Evolution of cortical activation during recovery from corticospinal tract infarction

BACKGROUND AND PURPOSE

Recovery from hemiparesis due to corticospinal tract infarction is well documented, but the mechanism of recovery is unknown. Functional MRI (fMRI) provides a means of identifying focal brain activity related to movement of a paretic hand. Although prior studies have suggested that supplementary motor regions in the ipsilesional and contralesional hemisphere play a role in recovery, little is known about the time course of cortical activation in these regions as recovery proceeds.

METHODS

Eight patients with first-ever corticospinal tract lacunes causing hemiparesis had serial fMRIs within the first few days after stroke and at 3 to 6 months. Six healthy subjects were used as controls. Statistically significant voxels during a finger-thumb opposition task were identified with an automated image processing program. An index of ipsilateral versus contralateral activity was used to compare relative contributions of the 2 hemispheres to motor function in the acute and chronic phases after stroke.

RESULTS

Controls showed expected activation in the contralateral sensorimotor cortex (SMC), premotor, and supplementary motor areas. Stroke patients differed from control patients in showing greater activation in the ipsilateral SMC, ipsilateral posterior parietal, and bilateral prefrontal regions. Compared with the nonparetic hand, the ratio of contralateral to ipsilateral SMC activity during movement of the paretic hand increased significantly over time as the paretic hand regained function.

CONCLUSIONS

The evolution of activation in the SMC from early contralesional activity to late ipsilesional activity suggests that a dynamic bihemispheric reorganization of motor networks occurs during recovery from hemiparesis.

Physiology and pathophysiology of poly(ADP-ribosyl)ation

One of the immediate eukaryotic cellular responses to DNA breakage is the covalent post-translational modification of nuclear proteins with poly(ADP-ribose) from NAD+ as precursor, mostly catalysed by poly(ADP-ribose) polymerase-1 (PARP-1). Recently several other polypeptides have been shown to catalyse poly(ADP-ribose) formation. Poly(ADP-ribosyl)ation is involved in a variety of physiological and pathophysiological phenomena. Physiological functions include its participation in DNA-base excision repair, DNA-damage signalling, regulation of genomic stability, and regulation of transcription and proteasomal function, supporting the previously observed correlation of cellular poly(ADP-ribosyl)ation capacity with mammalian life. The pathophysiology effects are mediated through PARP-1 overactivity, which can cause cell suicide by NAD+ depletion. It is apparent that the latter effect underlies the pathogenesis of a wide range of disease states including type-1 diabetes, ischaemic infarcts in various organs, and septic or haemorrhagic shock. Therefore pharmacological modulation of poly(ADP-ribosyl)ation may prove to be an exciting option for various highly prevalent, disabling and even lethal diseases.

Ursodeoxycholic acid aggravates bile infarcts in bile duct-ligated and Mdr2 knockout mice via disruption of cholangioles

BACKGROUND & AIMS

The effects of ursodeoxycholic acid (UDCA) in biliary obstruction are unclear. We aimed to determine the effects of UDCA in bile duct-ligated and in Mdr2 knockout (Mdr2(-/-)) mice with biliary strictures.

METHODS

Mice fed UDCA (0.5% wt/wt) or a control diet were subjected to common bile duct ligation (CBDL), selective bile duct ligation (SBDL), or sham operation. UDCA was also fed to 2-month-old Mdr2(-/-) mice. Serum biochemistry, liver histology, and mortality rates were investigated. The biliary tract was studied by plastination, India ink injection, and electron microscopy. The effects of UDCA on biliary pressure were determined by cholangiomanometry.

RESULTS

UDCA feeding in CBDL mice increased biliary pressure, with subsequent rupture of cholangioles and aggravation of hepatocyte necroses, resulting in significantly increased mortality. UDCA feeding in SBDL mice aggravated liver injury exclusively in the ligated lobe. Mdr2(-/-) mice developed liver lesions resembling sclerosing cholangitis characterized by biliary strictures and dilatations. UDCA induced bile infarcts in these animals.

