Effects of low intensity vibration on bone and muscle in rats with spinal cord injury.

UNLABELLED: Spinal cord injury (SCI) causes rapid and marked bone loss. The present study demonstrates that low-intensity vibration (LIV) improves selected biomarkers of bone turnover and gene expression and reduces osteoclastogenesis, suggesting that LIV may be expected to benefit to bone mass, resorption, and formation after SCI. INTRODUCTION: Sublesional bone is rapidly and extensively lost following spinal cord injury (SCI). Low-intensity vibration (LIV) has been suggested to reduce loss of bone in children with disabilities and osteoporotic women, but its efficacy in SCI-related bone loss has not been tested. The purpose of this study was to characterize effects of LIV on bone and bone cells in an animal model of SCI. METHODS: The effects of LIV initiated 28 days after SCI and provided for 15 min twice daily 5 days each week for 35 days were examined in female rats with moderate severity contusion injury of the mid-thoracic spinal cord. RESULTS: Bone mineral density (BMD) of the distal femur and proximal tibia declined by 5 % and was not altered by LIV. Serum osteocalcin was reduced after SCI by 20 % and was increased by LIV to a level similar to that of control animals. The osteoclastogenic potential of bone marrow precursors was increased after SCI by twofold and associated with 30 % elevation in serum CTX. LIV reduced the osteoclastogenic potential of marrow precursors by 70 % but did not alter serum CTX. LIV completely reversed the twofold elevation in messenger RNA (mRNA) levels for SOST and the 40 % reduction in Runx2 mRNA in bone marrow stromal cells resulting from SCI. CONCLUSION: The findings demonstrate an ability of LIV to improve selected biomarkers of bone turnover and gene expression and to reduce osteoclastogenesis. The study indicates a possibility that LIV initiated earlier after SCI and/or continued for a longer duration would increase bone mass.

Posttraumatic hypothermia is neuroprotective in a model of traumatic brain injury complicated by a secondary hypoxic insult.

OBJECTIVE: Human traumatic brain injury frequently results in secondary complications, including hypoxia. In previous studies, we have reported that posttraumatic hypothermia is neuroprotective and that secondary hypoxia exacerbates histopathologic outcome after fluid-percussion brain injury. The purpose of this study was to assess the therapeutic effects of mild (33 degrees C) hypothermia after fluid-percussion injury combined with secondary hypoxia. In addition, the importance of the rewarming period on histopathologic outcome was investigated. DESIGN: Prospective experimental study in rats. SETTING: Experimental laboratory in a university teaching hospital. INTERVENTION: Intubated, anesthetized rats underwent normothermic parasagittal fluid-percussion brain injury (1.8-2.1 atmospheres) followed by either 30 mins of normoxia (n = 6) or hypoxic (n = 6) gas levels and by 4 hrs of normothermia (37 degrees C). In hypothermic rats, brain temperature was reduced immediately after the 30-min hypoxic insult and maintained for 4 hrs. After hypothermia, brain temperature was either rapidly (n = 6) or slowly (n = 5) increased to normothermic levels. Rats were killed 3 days after traumatic brain injury, and contusion volumes were quantitatively assessed. MEASUREMENTS AND MAIN RESULTS: As previously shown, posttraumatic hypoxia significantly increased contusion volume compared with traumatic brain injury-normoxic animals (p <.02). Importantly, although posttraumatic hypothermia followed by rapid rewarming (15 mins) failed to decrease contusion volume, those animals undergoing a slow rewarming period (120 mins) demonstrated significantly (p <.03) reduced contusion volumes, compared with hypoxic normothermic rats. CONCLUSIONS: These data emphasize the beneficial effects of posttraumatic hypothermia in a traumatic brain injury model complicated by secondary hypoxia and stress the importance of the rewarming period in this therapeutic intervention.

Neuropathological protection after traumatic brain injury in intact female rats versus males or ovariectomized females.

