J. Leigh Leasure

Spatial and temporal gene expression profiling of the contused rat spinal cord

Microarray technology was used to examine gene expression changes following contusive injury of the adult rat spinal cord. To obtain a global understanding of the changes triggered by the injury, differential gene expression was examined spatially, using tissue samples from the epicenter of injury as well as 1 cm rostral and 1 cm caudal to the epicenter, and temporally, at 3 h, 24 h, 7 days, and 35 days post-injury. To filter out gene expression changes that were due to the laminectomy, samples of contused tissue were compared to laminectomy-only controls. We took advantage of four different, complementary methods of data analysis to detect differentially expressed genes. We have identified functional groups of genes that are differentially regulated in our model, including those associated with apoptosis, cell cycle, inflammation, and cholesterol metabolism. Our analysis has led to the identification of novel potential therapeutic targets within each group of genes that is discussed.

Social isolation prevents exercise-induced proliferation of hippocampal progenitor cells in female rats

Social isolation negatively affects the behavior and health of laboratory rats. Recently, it has been found that social isolation retards exercise‐induced neurogenesis in the hippocampal dentate gyrus (DG) of male rats (Stranahan et al. ( 2006 ) Nat Neurosci 9:526–533). Since male and female rats react differently to housing changes and exercise opportunities, we investigated whether social isolation would also suppress the exercise‐dependent increase in proliferation of dentate gyrus progenitor cells in females. Accordingly, female rats were housed either alone (isolated) or in groups (social) with (exercise) or without (sedentary) the opportunity to run in an exercise wheel. Proliferating progenitor cells were labeled with bromodeoxyuridine (BrdU). As expected, exercise increased the number of BrdU+ cells in socially housed animals. However, isolation prevented this running‐induced increase. Our results expand upon previous findings by showing that the female brain is also susceptible to the suppressive effect of social isolation on exercise‐induced neurogenesis.

Exercise neuroprotection in a rat model of binge alcohol consumption.

BACKGROUND Excessive alcohol intake produces structural and functional deficits in corticolimbic pathways that are thought to underlie cognitive deficits in the alcohol use disorders (AUDs). Animal models of binge alcohol administration support the direct link of high levels of alcohol consumption and neurotoxicity in the hippocampus and surrounding cortex. In contrast, voluntary wheel running enhances hippocampal neurogenesis and generally promotes the health of neurons. METHODS We investigated whether voluntary exercise prior to binge alcohol exposure could protect against alcohol-induced cell loss. Female Long-Evans rats exercised voluntarily for 14 days before undergoing 4 days of binge alcohol consumption. Brains were harvested immediately after the last dose of alcohol and examined for various histological markers of neurodegeneration, including both cell death (FluoroJade B) and cell birth (Ki67) markers. RESULTS Rats that exercised prior to binge exposure were significantly less behaviorally intoxicated, which was not a result of enhanced hepatic metabolism. Rats that exercised prior to binge alcohol consumption had reduced loss of dentate gyrus granule cells and fewer FluoroJade B positive cells in the dentate gyrus and associated entorhinal-perirhinal cortex compared to nonexercisers. However, exercise did not protect against cell death in the piriform cortex nor protect against alcohol-induced decreases in cell proliferation, evidenced by a similar alcohol-induced reduction in Ki67 labeled cells between exercise and sedentary rats. CONCLUSIONS We conclude that exercise can reduce behavioral sensitivity to ethanol intoxication and protect vulnerable brain areas from alcohol-induced cell death. Exercise neuroprotection of alcohol-induced brain damage has important implications in understanding the neurobiology of the AUDs as well as in developing novel treatment strategies.

Sustained sensorimotor impairments after endothelin-1 induced focal cerebral ischemia (stroke) in aged rats.

Despite recent advances, stroke remains a leading cause of neurological disability with the vast majority of victims being the elderly, who exhibit more severe neurological deficits and a reduced capacity to recover from these disabilities in comparison to young stroke survivors. The objective of the present study was to develop a model of focal ischemic stroke in aged rats using endothelin-1 (ET-1) to produce low mortality rates as well as reliable, robust sensorimotor deficits that resemble functional impairments associated with stroke in humans. Here, we studied the functional and histological outcome following unilateral ET-1 infusions into the sensorimotor cortex of aged rats (20-23 months old). This procedure resulted in low mortality rates (13.3%) and no loss in body weight one week following surgery. Functional assessment was performed using a number of reliable behavioural tests: staircase test (fine motor function), horizontal ladder (skilled locomotion), bilateral tactile stimulation test (somatosensory function) and cylinder test (postural weight support). Following ET-1 induced stroke, all tests demonstrated large and sustained sensorimotor deficits in both forelimb and hindlimb function that failed to improve over the 28-day testing period. In addition, histological assessment revealed a substantial loss of retrogradely labelled corticospinal neurons in the ipsilesional hemisphere following stroke. Our results establish a model for the use of aged rats in future preclinical studies, which will enhance assessment of the long-term benefit of potential neural repair and regenerative strategies.

