Delayed Intervention with Intermittent Hypoxia and Task Training Improves Forelimb Function in a Rat Model of Cervical Spinal Injury.

The reduction of motor, sensory and autonomic function below the level of an incomplete spinal cord injury (SCI) has devastating consequences. One approach to restore function is to induce neural plasticity as a means of augmenting spontaneous functional recovery. Acute intermittent hypoxia (AIH-brief exposures to reduced O2 levels alternating with normal O2 levels) elicits plasticity in respiratory and nonrespiratory somatic spinal systems, including improvements in ladder walking performance in rats with incomplete SCI. Here, we determined whether delayed treatment with AIH, with or without concomitant motor training, could improve motor recovery in a rat model of incomplete cervical SCI. In a randomized, blinded, sham-controlled study, rats were exposed to AIH for 7 days beginning at 4 weeks post-SCI, after much spontaneous recovery on a horizontal ladder-crossing task had already occurred. For up to 2 months post-treatment, AIH-treated rats made fewer footslips on the ladder task compared with sham-treated rats. Importantly, concomitant ladder-specific motor training was needed to elicit AIH-induced improvements, such that AIH-treated SCI rats receiving no motor training or nontask-specific treadmill training during the treatment week did not show improvements over sham-treated rats with SCI. AIH treatment combined with task-specific training did not improve recovery on two different reach-to-grasp tasks, however, nor on tasks involving unskilled forepaw use. In brief, our results indicate that task-specific training is needed for AIH to improve ladder performance in a rat model of incomplete cervical SCI.

Experimental model considerations for the study of protein-energy malnutrition co-existing with ischemic brain injury.

Protein-energy malnutrition (PEM) affects ~16% of patients at admission for stroke. We previously modeled this in a gerbil global cerebral ischemia model and found that PEM impairs functional outcome and influences mechanisms of ischemic brain injury and recovery. Since this model is no longer reliable, we investigated the utility of the rat 2-vessel occlusion (2-VO) with hypotension model of global ischemia for further study of this clinical problem. Male, Sprague-Dawley rats were exposed to either control diet (18% protein) or PEM induced by feeding a low protein diet (2% protein) for 7d prior to either global ischemia or sham surgery. PEM did not significantly alter the hippocampal CA1 neuron death (p = 0.195 by 2-factor ANOVA) or the increase in dendritic injury caused by exposure to global ischemia. Unexpectedly, however, a strong trend was evident for PEM to decrease the consistency of hippocampal damage, as shown by an increased incidence of unilateral or no hippocampal damage (p=0.069 by chi-square analysis). Although PEM caused significant changes to baseline arterial blood pH, pO(2), pCO(2), and fasting glucose (p<0.05), none of these variables (nor hematocrit) correlated significantly with CA1 cell counts in the malnourished group exposed to 2-VO (p>0.269). Intra-ischemic tympanic temperature and blood pressure were strictly and equally controlled between ischemic groups. We conclude that co-existing PEM confounded the consistency of hippocampal injury in the 2-VO model. Although the mechanisms responsible were not identified, this model of brain ischemia should not be used for studying this co-morbidity factor.

Protein-energy malnutrition alters thermoregulatory homeostasis and the response to brain ischemia.