An important consideration in traumatic brain injury (TBI) in females is the influence of hormones on recovery. Recent studies in both cerebral ischemia and TBI have demonstrated an attenuation in both damage and neurologic recovery following hormonal treatment. However, the ability of endogenous hormone levels to provide neuropathological protection after fluid percussion (FP) brain injury has not been studied. The purpose of this experiment was to determine whether endogenous circulating hormones in the female rat could provide neuroprotection compared to males and ovariectomized female animals. Sixty-four Sprague-Dawley rats underwent a moderate (1.7-2.2 atm) right parasagittal FP injury. Intact females (i.e., nonovariectomized) were subjected to injury either during the proestrous (TBI-FP, n = 18) phase of their cycle or nonproestrous (TBI-FNP, n = 19) phase. A separate group of females were ovariectomized (TBI-OVX, n = 10) 10 days prior to FP injury in order to reduce hormone levels. Male animals were also traumatized (TBI-M, n = 17). Appropriate sham controls (Sham-FP, n = 2; Sham-FNP, n = 2; Sham-OVX, n = 2; Sham-M, n = 2) also underwent all aspects of surgery except for the actual FP injury. All groups were sacrificed 3 days following TBI for analysis. Both intact female groups had significantly (p < 0.05) smaller cortical contusions compared to male animals. In addition to this finding, the TBI-FNP group was significantly (p < 0.04) different from the ovariectomized female animals. Ovariectomized rats had larger areas of damage compared to intact females. The TBI-OVX group's cortical contusion volume was similar to male animals. These results provide evidence for endogenous hormonal histopathological protection following parasagittal FP brain injury. The use of hormone therapy after TBI warrants continued exploration.

Delayed hemorrhagic hypotension exacerbates the hemodynamic and histopathologic consequences of traumatic brain injury in rats.

Alterations in cerebral autoregulation and cerebrovascular reactivity after traumatic brain injury (TBI) may increase the susceptibility of the brain to secondary insults, including arterial hypotension. The purpose of this study was to evaluate the consequences of mild hemorrhagic hypotension on hemodynamic and histopathologic outcome after TBI. Intubated, anesthetized male rats were subjected to moderate (1.94 to 2.18 atm) parasagittal fluid-percussion (FP) brain injury. After TBI, animals were exposed to either normotension (group 1: TBI alone, n = 6) or hypotension (group 2: TBI + hypotension, n = 6). Moderate hypotension (60 mm Hg/30 min) was induced 5 minutes after TBI or sham procedures by hemorrhage. Sham-operated controls (group 3, n = 7) underwent an induced hypotensive period, whereas normotensive controls (group 4, n = 4) did not. For measuring regional cerebral blood flow (rCBF), radiolabeled microspheres were injected before, 20 minutes after, and 60 minutes after TBI (n = 23). For quantitative histopathologic evaluation, separate groups of animals were perfusion-fixed 3 days after TBI (n = 22). At 20 minutes after TBI, rCBF was bilaterally reduced by 57% +/- 6% and 48% +/- 11% in cortical and subcortical brain regions, respectively, under normotensive conditions. Compared with normotensive TBI rats, hemodynamic depression was significantly greater with induced hypotension in the histopathologically vulnerable (P1) posterior parietal cortex (P < 0.01). Secondary hypotension also increased contusion area at specific bregma levels compared with normotensive TBI rats (P < 0.05), as well as overall contusion volume (0.96 +/- 0.46 mm(3) vs. 2.02 +/- 0.51 mm(3), mean +/- SD, P < 0.05). These findings demonstrate that mild hemorrhagic hypotension after FP injury worsens local histopathologic outcome, possibly through vascular mechanisms.

Chronic metabolic sequelae of traumatic brain injury: prolonged suppression of somatosensory activation.

Injuries to the brain acutely disrupt normal metabolic function and may deactivate functional circuits. It is unknown whether these metabolic abnormalities improve over time. We used 2-deoxyglucose (2-DG) autoradiographic image-averaging to assess local cerebral glucose utilization (lCMR(Glc)) of the rat brain 2 mo after moderate (1.7-2.1 atm) fluid-percussion traumatic brain injury (FPI). Four animal groups (n = 5 each) were studied: sham-injured rats with and without stimulation of the vibrissae-barrel field ipsilateral to injury; and animals with prior FPI, with or without this stimulation. In sham-injured rats, resting lCMR(Glc) was normal, and vibrissae stimulation produced right-sided metabolic activation of the ventrolateral thalamic and somatosensory-cortical projection areas. In rats with prior injury, lCMR(Glc) contralateral to injury was normal, but lCMR(Glc) of the ipsilateral forebrain was depressed by approximately 38-45% compared with shams. Whisker stimulation in rats with prior trauma failed to induce metabolic activation of either cortex or thalamus. Image-mapping of histological material obtained in the same injury model was undertaken to assess the possible influence of injury-induced regional brain atrophy on computed lCMR(Glc); an effect was found only in the lateral cortex at the trauma epicenter. Our results show that, 2 mo after trauma, resting cerebral metabolic perturbations persist, and the whisker-barrel somatosensory circuit shows no signs of functional recovery.

Secondary hypoxia following moderate fluid percussion brain injury in rats exacerbates sensorimotor and cognitive deficits.