CONCLUSIONS

UDCA aggravates bile infarcts and hepatocyte necroses in mice with biliary obstruction via disruption of cholangioles as a result of increased biliary pressure caused by its choleretic action.

Vascular mechanisms in the pathophysiology of human spinal cord injury

Vascular injury plays an important role in the primary and secondary injury mechanisms that cause damage to the acutely traumatized spinal cord. To understand the pathophysiology of human spinal cord injury, the authors investigated the vascular system in three uninjured human spinal cords using silicone rubber microangiography and analyzed the histological findings related to vascular injury in nine acutely traumatized human spinal cords obtained at autopsy. The interval from spinal cord injury to death ranged from 20 minutes to 9 months. The microangiograms of the uninjured human cervical cords demonstrated new information about the sulcal arterial system and the pial arteries. The centrifugal sulcal arterial system was found to supply all of the anterior gray matter, the anterior half of the posterior gray matter, approximately the inner half of the anterior and lateral white columns, and the anterior half of the posterior white columns. Traumatized spinal cord specimens in the acute stage (3-5 days postinjury) showed severe hemorrhages predominantly in the gray matter, but also in the white matter. The white matter surrounding the hemorrhagic gray matter showed a variety of lesions, including decreased staining, disrupted myelin, and axonal and periaxonal swelling. The white matter lesions extended far from the injury site, especially in the posterior columns. There was no evidence of complete occlusion of any of the larger arteries, including the anterior and posterior spinal arteries and the sulcal arteries. However, occluded intramedullary veins were identified in the degenerated posterior white columns. In the chronic stage (3-9 months postinjury), the injured segments showed major tissue loss with large cavitations, whereas both rostral and caudal remote sites showed well-demarcated necrotic areas indicative of infarction mainly in the posterior white columns. Obstruction of small intramedullary arteries and veins by the initial mechanical stress or secondary injury mechanisms most likely produced these extensive white matter lesions. Our studies implicate damage to the anterior sulcal arteries in causing the hemorrhagic necrosis and subsequent central myelomalacia at the injury site in acute spinal cord injury in humans.

The syndrome of bilateral paramedian thalamic infarction

Bilateral anterior paramedian thalamic infarction resulting from occlusion of a bilaterally distributed thalamosubthalamic paramedian artery was demonstrated on CT in two patients. Patient 1 presented with a transient coma followed by asterixis, hypersomnia, vertical gaze disturbances, profound Korsakoff amnesic syndrome, and a subcortical dementia. Patient 2, with a predominantly right-sided thalamic infarct, showed good recovery from amnesia and vertical gaze disturbances. However, patient 1 remained with severe amnesia and mild subcortical dementia at follow-up 1 year later. These and similar reported cases constitute a lacunar syndrome with characteristic clinical and CT features.

Deleterious effects of calcium channel blockade on pressure transmission and glomerular injury in rat remnant kidneys

Hypertensive mechanisms are postulated to play a major role in the progressive glomerulosclerosis (GS) after renal mass reduction. But, in contrast to converting enzyme inhibitors, BP reduction by calcium channel blockers, has not provided consistent protection. Radiotelemetric BP monitoring for 7 wk was used to compare nifedipine (N) and enalapril (E) in the rat approximately 5/6 renal ablation model. After the first week, rats received N, E, or no treatment (C). The overall averaged systolic BP in C (173 +/- 7 mmHg) was reduced by both E and N (P < 0.001), but E was more effective (113 +/- 2 vs. 134 +/- 3 mmHg, P < 0.01). GS was prevented by E (2 +/- 1 vs. 26 +/- 5% in C) but not by N (25 +/- 6%). GS correlated well with the overall averaged BP in individual animals of all groups, but the slope of the relationship was significantly steeper in N compared with C+E rats (P < 0.02), suggesting greater pressure transmission to the glomeruli and GS for any given BP. Since autoregulatory mechanisms provide the primary protection against pressure transmission, renal autoregulation was examined at 3 wk in additional rats. Autoregulation was impaired in C rats, was not additionally altered by E, but was completely abolished by N. These data demonstrate the importance of autoregulatory mechanisms in the pathogenesis of hypertensive injury and suggest that calcium channel blockers which adversely affect pressure transmission may not provide protection despite significant BP reduction.

