Hsiun Ing Chen

Exercise enhances the proliferation of neural stem cells and neurite growth and survival of neuronal progenitor cells in dentate gyrus of middle-aged mice

Aging is an important determinant of adult hippocampal neurogenesis as the proliferation of neural stem/precursor cells (NSCs) declines dramatically before middle age. Contrary to this, physical exercise is known to promote adult hippocampal neurogenesis. The objective of this study is to investigate the effects of mandatory treadmill running (TR) on neurogenesis, including 1) NSCs proliferation, 2) neurite outgrowth of neuronal progenitor cells, and 3) the survival of newborn neurons in dentate area of middle-aged animals. Compared with 3-mo-old mice, numbers of mitotic cells and neuronal progenitor cells decreased dramatically by middle age and remained at low levels after middle age. Five weeks of TR not only increased NSC proliferation and the number of immature neurons but also promoted the maturation and survival of immature neurons in middle-aged mice. The neurogenic and neurotrophic effects of TR were not due to the reduction of the age-related elevation of serum corticosterone. Significantly, 5 wk of TR restored the age-dependent decline of brain-derived neurotrophic factor and its receptor, TrkB, which are known to promote neuronal differentiation and survival. Taken together, mandatory running exercise alters the brain chemistries of middle-aged animals toward an environment that is favorable to NSC proliferation, survival, and maturation.

Upregulation of hippocampal TrkB and synaptotagmin is involved in treadmill exercise-enhanced aversive memory in mice.

Cognitive functions usually involve various synaptic proteins and neurotrophic factors in the hippocampus. However, whether treadmill exercise can improve learning and memory by upregulating some of these molecules remain unraveled. To address this question, male BALB/c mice were divided into control and exercise groups, the latter group went through 4 weeks of treadmill exercise training. At the end of exercise training period, they were either tested for passive avoidance (PA) performance or sacrificed for quantifying the hippocampal levels of brain-derived neurotrophic factor (BDNF), tropomyosin-related kinase B (TrkB, the BDNF receptor), synaptotagmin (a Ca(2+)-dependent synaptic vesicle protein), and SNAP-25 (a presynaptic vesicular fusion protein). Our results showed that treadmill exercise training (1) increased the retention latency without affecting the fear acquisition in the PA test, (2) transiently increased the hippocampal BDNF level at 1, 2, and 4h after the completion of exercise training, and (3) persistently increased the hippocampal protein levels of full-length TrkB, phosphorylated TrkB and synaptotagmin, but not truncated TrkB or SNAP-25. Moreover, the protein expression level of full-length TrkB or synaptotagmin was positively correlated with PA performance in mice. Finally, inhibition of TrkB signaling by K252a abolished the exercise-facilitated PA performance and upregulation of TrkB and synaptotagmin. Taken together, these data suggest that the upregulation of TrkB and synaptotagmin in the hippocampus contributes to the exercise-facilitated aversive memory.

Antioxidant administration inhibits exercise-induced thymocyte apoptosis in rats.

PURPOSE The purpose of this study was to investigate the effect of antioxidant on exercise-induced apoptosis in rat thymocytes. METHODS After exercise at 13.8 m x min(-1) for 60-90 min x d(-1) on a motor-driven drum exerciser for 2 consecutive days, rat thymocyte apoptosis was monitored by the feature of DNA fragmentation. To study the effect of antioxidant, rats were administered with butylated hydroxyanisole (BHA) for 7 d before exercise. RESULTS Exercise could induce thymocyte DNA fragmentation as detected on electrophoretic gel and by cell death detection ELISA kit. Further studies indicated that pretreatment with antioxidant BHA to rats resulted in a blockage of exercise-induced DNA fragmentation. The concentrations of glutathione (GSH) were not significantly changed in rat thymocytes after exercise with or without BHA treatment. CONCLUSION These results suggest that reactive oxygen species may play a role in thymocyte apoptosis induced by exercise. However, changes in GSH levels were not observed in this exercise model.

Chronic Exercise Increases Both Inducible and Endothelial Nitric Oxide Synthase Gene Expression in Endothelial Cells of Rat Aorta

Chronic exercise upregulates endothelial nitric oxide synthase (eNOS) gene expression. Whether the expression of inducible nitric oxide synthase (iNOS) is affected by exercise is unknown. We therefore investigated the effects of chronic exercise on iNOS and eNOS expression in isolated rat aortic endothelial and smooth muscle cells separately. Five-week-old male Wistar rats were randomly divided into control and exercise groups. After 10 weeks of running training, animals were sacrificed under ether anesthesia. The standard curve quantitative competitive reverse transcriptase-polymerase chain reaction method was used to quantify NOS mRNA expression in isolated endothelial/smooth muscle cells. To evaluate the functional role of iNOS, we examined phenylephrine-induced vascular responses with or without pretreatment with aminoguanidine. We found that (1) expression of iNOS and eNOS mRNA in endothelial cells was increased by chronic exercise and (2) chronic exercise blunted phenylephrine-induced vascular responses, probably by increasing NO release via iNOS. Our results show that chronic exercise increases both iNOS and eNOS gene expression in endothelium. These alterations may be partially responsible for the change in vascular response after exercise.

