Fredrik Boris-Möller

Long-lasting Neuroprotective Effect of Postischemic Hypothermia and Treatment With an Anti-inflammatory/Antipyretic Drug Evidence for Chronic Encephalopathic Processes Following Ischemia

BACKGROUND AND PURPOSE It has been recognized that postischemic pharmacological interventions may delay the evolution of neuronal damage rather than provide long-lasting neuroprotection. Also, fever complicates recovery after stroke in humans. Here we report the effects of late postischemic treatment with hypothermia and an antipyretic/anti-inflammatory drug, dipyrone, on cell damage at 1 week and 2 months of survival. METHODS Rats were subjected to 10 minutes of forebrain ischemia. Hypothermia (33 degrees C) was induced at 2 hours of recovery and maintained for 7 hours. Dipyrone (100 mg.kg-1IP) was given every 3 hours from 14 to 72 hours of recovery. Temperature was measured every 6 hours for 60 days. Neuronal damage was assessed at 7 days and 2 months of recovery. RESULTS From 17 to 72 hours of recovery, a period of hyperthermia was observed, which dipyrone abolished but postischemic hypothermia treatment did not. Dipyrone treatment diminished neuronal damage by 43% at 7 days, and at 2 months of survival, a minor (16%) protection was seen. Postischemic hypothermia treatment alone delayed neuronal damage. In contrast, combined treatment of hypothermia followed by dipyrone markedly diminished neuronal damage by more than 50% at both 7 days and 2 months of recovery. CONCLUSIONS Neuronal degeneration may be ongoing for months after a transient ischemic insult, and prolonged protective measures need to be instituted for long-lasting neuroprotective effects. Hyperthermia during recovery worsens ischemic damage, and processes associated with inflammation may contribute to the development of neuronal damage. An early and extended period of postischemic hypothermia provides a powerful and long-lasting protection if followed by treatment with anti-inflammatory/ antipyretic drug.

Hypothermia Prevents the Ischemia‐Induced Translocation and Inhibition of Protein Kinase C in the Rat Striatum

: The effect of hypothermia on the ischemia‐induced changes in the subcellular distribution of protein kinase C (PKC)(γ), ‐(βII), and ‐(α) and the activity of PKC was studied in striatal homogenates of rats subjected to 20 min of cerebral ischemia. The effect of post‐ischemic cooling was also studied. During normothermic ischemia, PKC(γ) and ‐(βII) increased 3.9‐and 2.9‐fold, respectively, in the particulate fraction, signifying a translocation of PKC to cell membranes. The levels of PKC(α) did not change significantly. PKC activity decreased during ischemia by 52% and 47% (p < 0.05) in the paniculate and cytosolic fractions, respectively, and remained inhibited for the 1 h recovery period. In hypothermic animals, there was no evidence of translocation, and the inhibition of PKC activity was completely abolished. Hypothermia induced in the recovery phase, however, did not affect PKC distribution or activity. The protective effect of intraischemic hypothermia may in part be due to the prevention of the ischemia‐induced translocation and subsequent downregulation of PKC, possibly through a temperature‐dependent modification of the cell membranes.

Intracerebral Microdialysis of Glutamate and Aspartate Two Vascular Territories after Aneurysmal Subarachnoid Hemorrhage

Cerebral ischemia associated with subarachnoid hemorrhage may have severe consequences for neuronal functioning. The excitatory amino acid neurotransmitters glutamate and aspartate have been shown to be of particular importance for ischemia and ischemic neuronal damage. For seven patients who underwent early surgery for ruptured intracranial aneurysms, intracerebral microdialysis of glutamate and aspartate was performed to monitor local metabolic changes in the medial temporal (all seven patients) and subfrontal cortex (Patients 4 through 7). Samples were collected every 30 or 60 minutes, using an autosampler. The results show that extracellular glutamate and aspartate concentrations can rise to very high levels after surgery for subarachnoid hemorrhage and aneurysm. These increased levels of excitatory amino acids correlated well with the clinical course and neurological symptoms of the patients. Simultaneous sampling from two vascular territories (middle cerebral artery and anterior cerebral artery) also showed that a rise in extracellular glutamate and aspartate in one territory is not necessarily parallel with a rise in the other. The application of the microdialysis technique with an on-line assay system might be of value in the future for continuous monitoring of ischemic events to optimize treatment with, for example, blockers of glutamatergic neurotransmission.

Preservation of brain temperature during ischemia in rats.

