Lack of exercise, via hindlimb suspension, impedes endogenous neurogenesis

Physical exercise as a preventive or disease-modifying treatment of dementia and brain aging

A rapidly growing literature strongly suggests that exercise, specifically aerobic exercise, may attenuate cognitive impairment and reduce dementia risk. We used PubMed (keywords exercise and cognition) and manuscript bibliographies to examine the published evidence of a cognitive neuroprotective effect of exercise. Meta-analyses of prospective studies documented a significantly reduced risk of dementia associated with midlife exercise; similarly, midlife exercise significantly reduced later risks of mild cognitive impairment in several studies. Among patients with dementia or mild cognitive impairment, randomized controlled trials (RCTs) documented better cognitive scores after 6 to 12 months of exercise compared with sedentary controls. Meta-analyses of RCTs of aerobic exercise in healthy adults were also associated with significantly improved cognitive scores. One year of aerobic exercise in a large RCT of seniors was associated with significantly larger hippocampal volumes and better spatial memory; other RCTs in seniors documented attenuation of age-related gray matter volume loss with aerobic exercise. Cross-sectional studies similarly reported significantly larger hippocampal or gray matter volumes among physically fit seniors compared with unfit seniors. Brain cognitive networks studied with functional magnetic resonance imaging display improved connectivity after 6 to 12 months of exercise. Animal studies indicate that exercise facilitates neuroplasticity via a variety of biomechanisms, with improved learning outcomes. Induction of brain neurotrophic factors by exercise has been confirmed in multiple animal studies, with indirect evidence for this process in humans. Besides a brain neuroprotective effect, physical exercise may also attenuate cognitive decline via mitigation of cerebrovascular risk, including the contribution of small vessel disease to dementia. Exercise should not be overlooked as an important therapeutic strategy.

Induction of striatal neurogenesis enhances functional recovery in an adult animal model of neonatal hypoxic-ischemic brain injury

While intraventricular administration of epidermal growth factor (EGF) expands the proliferation of neural stem/progenitor cells in the subventricular zone (SVZ), overexpression of brain-derived neurotrophic factor (BDNF) is particularly effective in enhancing striatal neurogenesis. We assessed the induction of striatal neurogenesis and consequent functional recovery after chronic infusion of BDNF and EGF in an adult animal model of neonatal hypoxic-ischemic (HI) brain injury. Permanent brain damage was induced in CD-1 (ICR) mice (P7) by applying the ligation of unilateral carotid artery and hypoxic condition. At 6 weeks of age, the mice were randomly assigned to groups receiving a continuous 2-week infusion of one of the following treatments into the ventricle: BDNF, EGF, BDNF/EGF, or phosphate buffered saline (PBS). Two weeks after treatment, immunohistochemical analysis revealed an increase in the number of BrdU(+) cells in the SVZ and striata of BDNF/EGF-treated mice. The number of new neurons co-stained with BrdU and betaIII-tubulin was also significantly increased in the neostriata of BDNF/EGF-treated mice, compared with PBS group. In addition, the newly generated cells were expressed as migrating neuroblasts labeled with PSA-NCAM or doublecortin in the SVZ and the ventricular side of neostriata. The new striatal neurons were also differentiated as mature neurons co-labeled with BrdU(+)/NeuN(+). When evaluated post-surgical 8 weeks, BDNF/EGF-treated mice exhibited significantly longer rotarod latencies at constant speed (48 rpm) and under accelerating condition (4-80 rpm), relative to PBS and untreated controls. In the forelimb-use asymmetry test, BDNF/EGF-treated mice showed significant improvement in the use of the contralateral forelimb. In contrast, this BDNF/EGF-associated functional recovery was abolished in mice receiving a co-infusion of 2% cytosine-b-d-arabinofuranoside (Ara-C), a mitotic inhibitor. Induction of striatal neurogenesis by the intraventricular administration of BDNF and EGF promoted functional recovery in an adult animal model of neonatal HI brain injury. The effect of Ara-C to completely block functional recovery indicates that the effect may be the result of newly generated neurons. Therefore, this treatment may offer a promising strategy for the restoration of motor function for adults with cerebral palsy (CP).

