Tracy K. McIntosh

Effects of traumatic brain injury on cerebral high-energy phosphates and pH: a 31P magnetic resonance spectroscopy study

Traumatic injuries to the CNS produce tissue damage both through mechanical disruption and through more delayed autodestructive processes. Delayed events include various biochemical changes whose nature and time course remain to be fully elucidated. Magnetic resonance spectroscopy (MRS) techniques permit repeated, noninvasive measurement of biochemical changes in the same animal. Using phosphorus MRS, we have examined certain biochemical responses of rats over an 8-h period following lateralized brain injury (1.5–2.5 atmospheres) using a standardized fluid-percussion model recently developed in our laboratory. Following injury, the ratio of phosphocreatine to inorganic phosphate (PCr/Pi) showed a biphasic decline: The first decline reached its nadir (4.8 ± 0.4 to 2.8 ± 0.7) by 40 min post-trauma with recovery by 100 min, followed by a second decline by 2 h that persisted for the remaining 6-h observation period (mean 2.5 ± 0.5). The first, but not the second, decrease in PCr/Pi was associated with tissue acidosis (pH 7.10 ± 0.03 to 6.86 ± 0.11). No changes in ATP occurred at any time during the injury observation period. Such changes may be indicative of altered mitochondrial energy production following brain injury, which may account for the reduced capacity of the cell to recover from traumatic injury.

Caspase-mediated cell death predominates following engraftment of neural progenitor cells into traumatically injured rat brain.

Neural progenitor cells (NPCs) have been shown to be a promising therapy for cell replacement and gene transfer in neurological diseases including traumatic brain injury (TBI). However, NPCs often survive poorly after transplantation despite immunosuppression, and the mechanisms of graft cell death are unknown. In this study, we evaluated caspase- and calpain-mediated mechanisms of cell death of neonatal mouse C17.2 progenitor cells, transplanted at 24 h following lateral fluid percussion brain injury (FP) in rats. Adult Male Sprague-Dawley rats (n = 30) were subjected to lateral FP injury (n = 18) or sham surgery (n = 12). C17.2 cells labeled with green fluorescent dye (CMFDA) were engrafted in the perilesional deep cortex, and animals were sacrificed at 24 h, 72 h and 1 week post-transplantation. Pro-apoptotic caspase-mediated cleavage products (Ab246) and calpain-mediated cleavage products (Ab38) were detected in the engrafted cells using immunohistochemistry. Only 2 to 4.5% of grafted NPCs were found to survive at 24 h post-transplantation, regardless of injury status of the host brain, although brain-injured animals had significantly fewer graft cells than sham-injured animals. Limited caspase and calpain-mediated graft cell death was observed in both sham- and brain-injured animals, and caspase-mediated graft cell death was significantly greater than calpain-mediated graft cell death in all animals. Brain-injured animals had significantly increased caspase-mediated graft cell death compared to sham-injured animals. These results suggest that both the caspase and calpain family of proteases are involved in graft cell death, and that caspase-mediated apoptotic graft cell death predominates in the acute post-traumatic period following TBI.

Alterations in regional concentrations of endogenous opioids following traumatic brain injury in the cat

Delayed injury following trauma to the central nervous system (CNS) may be due to the release or activation of endogenous factors. Endogenous opioid peptides have been proposed as one such class of injury factors, based on pharmacological studies demonstrating a therapeutic effect of naloxone and other opiate receptor antagonists following CNS injury. However, changes in brain opioid concentrations following injury have not been evaluated. In the present study, we measured regional alterations in dynorphin (ir-Dyn), leucine-enkephalin (ir-Enk) and beta-endorphin immunoreactivity (ir-End) following low- (1.0-2.0 atmospheres (atm)) or high- (3.0-4.0 atm) level fluid-percussion brain injury in the cat. A significant decrease in ir-End was observed in the hypothalamus at 2 h following high- but not low-level injury. No changes were observed in tissue ir-Enk following either level of injury. Severe brain trauma but not low-level injury caused a significant increase in ir-Dyn in the striatum, frontal cortex, parietal cortex, pons and medulla. In the anterior pituitary, a significant increase in ir-End and a significant decrease in ir-Dyn was observed at 2 h following both levels of injury. Pathological damage to brain tissue after injury was most pronounced in those regions showing significant increases in ir-Dyn but not other opioids. In the medulla, the increase in ir-Dyn but not ir-End or ir-Enk was also significantly correlated with a fall in systemic mean arterial pressure (MAP) at 2 h following high- but not low-level injury.(ABSTRACT TRUNCATED AT 250 WORDS)

The Maxi-K Channel Opener BMS-204352 Attenuates Regional Cerebral Edema and Neurologic Motor Impairment after Experimental Brain Injury

