myelinated tracts. There was no evidence of primary demyelination. Active phagocytosis of degenerating axons and myelin debris in foci of virus-associated necrosis was apparently restricted to CDV-containing macrophages. Demonstration of a productive CDV infection of choroid plexus epithelium 10 DPI and thereafter was identified as an intracranial source of free infectious virus.

Hippocampal neuron density and seizures in the Mongolian gerbil

Mongolian gerbils of the seizure-sensitive strain exhibit epileptic seizures in relation to changes in the environment, a characteristic which has been increased to about 100% by inbreeding. The seizures vary from animal to animal but are rather stable in the individual animal, which makes it possible to study the neuron densities in the hippocampus of the gerbil in relation to seizure type and seizure intensity. Five groups of gerbils with seizures ranging from minor movements and motor arrest to intense generalized convulsions were investigated with a quantitative method including cell counting by light microscope and estimation of possible brain shrinkage, as well as determination of nucleoli and nuclei diameters. The cell densities were determined in different areas of the pyramidal cells of the hippocampus (H-fields). The study discloses a reduction of cell densities in fields H2 and H3 in relation to intense generalized convulsions. It is suggested that the reduction in cell density in field H2 is a result of seizure activity, whereas the field H3 cell loss can be the result of both the hypoxia and the seizure activity.

Pathophysiology of "tethered cord syndrome"

The tethered cord syndrome is a clinical entity manifested by progressive motor and sensory changes in the legs, incontinence, back of leg pain, and scoliosis. In order to elucidate the pathophysiology involved in the tethered cord, the reduction/oxidation ratio (redox) was used in vivo of cytochrome alpha,alpha 3 to signal oxidative metabolic functioning in human examples of tethered cord and in animal models. Studies in experimental models indicate marked metabolic and electrophysiological susceptibility to hypoxic stress to lumbosacral cord under traction with greater weights (3, 4 or 5 gm). Similar effects were demonstrated in redox behavior of human tethered cord during surgical procedures. The authors conclude that symptoms and signs of tethered cord are concomitant with lumbosacral neuronal dysfunction which could be due to impairment of mitochondrial oxidative metabolism under constant or intermittent cord stretching. It is assumed that prolonged or accentuated neuronal dysfunction may lead to structural damage to the neuronal perikarya and later of the axons. Untethering procedures in human tethered cord improve oxidative metabolism, and probably facilitate the repair mechanism of injured neurons.