Glucocorticoid signaling and exercise-induced downregulation of the mineralocorticoid receptor in the induction of adult mouse dentate neurogenesis by treadmill running

Physical exercise is known to promote adult neurogenesis, although the underlying mechanisms remain unclear. Glucocorticoid (corticosterone in rodents) is a factor that is known to affect neurogenesis. As physical exercise modulates corticosterone secretion, we hypothesized that corticosterone signaling is involved in exercise-induced adult neurogenesis. We chose treadmill running (TR) to accurately define the intensity and duration of exercise. Our results showed that 5 weeks of TR increased the doublecortin (DCX)-positive neuronal progenitor cells (NPCs) in adult hippocampus and transiently increased the serum corticosterone level at the end of the TR protocol. This protocol reduced the levels of hippocampal mineralocorticoid receptor (MR); however, glucocorticoid receptor levels were unaltered. We then investigated whether reducing corticosterone levels by bilateral adrenalectomy (ADX) attenuated the TR-enhanced adult neurogenesis. Our results showed that ADX not only blocked the TR-induced downregulation of MR, but also reduced the number of TR-enhanced NPCs. In order to examine the role of MR downregulation in TR-induced adult neurogenesis, animals were treated repeatedly with a selective MR antagonist, spironolactone, for 3 weeks. The results revealed that spironolactone increased the number of spontaneously occurring and TR-induced NPC in the dentate area. Further analysis revealed that spironolactone treatment did not alter precursor cell proliferation, but increased the number of DCX-positive NPCs, suggesting that blockage of MR signaling either facilitates the differentiation of progenitor cells towards neurons and/or enhances the survival of NPCs. Taken together, the data indicated that induction of NPCs in the dentate area of adult hippocampus by TR is partly due to the downregulation of glucocorticoid/MR signaling, which subsequently enhances differentiation along a neuronal lineage and/or NPC survival.

Long-term compulsive exercise reduces the rewarding efficacy of 3,4-methylenedioxymethamphetamine

Although exercise has been known to regulate brain plasticity, its impact on psychostimulant reward and the associated mesolimbic dopamine system remained scarcely explored. A psychostimulant, 3,4-methylenedioxymethamphetamine (MDMA), is currently a worldwide abused drug of choice. We decided to examine the modulating effects of long-term, compulsive treadmill exercise on the hedonic value of MDMA in male C57BL/6J mice. MDMA-induced conditioned place preference (CPP) was used as a behavioral paradigm to indicate the reward efficacy of MDMA. We observed that sedentary control mice all demonstrated reliable MDMA-induced CPP with our conditioning protocol. Interestingly, pre-exposure to a treadmill exercise decreased the later MDMA-induced CPP in a running period-dependent manner. Specifically, mice undergoing a 12-week treadmill running exercise did not exhibit any approaching bias toward the MDMA-associated compartment in this CPP paradigm. Twelve weeks of treadmill running did not alter peripheral metabolism of MDMA 30min following single intraperitoneal injection of MDMA (3mg/kg). We further used microdialysis technique to study the underlying mechanisms for the impaired MDMA reward produced by the12-week exercise pre-exposure. We found that acute MDMA-stimulated dopamine release in nucleus accumbens was abolished in the exercised mice, whereas an obvious elevation of accumbal dopamine release was observed in sedentary control mice. Finally, the 12-week exercise program did not alter the protein levels of primary dopamine receptors, vesicular or membrane transporters in this area. We conclude that the long-term, compulsive exercise is effective in curbing the reward efficacy of MDMA possibly via its direct effect on reversing the MDMA-stimulated dopamine release in nucleus accumbens.

Onion decreases the ovariectomy-induced osteopenia in young adult rats

It has been suggested that fruit and vegetable consumption are associated with good bone health. Onion, in particular, has been verified in its efficacy in bone resorption activity. In this study, we further investigated the effects of an onion-containing diet on ovariectomy-induced bone loss using methods of serum marker assay, histomorphometric analysis and biomechanical tests. Sixty-four female Wistar rats (14-week-old) with sham operations or ovariectomy were assigned to 6 groups: CON, sham-operated control group; OVX, ovariectomized group; ALN, ovariectomized rats treated with alendronate (1 mg/kg/day, p.o.); and 3% ON, 7% ON and 14% ON, ovariectomized rats fed with diets containing 3%, 7% and 14% (wt/wt) onion powder, respectively. Animals were sacrificed after a six-week treatment course. In the serum marker assay, alendronate and all three onion-enriched diets significantly decreased serum calcium level (p<0.05). Both 14% ON group and the ALN group even showed similarly lower level of serum osteocalcin (p<0.05), suggesting a down-regulation of bone turnover. The histomorphometric analysis showed that ovariectomy markedly decrease bone trabeculae. The ALN and 14% ON rats were 80% and 46% higher, respectively, in BV/TV than the OVX rats (p<0.05), and the rats fed with onion-enriched food showed a lesser ovariectomy-induced bone loss in a dose-dependent manner. Additionally, both ALN and 14% ON groups had significantly more trabecular number, less separated trabeculae, and fewer osteoclasts (p<0.05), but the protective efficacy from the 14% onion-enriched diet was slightly inferior to that of alendronate. Ovariectomy also significantly decreased tissue weight and biomechanical strength in the OVX group (p<0.05). The ALN and 14% ON groups equivalently showed a lesser decrease in tissue weight, though the difference was not significant. On the other hand, both the ALN and 14% ON groups represented similar biomaterial properties of femurs, and both reduced the ovariectomy-induced decrease in bending load and bending energy (p<0.05). The present study further verified that an onion-enriched diet could counteract ovariectomy-induced bone loss and deterioration of biomechanical properties.