Human head trauma is frequently associated with respiratory problems resulting in secondary hypoxic insult. To document the behavioral consequences of secondary hypoxia in an established model of traumatic brain injury (TBI), intubated anesthetized animals were subjected to fluid percussion (FP) injury (1.87-2.17 atm) followed by 30 min of either normoxic (TBI-NO, n = 10) or hypoxic (TBI-HY, n = 11; pO2 = 30-40 mm Hg) gas levels. Sham animals (n = 19) underwent all manipulations except for the actual trauma. Animals were tested on various sensorimotor tasks beginning 3 days after FP injury along with cognitive testing on days 22 through 29 posttrauma. The secondary hypoxic insult exacerbated the sensorimotor deficits on beam-walking compared to those animals only receiving trauma. Cognitive impairments were also observed in the TBI-HY group in the hidden platform task compared to FP injury alone. These data indicate that a secondary hypoxic insult exacerbates both sensorimotor and cognitive deficits after TBI. This study provides direct evidence that incidences of hypoxia after brain trauma may potentially result in an increase in neurological deficits for the subpopulation of head injured patients undergoing hypoxic conditions further warranting strict monitoring of these events.

Exacerbation of cortical and hippocampal CA1 damage due to posttraumatic hypoxia following moderate fluid-percussion brain injury in rats.

OBJECT: Patients with head injuries often experience respiratory distress that results in a secondary hypoxic insult. The present experiment was designed to assess the histopathological consequences of a secondary hypoxic insult by using an established rodent model of traumatic brain injury (TBI). METHODS: Intubated anesthetized rats were subjected to moderate (1.94-2.18 atm) parasagittal fluid-percussion injury (FPI) to the brain. Following the TBI, the animals were maintained for 30 minutes by using either hypoxic (TBI-HY group, nine animals) or normoxic (TBI-NO, 10 animals) gas levels. Sham-operated animals also underwent all manipulations except for the FPI (sham-HY group, seven animals; and sham-NO group, seven animals). Three days after TBI the rats were killed, and quantitative histopathological evaluation was undertaken. Cortical contusion volumes were dramatically increased in the TBI-HY group compared with the TBI-NO group (p < 0.03). Qualitative assessment of cortical and subcortical structures demonstrated significant damage within the hippocampal areas, CA1 and CA2, of TBI-HY animals compared with the TBI-NO animals (both p < 0.03). There was also a significant increase in the frequency of damaged neuronal profiles within the middle and medial sectors of the CA1 hippocampus (p < 0.03) due to the hypoxic insult. CONCLUSIONS: The results of this study demonstrate that a secondary hypoxic insult following parasagittal FPI exacerbates contusion and neuronal pathological conditions. These findings emphasize the need to control for secondary hypoxic insults after experimental and human head injury.

Temporal and regional patterns of axonal damage following traumatic brain injury: a beta-amyloid precursor protein immunocytochemical study in rats.

Diffuse axonal injury (DAI) is an important consequence of human head trauma. This experimental investigation utilized the immunocytochemical visualization of beta-amyloid precursor protein (beta-APP) to document regional patterns of axonal injury after traumatic brain injury (TBI) and to determine the importance of injury severity on the magnitude of axonal damage. Rats underwent moderate (1.84-2.11 atm) or severe (2.38-2.52 atm) parasagittal fluid-percussion (F-P) brain injury or sham procedures. At 1, 3, 7 or 30 days after TBI, rats were perfusion-fixed and sections immunostained for the visualization of beta-APP. A regionally specific axonal response to TBI was documented after moderate F-P injury. Within the dorsolateral striatum, an early increase in beta-APP-positive axonal profiles at 24 hours (h) was followed by a significant decline at subsequent survival periods. In contrast, the frequency of reactive profiles was initially low within the thalamus, but increased significantly by day 7. Within the external capsule at the injury epicenter, numbers of immunoreactive axons increased significantly at 24 h and remained elevated throughout the subsequent survival periods. At multiple periods after TBI, selective cortical and thalamic neurons displayed increased staining of the perikarya. A significant increase in the overall frequency of beta-APP profiles was documented in the severe vs moderately injured rats at 72 h after TBI. These data indicate that parasagittal F-P brain injury (a) results in widespread axonal damage, (b) that axonal damage includes both reversible and delayed patterns, and (c) that injury severity is an important factor in determining the severity of the axonal response to TBI.

Hippocampally dependent and independent chronic spatial navigational deficits following parasagittal fluid percussion brain injury in the rat.

