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R Prado

Publications and source records attributed to R Prado.

At least 55 records · Page 3Linked to original sources
PubMed1990

A new mapping study of superoxide free radicals, vascular permeability and energy metabolism in central nervous system.

To study the role of free radicals in various pathophysiologies in the central nervous system (CNS), we have introduced a new simultaneous mapping technique of superoxide free radicals, vascular permeability and energy metabolism. The detection of superoxide anion in the CNS is based on the 380 nm chemiluminescence of 2-methyl-6-phenyl-3,7-dihydroimidazo [1,2-alpyrazin-3-one(CLA-phenyl)] upon reaction with superoxide in the frozen tissue section. The results show topographical relationships between activation of superoxide free radicals, increased vascular permeability, and changes of hydrogen transport system in the energy metabolism (Fig. 2). Prolonged formation of superoxide free radicals in the white matter without vasogenic oedema and necrotic tissue are interesting as a mechanism of progression of secondary tissue damage in ischaemic insults.

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PubMed1990

Photochemically induced cystic lesion in the rat spinal cord. I. Behavioral and morphological analysis.

The present study describes the production of a spinal cord lesion which is initiated by vascular occlusion resulting from the interaction between the photosensitizing dye erythrosin B and an argon laser beam. The lesion has characteristics similar to those of the central cavity thought to lead to the production of post-traumatic syringomyelia (PTS) in humans. The present study examines the behavioral and morphological characteristics of this injury over a 28-day period. Histological analysis revealed a cavity extending from the dorsal horns to lamina VIII, with some lateral and ventral pathways being spared. The cavity volume reached a maximum 7 days after lesion induction. Behavioral changes were assessed using six different tests of motor and reflex function (motor function, climbing, waterbath, inclined plane, withdrawal to pain, and withdrawal to extension). Lesioned animals exhibited flaccid paralysis for 3-5 days, which resolved afterward. The photochemically induced cavity should provide a reproducible model for examining the effects of cystic spinal cord injury on locomotor and reflex function.

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PubMed1988

A new model of embolic stroke produced by photochemical injury to the carotid artery in the rat.

We report a new model of embolic stroke in the rat, based on endothelial disruption and platelet aggregation in the carotid artery, which leads to distal embolization and focal brain infarction. The common carotid artery was irradiated for 6.5 minutes with the focused beam of an argon laser operated at a wavelength of 514.5 nm with a peak power of 2 W and an average power of 400 mw. Ipsilateral cerebral infarcts, ranging in size from 0.1 to 1.7 mm, were produced by platelet emboli in 12 of 13 rats. A total of 44 infarcts were observed in the 12 rats: 29 in the cortex, 6 in the hippocampus, 5 in the thalamus, and 4 in the basal ganglia. Scanning electron microscopy identified platelet aggregates in the carotid artery and in a deep cortical arteriole 50 minutes after the photochemical lesion. Twenty-four hours after the experiment, scanning electron microscopy of the carotid artery revealed damaged endothelium but few remaining adherent platelets. More intense laser irradiation in 8 rats, leading to carotid occlusion, produced an infarct in only 1. This new model can be used to study the acute and chronic pathological changes in the brain associated with platelet embolism.

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PubMed1988

Histological maturation of astroglial cells in the archicortex of young hypothyroid rats.

The maturation of fibrous astrocytes was studied in the archicortex (hippocampus) of rats rendered hypothyroid by perinatal administration of propylthiouracil (PTU). A decrease in the number of protoplasmic processes and end-feet in fibrous astrocytes from the cortical molecular layer was observed. The diameter of the perikaryon and length of the prolongations were also decreased. In animals rehabilitated after weaning, the diameter of the perikaryon and length of protoplasmic processes returned to normal while that of number of prolongations per astroglial cell remained unchanged. It is postulated that hypothyroidism induced immediately after birth impairs differentiation of astroglia in the archicortex of the rat brain, probably as a response secondary to altered neuronal and capillary development.

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PubMed1988

Hyperglycemia increases infarct size in collaterally perfused but not end-arterial vascular territories.

Hyperglycemia exacerbates neuronal injury in the setting of reversible brain ischemia, but its effect on focal thrombotic infarction has been less extensively characterized. We investigated this problem in two rat models of focal vascular occlusion. In Model I, the right middle cerebral artery (MCA) was exposed via a subtemporal craniotomy in halothane- and nitrous oxide-anesthetized Wistar rats and was occluded photochemically by irradiation with an argon ion laser following the intravenous administration of the photosensitizing dye rose bengal. Permanent MCA occlusion was combined with temporary bilateral common carotid artery ligation. In Model II, similarly anesthetized Sprague-Dawley rats were subjected to permanent photochemical occlusion of the right MCA without common carotid occlusion. In both models, rats were food deprived for 24 h and were administered varying amounts of 50% dextrose (or saline) 15 min prior to vascular occlusion to produce a spectrum of plasma glucose values, ranging from 5 to 44 mumol/ml. Brains were examined histologically 7 days following vascular occlusion, and computer-assisted planimetry was used to compute infarct volumes. In Model I, the volume of neocortical infarction ranged from 30.3 to 108.4 mm3 and exhibited a strong linear correlation with increasing preischemic plasma glucose values (r = 0.70). In contrast, the size of the smaller striatal infarct in this model was not correlated with plasma glucose level. In Model II, there was a prominent striatal infarct, ranging in volume from 14.4 to 96.4 mm3, while neocortical infarction occurred inconstantly. As in Model I, striatal infarct volume in Model II showed no correlation with plasma glucose level.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1988

Middle cerebral artery thrombosis: acute blood-brain barrier consequences.

