Ultrastructural changes in the edematous central nervous system. II. Cold-induced edema

Transcranial measurement of diffuse light reflectance from cold-injured brains in rats

Diagnosis of brain edema is important to manage severe head injuries and diseases, but there is no method of noninvasive bedside monitoring of brain edema. We speculate that brain edema changes the optical properties of brain tissue. To verify this speculation, we perform transcranial measurement of diffuse light reflectance from cold-injured brains in rats. To induce edema, a liquid nitrogen-cooled copper probe of 3 mm diameter was applied to the right parietal bone for 60 s under anesthesia. The rat skull was irradiated with 633-nm HeNe laser light and 532-nm Nd:YVO4 laser light, which were used to investigate changes in light scattering and blood flow, respectively. Reflectance intensity was measured as functions of time and position on the skull. We found that reflectance intensities were significantly decreased around the cold injury at both 633 and 532 nm, while reflectance was increased in the cold injury at 532 nm, indicating that cerebral blood volume was decreased in the cold injury. Under the condition of decreased cerebral blood volume, the decrease in reflectance intensity around the injury suggests that the scattering coefficient of brain tissue was reduced due to edema formation in this area.

Abnormal action-potential bursts and synchronized, GABA-mediated inhibitory potentials in an in vitro model of focal epilepsy

Focal, freeze-induced lesions were made in isolated hemispheres of turtle cerebral cortex in vitro, permitting the investigation of epileptiform discharges in a preparation with preserved intracortical circuitry. Freeze lesions resulted in interictal discharges and occasional ictal-like events. The interictal discharges were dependent upon activation of non-NMDA excitatory amino acid receptors and were affected by but did not require NMDA receptor activation. Voltage clamp and current clamp recordings revealed abnormal bursts of low-amplitude action potentials in 36% of recorded neurons, while large, repetitive inhibitory potentials, mediated by GABAA receptors, were recorded in 90% of the neurons. Thus, prominent findings in this model include abnormalities of both excitatory and inhibitory activity. Since these changes in neuronal excitability resulted from a localized physical injury, they may resemble the changes that occur in acute posttraumatic epilepsy.

Milacemide stimulates deficient glial Na+, K(+)-ATPase in freezing-induced epileptogenic cortex of cats

We investigated the influence of milacemide, a glycinamide derivative with putative antiepileptic activity, on the K(+)-activation of Na+,K(+)-ATPase in bulk isolated glial cells and synaptosomes of control and epileptogenic cortex of cats with a chronic freeze lesion. In the primary and secondary epileptic foci of non-treated animals, glial Na+,K(+)-ATPase lost its physiological K(+)-activation, while the synaptosomal enzyme was unchanged. These data reproduced previous work done on the kinetic measurement of the enzymic activities. In treated animals (500 mg/kg milacemide given orally for 2 weeks after the freeze lesion), the glial enzyme showed a normal K(+)-activation in the epileptic foci. These results confirm the existence of an abnormal glial Na+,K(+)-ATPase in cold-induced focal epilepsy and suggest that the antiepileptic activity of milacemide might be secondary to an activation of glial Na+,K(+)-ATPase, contributing to antagonize ictal transformation and seizure spread.

Relationship between epileptic activity and edema formation in the acute phase of cryogenic lesion

Following cryogenic lesions of the brain in the rabbit, ictal activity appears within min with a maximum at 2 h. Brain edema increases rapidly between 2-4 h with a maximum at 8 h. The glutamate concentration reaches 209% of control in the perilesional area at 2 h and the time course of glutamate/GABA ratio parallels the time course of epileptic activity. The impairment of Na+-K+-ATPase activity (rise of KMapp for K+) in the glial fraction coincides with the increase of edema. A positive correlation is found between the total amount of ictal activity and the total amount of edema in individual animals, suggesting that epilepsy may enhance edema formation.

The early phase of cryogenic lesions: an experimental model of seizures updated

Following cryogenic lesions in 64 rabbits, epileptic activity and gray matter edema were correlatively investigated during the initial phase (23 h). Indexes were developed to allow a quantitative assessment of epileptic activity. The indexes demonstrated that the early phase of cryogenic epilepsy is a very rapid phenomenon during the first 4 h postlesion. Epileptic activity precedes brain edema, and in individual animals, there is a significant positive correlation between the total amount of epileptic activity and the total amount of edema. The relationship between epileptic activity and brain edema are most likely interrelated at the level of pathophysiological mechanisms and several mechanisms can be postulated.

