Sharon Murphy

α-phenyl-tert-butyl-nitrone inhibits free radical release in brain concussion

Traumatic brain injury (TBI) is one of the important causes of mortality and morbidity. The pathogenesis of the underlying brain dysfunction is poorly understood. Recent data have suggested that oxygen free radicals play a key role in the primary and secondary processes of acute TBI. We report direct electron spin resonance (ESR) evidence of hydroxyl (.OH) radical generation in closed-head injury of rats. Moderate brain concussion was produced by controlled and reproducible mechanical, fixed, closed-head injury. A cortical cup was placed over one cerebral hemisphere within 20 min of the concussion, perfused with artificial cerebrospinal fluid (aCSF) containing the spin trap agent pyridyl-N-oxide-tert-butyl nitrone (POBN, 100 mM), and superfusate samples collected at 10 min intervals for a duration up to 130 min post brain trauma. In addition, POBN was administered systemically (50 mg/kg body wt.) 10 min pretrauma and 20 min posttrauma to improve our ability to detect free radicals. ESR analysis of the superfusate samples revealed six line spectra (alpha N = 15.4 G and alpha beta H = 2.5 G) characteristic of POBN-OH radical adducts, the intensity of which peaked 40 min posttrauma. The signal was undetectable after 120 min. Administration of alpha-phenyl-tert-butyl-nitrone (PBN), a spin adduct forming agent systemically (100 mg/kg body wt. IP 10 min prior to concussion) alone or along with topical PBN (100 mM PBN in aCSF), significantly (p < 0.001) attenuated the ESR signal, suggesting its possible role in the treatment of TBI.

Correlation of behavioral and cerebrovascular functions in the aging rat

Regional cerebral blood flow (rCBF), maze performance and the influence of environmental enrichment on these parameters were studied in Sprague-Dawley rats aged 6, 12 and 24 months. Learning ability in a complex sequential T-maze (Stone maze) progressively declined with increasing age in rats which were normally housed in standard caging. Environmental enrichment significantly improved maze performance but did not prevent the age-dependent impairment. Following completion of the learning studies, rCBF was measured in each of 13 brain regions in conscious, unrestrained, resting animals. In the absence of any significant change in cardiac output over the entire age range, rCBF was lower in all brain regions by an average of 16% in 12-14 month old rats and 8% in aged rats (24-26 months old); the occipital cortex, inferior and superior colliculi and hypothalamus were particularly affected regions in both age groups. The sharp reduction of rCBF that occurred between 6 and 12 months of age did not reflect, and probably preceded the progressive decline in maze performance. Such highly significant age-related changes in rCBF were not affected, however, by environmental enrichment procedures. This contrasts with the substantial influence of enrichment on maze performance. Finally, mean brain blood flow and mean cortical blood flow correlated inversely and significantly with average daily numbers of errors made by 24 month old rats during Stone maze acquisition.

Alcohol and Regional Blood Flow in Brains of Rats

Summary Alcohol, in large amounts, increases the blood flow to brains of man and other animals. To what extent blood flow to specific regions of the brain varies with smaller, nonanesthetizing doses has been the subject of the present study. A new radioisotopic method was employed which permitted the simultaneous measurement of blood flow to each of ten regions of the brain in unrestrained, unanesthetized animals as small as rats. Three doses of alcohol were used: a low dose causing no behavioral change, an intermediate dose causing lack of coordination but no loss of consciousness, and a high toxic dose producing anesthesia. The blood levels of alcohol causing various signs of intoxication were the same in rats and man. At the low dose, no changes were seen in brain blood flow. At the intoxicating dose slight, but insignificant, increases were seen in the basal ganglia, frontal cortex, and olfactory bulb, while hippocampal blood flow decreased. At the anesthetic dose, blood flow increased to the olfactory bulb and the brain stem and actually decreased slightly to the parietal cortex. Support of the depressed ventilation rate observed at this dose of ethanol restored the pCO2 and pO2 values to control levels but did not reverse the observed acidosis; cardiac output fell, signaling increased peripheral resistance. Under these circumstances, the flow of blood to all brain regions fell, most notably to the hippocampus, cerebellum, and parietal cortex. The effects of ethanol and pentobarbital are compared. We are indebted to Dr. D. Knowlton for the analyses of blood levels of ethanol. This work was supported in part by a grant from The Licensed Beverage Industries and by Public Health Service Grant NB05526.

