Lung Yu

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.

Differential effects of treadmill running and wheel running on spatial or aversive learning and memory: roles of amygdalar brain-derived neurotrophic factor and synaptotagmin I

Chronic exercise has been reported to improve cognitive function. However, whether and how different types of exercise affect various learning and memory tasks remain uncertain. To address this issue, male BALB/c mice were trained for 4 weeks under two different exercise protocols: moderate treadmill running or voluntary wheel running. After exercise training, their spatial memory and aversive memory were evaluated by a Morris water maze and by one‐trial passive avoidance (PA), respectively. Levels of neural plasticity‐related proteins, i.e. brain‐derived neurotrophic factor (BDNF), tropomyosin‐related kinase B (TrkB) and synaptotagmin I (Syt I), in hippocampus and amygdala were determined by ELISA or immunoblotting. Finally, the functional roles of these proteins in the basolateral amygdala were verified by locally blocking them with K252a (a TrkB kinase inhibitor), or lentivirus expressing Syt I shRNA. We found that (1) although both moderate treadmill running and wheel running improved the Morris water maze performance, only the former improved PA performance; (2) likewise, both exercise protocols upregulated the BDNF–TrkB pathway and Syt I in the hippocampus, whereas only treadmill exercise upregulated their expression levels in the amygdala; (3) local injection of K252a abolished the treadmill exercise‐facilitated PA performance and upregulation of amygdalar TrkB and Syt I; and (4) local administration of Syt I shRNA abolished the treadmill exercise‐facilitated PA performance and upregulation of amygdalar Syt I. Therefore, our results support the notion that different forms of exercise induce neuroplasticity changes in different brain regions, and thus exert diverse effects on various forms of learning and memory.

Treadmill exercise counteracts the suppressive effects of peripheral lipopolysaccharide on hippocampal neurogenesis and learning and memory

New neurons are continuously generated in hippocampal subgranular zone throughout life, and the amount of neurogenesis is suggested to be correlated with the hippocampus‐dependent function. Several extrinsic stimuli are known to modulate the neurogenesis process. Among them, physical exercise has advantageous effects on neurogenesis and brain function, while inflammation shows the opposite. Herein we showed that a moderate running exercise successfully restored the peripheral lipopolysaccharide (LPS)‐impaired neurogenesis in the dentate area. LPS treatment obstructed neuronal differentiation, but not proliferation. Exercise training facilitated both the proliferation of the neural stem cells and their differentiation into neurons. Interestingly, exercise replenished the LPS‐reduced levels of brain‐derived neurotrophic factor and its receptor, TrkB, and rescued the LPS‐disturbed performance in water maze; while the LPS‐elicited up‐regulation of tumor necrosis factor‐alpha and interleukin‐1β remained unaltered. In conclusion, our findings suggest that running exercise effectively ameliorates the LPS‐disturbed hippocampal neurogenesis and learning and memory performance. Such advantageous effects of running exercise are not due to the alteration of inflammatory response, but possibly by the restoring the LPS‐lessened brain‐derived neurotrophic factor signaling pathway.

Running exercise protects the substantia nigra dopaminergic neurons against inflammation-induced degeneration via the activation of BDNF signaling pathway

Parkinsons disease (PD) is characterized by a progressive and selective loss of dopaminergic (DA) neurons in the substantia nigra (SN). Although the etiology of PD remains unclear, neuroinflammation has been implicated in the development of PD. Running exercise (Ex) promotes neuronal survival and facilitates the recovery of brain functions after injury. Therefore, we hypothesize that Ex protects the DA neurons against inflammation-induced injury in the SN. An intraperitoneal lipopolysaccharide (LPS, 1 mg/kg) injection induced microglia activation in the SN within hours, followed by a reduction in the number of DA neurons. LPS reduced the level of dopamine in the striatum and impaired the performance of motor coordination. Furthermore, the levels of the brain-derived neurotrophic factor (BDNF) were reduced in the SN by the LPS treatment. Four weeks of Ex before LPS treatment completely prevented the LPS-induced loss of DA neurons, reduction of dopamine levels and dysfunction of motor movement. Ex did not change the LPS-induced status of microglia activation or the levels of cytokines/chemokines, but restored the levels of LPS-reduced BDNF-TrkB signaling molecules. Blocking the action of BDNF, through its receptor TrkB antagonist, abolished the Ex-induced protection against LPS-induced DA neuron loss. Intrastriatal perfusion of BDNF alone was sufficient to counteract the LPS-induced DA neuron loss. Altogether, our results show that Ex protects DA neurons against inflammation-induced insults. The neuroprotective effects of Ex are not due to the modulation of inflammation status, but rather to the activation of the BDNF-TrkB signaling pathway.

