Harold F. Young

Prolonged memory impairment in the absence of hippocampal cell death following traumatic brain injury in the rat

Prolonged neurological dysfunction that results from an insult to the brain is often attributed to irreversible structural damage such as loss of neurons or axonal degeneration. For example, following cerebral ischemia even partial hippocampal CA1 neuronal loss has been proposed to be sufficient to result in deficits in hippocampal dependent spatial memory. This study examined if hippocampal CA1 neuronal loss and/or axonal injury was necessary to produce prolonged spatial memory deficits resulting from traumatic brain injury (TBI). Prior to TBI Sprague-Dawley rats were trained on an 8-arm radial maze, a task sensitive to detecting specific lesions of the hippocampus or its extrinsic connections. Following a mild, moderate, or sham injury, rats were tested for working and reference memory for 25 days. After 25 days of maze testing, histological cell counts were made from consistent coronal sections of the mid-dorsal hippocampus. Rats subjected to mild or moderate TBI manifested working memory deficits for 5 and 15 days, respectively, after injury in the absence of overt (all brain regions) or quantitative (CA1 only) evidence of neuronal death. The number of CA1 pyramidal neurons of representative sections of the mid-dorsal hippocampi for injured maze-deficit rats and sham control rats were: 1626 (S.E.M. = +/- 66) and 1693 (S.E.M. = +/- 69) per 10(6) micron2, respectively. Additionally, no overt evidence of axonal injury was observed in any forebrain structure including major intrinsic or extrinsic connecting hippocampal pathways. These data strongly suggest that mild to moderate TBI is capable of producing prolonged spatial memory deficits in the rat without evidence of either neuronal cell death in the intrinsic hippocampus or overt axonal injury in hippocampal pathways.

Increased vulnerability of the midly traumatized rat brain to cerebral ischemia: the use of controlled secondary ischemia as a research tool to identify common or different mechanisms contributing to mechanical and ischemic brain injury

Abstract Fasted Wistar rats were subjected to either a mild mechanical injury, 6 min of transient forebrain ischemia, or a mild mechanical injury followed 1 h later by 6 min of forebrain ischemia. EEG and evoked potentials were assessed intermittently and morphological analyses were performed after 7 das postinjury survival. In all groups complete qualitative recovery of electrical activity and general behavior was observed with 7-day survival. However, rats subjected to combined concussion and ischemia displayed EEG spike activity and a delayed return of EEG and evoked potentials during acute recovery not evident in other groups. No overt neuronal cells loss was seen in trauma alone and was minimal or absent in ischemia alone. However, extensive bilateral CA1 and subicular pyramidal cell loss was found in the septal and mid-dorsal hippocampi in the combined trauma and ischemia group. In contrast, no overt axonal injury was found in any group. We conclude that even mild mechanical injury can potentiate selective ischemic hippocampal neuronal necrosis in the absence of overt axonal injury. This potentiation also occurs in conjunction with more generalized electrophysiological disturbances such as EEG evidence of postischemic neuronal hyperactivity suggesting that mild concussion may also decrease the threshold for post-ischemic neuronal excitation. These results suggest the potential of this model for examining common or different injury mechanisms in mechanical and ischemic brain injury.

The importance of brain temperature in patients after severe head injury: Relationship to intracranial pressure, cerebral perfusion pressure, cerebral blood flow, and outcome