Our objectives were to study the loss of heat from ischemic brain and to devise a method of maintaining brain temperature. Reversible forebrain ischemia was induced by carotid clamping and exsanguination in 30 anesthetized and artificially ventilated rats. Rectal, skull, and brain temperatures were measured, confirming previous findings that brain temperature falls by 4-5 degrees C during 15 minutes of ischemia unless measures are taken to maintain head temperature by external heating. Temperature gradients developed within the ischemic brain, superficial tissues being cooler than deep ones. These temperature gradients were reversed when skull temperature was maintained at core body (rectal) temperature by external heating. With rectal and skull temperatures maintained at 38 degrees, 37 degrees, 35 degrees, or 33 degrees C, brain temperatures nonetheless decreased by approximately 1 degree C during ischemia. This decrease in brain temperature could be prevented by placing the rat in a Plexiglas box with circulating air at temperatures close to that of the body core and a relative humidity of approximately 100%. We also found that, unless special precautions are taken, a temperature gradient develops between the brain and body core during recirculation.

Diminished neuronal damage in the rat brain by late treatment with the antipyretic drug dipyrone or cooling following cerebral ischemia

Abstract It has been shown that changes in body core temperature several hours after a transient ischemic insult affect neuronal survival. We report that body core temperature in normal rats fluctuates over a 24-h period, while in rats subjected to 10 min transient ischemia induced by occlusion of the common carotid arteries in combination with hypotension, body temperature persistently increases to above 38.5° C from 21 to 63 h following recirculation. The antipyretic drug dipyrone administered from 12 to 72 h recovery depresses body temperature to normothermic values and markedly diminishes neuronal damage in the neocortex and hippocampus when evaluated at 7 days of survival. Cooling the animals down to normothermic levels provided similar protection to that obtained with dipyrone treatment. These results suggest that hyperthermia occurring late during reperfusion aggravates delayed neuronal damage and can be effectively prevented by antipyretic drugs. The data imply that: (1) temperature-dependent processes occurring late during recovery are involved in delayed neuronal death, (2) inflammation may be an important factor in delayed neuronal death, (3) prostanoids and interleukins may contribute to this process (4) postischemic prolonged (days) temperature control is required for proper evaluation of drug therapy in brain ischemia models, and (5) fever in patients suffering brain ischemia should be impeded.

The effect of hypothermia on the expression of neurotrophin mRNA in the hippocampus following transient cerebral ischemia in the rat

The expression of the mRNAs of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT3) and the neurotrophin receptor, TrkB, was studied in the rat hippocampus by in situ hybridization following normothermic (37 degreesC) and protective hypothermic (33 degreesC) transient cerebral ischemia of 15 min duration. In the resistant dentate gyrus, normothermic ischemia transiently induced NGF mRNA at around 8 h of recovery, while the NT3 mRNA levels were depressed over at least a 24-h recovery period. The levels of BDNF and TrkB were transiently and markedly elevated with a maximal expression at 24 h of recovery. Intraischemic hypothermia reduced the induction of NGF mRNA, while the increase of BDNF mRNA expression occurred earlier during recovery, and the post-ischemic NT3 mRNA depression was not affected. Also, the expression of TrkB mRNA was enhanced, and occurred concomitantly with the elevation of BDNF mRNA. In contrast, there were no changes in neurotrophin and TrkB mRNA in the CA3 and CA1 regions. The expression of BDNF mRNA at 24 h after normothermic ischemia, was attenuated by intraischemic hypothermia. We conclude that, the expressions of NGF, BDNF, NT3 or TrkB mRNA in ischemia-sensitive hippocampal subregions are not increased by protective hypothermia. In contrast, hypothermia induces neurotrophin mRNA alterations in the ischemia-resistant dentate gyrus that may convey protection to sensitive regions.

Increased Levels of Glutamate in Patients with Subarachnoid Haemorrhage as Measured by Intracerebral Microdialysis

Cerebral ischemia associated with subarachnoid haemorrhage (SAH) may have severe consequences for neuronal function leading to reversible or permanent neurological deficits. The excitatory amino acid neurotransmitters, such as glutamate, have been shown to be of particular importance for ischemic neuronal damage. In seven patients who underwent early surgery for a ruptured intracranial aneurysm, microdialysis of glutamate was performed in order to monitor local metabolic changes in the medial temporal tall patients) and subfrontal cortex (four patients). The preliminary results indicate that: (i) extracellular glutamate concentrations may rise to very high levels after SAH and aneurysm surgery, (ii) the increased levels of excitatory amino acids correlate with the clinical course, and (iii) a rise in extracellular glutamate in one region is not necessarily paralleled with a rise in the other, as seen by the simultaneous sampling from two different vascular territories.