Quantitative nuclear magnetic resonance imaging: characterisation of experimental cerebral oedema

Magnetic resonance imaging (MRI) has been used quantitatively to define the characteristics of two different models of experimental cerebral oedema in cats: vasogenic oedema produced by cortical freezing and cytotoxic oedema induced by triethyl tin. The MRI results have been correlated with the ultrastructural changes. The images accurately delineated the anatomical extent of the oedema in the two lesions, but did not otherwise discriminate between them. The patterns of measured increase in T1' and T2' were, however, characteristic for each type of oedema, and reflected the protein content. The magnetisation decay characteristics of both normal and oedematous white matter were monoexponential for T1 but biexponential for T2 decay. The relative sizes of the two component exponentials of the latter corresponded with the physical sizes of the major tissue water compartments. Quantitative MRI data can provide reliable information about the physico-chemical environment of tissue water in normal and oedematous cerebral tissue, and are useful for distinguishing between acute and chronic lesions in multiple sclerosis.

Tracer permeability of rat cortical blood vessels during regional hypothermia

Using lanthanum nitrate as a tracer, the permeability of rat cortical blood vessels was investigated during regional hypothermia of the cerebral cortex by electron microscopy. The concentration of K+ ions in the extracellular space of the cortex was determined using an ion-selective micro-electrode. Only at temperatures below about 7 degrees C was an extravasation of tracer observed in a number of cortical capillaries and arterioles, where some of the tight junctions became widened and permeable. In a few cases penetration of the tracer into vacuoles of phagocytosing pericytes or macrophages was found. The extravasation of the tracer could mainly be observed in vessels on and below the cortical surface, less often in deeper cortical parts. At the same degree of hypothermia, the K+ concentration in the extracellular space increased, reaching a maximal value of ca. 6 mmol/l at a depth of about 200 micron. As could be shown in one previous experiment, the K+ concentration reached normal values again after rewarming to 37 degrees C for 15 min, but an extravasation of the tracer was still observed. The role of the endothelial tight junctions and of the astrocytes together with the pericytes (or macrophages) is discussed regarding their importance for the effectiveness of the blood-brain barrier system.

The effect of dexamethasone on tissue water distribution and proton relaxation in Panc02 tumors

The present experiments were conducted to determine the effects of dexamethasone mediated changes in tumor water distribution on proton relaxation times (T1, T2) in a murine pancreatic adenocarcinoma (Panc02). Spin lattice (T1) and spin-spin(T2) relaxation times were determined by ex vivo methods (10 MHz) and by in vivo imaging techniques (6.25 MHz) at various intervals after single or multiple dexamethasone treatments. In complementary studies, dexamethasone mediated changes in tumor capillary permeability, tumor water distribution, relative tumor blood flow and tumor cell proliferation were also determined. Proton spin lattice (T1) and spin-spin (T2 relaxation times for Panc02 tumors shortened within two hours of a single dexamethasone treatment. The time course and magnitude of this response was dexamethasone dose dependent. The time dependent changes in T1 and T2 after dexamethasone were similar at 10 MHz (ex vivo) and 6.25 MHz (in vivo imaging). Although dexamethasone produced little or no change in total tumor water content and tumor cell proliferation, transient changes in the physiologic distribution of tumor water were clearly demonstrated. The data supports the idea that dexamethasone induced changes in the distribution of tumor water were mediated by changes in capillary permeability and tumor blood flow. These physiologic responses produced serial changes in tumor extracellular extravascular water content that were consistent with the observed changes in tumor T1 and T2. The results from these experiments might imply that therapy associated changes in tumor proton relaxation times may not only reflect changes in tissue water content, but may also reflect physiologic responses which alter the distribution of tissue water and solute.