Somatosensory cerebral evoked potentials after vascular lesions of the brain-stem and diencephalon

Clinical and electrophysiological observations are described in 7 patients with clinically well-identified vascular lesions of the brain-stem or diencephalon. In the patients of Group A with a thalamic syndrome, the somatosensory cerebral evoked potentials had a reduced voltage and increased latency on the affected side. No significant anomalies were recorded in the patients of Group B with a Wallenberg or Weber syndrome. In patients of group C with a locked-in syndrome, the cerebral evoked potentials presented marked bilateral anomalies which provided interesting data about the extension of the pontine vascular lesions into the tegmentum. The pathophysiological mechanisms involved in the changes of average cerebral evoked potentials and in the slowing of corticipetal conduction are discussed.

Cerebral ischemia and reactive hyperemia. Studies of cortical blood flow and microcirculation before, during, and after temporary occlusion of middle cerebral artery of squirrel monkeys

Correlative studies of cortical blood flow measured by the 85 Kr washout technique and observations of the cortical blood vessels of 10 squirrel monkeys subjected to temporary occlusion of the middle cerebral artery are described. During occlusion, cortical blood flow in core areas of ischemia decreased to 0.12 to 0.90 ml/g/min (20 to 50% of preocclusion values) and became pressure dependent with failure of autoregulation. After release of the occluding clip, cortical blood flow was restored. Correlation between degree of vascular reaction judged by observation of the cortex and degree of hyperemia as determined by cortical blood flow was poor. There was incomplete correlation between the degree of hyperemia and the degree of preceding ischemia. Hyperemia, or "luxury perfusion," manifested by red venous blood, appears to be related to failure of cerebral tissue to utilize available oxygen as well as to "reactive" hyperemia, or supernormal blood flow, in regions previously ischemic. There was no demonstrable gradual failure of collateral circulation during occlusion. Cerebral edema was progressive and even progressed after restoration of cortical blood flow; it was incompletely correlated with the degree of ischemia and degree of hyperemia.

The course of the remnant kidney model in mice

The remnant kidney model was produced in mice by unilateral nephrectomy and partial infarction of the remaining kidney. Control mice underwent laparotomy only. The mice were studied for up to 44 weeks. No quantitative differences were noted in systolic arterial pressure, proteinuria, or histopathology between control mice and those with a remnant kidney. Glomerular enlargement occurred in the remnant kidney.

Cellular responses to hypoxia after renal segmental infarction

BACKGROUND

Hypoxia is believed to play an important role in the pathogenesis of acute and chronic kidney disease. However, the impact of low oxygen tensions on cellular functions in the kidney and potential adaptive responses are poorly understood.

METHODS

In order to assess the effects of regional hypoxia, we induced large segmental renal infarcts in rats by renal artery branch ligation to create an oxygen gradient vertical to the corticomedullary axis and studied the effects on cell morphology, the induction of hypoxia-inducible transcription factors (HIF), the expression of HIF target genes, and cell proliferation.

RESULTS

Pimonidazol protein adduct immunohistochemistry, a marker for severe tissue hypoxia, verified a continuous area of hypoxic renal tissue extending from the cortex to the papilla, in which tubular necrosis developed subsequently. Within this area local sparing of pimonidazol staining and tissue preservation was found around arcuate veins, indicating regional oxygen supply via diffusion from venous blood. HIF-1alpha was up-regulated within 1 hour and for up to 7 days predominantly in the border zone of the infarct in tubular cells, glomerular cells, resident interstitial cells, capillary endothelial cells, and infiltrating macrophages. HIF-2alpha expression was less prominent and confined to resident and infiltrating peritubular cells in the cortex. HIF expression was colocalized with regional up-regulation of the hypoxia-inducible genes heme oxygenase-1 and vascular endothelial growth factor (VEGF), and was followed by capillary and tubular proliferation.

