Ketamine Decreases Cerebral Infarct Volume and Improves Neurological Outcome Following Experimental Head Trauma in Rats

Abstract

In brain injury, concentrations of extracellular excitatory amino acids are increased and stimulate glutamate receptors in general and the N-methyl-D-aspartate (NMDA)-preferring subtype in particular. That stimulation causes substantial calcium influx, which appears to initiate a cascade of events leading to neuronal death. Blockage of NMDA receptors with specific antagonists or noncompetitive ion channel blockers provides protection against excitatory amino acid-induced neurotoxicity. We previously reported that the NMDA receptor antagonist dizocilpine maleate improved the neurological severity score (NSS) after head trauma in rats. The present study was designed to determine whether ketamine, a NMDA receptor antagonist like dizocilpine maleate, improves neurological outcome following head trauma in rats. Thirty-two male Sprague-Dawley rats (235-250 g) were divided into four groups. Groups A and B were surgically prepared only. Groups C and D were surgically prepared and then a nonpenetrating impact was delivered to the cranium over the left hemisphere. Groups A and C received no treatment. Groups B and D were treated with ketamine, 180 mg/kg i.p., 1 h after head trauma. The NSS was determined at 1, 2, 4, 10, 24, and 48 h following head trauma. After killing at 48 h, cortical slices were taken adjacent to the lesion on the traumatized hemisphere and from comparable sites on the nontraumatized hemisphere to measure the tissue specific gravity and water content. Brains were then placed in 4% formaldehyde and the volume of hemorrhagic necrosis measured 4 days later. Head trauma increased the NSS and, in the traumatized hemisphere, decreased the specific gravity, increased the water content, and caused cerebral infarction. With ketamine, the NSS at 24 and 48 h following head trauma was 7.4 +/- 2.6 and 6.7 +/- 2.6 (mean +/- SEM), respectively, significantly improved compared to the NSS in the untreated group of 12.6 +/- 2.6 and 11.3 +/- 2.6, respectively (p <0.02, Mann-Whitney U test). With ketamine, the volume of hemorrhagic necrosis was 88.0 +/- 23.1 mm, significantly less than that in the untreated group (147.4 +/- 22.4 mm; p <0.05, unpaired t test). The brain tissue specific gravity and water content at 48 h and the rectal temperature at 4 and 48 h after head trauma were not significantly different between treated and untreated groups. It is concluded that in this model of closed cranial impact, ketamine improves neurological outcome and decreases the volume of hemorrhagic necrosis without altering brain edema.