Changes in the extracellular levels of glutamate and aspartate during ischemia and hypoglycemia : effects of hypothermia

Abstract Hypothermia (33° C) dramatically diminishes ischemic but not hypoglycemic brain damage. The beneficial effects of hypothermia in ischemia have been partly attributed to a reduction in the ischemia-induced increase in synaptic levels of glutamate or aspartate. With the microdialysis technique, we studied the effects of hypothermia (33° C) on the brain extracellular levels of glutamate and aspartate during hypoglycemia, ischemia, and their combination. In isoelectric hypoglycemia, striatal levels of glutamate and aspartate frequently show large transients of transmitter release occurring during both normothermia and hypothermia, whereas in the cortex levels of glutamate and aspartate are slightly lower during hypothermia compared with normothermia. In both regions studied, complete ischemia induced by i.v. KCl results in a progressive increase in glutamate and aspartate levels over time. In normoglycemic animals, hypothermia markedly attenuates the increase in glutamate and aspartate levels in the striatum but not in the cortex. Also in hypoglycemic animals, complete ischemia causes a progressive increase in the glutamate and aspartate levels. However, hypothermia affects only striatal glutamate levels. Since hypothermia protects both cortex and striatum against ischemic brain injury and not against hypoglycemic injury, presumably the protective effect of hypothermia is due to factors other than prevention of glutamate or aspartate overflow.

A New Method of Selective, Rapid Cooling of the Brain: An Experimental Study.

PurposeTo determine whether retrograde perfusion of cooled blood into one internal jugular vein (IJV) in the pig can selectively reduce the brain temperature without affecting the core body temperature (CBT).MethodsIn 7 domestic pigs, the left IJV was catheterized on one side and a catheter placed with the tip immediately below the rete mirabile. Thermistors were placed in both brain hemispheres and the brain temperature continuously registered. Thermistors placed in the rectum registered the CBT. From a catheter in the right femoral vein blood was aspirated with the aid of a roller pump, passed through a cooling device, and infused into the catheter in the left IJV at an initial rate of 200 ml/min.ResultsImmediately after the start of the infusion of cooled blood (13.8°C) into the IJV, the right brain temperature started to drop from its initial 37.9°C and reached 32°C within 5 min. By increasing the temperature of the perfusate a further drop in the brain temperature was avoided and the brain temperature could be kept around 32°C during the experiment. In 4 of the animals a heating blanket was sufficient to compensate for the slight drop in CBT during the cooling period.ConclusionsWe conclude that brain temperature can be reduced in the pig by retrograde perfusion of the internal jugular vein with cooled blood and that the core body temperature can be maintained with the aid of a heating blanket.

Extracellular pH in the Rat Brain during Hypoglycemic Coma and Recovery

It has previously been shown that hypoglycemic coma is accompanied by marked energy failure and by loss of cellular ionic homeostasis. The general proposal is that shortage of carbohydrate substrate prevents lactic acid formation and thereby acidosis during hypoglycemic coma. The objective of the present study was to explore whether rapid downhill ion fluxes, known to occur during coma, are accompanied by changes in extra-and/or intracellular pH (pHe and/or pHi), and how these relate to the de- and repolarization of cellular membranes. Cortical pHe was recorded by microelectrodes in insulin-injected rats subjected to 30 min of hypoglycemic coma, with cellular membrane depolarization. Some rats were allowed up to 180 min of recovery after glucose infusion and membrane repolarization. Arterial blood gases and physiological parameters were monitored to maintain normotension, normoxia, normocapnia, and normal plasma pH. Following depolarization during hypoglycemia, a prompt, rapidly reversible alkaline pHe shift of about 0.1 units was observed in 37/43 rats. Immediately thereafter, all rats showed an acid pH shift of about 0.2 units. This shift developed during the first minute, and pHe remained at that level until repolarization was induced. Following repolarization, there was an additional, rapid, further lowering of pHe by about 0.05 units, followed by a more prolonged decrease in pHe that was maximal at 90 min of recovery (ΔpHe of approximately −0.4 units). The pHe then slowly normalized but was still decreased (−0.18 pH units) after 180 min when the experiment was terminated. The calculated pHi showed no major alterations during hypoglycemic coma or after membrane repolarization following glucose administration. The results demonstrate that hypoglycemic coma is accompanied by a decrease in pHe of almost the same magnitude as observed in status epilepticus, and that a lingering extracellular acidosis is observed during recovery from hypoglycemia. It is proposed that, at least in part, the initial extracellular alkaline/acid shift is caused by H+ influx or HCO3− outflux (alkaline shift) followed by H+ efflux or HCO3− influx (acid shift) through conductance channels that are opened during depolarization. The alkaline shift appears before the depolarization has occurred and the acid shift after the depolarization, when mainly the chemical gradient provides the driving force. It is speculated that Na+/H+ exchange contributes to the further extracellular acidification seen during repolarization.