CONCLUSION

Our findings illustrate a marked potential of renal tissue to respond to regional ischemia and initiate adaptive reactions, including angiogenesis.

Thalamic infarctions: differential effects on vestibular function in the roll plane (35 patients)

We determined the subjective visual vertical (SVV), ocular torsion (OT), skew deviation, and lateral head tilt in 35 patients with acute thalamic infarctions (14 paramedian, 17 posterolateral, and four anterior polar) and in five patients with mesodiencephalic hemorrhages to obtain the tonic effects on vestibular function in the roll plane. Eight of 14 paramedian infarctions had complete ocular tilt reaction (OTR) with contraversive head tilt, skew deviation, OT, and SVV tilt. The OTR was due to ischemia of the rostral midbrain tegmentum, including the interstitial nucleus of Cajal (INC), and not to thalamic ischemia. Thus, the INC (and the rostral interstitial nucleus of the medial longitudinal fascicle) is the most rostral brainstem structure mediating eye-head coordination in roll. Eleven of 17 posterolateral infarctions exhibited moderate SVV tilts that were either ipsiversive or contraversive. In these 11 cases, vestibular thalamic nuclei (nucleus ventro-oralis intermedius, nucleus ventrocaudalis externus, and nucleus dorsocaudalis) were involved; infarctions in the remaining six were more ventromedial. Anterior polar infarctions did not affect vestibular function in roll.

Diffusion-weighted MRI of spinal cord infarction

Infarction is a rare cause of spinal cord dysfunction. Whereas diffusion-weighted (DW) MRI has been established as a highly sensitive technique for assessing acute cerebral ischemia, its role in spinal cord infarction remains to be determined. The purpose of this study is to present the signal characteristics of acute spinal cord ischemia using DWMRI within the first two days and after one week. MRI including DW imaging (DWI) was performed in three patients with acute spinal cord dysfunction 8, 12 and 30 hours after the onset of symptoms and repeated after one week in two patients. Two initial scans included EPI DW sequences in transverse and sagittal orientation. The remaining examinations were performed with an optimised high-spatial resolution DWI sequence in the transverse plane. The diagnosis of spinal cord ischemia was established by imaging, clinical history and CSF analysis. T2 signal abnormality and restricted diffusion was demonstrated in all initial examinations. Transverse DW sequences had the highest sensitivity. The spinal infarctions were mainly located in the centre of the spinal cord and the grey matter. Contrast enhancement was absent. After one week, the restricted diffusion had normalised (pseudo normalisation) whereas the T2 signal changes had become more prominent. Restricted diffusion in the course of spinal cord ischemic infarction can be demonstrated using DW-MRI. Whereas a diffusion abnormality can be found after few hours, it does not last for longer than one week. At this time, the establishment of the diagnosis has to rely mainly on T2-weighted images with additional post contrast T1-weighted images being useful.

Infarcts in the territory of the deep perforators from the carotid system

We studied risk factors and presumed causes of infarct in 100 consecutive patients with a first stroke, who had an appropriate CT-proven infarct in the territory of the deep perforators from the carotid system (ITDPCS). The infarct involved the territory of the lenticulostriate arteries in 65 cases, the anterior choroidal artery in 23 cases, watershed zones between these two territories in four cases, and another territory in eight cases. In 42% of the patients, we felt the cause of the infarct to be small-artery disease. In 36%, at least one source of embolism was present (in 27% from the internal carotid artery, in 17% from the heart), either with (25%) or without (10%) associated hypertension (HT) and diabetes mellitus (DM). Other possible less common etiologies included migraine, syphilitic angiitis, and systemic diseases. We have confirmed that HT or DM are the most common etiologic factors of ITDPCS. However, large-artery disease and cardioembolism may be more important than previously assumed.