Co-existing protein-energy malnutrition (PEM), characterized by deficits in both protein and energy status, impairs functional outcome following global ischemia and has been associated with increased reactive gliosis. Since temperature is a key determinant of brain damage following an ischemic insult, the objective was to investigate whether alterations in post-ischemic temperature regulation contribute to PEM-induced reactive gliosis following ischemia. Male Sprague-Dawley rats (190-280 g) were assigned to either control diet (18% protein) or PEM induced by feeding a low protein diet (2% protein) for 7 days prior to either global ischemia or sham surgery. There was a rapid disruption in thermoregulatory function in rats fed the low protein diet as assessed by continuous recording of core temperature with bio-electrical sensor transmitters. Both daily temperature fluctuation and mean temperature increased within the first 24 hours, and these remained significantly elevated throughout the 7 day pre-ischemic period (p < 0.027). In the immediate post-surgical period, PEM decreased body temperature to a greater extent than that in well-nourished controls (p = 0.003). The increase in daily temperature fluctuation caused by PEM persisted throughout the 7 day post-surgical period (p < 0.001), and this interacted with the effects of global ischemia on days 8 (p = 0.018) and 11 (p = 0.021). The astrocytic and microglial responses induced at 7 days after global ischemia were not influenced by PEM, but this preliminary analysis needs to be confirmed with a more reliable global ischemia model. In conclusion, exposure to a low protein diet rapidly impairs the ability to maintain thermoregulatory homeostasis, and the resultant PEM also diminishes the ability to thermoregulate in response to a challenge. Since temperature regulation is a key determinant of brain injury following ischemia, these findings suggest that the pathophysiology of brain injury could be altered in stroke victims with coexisting PEM.

Protein-energy malnutrition alters hippocampal plasticity-associated protein expression following global ischemia in the gerbil.

Previously it has been demonstrated that protein-energy malnutrition (PEM) impairs habituation in the open field test following global ischemia. The present study examined the hypothesis that PEM exerts some of its deleterious effects on functional outcome by altering the post-ischemic expression of the plasticity-associated genes brain-derived neurotrophic factor (BDNF), its receptor tropomyosin-related kinase B (trkB), and growth-associated protein-43 (GAP-43). Male, Mongolian gerbils (11-12 wk) were randomized to either control diet (12.5% protein) or PEM (2% protein) for 4 wk, and then underwent 5 min bilateral common carotid artery occlusion or sham surgery. Tympanic temperature was maintained at 36.5 ± 0.5°C during surgery. Brains collected at 1, 3 and 7 d post-surgery were processed by in-situ hybridization or immunofluorescence. BDNF and trkB mRNA expression was increased in hippocampal CA1 neurons after ischemia at all time points and was not significantly influenced by diet. However, increased trkB protein expression after ischemia was exacerbated by PEM at 7 d in the CA1 region. Post-ischemic GAP-43 protein increased at 3 and 7 d in the CA1 region, and PEM intensified this response and extended it to the CA3 and hilar regions. PEM exerted these effects without exacerbating CA1 neuron loss caused by global ischemia. The findings suggest that PEM increases the stress response and/or hyper-excitability in the hippocampus after global ischemia. Nutritional care appears to have robust effects on plasticity mechanisms important to recovery after brain ischemia.

Can a reward-based behavioural test be used to investigate the effect of protein-energy malnutrition on hippocampal function?

Our laboratory is investigating the effects of protein-energy malnutrition (PEM) on cognitive outcome following global ischemia. Here, we investigated whether PEM independently impairs working memory in the T-maze and if the associated food reward reverses PEM. Gerbils were fed 12.5% (control diet) or 2% protein. A loss of body weight (20.1%) in the 2% protein group and decreased food intake and serum albumin concentration compared to controls (17.5% and 18.2%, respectively) indicated that PEM was achieved. Based on T-maze criterion frequently used in ischemia studies, no difference was observed in the mean (+/- SEM) number of trials required (control 5.2 +/- 0.7; PEM 4.9 +/- 0.4; p = 0.758) or the number of animals reaching criterion (control 10/12; PEM 12/12; p = 0.140). Using more stringent criterion, PEM animals required fewer trials (control 7.3 +/- 0.7; PEM 5.4 +/- 0.4; p = 0.035), and more reached criterion (control 8/12; PEM 12/12; p = 0.028). PEM may increase motivation to obtain a food reward.

The FOOD Trial Collaboration: nutritional supplementation strategies and acute stroke outcome.

Results from three large, randomized, multicenter FOOD (Feed or Ordinary Food) Collaboration Trials showed no reduction in death or poor outcome with routine oral protein-energy supplementation of stroke patients who were primarily well nourished upon admission to the hospital. Nasogastric tube feeding was favored over percutaneous endoscopic gastrostomy as the early route of feeding in dysphagic stroke patients.