Chronic treadmill running in normotensive rats resets the resting blood pressure to lower levels by upregulating the hypothalamic GABAergic system

Objective The cardiovascular integration center not only sends out signals to offset the stimulus-induced responses but also resets the resting blood pressure. We hypothesize that GABAergic adaptations in the hypothalamus participate in the chronic exercise-induced cardiovascular resetting effects in conscious normotensive animals. Methods Male Wistar rats were subjected to chronic moderate exercise (CME, 8-week treadmill running at moderate intensity). A biotelemetry system was used to measure blood pressure, heart rate, autonomic nervous activities, baroreflex sensitivity and endogenous GABAergic activities in the paraventricular nucleus and the posterior hypothalamic area. Hypothalamic specimens were collected for quantifying GABA-related proteins and GABAergic neurons. Results CME reduced resting blood pressure, heart rate, sympathetic activity and enhanced parasympathetic activity and baroreflex sensitivity. Additionally, CME elevated the resting level of hypothalamic GABAergic activities, increased the percentage of GABAergic neurons in the hypothalamus and upregulated the hypothalamic protein levels of neuronal nitric oxide synthase, GAD67 and gephyrin, but not GABAA receptor. Moreover, a single bout of moderate exercise transiently elevated blood pressure and heart rate with prolonged high levels of neural controls (sympathetic activity, baroreflex sensitivity and hypothalamic GABAergic activities). CME accelerated the postexercise recovery in cardiovascular parameters and neural control alterations. Conclusion Chronic treadmill running in normotensive rats augmented the GABAergic system in both paraventricular nucleus and posterior hypothalamic area, resulting in lower resting blood pressure, heart rate and sympathetic tone under conscious unrestraint conditions. This study provides insight into mechanisms important for explaining how chronic exercise resets the resting blood pressure.

Chronic treadmill exercise in rats delicately alters the Purkinje cell structure to improve motor performance and toxin resistance in the cerebellum.

Although exercise usually improves motor performance, the underlying cellular changes in the cerebellum remain to be elucidated. This study aimed to investigate whether and how chronic treadmill exercise in young rats induced Purkinje cell changes to improve motor performance and rendered the cerebellum less vulnerable to toxin insults. After 1-wk familiarization of treadmill running, 6-wk-old male Wistar rats were divided into exercise and sedentary groups. The exercise group was then subjected to 8 wk of exercise training at moderate intensity. The rotarod test was carried out to evaluate motor performance. Purkinje cells in cerebellar slices were visualized by lucifer yellow labeling in single neurons and by calbindin immunostaining in groups of neurons. Compared with sedentary control rats, exercised rats not only performed better in the rotarod task, but also showed finer Purkinje cell structure (higher dendritic volume and spine density with the same dendritic field). The exercise-improved cerebellar functions were further evaluated by monitoring the long-lasting effects of intraventricular application of OX7-saporin. In the sedentary group, OX7-saporin treatment retarded the rotarod performance and induced ∼60% Purkinje cell loss in 3 wk. As a comparison, the exercise group showed much milder injuries in the cerebellum by the same toxin treatment. In conclusion, exercise training in young rats increased the dendritic density of Purkinje cells, which might play an important role in improving the motor performance. Furthermore, as Purkinje cells in the exercise group were relatively toxin resistant, the exercised rats showed good motor performance, even under toxin-treated conditions.

Early postinjury exercise reverses memory deficits and retards the progression of closed-head injury in mice

Exercise benefits the brain in many ways, e.g. promoting neuron repair and inhibiting neuroinflammation. However, current clinical practices often advise patients suffering head injury to rest during the post‐traumatic period. This study used a mouse model to investigate whether and how exercise retarded the brain structural and functional losses induced by a head impact. An early moderate‐exercise protocol (starting 2 days postimpact and lasting for 7 or 14 days) reversed the impact‐induced rapid loss of recognition memory and prevented most of the delayed neuronal loss and neuroinflammation. However, the same exercise protocol started 9 days postimpact was unable to restore deficits in the recognition memory, even though it still retarded the late‐phase neuroinflammation. These beneficial effects of exercise were probably mediated by the timely recovery of neurotrophic factors (brain‐derived neurotrophic factor and mitogen‐activated protein kinase phosphatase‐1) in the injured brain.