High blood viscosity syndrome in cerebral infarction

Determinations of whole blood viscosity by means of a cone plate viscometer at 37°C and at shear rates of 212, 42, 21 and 11 sec -1 were done in 50 patients with recent cerebral infarction of the carotid system, and the values compared to a control group of 50 patients of the same age. In stroke patients a statistically significant elevation of blood viscosity over the whole range of shear rates was demonstrated, more obviously significant at low shear rates (P < 0.0001) such as occur in small vessels. Since the mean hematocrit levels of both groups were in the normal range, it was considered that hematocrit values estimated from peripheral blood do not necessarily give accurate information about viscosity levels existing at the same time.

In cases of severe cerebral infarction without angiographically demonstrable stenotic or obstructive lesions, it was suggested that high blood viscosity impairs hemodynamic conditions in the cerebral microvasculature in addition to narrow arteriosclerotic vessels, changes in flow velocity gradients and insufficient collateral circulation.

A primate model of nonarteritic anterior ischemic optic neuropathy

PURPOSE

Nonarteritic anterior ischemic optic neuropathy (NAION) is an optic nerve (ON) stroke and a leading cause of sudden ON-related vision loss. A primate (p)NAION model is crucial to further understanding of the clinical disorder and can provide information regarding the pathophysiology of other central nervous system (CNS) ischemic axonopathies. In the current study, a primate model of NAION was developed, and short-and long-term responses to this condition were characterized.

METHODS

pNAION was induced with a novel photoembolic mechanism. Short-and long-term responses were evaluated by minimally invasive testing (electrophysiology, fundus photography, indocyanine green and fluorescein angiography, and magnetic resonance imaging) and compared with histologic and immunohistochemical findings.

RESULTS

Optic disc edema, similar to that observed in cases of human NAION was seen 1 day after induction, with subsequent resolution associated with the development of optic disc pallor. Magnetic resonance imaging (MRI) performed 3 months after induction revealed changes consistent with ON atrophy. Electrophysiological studies and vascular imaging suggest an ON-limited infarct with subsequent axonal degeneration and selective neuronal loss similar to that seen in human NAION. ON inflammation was evident 2 months after induction at the site of the lesion and at distant sites, suggesting that inflammation-associated axonal remodeling continues for an extended period after ON infarct.

CONCLUSIONS

pNAION resembles human NAION in many respects, with optic disc edema followed by loss of cells in the retinal ganglion cell (RGC) layer and ON remodeling. This model should be useful for evaluating neuroprotective and other treatment strategies for human NAION as well as for other ischemic processes that primarily affect CNS white-matter tracts.

Representation of the visual field in the occipital striate cortex

The representation of the field of vision in the human striate cortex is based on the Holmes map in which about 25% of the surface area of the striate cortex is allocated to the central 15 degrees of vision. Following the introduction of computed tomography of the brain, the accuracy of the Holmes map was apparently confirmed by clinical/radiological correlation, but a revision has been proposed by Horton and Hoyt based on a magnetic resonance imaging study of three patients with visual field defects due to striate lesions. They propose that the central cortical representation of vision occupies a much larger area. This study reviews the perimetric and imaging findings in a larger series of patients with striate cortical disease and provides support for the revised representation. The clinical phenomenon of macular sparing and its relation to representation of the macula at the occipital pole is also discussed.