Extensive intraneuronal spread of horseradish peroxidase from a focus of vasogenic edema into remote areas of central nervous system. Observations on mouse central nervous system subjected to cortical cold injury

A study was made of the uptake of horseradish peroxidase (HRP) into neurons from a cryogenic cortical lesion in the mouse brain associated with vasogenic edema, following intravenous administration of the tracer. Particular emphasis was placed on the axonal spread of HRP from the primary lesion to other areas of the central nervous system. The distribution of HRP was studied by light microscopy, using highly sensitive histochemical methods, 3-144 h after the onset of the injury. Extravasated HRP was taken up into nerve cell bodies in and around the primary lesion, forming different patterns of labelling: (1) granular, (2) diffuse, and (3) a combination of granular and diffuse staining. Granularity is considered to be the result of HRP accumulation in lysosomes occurring in undamaged or slightly damaged nerve cells, whereas the diffuse, non-granular pattern presumably occurs in severely damaged neurons. Nerve cell bodies containing HRP reaction product were also found in the contralateral cortex, ipsilateral thalamus, substantia nigra, amygdala and ventral tegmental area, presumably a consequence of retrograde axonal transport of the tracer from the primary injury. HRP-containing axons were present in the corpus callosum and in the pyramidal tract of the injured hemisphere all the way down to the cervical spinal cord. Labelling of axonal terminals and preterminal axons in the ipsilateral thalamus, entopeduncular nucleus, subthalamic nucleus, substantia nigra and pons indicated anterograde transport of HRP to these regions. Thus very extensive intraneuronal spread of a macromolecular edema component takes place from a primary focal brain lesion to areas located far away from but neuroanatomically connected to this injured region. The brain thus seems to be affected by focal vasogenic edema in many more ways than are recognized at present.

Marek's disease virus-induced transient paralysis: a comparison of lesions in susceptible and resistant lines of chickens

A study was conducted to determine the causative lesion of Marek's disease virus-induced transient paralysis. Brain histologic lesions were quantitated and compared in genetically resistant and susceptible inbred chickens. Comparisons were made 11 days post inoculation (PI) of virus when clinical signs were evident in susceptible birds and on day 17 PI when these signs had remitted. Clinically-affected birds from the susceptible line on day 11 PI had consistent evidence of neuropil vacuolation compatible with brain edema; two of these birds also had vasculitis. These lesions were absent in both clinically-recovered birds from this line evaluated on day 17 PI and genetically resistant birds studied on day 11 PI. Our findings suggest that the causative lesion of transient paralysis is vasogenic brain edema.

Acute changes in regional brain water content following experimental closed head injury

A Remington humane stunner was used to deliver blows to the skulls of anesthetized cats. The animals were sacrificed at 30 minutes or 1, 2, or 6 hours after trauma and selected for data collection on the basis of the following two categories of gross intracranial pathology: 1) unilateral contusion, with subarachnoid hemorrhage (SAH); or 2) SAH only. For selected cats, specific gravity was measured in 5- to 10-mg samples of uncontused tissue taken from coronal slices at the level of the frontoparietal suture. The regions tested included dorsal cerebral cortex, subcortical white matter, deep white matter, and caudate nucleus. Specific gravity data from injured animals were compared with those from similar areas in uninjured anesthetized cats to test for cerebral edema. At 30 minutes after head injury, contused hemispheres had significant edema of all tested except the caudate nucleus. Edema of the subcortical and deep white matter increased with time after the injury. Increase in water content of the cerebral cortex was transient and appeared unrelated to contusion. The caudate nucleus was edematous only at 6 hours, suggesting movement of fluid from the deep white matter compartment into the nucleus. The hemispheres opposite the contusion and those related to SAH had, with one exception, an absence of edema in the white matter and caudate nucleus, but a transient increase in water content of the cerebral cortex. These findings suggest that, in the presence of contusion, cerebral edema can contribute to brain swelling as early as 30 minutes after closed head trauma. In addition, a transient and minimal cortical edema, perhaps related to ischemia, occurred in all groups of hemispheres examined.

Dynamics of cerebral edema. The role of an intact vascular bed in the production and propagation of vasogenic brain edema

Brain edema was produced in cats by a standardized cortical freezing lesion. With a careful microsurgical tehnique, the injured cortex was removed as a single piece, either immediately after induction or at 2, 4, or 8 hours after lesion production. The injured brain was either discarded or replaced in its bed. Brain edema and the defect in the blood-brain barrier were assessed by determining percent dry weight, increase in volume of white matter, and spread of Evans' blue by planimetry. The results indicate that 1) if the lesion is removed immediately after production, formation of the expected vasogenic brain edema is completely abolished; 2) replacement of the frozen brain is unable to induce significant increase in permeability of the surrounding blood-brain barrier or a significant amount of brain edema; and 3) if the lesion is removed at 2, 4, or 8 hours with or without replacement, advancement of the edema front and increase in the amount of edema is stopped. It appears that an intact vascular bed is necessary for the extracellular fluid component of brain edema, and that no edemagenic factors exist within the injured brain in this model that influence either the production or propagation of the increased extracellular fluid volume.