Previous reports have documented spatial navigational deficits following experimental traumatic brain injury (TBI), although the majority of the work to date has involved assessment at acute intervals following TBI, and has focused on tasks sensitive to hippocampal dysfunction. The present experiments were designed to investigate the chronic consequences of TBI, and the possible contribution of extrahippocampal dysfunction to TBI-induced spatial navigational deficits, in a moderate parasagittal fluid percussion TBI model. In Experiment 1, animals were pre-trained in a water maze, subjected to TBI or sham procedures, and re-evaluated in the water maze 48 h following the insult. Six to 8 weeks following TBI, the same animals were required to navigate to a different platform location. TBI animals exhibited significant deficits in retention of previously learned spatial information at the 48 h interval, and marginally impaired acquisition of a novel platform location during the chronic test sessions. In Experiment 2, animals were required to navigate to novel spatial locations using cued (to evaluate extrahippocampal function) as well as non-cued variants of the water maze task during the 8 week period following the insult. Injured animals exhibited deficits in both tasks which gradually diminished over the course of testing. The results of these experiments indicate that moderate TBI is accompanied by both retention and acquisition deficits, and that some of the navigational deficits observed in the water maze can be attributed to extrahippocampal damage. The possible recovery of spatial navigational ability following parasagittal TBI at moderate intensities is also discussed.

Chronic histopathological consequences of fluid-percussion brain injury in rats: effects of post-traumatic hypothermia.

Early outcome measures of experimental traumatic brain injury (TBI) are useful for characterizing the traumatic severity as well as for clarifying the pathomechanisms underlying patterns of neuronal vulnerability. However, it is increasingly apparent that acute outcome measures may not always be accurate predictors of chronic outcome, particularly when assessing the efficacy of potential therapeutic regimens. This study examined the chronic histopathological outcome in rats 8 weeks following fluid-percussive TBI coupled with moderate post-traumatic brain hypothermia, a protocol that provides acute neuronal protection. Animals received a moderate parasagittal percussive head injury (2.01-2.38 atm) or sham procedure followed immediately by 3 h of brain hypothermia (30 degrees C) or normothermia (37 degrees C). Eight weeks following TBI, serial tissue sections were stained with hematoxylin and eosin or immunostained for glial fibrillary acidic protein. Tissue damage, gliosis and immunoreactive astrocytes were observed in the ipsilateral thalamus, hippocampus, and in the neocortex lateral to the injury site. Within the thalamus, focal necrosis was restricted to selective thalamic nuclei. Significant hippocampal cell loss was found in the ipsilateral dentate hilar region of both TBI groups. Quantitative volume measurements revealed significant decreases in cortical, thalamic and hippocampal volume ipsilateral to the impact in both TBI groups. Lateral ventricles were substantially enlarged in the TBI-normothermia group, an effect which was significantly attenuated by post-TBI hypothermia. The attenuation of lateral ventricular dilation by post-traumatic hypothermia is indicative of chronic neuroprotection in this TBI model. These data provide new information concerning the chronic histopathological consequence of experimental TBI and the relevance of this trauma model to chronic human head injury.

Posttraumatic brain hypothermia provides protection from sensorimotor and cognitive behavioral deficits.

The purpose of this study was to determine the degree of sensorimotor and cognitive protection conferred by posttraumatic brain hypothermia. Baseline measurements were taken on sensorimotor tasks involving forelimb placing and beam-walking, as well as on a spatial navigational task utilizing the water maze. Twenty-four hours after the last baseline measurements, normothermic (37 degrees C) animals were subjected to a fluid percussion pulse (1.9-2.4 atm) over the right parietal sensorimotor cortex. Following trauma, brain temperature was maintained for 3 h at either normothermic (37 degrees C, group TBI-N, n = 12) or hypothermic levels (30 degrees C, group TBI-H, n = 11). Shams (n = 10) underwent all surgical procedures including posttraumatic brain injury (TBI) temperature manipulation, but were not subjected to the fluid percussive pulse. Beam-walking and forelimb placing measures were begun 24 h post-TBI and continued for 2 weeks. Animals were tested on the water maze task for 2 days beginning 24 h post-TBI. TBI produced substantial deficits in contralateral limb placing, which recovered over approximately one week. Hypothermia provided partial protection from these deficits, with TBI-H animals exhibiting intermediate scores that differed from both sham and TBI-N animals (p < 0.03). In the water maze, there was a distinction between groups in the ability to navigate 48 h after TBI. TBI-N animals performed significantly worse than sham and TBI-H animals (both p < 0.01), whereas there was no significant difference between the scores of sham and TBI-H animals. The present data demonstrate that moderate postinjury brain hypothermia can provide protection from sensorimotor and cognitive behavioral deficits as well as neuropathology in a model of traumatic brain injury associated with early neuronal and microvascular injury.