Differential response of hippocampal subregions to stress and learning.

The hippocampus has two functionally distinct subregions–the dorsal portion, primarily associated with spatial navigation, and the ventral portion, primarily associated with anxiety. In a prior study of chronic unpredictable stress (CUS) in rodents, we found that it selectively enhanced cellular plasticity in the dorsal hippocampal subregion while negatively impacting it in the ventral. In the present study, we determined whether this adaptive plasticity in the dorsal subregion would confer CUS rats an advantage in a spatial task–the radial arm water maze (RAWM). RAWM exposure is both stressful and requires spatial navigation, and therefore places demands simultaneously upon both hippocampal subregions. Therefore, we used Western blotting to investigate differential expression of plasticity-associated proteins (brain derived neurotrophic factor [BDNF], proBDNF and postsynaptic density-95 [PSD-95]) in the dorsal and ventral subregions following RAWM exposure. Lastly, we used unbiased stereology to compare the effects of CUS on proliferation, survival and neuronal differentiation of cells in the dorsal and ventral hippocampal subregions. We found that CUS and exposure to the RAWM both increased corticosterone, indicating that both are stressful; nevertheless, CUS animals had significantly better long-term spatial memory. We also observed a subregion-specific pattern of protein expression following RAWM, with proBDNF increased in the dorsal and decreased in the ventral subregion, while PSD-95 was selectively upregulated in the ventral. Finally, consistent with our previous study, we found that CUS most negatively affected neurogenesis in the ventral (compared to the dorsal) subregion. Taken together, our data support a dual role for the hippocampus in stressful experiences, with the more resilient dorsal portion undergoing adaptive plasticity (perhaps to facilitate escape from or neutralization of the stressor), and the ventral portion involved in affective responses.

Region-specific response of the hippocampus to chronic unpredictable stress

The objective of the present study was to determine whether chronic unpredictable stress (CUS) would induce hippocampal neuroplasticity in a region‐specific manner. Recent evidence suggests that the hippocampus has two functionally distinct subsections. The dorsal (septal) portion appears to be primarily associated with spatial navigation, while the ventral (temporal) region has been linked to affect‐related functions, such as anxiety. Chronic stress has previously been shown to negatively affect the hippocampus by decreasing survival of progenitor cells, although it has also been shown to increase adaptive responses, such as increased expression of neuropeptide Y (NPY) and ΔFosB. Whether such events occur in a region‐specific manner has not been investigated. We hypothesized that CUS would selectively impact cell survival, NPY, and ΔFosB expression in the more affect‐related ventral subregion. Individually housed Long‐Evans rats (n = 31) were divided into two groups: stressed and control. Stressed animals were exposed daily to an unpredictable schedule of ethologically relevant stressors, such as predator odors, forced swim, and open field exposure. All rats were injected with bromodeoxyuridine (BrdU) daily during the first 5 days of CUS in order to label dividing progenitor cells. Unbiased stereology was used to quantify BrdU+, NPY+, and ΔFosB+ cells in dorsal and ventral hippocampal subregions. In support of our hypothesis, we found that CUS selectively decreased cell survival in the ventral subregion. However, both NPY and ΔFosB were significantly increased only in the dorsal hippocampus. These results suggest that stress‐induced adaptive neuroplasticity occurs primarily in the dorsal subregion, which may coincide with behavioral aspects of the stress response, such as avoidance or amelioration of the stressor.

