licostinel and Hematoma--Subdural

Acute subdural hematoma (SDH) complicates 20% of severe human head injuries and causes death or severe disability in 60% of these cases, due to brain swelling and high intracranial pressure. Although the mechanisms for these phenomena are unknown, previous studies have implicated excitatory amino acid-mediated mechanisms in both humans and animal models. The authors therefore performed in vivo autoradiography using 125I-MK-801, a high-affinity noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, as a tracer to evaluate NMDA ion channel activation spatially and temporally as a factor causing cytotoxic swelling. Acute SDH was induced in 16 anesthetized rats using 0.4 ml autologous venous blood. Fifty microcuries of 125I-MK-801 was injected via an aortic arch cannula 30 minutes after onset of SDH. The effect of a new putatively neuroprotective drug, ACEA-1021, a glycine-specific binding site NMDA antagonist, on 125I-MK-801 binding was tested on five animals "Nonspecific" 125I-MK-801 binding in the rat brain was assessed by pretreatment with "cold" (nonradiolabeled) MK-801 in five more animals. Four hours later the animals were sacrificed and brain sections were apposed to radiation-detecting high-sensitivity photographic film with precalibrated plastic standards for 4 weeks. A striking and highly significant 1.7- to 4.8-fold increase in 125I-MK-801 binding was seen in the penumbra of viable tissue surrounding the ischemic zone beneath the acute SDH, when compared to contralateral hemisphere binding (p < 0.001). The MK-801 pretreatment markedly reduced 125I-MK-801 uptake in this penumbral zone (4.73 +/- 0.36 nCi/mg control vs. 2.85 +/- 0.08 nCi/mg cold MK-801; p < 0.0001), indicating that the increased binding in the penumbra of the lesion was due to NMDA ion channel activation. Pretreatment with ACEA-1021 reduced 125I-MK-801 uptake by 28% (3.41 +/- 0.26 nCi/mg vs. 4.73 +/- 0.36 nCi/mg; p < 0.05), indicating that this agent prevents opening of the NMDA ion channel and, thus, exposure of its receptor for MK-801 binding. These studies show intense foci of penumbral NMDA receptor-mediated ion channel activation after onset of SDH, which is markedly reduced by an NMDA antagonist. Such agents are thus likely to reduce cell swelling after SDH occurs.

Topics: Animals; Autoradiography; Brain; Disease Models, Animal; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Hematoma, Subdural; Humans; Male; Quinoxalines; Rats; Rats, Sprague-Dawley

Acute subdural hematoma (SDH) complicates about 20% of severely head-injured patients, and death and severe disability frequently result, yet over half of these patients may have been conscious, at some time after injury, implying secondary mechanisms of brain damage. Drugs that block the "excitotoxic" effects of glutamate at the N-methyl-D-aspartate (NMDA) receptor have generally been effective in reducing ischemic brain damage associated with SDH in animal models, yet these agents all appear to be associated with major behavioral side effects, in conscious patients, at neuroprotective doses. We therefore evaluated the effects of treatment with a novel antagonist for the glycine binding site of the NMDA receptor (ACEA1021) upon ischemic brain damage, in the rat SDH model. ACEA1021 may be free of psychomotor effects, and may thus permit high dose therapy in conscious trauma and stroke patients. SDH was produced by the slow injection of 0.4 mL autologous blood into the subdural space overlying the parietal cortex. brain damage was assessed histologically at 8 coronal planes, in animals sacrificed 4 h after induction of hematoma. Both pre- and posttreatment with ACEA1021 significantly reduced hemispheric ischemic damage produced by SDH. The magnitude of neuroprotection with this compound (26 to 39% reduction in infarct size) is similar to other NMDA antagonists, and the robust posttreatment effect implies that human studies with this compound should be performed in head injured patients, subject to completion of toxicology testing.

Topics: Animals; Binding, Competitive; Blood Pressure; Brain Ischemia; Excitatory Amino Acid Antagonists; Glycine; Hematoma, Subdural; Humans; Male; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Time Factors