Robert J. Hamm

Marked Protection by Moderate Hypothermia after Experimental Traumatic Brain Injury

These experiments examined the effects of moderate hypothermia on mortality and neurological deficits observed after experimental traumatic brain injury (TBI) in the rat. Brain temperature was measured continuously in all experiments by intraparenchymal probes. Brain cooling was induced by partial immersion (skin protected by a plastic barrier) in a water bath (0°C) under general anesthesia (1.5% halothane/70% nitrous oxide/30% oxygen). In experiment I, we examined the effects of moderate hypothermia induced prior to injury on mortality following fluid percussion TBI. Rats were cooled to 36°C (n = 16), 33°C (n = 17), or 30°C (n = 11) prior to injury and maintained at their target temperature for 1 h after injury. There was a significant (p < 0.04) reduction in mortality by a brain temperature of 30°C. The mortality rate at 36°C was 37.5%, at 33°C was 41%, and at 30°C was 9.1%. In experiment II, we examined the effects of mod erate hypothermia or hyperthermia initiated after TBI or long-term behavioral deficits. Rats were cooled to 36°C (n = 10), 33°C (n = 10), or 30°C (n = 10) or warmed to 38°C (n = 10) or 40°C (n = 12) starting at 5 min after injury and maintained at their target temperatures for 1 h. Hypothermia-treated rats had significantly less beam-walking beam-balance, and body weight loss deficits compared to normothermic (38°C) rats. The greatest protection was observed in the 30°C hypothermia group. Since a temperature of 30°C can be induced in humans by surface cooling without coagulopathy or ventricular fibrillation, hypothermia to 30°C may have potential clinical value for treatment of human brain injury.

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.

Estrogen affects performance of ovariectomized rats in a two-choice water-escape working memory task

To determine if estrogen would protect treated rats from deficits in performance on a working memory task across time, 18 female 6-month-old Sprague-Dawley rats were trained to a criterion on a water-escape spatial delayed matching-to-sample problem. Following training, rats were ovariectomized, and nine were maintained on estrogen (polyestradiol-phosphate, 0.5 mg every 3 weeks) and nine on its vehicle for 200 days. After recovery from surgery, the rats were tested for performance every 6 weeks under three conditions: 5 min retention interval (RI); 30 min RI; and 30 min RI with an emotional experience during the RI. Analysis of correct choices revealed that estrogen-treated rats made more correct choices (p < .05) than controls on the 5 min undisturbed interval; estrogen tended to impair performance on the emotionally distracting interval. Estrogen apparently protected working memory on the undisturbed trials and might be pertinent to the maintenance of memory in female mammals.

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.

Basic fibroblast growth factor-enhanced neurogenesis contributes to cognitive recovery in rats following traumatic brain injury

Stem/progenitor cells reside throughout the adult CNS and are actively dividing in the subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampus. This neurogenic capacity of the SVZ and DG is enhanced following traumatic brain injury (TBI) suggesting that the adult brain has the inherent potential to restore populations lost to injury. This raises the possibility of developing strategies aimed at harnessing the neurogenic capacity of these regions to repair the damaged brain. One strategy is to enhance neurogenesis with mitogenic factors. As basic fibroblast growth factor (bFGF) is a potent stem cell mitogen, we set out to determine if an intraventricular administration of bFGF following TBI could affect the levels of injury-induced neurogenesis in the SVZ and DG, and the degree to which this is associated with cognitive recovery. Specifically, adult rats received a bFGF intraventricular infusion for 7 days immediately following TBI. BrdU was administered to animals daily at 2-7 days post-injury to label cell proliferation. At 1 or 4 weeks post-injury, brain sections were immunostained for BrdU and neuronal or astrocytic markers. We found that injured animals infused with bFGF exhibited significantly enhanced cell proliferation in the SVZ and the DG at 1 week post-TBI as compared to vehicle-infused animals. Moreover, following bFGF infusion, a greater number of the newly generated cells survived to 4 weeks post-injury, with the majority being neurons. Additionally, animals infused with bFGF showed significant cognitive improvement. Collectively, the current findings suggest that bFGF-enhanced neurogenesis contributes to cognitive recovery following TBI.

Cognitive impairment following traumatic brain injury: the effect of pre- and post-injury administration of scopolamine and MK-801

In order to examine the effectiveness of pre- and post-injury administration of muscarinic cholinergic and NMDA antagonists in reducing cognitive deficits following traumatic brain injury (TBI), rats were injected with either scopolamine (1 mg/kg) or MK-801 (0.3 mg/kg) 15 min prior to or 15 min after fluid percussion TBI. Cognitive performance was assessed with the Morris water maze procedure on days 11-15 after TBI or sham injury. When scopolamine and MK-801 were injected 15 min before injury, Morris water maze deficits were significantly reduced (P < 0.01 and P < 0.05, respectively). When scopolamine and MK-801 were injected 15 min after TBI, neither drug was effective in attenuating Morris water maze deficits. Consistent with other research, these results suggest that the cognitive deficits produced by TBI are the consequence of a brief period of excessive excitation of cholinergic and NMDA receptor systems. The results of this experiment also suggest that the temporal therapeutic window for the treatment of cognitive dysfunction with receptor antagonist intervention appears to be quite brief (< 15 min) in the rat.