Brain temperature was continuously measured in 58 patients after severe head injury and compared to rectal temperature, intracranial pressure, cerebral blood flow, and outcome after 3 months. The temperature difference between brain and rectal temperature was also calculated. Mild hypothermia (34-36 degrees C) was also used to treat uncontrollable intracranial pressure (ICP) above 20 mm Hg when other methods failed. Brain and rectal temperature were strongly correlated (r = 0.866; p < 0.001). Four groups were identified. The mean brain temperature ranged from 36.9 +/- 0.4 degrees C in the normothermic group to 38.2 +/- 0.5 degrees C in the hyperthermic group, 35.3 +/- 0.5 degrees C in the mild therapeutic hypothermia group, and 34.3 +/- 1.5 degrees C in the hypothermia group without active cooling. The mean DeltaT(br-rect) was positive for patients with a T(br) above 36.0 degrees C (0.0 +/- 0.5 degrees C) and negative for patients during mild therapeutic hypothermia (-0.2 +/- 0.6 degrees C) and also in those with a brain temperature below 36 degrees C without active cooling (0.8 +/- -1.4 degrees C) - the spontaneous hypothermic group. The cerebral perfusion pressure (CPP) was increased significantly by active cooling compared to the normothermic and hyperthermic groups. The mean cerebral blood flow (CBF) in patients with a brain temperature between 36.0 degrees C and 37.5 degrees C was 37.8 +/- 14.0 mL/100 g/min. The lowest CBF was measured in patients with a brain temperature <36.0 degrees C and a negative brain-rectal temperature difference (17.1 +/- 14.0 mL/100 g/min). A positive trend for improved outcome was seen in patients with mild hypothermia. Simultaneous monitoring of brain and rectal temperature provides important diagnostic and prognostic information to guide the treatment of patients after severe head injury (SHI) and the wide differentials that can develop between the brain and core temperature, especially during rapid cooling, strongly supports the use of brain temperature measurement if therapeutic hypothermia is considered for head injury care.

Effects of scopolamine treatment on long-term behavioral deficits following concussive brain injury to the rat

Scopolamine (0.1, 1.0, or 10.0 mg/kg) or saline was systemically (i.p.) administered to rats 15 min prior to concussive fluid percussion brain injury. Animals pretreated with the 1.0 mg/kg dose exhibited significantly (P less than 0.05) less motor deficits and less body weight loss and recovered to baseline performance sooner than saline-treated rats. Mortality and associated convulsions were significantly lower in rats pretreated with the 1.0 mg/kg dose of scopolamine. A 1.0 mg/kg dose of scopolamine administered (i.p.) 30 s after injury also significantly reduced behavioral deficits. No differences were observed between saline- and scopolamine-treated animals in either the incidence or duration of transient apnea following injury. A 1.0 mg/kg dose of scopolamine administered (i.p.) 15 min prior to epidural clip compression of the spinal cord had no effect on the severity of motor function deficits assessed by an inclined plane test. The data from these experiments suggest muscarinic cholinergic involvement in at least some of the long-term behavioral deficits following mild and moderate levels of brain injury. These results suggest that muscarinic cholinergic antagonists may prove beneficial in the treatment of human head injury.

MULTIPARAMETRIC CONTINUOUS MONITORING OF BRAIN METABOLISM AND SUBSTRATE DELIVERY IN NEUROSURGICAL PATIENTS

Brain function and tissue integrity are highly dependent on continuous oxygen supply and clearance of CO2. Aerobic metabolism is the major energy source to normal brain, however, during hypoxia and ischemia, lactate accumulation may sometimes be seen, indicating anaerobic glycolysis after severe head injury. Current monitoring techniques often fail to detect such events which can affect substrate delivery to the injured brain. We have recently adapted a method for continuous monitoring of brain tissue pO2, pCO2, pH and temperature, using a single sensor. The multiparameter sensor is inserted into brain tissue, via a new three lumen bolt, together with a standard ventriculostomy catheter and a microdialysis probe. The system has been left in place as long as needed, but never more than 7 days. All readings were compared to clinical parameters, and outcome. Stable measurements could be obtained in the first group of 20 patients, after calibration and rigid fixation, using the new bolt. Severely head injured patients had brain oxygen levels of less than 25-30 mmHg for the first hours after injury. Thereafter two patterns could be seen. Patients with favorable outcome had a slow increase in brain oxygen, and brain CO2 decreased to normal values, as long as the cerebral perfusion pressure (CPP) was kept above 70 mmHg. However, in those patients with secondary ischemic events, and bad outcome, a further decline in brain oxygen to anaerobic levels (< 20 mmHg) was seen. For these patients, both decreased and increased brain CO2 levels could be seen. Brain CO2 levels of 90-150 mmHg were consistently seen after brain death. Brain pH was inversely related to brain CO2 for all patients. Brain glucose and lactate in patients with poor outcome were 639 microM l-1 +/- 330, and 1642 microM l-1 +/- 788, whereas patients with good outcome had brain glucose levels of 808 microM l-1 +/- 321 and lactate levels of 1001 microM l-1 +/- 417. Extended neuromonitoring using a combined sensor for brain oxygen, CO2, pH and temperature measurements, as well as a microdialysis probe for glucose and lactate analysis may optimize the management of comatose neurosurgical patients in the future, by allowing a fuller understanding of dynamic factors affecting brain metabolism.