Endothelial cell activation following moderate traumatic brain injury

Abstract Traumatic brain injury (TBI) initiates a cascade of acute and chronic injury responses which include disturbances in the cerebrovasculature that may result in the activation of the microvascular endothelial development of a dysfunction endothelium. The present study examines endothelial cell (EC) activation in a percussion model of moderate TBI. The criteria for endothelial activation used in these studies was surface expression of a number of markers collectively termed endothelial activation antigens. Temporal induction of the major histocompatibility (MHC) class II molecules, E-selectin (CD62E), vascular cell adhesion molecule (VACM-1) (CD106) as well as altered expression of constitutively expressed intercellular adhesion molecule-1 (ICAM-1) (CD54), the glucose transporter protein (glut-1), the transferrin receptor (tfR) (CD71), and MHC class I molecules was examined at various times following impact. Induction of E-selectin and increased expression of ICAM-1 was seen by 2 h post-impact (PI) and was sustained through 24 h PI. Decreased expression of immunologically reactive glut-1 and tfR was observed by 2–4 h PI and remained low up to 24 h PI. No induction of VCAM-1, MHC class II molecules or altered constitutive expression or MHC class I molecules was seen. Changes in EC activation were observed predominantly at the site of impact and were diminished temporarily. These results indicate that mild concussive injury to the brain results in activation of the endothelium. [Neurol Res 2001; 23: 175-182]

Hormones and regional brain blood flow

Acute effects of the hormones, estradiol-17beta and alphaMSH, and of neonatal pretreatment with alphaMSH on the flow of blood to regions of the brains of conscious adult rats have been determined with an indicator distribution technique. As previously reported, flows were reduced in most areas within 10 min after intravenous administration of alphaMSH; only the occipital cortex was spared. Though these effects were transitroy for most areas, perfusion of pons and medulla, cerebellum, hippocampus and parietal cortex was still low by 20 min. However, pretreatment with alphaMSH during infancy led to persistent behavioral changes which were not accompanied by flow differences. Assuming that flow changes reflect functional changes, the rapid responses to alphaMSH suggest an explanation for the effects of this hormone on visual learning and on the determination of subsequent learning behavior. By contrast, estradiol, within 10 min after injection, increased flow to most regions of the brain, especially the frontal cortex, hippocampus, basal ganglia and cerebellum; females were more affected than males. Flow changes were greater than those elicited by more obvious behavior-modifying drugs. Compared to alphaMSH, the flow data for estradiol suggest a physiologic basis for a behavioral effect which is likely to be different yet, perhaps, equally profound.

MSH affects regional perfusion of the brain

With the single exception of the occipital cortex, the flow of blood to most regions of the brains of conscious, unrestrained rats was reduced within 10 min after intravenous administration of alphaMSH. Though these effects were transitory for most regions of the brain, perfusion of cerebellum, pons and medulla, hippocampus, and parietal cortex was still significantly low by 20 min. Assuming that flow changes reflect functional changes, these early responses to alphaMSH suggest an explanation for the effects of this hormone in which visual learning is improved.

An analog of ACTH/MSH4-9, ORG-2766, reduces permeability of the blood-brain barrier.