The effect of middle cerebral artery (MCA) thrombosis on the integrity of the blood-brain barrier (BBB) was studied in rats using horseradish peroxidase (HRP). Endothelial injury with subsequent platelet thrombosis was produced by means of a rose bengal-sensitized photochemical reaction, facilitated by irradiating the right proximal MCA segment with the focused beam of an argon laser. At 15 minutes following thrombosis formation, diffuse leakage of HRP was observed bilaterally within cortical and subcortical brain areas. Peroxidase extravasation was most dense within the territory of the occluded artery including neocortical areas and dorso-lateral striatum. Contralaterally, a similar distribution was observed but with less intense HRP leakage. Ultrastructural studies demonstrated an increase in permeability to HRP within arterioles, venules and capillaries. At these sites, the vascular endothelium contained HRP-filled pinocytotic vesicles and tubular profiles. Although less intense, bilateral HRP leakage was also observed following MCA stenosis or femoral artery occlusion. Endothelial-platelet interactions at the site of vascular injury may be responsible for releasing substances or neurohumoral factors which contribute to the acute opening of the BBB.

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PubMed1988

Photochemically stimulated blood-borne factors induce blood-brain barrier alterations in rats.

We have tested the hypothesis that blood-borne substances released from a site of vascular thrombosis can lead to acute alterations in the blood-brain barrier. The right common carotid artery of rats was photothrombosed using a dye/light insult. Rats were given the photosensitizing dye rose bengal and irradiated for 4 minutes with an argon laser beam focused onto the exposed common carotid artery. During the irradiation, 3 ml of blood was taken from the right external carotid artery. After 10 minutes, the blood was infused into the external carotid artery of a recipient rat that had received horseradish peroxidase. Fifteen minutes after blood infusion, bilateral peroxidase extravasation was noted within cortical and subcortical areas of recipient rats, being most intense ipsilaterally. Ultrastructural studies demonstrated peroxidase reaction product within numerous endothelial vesicles of arteriolar segments. Infusion of blood from control rats did not produce similar changes. Thus, photoinduced vascular thrombosis of a large feeding artery leads to the formation of blood-borne factors that acutely alter cerebral vascular permeability.

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PubMed1987

Argon laser-induced arterial photothrombosis. Characterization and possible application to therapy of arteriovenous malformations.

The common carotid, femoral, and middle cerebral arteries in the rat have been occluded thrombotically by means of a rose bengal dye-sensitized photochemical reaction initiated in vascular endothelium by the 514.5-nm beam of an argon laser, focused for maximum excitation efficiency of the photosensitizer according to a derived criterion. The total energy required for vessel occlusion was approximately 1 joule (J) for the middle cerebral artery and 140 to 180 J for the femoral and carotid arteries. At energy fluences (energy deposited per unit area) of 3.5 kJ/sq cm for the middle cerebral artery and 35 kJ/sq cm for the larger arteries, occlusion was observed within 3 minutes. The middle cerebral artery thrombus consisted entirely of aggregated platelets; in the larger arteries the thrombi were composed of platelet aggregates and groups of red blood cells interspersed within a matrix of coagulum. Vessels irradiated similarly in the absence of rose bengal dye displayed no morphological or functional damage. Because the photochemical reaction is mediated by electronic-state transitions, the process of photothrombosis (as opposed to photocoagulation) can be initiated in vessels with high flow rates without the requirement of increased temperature. The photothrombotic technique may be useful in the treatment of arteriovenous malformations owing to its significant enhancement of the efficiency and permanency of vessel occlusion.

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PubMed1987

Photochemically induced graded spinal cord infarction. Behavioral, electrophysiological, and morphological correlates.

Neurological and morphological outcome was evaluated in a rat model of graded spinal cord infarction initiated by a photochemical reaction. In this model, light-dye interactions induce primary microvascular stasis, resulting in consistent patterns of tissue necrosis. Four groups of rats underwent photoinduction times ranging from 30 seconds to 10 minutes. Neurological and electrophysiological functions were assessed starting 1 week after irradiation and continuing for 8 weeks. A functional neurological score was obtained by combining results from sensory and motor tasks, and electrophysiological function was evaluated from the somatosensory evoked potential recordings. In rats irradiated for short periods (30 seconds and 1 minute) mild behavioral deficits were documented. In contrast, electrical conduction was suppressed acutely in both groups; this recovered by 8 weeks to baseline or near baseline in the 30-second group but not in the 1-minute group. In rats irradiated for longer periods (5 and 10 minutes), severe behavioral and conduction abnormalities were detected at both the subacute and chronic testing periods. Although no significant difference in behavior was documented between the 5- and 10-minute groups acutely, the rats with 5-minute photoinduction time demonstrated a significant improvement in behavior over time whereas the group with 10-minute photoinduction time showed no improvement. A severe conduction block was present in both animal groups during the course of the study. Histopathological examination combined with morphometric measurements of the lesion area in cross section revealed four different degrees of spinal cord necrosis which correlated significantly with photoinduction times and neurological scores at 8 weeks. Reproducible degrees of ischemic damage to spinal cord parenchyma following primary microvascular occlusion result in a predictable sequence of behavioral and functional abnormalities, which in some cases recover with time.

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PubMed1986

Photochemically induced spinal cord injury in the rat.

We have developed in the rat a minimally invasive model of reproducible spinal cord injury initiated photochemically. With the exposed spinal column intact, 560 nm irradiation of the translucent dorsal surface induces excitation of the systemically injected dye, rose Bengal, in the spinal cord microvasculature. The resultant photochemical reaction leads to vascular stasis. Histopathological changes at 7 days include hemorrhagic necrosis of the central gray matter, edematous pale-staining white matter tracts and vascular congestion. At the level of cord irradiation (T8) the entire cord thickness is necrosed except for the periphery of the anterior funiculus. Voluntary motor function is consistently lost in the subacute phase of injury.

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