Glutamate Release and Cerebral Blood Flow After Severe Human Head Injury

Elevations of extracellular glutamate have been found in patients with prolonged brain ischemia and focal cerebral contusions, following severe head injury. About 30% of severely head injured patients develop cerebral ischemia, defined as CBF < 18 ml/100g/min. Patients with both global and regional cerebral ischemia have the worst outcome. However, the relationship between CBF and EAA release is not well understood in head injured humans, and may differ from the findings in normal animals. To study the relationship between EAA release and CBF after severe head injury, we performed cerebral blood flow measurements using stable xenon enhanced computed tomography and correlated these with glutamate release in the extracellular fluid, measured by continuous microdialysis, in 25 severely head injured patients. Sustained cerebral blood flow reductions below the threshold for ischemic neuronal damage was closely related to massive excitatory amino acid release, as in previous animal studies. In patients without secondary ischemia, or focal contusions, delayed post-traumatic glutamate release appeared to be only transient or did not occur at all.

Effects of anticholinergic treatment on transient behavioral suppression and physiological responses following concussive brain injury to the rat

Increasing doses (0.1, 1.0, 10.0 mg/kg) of scopolamine were systemically (i.p.) administered to rats subjected to moderate fluid percussion brain injury. Scopolamine treatment (1.0 mg/kg, i.p.) 15 min prior to trauma significantly reduced mortality and the duration of transient behavioral suppression assessed by a variety of measures. No differences were observed between saline- and scopolamine-treated animals in either the incidence or duration of transient apnea associated with injury. Preinjury treatment with methylscopolamine (1.04 mg/kg) or mecamylamine (1.0 mg/kg) had no effect on transient behavioral suppression. Except for increased heart rate, preinjury treatment with scopolamine (1.0 mg/kg) did not significantly alter systemic physiological responses to injury. Rats treated with scopolamine (1.0 mg/kg, i.p.) 30 s after injury tended to have shorter durations of reflex and response suppression. These experiments suggest that antimuscarinics can attenuate components of transient behavioral suppression associated with concussive brain injury. These findings are consistent with previous experimental and clinical observations and lend further support to the hypothesis that activation of a muscarinic system within the CNS mediates components of reversible traumatic unconsciousness following cerebral concussion.

Relationship between brain temperature, brain chemistry and oxygen delivery after severe human head injury: The effect of mild hypothermia

Abstract We studied brain temperature and the effect of mild hypothermia in 58 patients after severe head injury (SHI). Brain tissue oxygen tension (ptiO2), carbon dioxide tension (ptiCO2), tissuie pH (pHti) and temperature (Tbr) were measured using a multiparameter probe. Microdialysis was performed to measure glucose, lactate, glutamate, and aspartate in the extracellular fluid. Mild hypothermia (34° – 36°C) was employed in 33 selected patients who had persistent increased intracranial pressure (ICP > 20 mmHg). Mild induced hypothermia decreased brain oxygen significantly from 33 ± 24 mmHg to 30 ± 22 mmHg (p < 0.05). The ptiCO2 (46 ± 8 mmHg) was also significantly lower during mild hypothermia (40.4 ± 4.0 mmHg), p < 0.0001). The pH i increased from 7.13 ± 0.15 to 7.24 ± 0.10 (p < 0.0001) under hypothermic conditions. Induced hypothermia may protect patients from secondary ischemic events by lowering the critical ptiO2 threshold, reducing anaerobic metabolism, and decreasing the release of excitatory aminoacids. However, patients with spontaneous brain hypothermia on admission (Tbr < 36.0°C) showed significantly higher levels of glutamate as well as lactate, compared to all other patients, and had a worse outcome. Spontaneous brain hypothermia carries a poor prognosis, and was characterized by markedly abnormal brain metabolic indices. [Neurol Res 2002; 24: 161-168]