Exercise Enhances Hippocampal Recovery following Binge Ethanol Exposure

Binge drinking damages the brain, and although a significant amount of recovery occurs with abstinence, there is a need for effective strategies to maximize neurorestoration. In contrast to binge drinking, exercise promotes brain health, so the present study assessed whether it could counteract ethanol-induced damage by augmenting natural self-repair processes following one or more binge exposures. Adult female rats were exposed to 0 (control), 1 or 2 binges, using an established 4-day model of binge-induced neurodegeneration. Half of the animals in each group remained sedentary, or had running wheel access beginning 7 days after the final binge, and were sacrificed 28 days later. To assess binge-induced hippocampal damage and exercise restoration, we quantified volume of the dentate gyrus and number of granule neurons. We found that a single binge exposure significantly decreased the volume of the dentate gyrus and number of granule neurons. A second binge did not exacerbate the damage. Exercise completely restored baseline volume and granule neuron numbers. To investigate a potential mechanism of this restoration, we administered IdU (a thymidine analog) in order to label cells generated after the first binge. Previous studies have shown that neurogenesis in the dentate gyrus is decreased by binge alcohol exposure, and that the hippocampus responds to this insult by increasing cell genesis during abstinence. We found increased IdU labeling in binge-exposed animals, and a further increase in binged animals that exercised. Our results indicate that exercise reverses long-lasting hippocampal damage by augmenting natural self-repair processes.

Exercise and Alcohol Consumption: What We Know, What We Need to Know, and Why it is Important.

Exercise provides a wealth of benefits to brain and body, and is regarded as a protective factor against disease. Protective factors tend to cluster together – that is, people who engage in one healthy behavior, such as exercise, also engage in other healthy behaviors, such as maintaining a nutritious diet and getting sufficient sleep. In contrast to exercise, alcohol consumption is not typically regarded as a health-promoting behavior, although moderate intake has been associated with a lower risk of cardiovascular disease. Surprisingly, several large, population-based studies have shown a positive association between physical activity and alcohol intake. The present review focuses on what is known about this relationship, including potential neural bases as well as moderating factors, and discusses important directions for further study, such as a more thorough characterization of people who both drink and exercise. We focus on ramifications for intervening with people who have alcohol use disorders, as exercise has been assessed as both a treatment and preventive measure, with mixed results. We believe that, in order for such interventions to be effective, clinical trials must distinguish treatment-seeking populations from non-treatment-seeking ones, as well as ensure that the use of exercise as a tool to decrease alcohol consumption is made explicit. We posit that a better understanding of the relationship between physical activity and alcohol intake will maximize intervention efforts by informing the design of clinical trials and research-driven prevention strategies, as well as enable individuals to make educated decisions about their health behaviors.

Neurogenesis, Exercise, and Cognitive Late Effects of Pediatric Radiotherapy

Brain cancer is a common type of childhood malignancy, and radiotherapy (RT) is a mainstay of treatment. RT is effective for tumor eradication, and survival rates are high. However, RT damages the brain and disrupts ongoing developmental processes, resulting in debilitating cognitive “late” effects that may take years to fully manifest. These late effects likely derive from a long-term decrement in cell proliferation, combined with a neural environment that is hostile to plasticity, both of which are induced by RT. Long-term suppression of cell proliferation deprives the brain of the raw materials needed for optimum cognitive performance (such as new neurons in the hippocampus and new glia in frontal cortex), while chronic inflammation and dearth of trophic substances (such as growth hormone) limit neuroplastic potential in existing circuitry. Potential treatments for cognitive late effects should address both of these conditions. Exercise represents one such potential treatment, since it has the capacity to enhance cell proliferation, as well as to promote a neural milieu permissive for plasticity. Here, we review the evidence that cognitive late effects can be traced to RT-induced suppression of cell proliferation and hostile environmental conditions, as well as emerging evidence that exercise may be effective as an independent or adjuvant therapy.

The Control of Movement Following Traumatic Brain Injury

Traumatic brain injury (TBI) results in a variety of impairments in cognition, mood, sensation, and movement, depending upon the location and severity of injury. Although not as extensively studied as cognitive impairments, motor impairments are common, especially in moderately to severely injured patients. The recovery of these deficits is not usually complete; however, extensive effort is put into the rehabilitation of motor skills to enhance independence and quality of life. Understanding the motor recovery process and how it can be influenced by rehabilitation has been extensively studied in animal models of stroke and focal lesions, albeit to a lesser extent following animal models of TBI. Injury-induced neural plasticity is intricately involved in motor recovery and influenced by behavioral compensation and rehabilitation following stroke and focal lesions. New studies in animal models of TBI indicate that neural plasticity and the processes of motor recovery and rehabilitation following brain injury may not mirror those processes shown to occur following stroke. Further examination of motor recovery, rehabilitation, and plasticity in animal models of TBI as well as in individuals with TBI will be necessary to fully understand the control of movement following brain injury.