Striatal stimulation nurtures endogenous neurogenesis and angiogenesis in chronic-phase ischemic stroke rats

Deep brain stimulation (DBS) is used to treat a variety of neurological disorders including Parkinson's disease. In this study, we explored the effects of striatal stimulation (SS) in a rat model of chronic-phase ischemic stroke. The stimulation electrode was implanted into the ischemic penumbra at 1 month after middle cerebral artery occlusion (MCAO) and thereafter continuously delivered SS over a period of 1 week. Rats were evaluated behaviorally coupled with neuroradiological assessment of the infarct volumes using magnetic resonance imaging (MRI) at pre- and post-SS. The rats with SS showed significant behavioral recovery in the spontaneous activity and limb placement test compared to those without SS. MRI visualized that SS also significantly reduced the infarct volumes compared to that at pre-SS or without SS. Immunohistochemical analyses revealed a robust neurogenic response in rats that received SS characterized by a stream of proliferating cells from the subventricular zone migrating to and subsequently differentiating into neurons in the ischemic penumbra, which exhibited a significant GDNF upregulation. In tandem with this SS-mediated neurogenesis, enhanced angiogenesis was also recognized as revealed by a significant increase in VEGF levels in the penumbra. These results provide evidence that SS affords neurorestoration at the chronic phase of stroke by stimulating endogenous neurogenesis and angiogenesis.

Impaired neural stem/progenitor cell proliferation in streptozotocin-induced and spontaneous diabetic mice

Diabetes mellitus is associated with adverse complications in many organ systems including the brain. Accumulating evidence indicates that diabetes, regardless of its type, impairs adult neurogenesis in the dentate gyrus (DG) of the hippocampus (HPC). However, the effects of the disease on neurogenesis in the subventricular zone (SVZ) are not well established. We induced diabetes in male NOD/SCID (non-obese diabetic/severe combined immunodeficiency) mice and C57BL/6 mice with a single intraperitoneal injection of streptozotocin (STZ). On day 7 or day 21 after STZ injection mice received the thymidine analog 5-bromo-2'-deoxyuridine (BrdU) for labeling of proliferative cells. Mice were sacrificed 24h later and brain coronal sections were stained with anti-BrdU antibodies. Neural stem/progenitor cell (NSC/NPC) proliferation, as revealed by BrdU-labeled cells, was markedly decreased in the subgranular zone of the DG in STZ-treated diabetic mice. A similar reduction of NSC/NPC proliferation was seen in the SVZ. Reduced DG and SVZ cell proliferation was also found in diabetic NOD mice, a model of spontaneous diabetes, and the reduction was attenuated by bilateral adrenalectomy (Adx). Adx did not alter blood glucose or insulin levels in either prediabetic or diabetic NOD mice, but Adx partly increased mRNA levels of hippocampal and SVZ brain-derived neurotrophic factor (BDNF), a crucial regulator of NSC/NPC proliferation. Moreover, NOD and NOD/SCID mice showed a more rapid reduction of NSC/NPC proliferation than C57BL/6 mice in response to diabetes. Thus, we conclude that diabetes inhibits cell proliferation in both the SVZ and HPC, and inhibition was associated with elevated glucocorticoid levels and reduced BDNF expression.

Voluntary exercise enhances survival and migration of neural progenitor cells after intracerebral haemorrhage in mice

PRIMARY OBJECTIVE

This study explored the long-term effects of exercise on the proliferation, survival and migration of endogenous neural progenitor cells (NPCs) in the subventricular zone (SVZ) of the brain after intracerebral haemorrhage (ICH).

RESEARCH DESIGN

ICH was induced by an injection of collagenase into the striatum. Animals in the voluntary running exercise group ran freely on a running wheel for 1, 3 and 6 weeks following the induction of ICH.

METHODS AND PROCEDURE

Immunohistochemical labelling was performed to incorporate specific cell markers, such as Ki67 (proliferating cells), 5-bromodeoxyuridien (BrdU; surviving newborn cells) and doublecortin (DCX; neuroblasts or migrating cells).

MAIN OUTCOMES AND RESULTS

Voluntary exercise for 3 and 6 weeks sustained more Ki67- or BrdU-immunostained cells in the SVZ after ICH than in the brains of sedentary mice. DCX-immunostained cells were more prominent in the striatum of the group that had exercised for 6 weeks compared to the time-matched sedentary group. Moreover, it was observed that proliferating green fluorescent protein (GFP)-positive cells that were infected with retrovirus were located more distally from the injection site in the exercise group than in the sedentary group.

CONCLUSIONS

These data indicate that long-term exercise may enhance the proliferation and survival of NPCs and their migration toward injured areas, suggesting that exercise may contribute to neuronal injury recovery in cell-based therapies after ICH.