Mitochondrial KATPchannels in hindlimb remote ischemic preconditioning of skeletal muscle against infarction

We previously demonstrated in the pig that instigation of three cycles of 10 min of occlusion and reperfusion in a hindlimb by tourniquet application (∼300 mmHg) elicited protection against ischemia-reperfusion injury (infarction) in multiple distant skeletal muscles subsequently subjected to 4 h of ischemia and 48 h of reperfusion, but the mechanism was not studied. The aim of this project was to test our hypothesis that mitochondrial ATP-sensitive potassium (KATP) (mKATP) channels play a central role in the trigger and mediator mechanisms of hindlimb remote ischemic preconditioning (IPC) of skeletal muscle against infarction in the pig. We observed in the pig that hindlimb remote IPC reduced the infarct size of latissimus dorsi (LD) muscle flaps (8 × 13 cm) from 45 ± 2% to 22 ± 3% ( n = 10; P < 0.05). The nonselective KATPchannel inhibitor glibenclamide (0.3 mg/kg) or the selective mKATPchannel inhibitor 5-hydroxydecanoate (5-HD, 5 mg/kg), but not the selective sarcolemmal KATP(sKATP) channel inhibitor HMR-1098 (3 mg/kg), abolished the infarct-protective effect of hindlimb remote IPC in LD muscle flaps ( n = 10, P < 0.05) when these drugs were injected intravenously at 10 min before remote IPC. In addition, intravenous bolus injection of glibenclamide (1 mg/kg) or 5-HD (10 mg/kg) at the end of hindlimb remote IPC also abolished the infarct protection in LD muscle flaps ( n = 10; P < 0.05). Furthermore, intravenous injection of the specific mKATPchannel opener BMS-191095 (2 mg/kg) at 10 min before 4 h of ischemia protected the LD muscle flap against infarction to a similar extent as hindlimb remote IPC, and this infarct-protective effect of BMS-191095 was abolished by intravenous bolus injection of 5-HD (5 mg/kg) at 10 min before or after intravenous injection of BMS-191095 ( n = 10; P < 0.05). The infarct protective effect of BMS-191095 was associated with a higher muscle content of ATP at the end of 4 h of ischemia and a decrease in muscle neutrophilic myeloperoxidase activity at the end of 1.5 h of reperfusion compared with the time-matched control ( n = 10, P < 0.05). These observations led us to conclude that mKATPchannels play a central role in the trigger and mediator mechanisms of hindlimb remote IPC of skeletal muscle against infarction in the pig, and the opening of mKATPchannels in ischemic skeletal muscle is associated with an ATP-sparing effect during sustained ischemia and attenuation of neutrophil accumulation during reperfusion.

Local cerebral blood volume in head-injured patients. Determination by emission computed tomography of 99mTc-labeled red cells

Local cerebral blood volume (CBV) was mapped in 10 normal subjects and in 30 patients after head injury. In normal subjects, the mean CBV was 4.34 ml/100 gm. The coefficient of variation was 12% for the group mean, and 3% for values obtained in duplicate studies of individuals. Patients with head injuries were divided into three groups according to the stage of their illness: acute illness, early recovery, and later recovery. Averages of mean CBV were within one standard deviation of normal. In contrast, consistent changes were found in serial studies of the mean CBV in the same patient. Compared to recovery values, levels of mean CBV measured soon after injury were reduced, largely at the expense of the gray-matter compartment. In five adults with predominantly unilateral lesions, there was an average early reduction in mean CBV and cerebral blood flow of 15% and 36%, respectively. In three children with diffuse brain swelling, there was an average early mean CBV reduction of 12%; a single child had early increased mean CBV at a time when intracranial pressure was high. Greater changes were seen in local CBV on individual sections. There were mixed zones of hypervolemia and hypovolemia in regions of infarction and intracerebral hematoma. Subdural hematomas had consistent medial margins of increased local CBV, representing dilated blood vessels of the underlying cortex. The presence and displacement of this hypervolemic zone were sensitive indicators of persistent subdural collection and mass effect, even when the collection was lucent to x-ray computed tomography.