Sexual differences and estrous cycle in methamphetamine-induced dopamine and serotonin depletions in the striatum of mice

Summary. Four consecutive doses (10 mg/kg) of methamphetamine, s.c., produced a substantial striatal dopamine depletion in both sexes of BALB/c and C57BL/6J mice. Male C57BL/6J mice exhibited greater dopamine depletions in the striatum compared to female C57BL/6J mice. In contrast, male and female BALB/c mice demonstrated an equivalent magnitude of striatal dopamine depletion. Regardless of sex, C57BL/6J mice demonstrated approximately 1.4 to 2.2 times greater dopamine depletions in the striatum compared to BALB/c mice. Moreover, methamphetamine caused 4 times greater serotonin depletions in male as opposed to female BALB/c mice while sparing either sex of the C57BL/6J mice. Furthermore, female mice of both strains appeared to have the greatest basal dopamine levels during proestrus and the lowest basal dopamine levels during diestrus. Likewise, female mice of both strains exhibited the lowest dopamine depletions in the striatum when the dosing regimen of methamphetamine started at proestrus whereas the greatest dopamine depletions in the striatum occurred when the regimen started during diestrus. These results suggest that sex hormones and other modulating factors may play a role in methamphetamine-induced dopamine and serotonin neurotoxicity.

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.

Treadmill exercise enhances passive avoidance learning in rats : The role of down-regulated serotonin system in the limbic system

While serotonin (5-HT) may impair learning and memory, exercise has been reported to improve them. Whether chronic exercise can facilitate fear memory via regulating the serotonin system is unknown. We examined the effects of 4-week treadmill exercise training on levels of 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA), the protein expression of its receptor 5-HT(1A) and transporter in the amygdala, hippocampus and prefrontal cortex of male Sprague-Dawley rats. Our results demonstrated that treadmill exercise (1) improved the passive avoidance learning performance; (2) decreased the 5-HT level in the hippocampus; (3) decreased the expression of 5-HT(1A) receptor in the amygdala without altering the transporter expression. Moreover, pretreatment with 0.1 mg/kg 8-hydroxy-di-n-propylamino tetralin, a selective 5-HT(1A) receptor agonist, impaired the passive avoidance performance and completely abolished the exercise-enhanced fear memory. Our results suggest that down-regulation of the 5-HT system in the limbic system, i.e., the reduction of the hippocampus 5-HT content and the amygdala 5-HT(1A) receptor expression, may be involved in the exercise-enhanced fear memory.

Estrogen and progesterone distinctively modulate methamphetamine-induced dopamine and serotonin depletions in C57BL/6J mice

Summary. Intra-striatal infusion of a high dose (100 μg/3 μl) of methamphetamine produced long-lasting depletions of striatal dopamine and serotonin in both male and female mice. Male mice exhibited a greater depletion of striatal dopamine and serotonin than female mice. A similar trend of sexual differences was observed when 4 cumulative doses of methamphetamine were administered systemically. Thus, the sexual differences in methamphetamine-induced neurotoxicity in the striatum are probably not due to their differences in peripheral metabolism of methamphetamine. Moreover, ovariectomized (OVX) mice supplemented with 3 daily doses of estradiol benzoate (EB) at high or physiological levels, 3 daily doses of progesterone (P), and 2 doses of EB followed by 1 dose of P all demonstrated higher striatal dopamine levels following methamphetamine treatment as compared to vehicle-supplemented controls. The OVX mice pretreated with 3 daily doses of P exhibited the highest striatal serotonin levels after methamphetamine administration of all groups. In conclusion, sexual differences observed in methamphetamine-induced striatal neurotoxicity may be modulated by ovarian hormones.