Large-conductance, calcium-activated potassium (maxi-K) channels regulate neurotransmitter release and neuronal excitability, and openers of these channels have been shown to be neuroprotective in models of cerebral ischemia. The authors evaluated the effects of postinjury systemic administration of the maxi-K channel opener, BMS-204352, on behavioral and histologic outcome after lateral fluid percussion (FP) traumatic brain injury (TBI) in the rat. Anesthetized Sprague-Dawley rats (n = 142) were subjected to moderate FP brain injury (n = 88) or surgery without injury (n = 54) and were randomized to receive a bolus of 0.1 mg/kg BMS-204352 (n = 26, injured; n = 18, sham), 0.03 mg/kg BMS-204352 (n = 25, injured; n = 18, sham), or 2% dimethyl sulfoxide (DMSO) in polyethylene glycol (vehicle, n = 27, injured; n = 18, sham) at 10 minutes postinjury. One group of rats was tested for memory retention (Morris water maze) at 42 hours postinjury, then killed for evaluation of regional cerebral edema. A second group of injured/sham rats was assessed for neurologic motor function from 48 hours to 2 weeks postinjury and cortical lesion area. Administration of 0.1 mg/kg BMS-204352 improved neurologic motor function at 1 and 2 weeks postinjury (P < 0.05) and reduced the extent of cerebral edema in the ipsilateral hippocampus, thalamus, and adjacent cortex (P < 0.05). Administration of 0.03 mg/kg BMS-204352 significantly reduced cerebral edema in the ipsilateral thalamus (P < 0.05). No effects on cognitive function or cortical tissue loss were observed with either dose. These results suggest that the novel maxi-K channel opener BMS-204352 may be selectively beneficial in the treatment of experimental TBI.

Thyrotropin‐Releasing Hormone and Central Nervous System Trauma

TRH and TRH analogues improve physiological function, survival, and neurological outcome in a variety of models of CNS trauma, including impact spinal cord injury in cats and rats, fluid-percussion-induced brain injury in rats, and compression-induced brain injury in cats. The mechanism by which TRH improves such functions may relate to its ability to improve blood flow and metabolism in the region of injury. Beneficial effects on blood flow may possibly relate to antagonism of the physiological effects of endogenous opioids, leukotrienes, or platelet-activating factor.

Methodological Considerations Regarding Single-Cell Gene Expression Profiling for Brain Injury

Genomic microarrays are rapidly becoming ubiquitous throughout a wide variety of biological disciplines. As their use has grown during the past few years, many important discoveries have been made in the fields of central nervous system (CNS) injury and disease using this emerging technology. In addition, single-cell mRNA amplification techniques are now being used along with microarrays to overcome many of the difficulties associated with the cellular heterogeneity of the brain. This development has extended the utility of gene expression profiling and has provided researchers with exciting new insights into the neuropathology of CNS injury and disease at a molecular and cellular level. New methodological, standardization, and statistical techniques are currently being developed to improve the reproducibility of microarrays and facilitate the analysis of large amounts of data. In this review, we will discuss the application of these techniques to experimental, clinically relevant models of traumatic brain injury.

Opiate antagonists in traumatic shock

In experimental animal studies, opiate receptor antagonists (such as naloxone) and physiological opiate antagonists (thyrotropin-releasing hormone [TRH]) have been used with some success to improve outcome and physiological variables following traumatic shock associated with hypovolemia, spinal cord trauma, and head injury. Naloxone at high doses (in the mg/kg range) improves blood pressure and survival following hypovolemic shock in some species subjected to fixed-pressure shock. Similarly, naloxone treatment in the same dose range improves blood pressure and outcome following traumatic spinal shock as well as shock associated with traumatic head injury in selected animal models. The high doses of naloxone required in these studies suggest that the beneficial effects may be due to actions at relatively naloxone-insensitive opiate receptors, such as the κ-receptor. Changes in the putative κ-receptor ligand dynorphin are found after hypovolemic shock and traumatic injury to the brain or spinal cord. Opiate receptor antagonists with increased selectivity for the κ-receptor may be superior to naloxone in the treatment of these conditions. TRH or TRH analogs similarly improve blood pressure and outcome following hypovolemic or spinal shock. Clinical trials of naloxone (at high doses) in human spinal cord injury have begun, and there are plans for clinical trials of naloxone in human head trauma and of TRH in human spinal cord injury.

Opiate Antagonists In CNS Injury

Traumatic insults to the central nervous system (CNS) may produce tissue injury through both direct and indirect (secondary) mechanisms. This secondary injury process appears to result from the release or activation of endogenous “autodestructive” factors in response to the original insult. Delayed injury may be associated with reduction in blood flow and/or an alteration of the local metabolic environment. Recently, endogenous opioids have been implicated as secondary injury factors following CNS trauma. The rationale for this hypothesis has been based primarily on the therapeutic effects of opiate-receptor antagonists in a variety of experimental CNS trauma models. This review summarizes the use of opiate-receptor antagonists in the treatment of CNS injury.