Protective effects of steroids on the corticomicrocirculation injured by cold

✓ Early microcirculatory changes after focal cold injury of the cerebral cortex were examined in dogs with and without steroids by serial fluorescein angiography of the brain (FAB), by measurement of the diameter of epicerebral vessels, and by measurement of cerebral blood flow with the clearance method using krypton-85 and xenon-133. Changes in the transcerebral vessels were examined by x-ray projection microangiography.

Within 30 minutes of the injury, the cortical area injured by a temperature of −65° C showed a reduction in blood flow of 60%. When treated with steroids and while still at the same temperature, blood flow was reduced by only 35%. Serial FAB revealed slowing and arrest of flow in the epicerebral microcirculation which could be noted first in the small veins, then in the medium-sized veins and small arteries. Fluorescein dye leaked from the epicerebral vessels, around the small veins, then around larger veins and small arteries. Some leakage of dye from medium-sized arteries was noted 2 hours after injury. This sequence of slowing and arrest of the microcirculation, with exit of dye from intact arterial vessels, identified here for the first time in relation to a cortical freezing lesion, may help to explain the development of later brain edema which spreads widely in the subcortical white matter. After steroids, improvement of the microcirculation was present as defined by cortical blood flow, fluorescein angiography, and x-ray projection microangiography.

The mechanism of spinal cord cavitation follwing spinal cord transection. Part 2. Electron microscopic observations

The authors report their findings by electron microscopy after microsurgical subpial spinal cord transection in dogs. After cord transection, conspicuous myelin microcysts are formed in a background of otherwise intact cord tisue at a distance of 1 to 2 mm from the cut end of the cord, both proximal and distal to the transection, Seen through the electron microscope, the microcysts iss a myelin sac distended by fluid under pressure, containing a swollen axon filled with excessive axoplasmic organelles; that is, a terminal club. Later the microcysts and terminal clubs rupture. The large spaces within the microcysts are opened to heretofore small extracellular spaces and the spinal cord tissues are destroyed. Thus, microcysts are precursors of large cavitites seen at the ends of transcreted cord stumps. The formation of microcysts and their subsequent rupture, which leads to cord cavitation, is interpreted as an inherent response of cord tissue to injury, and the result of an abortive attempt at cord regeneration.

Role of pressure gradients and bulk flow in dynamics of vasogenic brain edema

The authors present the results of an investigation of the vasogenic type of brain edema using cold injury in cats as a model. Their findings indicate that bulk flow and not diffusion should be considered the main mechanism for the spread of edema through the white matter. This conclusion is based on: 1) comparison of the distances actually traveled by various substances during edema spread with those calculated theoretically for migration of the substances by diffusion; 2) coincidence in the speed of movement by two substances (sucrose and albumin) with widely different diffusion coefficients; 3) measurement of interstitial fluid pressure (IFP) at various distances from the lesion showing the presence of increased IFP in the lesion area and decreasing pressures along the edema pathway toward the normal tissue; and 4) the fact that spreading of edema can be significantly impeded by inducing before the cold lesion an intracellular type of brain edema that reduces the size of the extracellular space (ECS) and increases the resistance to flow of edema fluid. The pressure-volume curve of the brain ECS, as derived from determinations of IFP and tissue water content, indicates that initial steep slope in IFP probably represents the high resistance to fluid mobility through the small diameter extracellular channels and the counteracting resistance of the intermingled structures of brain parenchyma to be separated. Once the IFP exceeds these opposing forces, the ECS dilates, fluid mobility increases, and the edema front advances.

