Holly Soares

Temporal and spatial characterization of neuronal injury following lateral fluid-percussion brain injury in the rat

Abstract The pattern of neuronal injury following lateral fluid-percussion (FP) brain injury in the rat was systematically characterized at sequential time points to identify selectively vulnerable regions and to determine the temporal contribution of primary and delayed neuropathological events. Male Sprague-Dawley rats (n = 28) were killed 10 min, 2 h, 12 h, 24 h, 4 days, and 7 days following a lateral FP brain injury of moderate severity (2.2 atm), or 24 h after a sham injury. Brain sections were stained and analyzed using Nissl, acid fuchsin, and silver staining methods to identify regions with injured neurons or with visible lesions. Extensive numbers of acid fuchsin or silver-stained neurons were observed as early as 10 min after the FP brain injury in regions extending from the caudate/putamen to the pons. The frequency of injured neurons was greatest in the ipsilateral cortex, hippocampus, and thalamus, and a visible loss of Nissl-stained neurons was observed in these regions beginning at 12 h after the FP brain injury. Acid fuchsin-stained neurons were restricted to the same brain regions for all of the survival periods and gradually decreased in numbers between 24 h and 7 days after injury. These findings suggest that lateral FP brain injury in the rat produces a combination of focal cortical contusion and diffuse subcortical neuronal injury, which is present within minutes of the impact, progresses to a loss of neurons by 12 h, and does not markedly expand into other brain regions with survival periods up to 7 days. Furthermore, the acute onset and rapid evolution of the neuronal injury process may have important implications when considering a window of opportunity for pharmacological intervention.

Effect of Noncompetitive Blockade of N‐Methyl‐d‐Aspartate Receptors on the Neurochemical Sequelae of Experimental Brain Injury

Abstract: Pharmacological inhibition of excitatory neurotransmission attenuates cell death in models of global and focal ischemia and hypoglycemia, and improves neurological outcome after experimental spinal cord injury. The present study examined the effects of the noncompetitive N‐methyl‐d‐aspartate receptor blocker MK‐801 on neurochemical sequelae following experimental fluid‐percussion brain injury in the rat. Fifteen minutes after fluid‐percussion brain injury (2.8 atmospheres), animals received either MK‐801 (1 mg/ kg, i.v.) or saline. MK‐801 treatment significantly attenuated the development of focal brain edema at the site of injury 48 h after brain injury, significantly reduced the increase in tissue sodium, and prevented the localized decline in total tissue magnesium that was observed in injured tissue of saline‐treated animals. Using phosphorus nuclear magnetic resonance spectroscopy, we also observed that MK‐801 treatment improved brain metabolic status and promoted a significant recovery of intracellular free magnesium concentrations that fell precipitously after brain injury. These results suggest that excitatory amino acid neurotransmitters may be involved in the pathophysiological sequelae of traumatic brain injury and that noncompetitive N‐methyl‐d‐aspartate receptor antagonists may effectively attenuate some of the potentially deleterious neurochemical sequelae of brain injury.

Development of prolonged focal cerebral edema and regional cation changes following experimental brain injury in the rat

Abstract: The present study examined the formation of regional cerebral edema in adult rats subjected to lateral (parasagittal) experimental fluid‐percussion brain injury. Animals receiving fluid‐percussion brain injury of moderate severity over the left parietal cortex were assayed for brain water content at 6 h, 24 h, and 2, 3, 5, and 7 days post injury. Regional sodium and potassium concentrations were measured in a separate group of animals at 10 min, 1 h, 6 h, and 24 h following fluid‐percussion injury. Injured parietal cortex demonstrated significant edema, beginning at 6 h post injury (p < 0.05) and persisting up to 5 days post injury. In the hippocampus ipsilateral to the site of cortical injury, significant edema occurred as early as 1 h post injury (p < 0.05), with resolution of water accumulation beginning at 3 days. Sodium concentrations significantly increased in both injured cortex (1 h post injury, p < 0.05) and injured hippocampus (10 min post injury, p < 0.05). Potassium concentrations fell significantly 1 h post injury within the injured cortex (p < 0.05), whereas significant decreases were not observed until 24 h post injury within the injured hippocampus. Cation alterations persisted throughout the 24‐h post injury period. These results demonstrate that regional brain edema and cation deregulation occur in rats subjected to lateral fluid‐percussion brain injury and that these changes may persist for a prolonged period after brain injury.

Fetal cortical transplants in adult rats subjected to experimental brain injury.