Regional uptakes of a diffusion-limited substance, antipyrine, were compared to those of a highly diffusible substance, iodoantipyrine, in brains of conscious, unrestrained rats. The method included simultaneous measurements of regional cerebral blood flow. Within 10 min after intravenous injection of a behaviorally active analog of ACTH/MSL4-9, ORG-2766, the relative extraction of antipyrine was reduced in most regions of the brain, significantly in hypothalamus, hippocampus, parietal cortex and frontal cortex. The occipital cortex and brain stem were least affected. Since the flow of blood was not changed significantly in any region at this time, we conclude that the changes in extraction reflect a reduction in permeability of the blood-brain barrier. These results suggest that the behavioral responses to peripherally administered fragments of ACTH/MSH may depend, in part, on some action in the blood-brain barrier. These observations also suggest a mechanism by which such peptides may influence the behavioral effects of diffusion-limited drugs.

Cerebrovascular permeability and cognition in the aging rat

Regional cerebrovascular permeability-capillary surface area products (rPS) and brain vascular space (BVS) were measured in aging, conscious, unrestrained Sprague-Dawley rats. Three groups of animals were examined: young-mature (6 months), middle-aged (12-14 months), and old (24-26 months) rats. Complex maze learning had been previously characterized in these same animals. Maze learning declined with age. Brain vascular space did not differ significantly with age in any brain region. However, small, but significant age-dependent decreases in rPS (25-33%) were observed. These decreases occurred mainly in the old animals in the basal ganglia and parietal cortex, and in the middle-aged and old rats in the olfactory bulbs. Significant and unexpected positive average correlations between brain permeability-capillary surface area products (PS) and learning errors occurred primarily in young rats and were attributable mainly to changes in 5 of 14 brain regions; hypothalamus, hippocampus, parietal cortex, septal area and superior colliculus. The higher correlations between maze learning errors and PS in young animals may indicate dynamic regulation of this cerebrovascular parameter which is lessened with aging. Average correlations between PS and cerebral blood flow also were determined and found to be generally small and not significant for most brain regions and age groups.

Oxypurinol inhibits free radical release from the cerebral cortex of closed head injured rats.

Traumatic brain injury (TBI) is a significant cause of mortality and morbidity. Although the sequence of events underlying the resultant neuronal loss is still poorly understood, there are indications that oxygen-free radical generation is critically involved. Free radical generation in the cerebral cortex of closed head injury rats was monitored by measuring free radical release into cortical superfusates containing the spin trap agent 4-pyridyl-1-oxide-N-tert-butylnitrone (POBN, 100 mM). ESR analysis of the superfusates revealed six line spectra (alpha N = 15.4 G and alpha H beta = 2.5 G) characteristic of POBN-OH adducts. Administration of oxypurinol (40 mg/kg) 15 min prior to TBI prevented the formation of these radical adducts.

Alterations in CNS gene expression in a rodent model of moderate traumatic brain injury complicated by acute alcohol intoxication

The combined effects of acute alcoholic intoxication and moderate traumatic brain injury (TBI) on zif/268, glial fibrillary acidic protein (GFAP), and preproenkephalin (PPE) mRNA expression were examined. Adult male Wistar rats received ip injections of a 5% alcohol solution (2.4 g/kg in a final volume of 20 ml isotonic saline) 10 min prior to fixed-head, mechanical injury. Using Northern analysis, a transient three- to fourfold induction of zif/268 mRNA levels was observed 45 min after injury in both TBI and alcohol-treated rats. This induction occurred in regions close to the impact site, namely, the olfactory bulb (OB) and frontal cortex (FTCTX) but not in the more distal piriform/amygdala cortex (P/A). No PPE mRNA changes were observed at 45 min for any experimental group. By 6 h, zif/268 transcript levels returned to or fell below basal levels in the OB and FTCTX while GFAP mRNA levels began to increase in TBI rats. At 24 h, GFAP mRNA levels were greatly increased in all three brain regions of TBI rats. However, alcohol inhibited the temporal induction of GFAP mRNA in the FTCTX and P/A triggered by TBI at 6 and 24 h. These results suggest that although acute alcohol intoxication prior to TBI does not influence gene expression patterns immediately after injury, it may minimize the transcriptional activation of astrocytes particularly in more distant brain regions that were influenced by the impact in nonintoxicated rats.