Cocaine-but not methamphetamine-associated memory requires de novo protein synthesis

Context-induced drug craving and continuous drug use manifest the critical roles of specific memory episodes associated with the drug use experiences. Drug-induced conditioned place preference (CPP) in C57BL/6J mouse model, in this regard, is an appropriate behavioral paradigm to study such drug use-associated memories. Requirement of protein synthesis in various forms of long-term memory formation and storage has been phylogenetically demonstrated. This study was undertaken to study the requirement of protein synthesis in the learning and memory aspect of the conditioned place preference induced by cocaine and methamphetamine, two abused drugs of choice in local area. Since pCREB has been documented as a candidate substrate for mediating the drug-induced neuroadaptation, the pCREB level in hippocampus, nucleus accumbens, and prefrontal cortex was examined for its potential participation in the formation of CPP caused by these psychostimulants. We found that cocaine (2.5 and 5.0 mg/kg/dose)-induced CPP was abolished by the pretreatment of anisomycin (50 mg/kg/dose), a protein synthesis inhibitor, whereas methamphetamine (0.5 or 1.0 mg/kg/dose)-induced CPP was not affected by the anisomycin pretreatment. Likewise, cocaine-induced CPP was mitigated by another protein synthesis inhibitor, cycloheximide (15 mg/kg/injection) pretreatment, whereas methamphetamine-induced CPP remained intact by such pretreatment. Moreover, anisomycin treatment 2h after each drug-place pairing disrupted the cocaine-induced CPP, whereas the same treatment did not affect methamphetamine-induced CPP. An increase of accumbal pCREB level was found to associate with the learning phase of cocaine, but not with the learning phase of methamphetamine. We further found that intraaccumbal CREB antisense oligodeoxynucleotide infusion diminished cocaine-induced CPP, whereas did not affect the methamphetamine-induced CPP. Taken together, these data suggest that protein synthesis and accumbal CREB phosphorylation are essential for the learning and consolidation of the cocaine-induced CPP, whereas methamphetamine-induced CPP may be unrelated to the synthesis of new proteins.

Interactions between amyloid-β and hemoglobin: implications for amyloid plaque formation in Alzheimer's disease.

Accumulation of amyloid-β (Aβ) peptides in the brain is one of the central pathogenic events in Alzheimers disease (AD). However, why and how Aβ aggregates within the brain of AD patients remains elusive. Previously, we demonstrated hemoglobin (Hb) binds to Aβ and co-localizes with the plaque and vascular amyloid deposits in post-mortem AD brains. In this study, we further characterize the interactions between Hb and Aβ in vitro and in vivo and report the following observations: 1) the binding of Hb to Aβ required iron-containing heme; 2) other heme-containing proteins, such as myoglobin and cytochrome C, also bound to Aβ; 3) hemin-induced cytotoxicity was reduced in neuroblastoma cells by low levels of Aβ; 4) Hb was detected in neurons and glial cells of post-mortem AD brains and was up-regulated in aging and APP/PS1 transgenic mice; 5) microinjection of human Hb into the dorsal hippocampi of the APP/PS1 transgenic mice induced the formation of an envelope-like structure composed of Aβ surrounding the Hb droplets. Our results reveal an enhanced endogenous expression of Hb in aging brain cells, probably serving as a compensatory mechanism against hypoxia. In addition, Aβ binds to Hb and other hemoproteins via the iron-containing heme moiety, thereby reducing Hb/heme/iron-induced cytotoxicity. As some of the brain Hb could be derived from the peripheral circulation due to a compromised blood-brain barrier frequently observed in aged and AD brains, our work also suggests the genesis of some plaques may be a consequence of sustained amyloid accretion at sites of vascular injury.