Fetal cortical tissue was injected into injured adult rat brains following concussive fluid percussion (FP) brain injury. Rats subjected to moderate FP injury received E16 cortex transplant injections into lesioned motor cortex 2 days, 1 week, 2 weeks, and 4 weeks post injury. Histological assessment of transplant survival and integration was based upon Nissl staining, glial fibrillary acidic protein (GFAP) immunocytochemistry, and staining for acetylcholinesterase. In addition to histological analysis, the ability of the transplants to attenuate neurological motor deficits associated with concussive FP brain injury was also tested. Three subgroups of rats receiving transplant 1 week, 2 weeks, and 4 weeks post injury Were chosen for evaluation of neurological motor function. Fetal cortical tissue injected into the injury site 4 weeks post injury failed to incorporate with injured host brain, did not affect glial scar formation, and exhibited extensive GFAP immunoreactivity. No improvement in neurological motor function was observed in animals receiving transplants 4 weeks post injury. Conversely, transplants injected 2 days, 1 week, or 2 weeks post injury survived, incorporated with host brain, exhibited little GFAP immunoreactivity, and successfully attenuated glial scarring. However, no significant improvement in motor function was observed at the one week or two week time points. The inability of the transplants to attenuate motor function may indicate inappropriate host/transplant interaction. Our results demonstrate that there exists a temporal window in which fetal cortical transplants can attenuate glial scarring as well as be successfully incorporated into host brains following FP injury.

Comparison of CNS homing pattern among murine TH cell lines responsive to myelin basic protein

A myelin basic protein (MBP)-reactive TH cell line capable of inducing experimental allergic encephalomyelitis (EAE), and a MBP-reactive TH cell clone that does not cause EAE were labeled with a fluorescent vital dye, and transferred into naive syngeneic SJL/J mice. Animals were killed before the appearance of symptoms (3 and 4 days post-injection). Sections obtained from the spleen, spinal cord and brain of both groups of animals were examined by fluorescence microscopy to localize labeled TH cells. At all time points examined, the spleens of both groups contained innumerable labeled cells. The spinal cords and brains of animals that had received EAE-causing cells had a basal level of 20 labeled cells/cm2 at 3 days; this number increased rapidly to 150 cells/cm2 in the spinal cord at 4 days. Perivascular infiltrates and small foci of astrogliosis were already apparent in this group 3 days after injection. The spinal cords and brains of animals that had received the non-EAE-causing TH cells contained 50 labeled cells/cm2 at 3 days. The density of these transferred cells, as compared to that of the EAE-causing cells, suggested that they have an unaltered CNS-homing capability. However, by 4 days, the number of non-EAE-causing labeled cells had returned to near basal level. Our findings suggest that discrimination between disease and non-disease causing MBP-responsive TH cells occurs within the first 3 days following transfer, requires the presence in the CNS of a limited number of TH cells, and depends on yet unidentified TH cell factor(s).

Development of Regional Cerebral Oedema After Lateral Fluid-Percussion Brain Injury in the Rat

Most studies attempting to characterize post-traumatic oedema formation have focused on the acute postinjury period. We have recently developed a new model of lateral (parasagittal) fluidpercussion (FP) brain injury in the rat. The purpose of the present study was to characterize the temporal course of oedema formation and resolution in this experimental model of brain injury. Male Sprague-Dawley rats (n = 67) were anaesthetized and subjected to FP brain injury of moderate severity. Animals were sacrified at 1 hour, 6 hours, 24 hours, 2 days, 3 days, 5 days and 7 days after brain injury, brains removed and assayed for water content using either specific gravitimetric or wet weight/dry weight techniques. In the injured left parietal cortex, a significant increase in water content was observed by 6 hours postinjury (p less than 0.05) that persisted up to 5 days postinjury. A prolonged and significant increase in water content was also observed in the left (ipsilateral) hippocampus which began at 1 hour postinjury (p less than 0.05) and continued up to 3 days. Other regions examined showed no significant regional oedema after brain injury. These results suggest that lateral FP brain injury produces an early focus oedema that persists for a prolonged period after trauma. This model may be useful in the evaluation of novel pharmacological therapies designed to reduce cerebral oedema after brain injury.

N-Methyl-D-Aspartate (NMDA) Receptor Antagonists in the Treatment of Experimental Brain Injury: 31P Magnetic Resonance Spectroscopy and Behavioral Studies

The excitatory amino acid neurotransmitters (EAA) glutamate and aspartate and their various analogs can produce cell swelling and cell death after direct application to neurons (Olney 1978). Recent data also exist to support the hypothesis that these “excitotoxins” participate in the tissue damage caused by brain hypoxia and/or ischemia since both in vivo and in vitro treatment with N-methyl-D-aspartate (NMDA) receptor antagonists appears to protect against cell death (Rothman and Olney 1986, Simon et al. 1984). Because it is possible that EAA receptor activation may contribute to delayed damage after brain trauma, we evaluated the therapeutic efficacy of MK-801, a centrally-active, antagonist of the NMDA receptor, on brain metabolism (as measured by phosphorus nuclear magnetic resonance spectroscopy (31P MRS)) and neurological outcome after fluid-percussion (FP) brain injury in the rat.