Treatment of recurrent malignant glioma by repeated intracerebral injections of human recombinant interleukin-2 alone or in combination with systemic interferon-α. Results of a phase I clinical trial

SummaryNine patients with a recurrent malignant glioma were treated with repeated intracavitary or intracerebroventricular injections of human recombinant interleukin-2 (rIL-2) alone or in combination with systemic interferon-α (IFN-α). Five patients received only rIL-2 and four were treated with rIL-2 plus subcutaneous injections of IFN-α. Therapy was administered on a Monday, Wednesday, Friday schedule for up to 10 weeks, beginning with a dose of 10,000 IU rIL-2/injection. Doses were escalated every two weeks until some toxicity was apparent. The maximum amount of rIL-2 any one patient in this group received was 580,000 IU. Patients on combination immunotherapy were held at an rIL-2 dosage of 10,000 IU while IFN-α, which began at 3 million IU, was escalated every other week up to 18 million IU/dose. They were then held at that IFN-α dosage and rIL-2 was increased to 50,000 IU. The total amount of rIL-2 and IFN-α any one in this group received was 510,000IU and 417 million IU, respectively. Repeated injections of 10,000 IU rIL-2 were well-tolerated by all nine patients and no change in their functional status was seen. At doses at 50,000 IU. rIL-2, increased edema around the tumor cavity was observed by MRI/CT scand in 3/5 patients and clinical side-effects in the form of somnolence and headache along with some morbidity specifically associated with tumor location were also seen. Patients receiving rIL-2 + IFN-α showed progressive fatigue, muscle weakness, and occasionally nausea. Two of these patients showed increased peritumoral edema on MRI/CT scan. Neither hematological abnormalities nor changes from baseline values were seen in blood samples from any of the patients. MRI/CT scans made at the conclusion of immunotherapy indicated tumor progression in two of the patients treated with rIL-2 alone while no tumor growth at the site of treatment occurred in the other two or in the four treated with the combination of rIL-2 and IFN-α. Further clinical testing of rIL-2 in combination with IFN-α is indicated.

The development of MDA-7/IL-24 as a cancer therapeutic.

The cytokine melanoma differentiation associated gene 7 (mda-7) was identified by subtractive hybridization as a protein whose expression increased during the induction of terminal differentiation, and that was either not expressed or was present at low levels in tumor cells compared to non-transformed cells. Based on conserved structure, chromosomal location and cytokine-like properties, MDA-7, was classified as a member of the interleukin (IL)-10 gene family and designated as MDA-7/IL-24. Multiple studies have demonstrated that expression of MDA-7/IL-24 in a wide variety of tumor cell types, but not in corresponding equivalent non-transformed cells, causes their growth arrest and rapid cell death. In addition, MDA-7/IL-24 has been noted to radiosensitize tumor cells which in part is due to the generation of reactive oxygen species (ROS) and ceramide that cause endoplasmic reticulum stress and suppress protein translation. Phase I clinical trial data has shown that a recombinant adenovirus expressing MDA-7/IL-24 (Ad.mda-7 (INGN-241)) was safe and had measurable tumoricidal effects in over 40% of patients, strongly arguing that MDA-7/IL-24 could have significant therapeutic value. This review describes what is presently known about the impact of MDA-7/IL-24 on tumor cell biology and its potential therapeutic applications.