Lactate administration attenuates cognitive deficits following traumatic brain injury.

Moderately head injured patients often suffer long term neurological sequelae. There is no therapy for brain trauma and current treatments aim only to minimize secondary damage. These secondary effects are often triggered by the inability to re-establish ionic homeostasis after injury, due to large energy demands. Recent reports have demonstrated that neurons are capable of utilizing lactate as an energy source, thus this report examines the usefulness of lactate administration in the attenuation of behavioural deficits following a moderate brain injury. Lactate infusion (i.v.) was started 30 min after lateral fluid percussion injury and continued for 3 h. Cognitive deficits were determined using the Morris water maze. Lactate infused injured animals demonstrated significantly less cognitive deficits than saline infused injured animals. Thus, lactate infusion attenuated the cognitive deficits normally observed in this model, and therefore may provide moderately head injured patients with a treatment to help ameliorate the sequelae.

The effect of age on motor and cognitive deficits after traumatic brain injury in rats

Age is one of the most important predictors of outcome after human traumatic brain injury. This study used fluid percussion brain injury to investigate the effects of aging on outcome after brain injury in rats. Three-month-old (n = 8) and 20-month-old (n = 11) rats were injured at a low level (1.7-1.8 atm) of fluid percussion brain injury or received a sham injury (n = 6 for both age groups). Body weight and motor function (beam balance and beam walking) were assessed before injury and for the first 5 days after injury. Cognitive outcome was assessed with the Morris water maze on Days 11 to 15 after injury. Injury did not produce significant weight loss in either age group. At the low level of brain injury used in this study, the 3-month-old rats did not demonstrate any significant motor deficits on the beam-balance or beam-walking tasks. However, the 20-month-old rats displayed significant beam-balance deficits on each of the 5 postinjury test days and significant beam-walking deficits for the first 3 postinjury days. Although Morris water maze performance was impaired in both age groups, the magnitude of impairment was greater in the aged animals. These data demonstrate that traumatic brain injury in the aged animal is marked by increased motor and cognitive deficits, in the absence of pronounced compromise of the animals general health.(ABSTRACT TRUNCATED AT 250 WORDS)

Postinjury administration of L-deprenyl improves cognitive function and enhances neuroplasticity after traumatic brain injury.

The rat model of combined central fluid percussion traumatic brain injury (TBI) and bilateral entorhinal cortical lesion (BEC) produces profound, persistent cognitive deficits, sequelae associated with human TBI. In contrast to percussive TBI alone, this combined injury induces maladaptive hippocampal plasticity. Recent reports suggest a potential role for dopamine in CNS plasticity after trauma. We have examined the effect of the dopamine enhancer l-deprenyl on cognitive function and neuroplasticity following TBI. Rats received fluid percussion TBI, BEC alone, or combined TBI + BEC lesion and were treated once daily for 7 days with l-deprenyl, beginning 24 h after TBI alone and 15 min after BEC or TBI + BEC. Postinjury motor assessment showed no effect of l-deprenyl treatment. Cognitive performance was assessed on days 11-15 postinjury and brains from the same cases examined for dopamine beta-hydroxylase immunoreactivity (DBH-IR) and acetylcholinesterase (AChE) histochemistry. Significant cognitive improvement relative to untreated injured cases was observed in both TBI groups following l-deprenyl treatment; however, no drug effects were seen with BEC alone. l-Deprenyl attenuated injury-induced loss in DBH-IR over CA1 and CA3 after TBI alone. However, after combined TBI + BEC, l-deprenyl was only effective in protecting CA1 DBH-IR. AChE histostaining in CA3 was significantly elevated with l-deprenyl in both injury models. After TBI + BEC, l-deprenyl also increased AChE in the dentate molecular layer relative to untreated injured cases. These results suggest that dopaminergic/noradrenergic enhancement facilitates cognitive recovery after brain injury and that noradrenergic fiber integrity is correlated with enhanced synaptic plasticity in the injured hippocampus.

Postinjury scopolamine administration in experimental traumatic brain injury

A single bolus dose of scopolamine (1.0 mg/kg) or saline (equal volume) was injected (i.p.) at 15, 30 or 60 min after fluid percussion traumatic brain injury in the rat. Scopolamine administered at 15 min postinjury significantly reduced beam walking deficits and body weight loss assessed for 5 days after injury. Scopolamine treatment at 30 or 60 min postinjury had no effect on behavioral outcome assessed for 5 days after injury. Plasma concentrations of scopolamine were measured with a radioreceptor assay. The plasma half-life for scopolamine was 21.6 min in injured rats and 17.3 min in normal rats (P less than 0.05). These results, along with evidence from previous studies, suggest that a brief period of excessive neuronal excitation can produce relatively long-lasting behavioral deficits. The temporal effectiveness of receptor antagonist intervention in this process appears to be brief.