Captivity reduces hippocampal volume but not survival of new cells in a food-storing bird

In many naturalistic studies of the hippocampus wild animals are held in captivity. To test if captivity itself affects hippocampal integrity, adult black-capped chickadees (Poecile atricapilla) were caught in the fall, injected with bromodeoxyuridine to mark neurogenesis, and alternately released to the wild or held in captivity. The wild birds were recaptured after 4-6 weeks and perfused simultaneously with their captive counterparts. The hippocampus of captive birds was 23% smaller than wild birds, with no hemispheric differences in volume within groups. Between groups there was no statistically significant difference in the size of the telencephalon, or in the number and density of surviving new cells. Proximate causes of the reduced hippocampal volume could include stress, lack of exercise, diminished social interaction, or limited caching opportunity-a hippocampal-dependent activity. The results suggest the avian hippocampus-a structure essential for rapid, complex relational and spatial learning-is both plastic and sensitive, much as in mammals, including humans.

Exercise exerts neuroprotective effects on Parkinson's disease model of rats

Recent studies demonstrate that rehabilitation ameliorates physical and cognitive impairments of patients with stroke, spinal cord injury, and other neurological diseases and that rehabilitation also has potencies to modulate brain plasticity. Here we examined the effects of compulsive exercise on Parkinson's disease model of rats. Before 6-hydroxydopamine (6-OHDA, 20 microg) lesion into the right striatum of female SD rats, bromodeoxyuridine (BrdU) was injected to label the proliferating cells. Subsequently, at 24 h after the lesion, the rats were forced to run on the treadmill (5 days/week, 30 min/day, 11 m/min). As behavioral evaluations, cylinder test was performed at 1, 2, 3, and 4 weeks and amphetamine-induced rotational test was performed at 2 and 4 weeks with consequent euthanasia for immunohistochemical investigations. The exercise group showed better behavioral recovery in cylinder test and significant decrease in the number of amphetamine-induced rotations, compared to the non-exercise group. Correspondingly, significant preservation of tyrosine hydroxylase (TH)-positive fibers in the striatum and TH-positive neurons in the substantia nigra pars compacta (SNc) was demonstrated, compared to the non-exercise group. Additionally, the number of migrated BrdU- and Doublecortin-positive cells toward the lesioned striatum was increased in the exercise group. Furthermore, brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor increased in the striatum by exercise. The results suggest that exercise exerts neuroprotective effects or enhances the neuronal differentiation in Parkinson's disease model of rats with subsequent improvement in deteriorated motor function.

Emerging treatments for traumatic brain injury

BACKGROUND

This review summarizes promising approaches for the treatment of traumatic brain injury (TBI) that are in either preclinical or clinical trials.

OBJECTIVE

The pathophysiology underlying neurological deficits after TBI is described. An overview of select therapies for TBI with neuroprotective and neurorestorative effects is presented.

METHODS

A literature review of preclinical TBI studies and clinical TBI trials related to neuroprotective and neurorestorative therapeutic approaches is provided.

RESULTS/CONCLUSION

Nearly all Phase II/III clinical trials in neuroprotection have failed to show any consistent improvement in outcome for TBI patients. The next decade will witness an increasing number of clinical trials that seek to translate preclinical research discoveries to the clinic. Promising drug- or cell-based therapeutic approaches include erythropoietin and its carbamylated form, statins, bone marrow stromal cells, stem cells singularly or in combination or with biomaterials to reduce brain injury via neuroprotection and promote brain remodeling via angiogenesis, neurogenesis, and synaptogenesis with a final goal to improve functional outcome of TBI patients. In addition, enriched environment and voluntary physical exercise show promise in promoting functional outcome after TBI, and should be evaluated alone or in combination with other treatments as therapeutic approaches for TBI.

Injection of muscimol, a GABAa agonist into the anterior thalamic nucleus, suppresses hippocampal neurogenesis in amygdala-kindled rats

The relationship between neurogenesis and epilepsy remains to be solved so far, although aberrant electric circuit recognized in epilepsy might be involved in neurogenesis. In this study, neurogenesis and the proliferation of astrocytes in the subgranular zone of the hippocampus were explored using unilateral amygdala-kindled rats with or without muscimol, a gamma-aminobutyric acid a (GABAa) agonist injection into the bilateral anterior thalamic nuclei (AN). Muscimol injection significantly ameliorated the behavioral scores of epilepsy without any significant alteration on the electroencephalography recorded at the stimulated basolateral amygdala, thus suggesting that muscimol injection might affect the secondary generalization, but not the initial discharge itself. The number of bromodeoxyuridine (BrdU), BrdU/doublecortin and BrdU/glial fibrillary acidic protein-positive cells in the subgranular zone of kindled animals increased markedly. Muscimol injection significantly suppressed neurogenesis, but not the proliferation of astrocyte, in the subgranular zone of the non-stimulated side, probably through the suppression of secondary generalization via AN. The results might indicate the underlying relationships between neurogenesis and epilepsy, that epileptic propagation in unilateral amygdala-kindled rats might go through AN into the contralateral side with subsequent neurogenesis, although further studies need to clarify the hypothesis.