Ultrastructural blood-brain barrier alterations and edema formation in acute spinal cord trauma

Endothelial changes leading to edema formation are examined in the primate spinal cord (Macaca mulatta) following a lesion created by a 20-gm weight falling 15 cm onto the exposed dura. Intravascular perfusion of a paraformaldehydeglutaraldehyde solution followed by carbon black provides adequate fixation of vascular structures and glial elements. Myelin is poorly preserved. Ultrastructural alterations of the blood-brain barrier consist of loss of integrity of the endothelial tight junctions. Edema caused by vascular disruption and parenchymatous extravasation of intravascular contents is observed along with glial swelling. Interglial gap junctions persist in areas of marked cellular seperation and do not impede the migration of edema fluid.

Nuclear magnetic resonance studies in normal and edematous brain tissue

The nmr relaxation rate results show unequivocally that there are at least two fractions of tissue water in both normal and edematous white matter which do not exchange on an nmr time scale (i.e. at times of the order of milli-seconds to fraction of a second). In conjunction with the electron microscopic determination of the extracellular volumes of normal and edematous white matter, the relaxation results can be interpreted in terms of the following model. The two slowly-exchanging water components giving rise to the non-exponential relaxation correspond to cellular and extracellular water; edema changes the relaxation rate of the extracellular component much more than that of the cellular component (the extracellular component becoming more "liquid-like" in its relaxation). Such behavior is consistent with the properties of the extracellular water being due to rapid exchange between motionally restricted water adsorbed at the surface of myelin sheaths, and relatively unrestricted, bulk water. Edema presumably increases the relative amount of the "bulk" water between the axons.

Ultrastructural alterations in the dog brain after profound hypothermia induced by extracorporeal circuit

This study has demonstrated that hypothermia with or without circulatory arrest produced ultrastructural alterations in the dog brain. Fluid accumulation in the perivascular area and in the neuropil persists for at least seven days. Neurons in all areas of the brain studied are quite resistant to fluid alterations. Minimal changes occurring in neurons appear to be reversible from these studies with no neuronal necrosis, even with cooling to 10°C. Endothelial cells and oligodendrocytes exhibit essentially normal morphology in all experimental groups. Astrocytes and their processes undergo the most severe alterations, with cellular changes greater in dogs subjected to 60 minutes than to 30 minutes of cardiac arrest, and progressive degrees of damage occurring with increases in postpumping time prior to sacrifice. Our studies indicate cytological damage increases for longer periods posthypothermia than earlier reports which noted a resolution at 72 hours of the edema observed at 24 hours. We have demonstrated with the electron microscope (EM) that edema persists for at least seven days.

The application of new developments in the pumping technique such as improved filtering of microemboli may reduce the pathological alterations described in this study and aid the clinical management of patients subjected to hypothermia.

Detection of experimental and clinical brain edema using an electrical impedance method

✓ To clarify the development of brain edema, the electrical impedance of white matter was measured with intracerebral implanted electrodes in cold-induced edema in the cat and in cases of edema after major intracranial surgery. Impedance measurements were made at 50 kc using a tetrapolar electrode method with a pair of concentric platinum electrodes. The impedance of the brain gradually decreased 25% after several hours of cold application. The amount of increase of sulfate space of brain showed a good correlation with decrease of impedance. In four postoperative cases of brain tumor, a 7.5% to 25% decrease of impedance was observed within several hours of surgery. A severe case of brain edema, in which the prognosis was poor, showed marked intracranial pressure and 25% decrease of impedance.

A structural analysis of the myelin sheath in the central nervous system

The cerebral white matter of rats subjected to a variety of noxious experimental conditions was examined in the electron microscope. Several unusual configurations of the myelin sheath are identified in addition to the usual configuration. These variations include the presence of (a) formed organelles within the inner and outer loops, (b) isolated islands of cytoplasm in unfused portions of the major dense lines, (c) apparently unconnected cell processes between the sheath and the axon, and (d) concentric, double myelin sheaths. A generalized model of the myelin sheath based on a hypothetical unrolling of the sheath is described. It consists of a shovel-shaped myelin sheet surrounded by a continuous thickened rim of cytoplasm. Most of the unusual myelin configurations are explained as simple variations on this basic theme. With the help of this model, an explanation of the formation of the myelin sheath is offered. This explanation involves the concept that myelin formation can occur at all cytoplasmic areas adjacent to the myelin proper and that adjacent myelin lamellae can move in relation to each other.