Why cotton wool spots should not be regarded as retinal nerve fibre layer infarcts

Cotton wool spots (CWSs) comprise localised accumulations of axoplasmic debris within adjacent bundles of unmyelinated ganglion cell axons. Their formation is widely held to reflect focal ischaemia from terminal arteriolar occlusion, but credible evidence supporting this view is lacking. CWSs are here purported to be nothing more than sentinels of retinal nerve fibre layer pathology, hence their recommended redesignation "cotton wool sentinels." After branch arteriolar occlusion, CWSs evolve as boundary sentinels of infarction, their uniform width suggesting a glial constraint to axonal expansion. In pre-proliferative diabetic retinopathy, CWSs form a C-shaped chain nasal to the disc and around the macula where they constitute sentinels of ischaemia affecting the entire retinal mid-periphery. The polymorphous CWSs evolving during acute panretinal hypoperfusion represent sentinels of an ischaemic penumbra. Those surrounding the disc in Purtscher's traumatic angiopathy are sentinels of neuronal damage from transient venous hyperdistension that overwhelms the protection afforded by peripapillary axonal decompartmentalisation.

Blood pressure and renal outcomes in patients with kidney infarction and hypertension

OBJECTIVE

To assess the causes and frequency of kidney infarction associated with hypertension, and the blood pressure and renal function outcomes.

METHODS

We analyzed the records of patients with kidney infarction documented by angiography and referred to a hypertension unit.

RESULTS

Spontaneous kidney infarction was documented in 55 of 18,287 patients and was associated with renal artery disease in 41 cases. Twenty-five patients had a longstanding history of hypertension at referral, and 30 patients presented with acute hypertension. Patients with acute hypertension were more likely to report a history of lumbar pain and to develop malignant hypertension than patients with longstanding hypertension; they also had higher plasma renin concentrations. Data for long-term follow-up after referral were available for 36 patients, including 15 patients who underwent surgery or renal artery angioplasty. From referral to most recent follow-up, the blood pressure decreased from 176/111 to 143/89 mmHg in patients with longstanding hypertension, and from 183/111 to 127/80 mmHg in those with acute hypertension (P = 0.007/0.041 for between-group differences). Three patients with acute hypertension had normal blood pressure without treatment at follow-up. Patients with long-term follow-up displayed no change in the glomerular filtration rate.

CONCLUSION

Kidney infarction is a rare cause of hypertension, usually associated with renal artery lesions. In cases of kidney infarction with acute hypertension, the blood pressure outcome is favorable following intervention and/or medication, and hypertension may resolve spontaneously.

The effect of cerebral infarction on the regional cerebral blood flow of the contralateral hemisphere

Regional cerebral blood flow (rCBF) measurements were performed over the contralateral hemisphere by the 133Xe intracarotid injection method in 20 patients with acute cerebral infarction in the territory of the internal carotid artery. The rCBF was found to be reduced, sometimes remarkably, in all of the patients. The mean reduction was 30 percent to 36 percent from the lowest normal value for the mean age of these patients. In the younger age group (40 to 59) the reduction was greater, 40 percent to 47 percent from the lowest normal value for this age. tthe rCBF depression was not related to cerebral dominance, previous hypertension or arterial PCO2 levels. The occurred in both patients who were fully alert and those with disturbances or consciousness, although it tended to be more diminished in the latter. tit can be assumed that the flow reduction in the nonaffected hemisphere is part of a general phenomenon affecting the entire brain and caused by globally reduced cerebral metabolism.

Conduction block in neuropathies with necrotizing vasculitis

Thirty-two patients with a mononeuropathy multiplex associated with a systemic necrotizing vasculitis were studied. The main abnormality was a loss of motor and sensory axons confirmed by electrophysiological and histological methods. A conduction block was observed in five patients, but only one was at a usual site of compression. Based on previous pathological studies and the experimental data in human and animals, the mechanism of the block is proposed to be ischemic. It is suggested that a conduction block in one nerve in a neuropathy with two or more individual nerves affected and with electrophysiological features of axonal degeneration may be due to a vasculitis.