Changes in the Gene Expression of Gaba(a) Receptor Alpha1 and Alpha2 Subunits and Metabotropic Glutamate Receptor 5 in the Basal Ganglia of the Rats with Unilateral 6-Hydroxydopamine Lesion and Embryonic Mesencephalic Grafts

By using an animal model of parkinsonism, we examined the expression of GABA(A) receptor (R) and metabotropic glutamate receptor (mGluR) 5 in the basal ganglia after transplantation with dopamine-rich tissue. The adult rats were unilaterally lesioned by the injection of 6- hydroxydopamine to their left medial forebrain bundles. At 5 -10 weeks following the dopaminergic denervation, the levels of GABA(A)R in the left caudate- putamen and globus pallidus were about 20 and 16% lower than that of the right intact ( control) sides, as shown by [3H]flunitrazepam binding autoradiography on the brain sections. However, the receptor density increased to around 132 and 130% of control levels in the entopeduncular nucleus and substantia nigra pars reticulata of the lesioned sides. Furthermore, in situ hybridization analysis exhibited parallel trends of changes in the levels of the GABA(A)R alpha1 and alpha2 subunit and mGluR5 mRNAs in the neurons of the brain regions with that of the proteins detected by the binding assay. A number of the rats 5 weeks postlesion were transplanted with the ventral mesencephalon of the embryonic rat into their left striata. Five weeks later, the changes in the [3H] flunitrazepam binding seemed to be recovered by approximately 50-63% on the grafted sides of the areas. Moreover, the transplantation appeared to produce a nearly complete reversal of the lesion-induced alterations in the levels of the mRNAs. Thus, the data indicate the mechanism of gene regulation for the modified expression of the receptors and could implicate the participation of the receptors in the pathogenesis of Parkinson's disease

Donepezil rescues spatial learning and memory deficits following traumatic brain injury independent of its effects on neurogenesis.

Traumatic brain injury (TBI) is ubiquitous and effective treatments for it remain supportive largely due to uncertainty over how endogenous repair occurs. Recently, we demonstrated that hippocampal injury-induced neurogenesis is one mechanism underlying endogenous repair following TBI. Donepezil is associated with increased hippocampal neurogenesis and has long been known to improve certain aspects of cognition following many types of brain injury through unknown mechanisms. By coupling donepezil therapy with temporally regulated ablation of injury-induced neurogenesis using nestin-HSV transgenic mice, we investigated whether the pro-cognitive effects of donepezil following injury might occur through increasing neurogenesis. We demonstrate that donepezil itself enhances neurogenesis and improves cognitive function following TBI, even when injury-induced neurogenesis was inhibited. This suggests that the therapeutic effects of donepezil in TBI occur separately from its effects on neurogenesis

Apolipoprotein E regulates the maturation of injury-induced adult-born hippocampal neurons following traumatic brain injury.

Various brain injuries lead to the activation of adult neural stem/progenitor cells in the mammalian hippocampus. Subsequent injury-induced neurogenesis appears to be essential for at least some aspects of the innate recovery in cognitive function observed following traumatic brain injury (TBI). It has previously been established that Apolipoprotein E (ApoE) plays a regulatory role in adult hippocampal neurogenesis, which is of particular interest as the presence of the human ApoE isoform ApoE4 leads to significant risk for the development of late-onset Alzheimer's disease, where impaired neurogenesis has been linked with disease progression. Moreover, genetically modified mice lacking ApoE or expressing the ApoE4 human isoform have been shown to impair adult hippocampal neurogenesis under normal conditions. Here, we investigate how controlled cortical impact (CCI) injury affects dentate gyrus development using hippocampal stereotactic injections of GFP-expressing retroviruses in wild-type (WT), ApoE-deficient and humanized (ApoE3 and ApoE4) mice. Infected adult-born hippocampal neurons were morphologically analyzed once fully mature, revealing significant attenuation of dendritic complexity and spine density in mice lacking ApoE or expressing the human ApoE4 allele, which may help inform how ApoE influences neurological diseases where neurogenesis is defective

Traumatic Brain Injury-Induced Hippocampal Neurogenesis Requires Activation of Early Nestin-Expressing Progenitors

It is becoming increasingly clear that brain injuries from a variety of causes stimulate neurogenesis within the hippocampus. It remains unclear, however, how robust this response may be and what primary cell types are involved. Here, using a controlled cortical impact model of traumatic brain injury on a previously characterized transgenic mouse line that expresses enhanced green fluorescent protein (eGFP) under the control of the nestin promoter, we demonstrate that it is the earliest type-1 quiescent progenitor cells that are induced to proliferate and migrate outside the subgranular layer of the dentate gyrus. This type-1 cell activation occurs at the same time that we observe adjacent but more differentiated doublecortin-expressing progenitors (type-2 cells) being eliminated. Also, although type-2 cells remain intact in the contralateral (uninjured) dentate gyrus, the type-1 cells there are also activated and result in increased numbers of the doublecortin-expressing type-2 cells. In addition, we have generated a novel mouse transgenic that expresses a modified version of the herpes simplex virus thymidine kinase along with eGFP that allows for the visualization and inducible ablation of early dividing progenitors by exposing them to ganciclovir. Using this transgenic in the context of traumatic brain injury, we demonstrate that these early progenitors are required for injury-induced remodeling to occur. This work suggests that injury-induced hippocampal remodeling following brain injury likely requires sustained activation of quiescent early progenitors

Valganciclovir chow inhibited neurogenesis in nestin-HSV-TK mice.

<p>(A and B) The representative section demonstrates that rare CldU/NeuN double-labeled cells (arrow) were observed in the dentate gyrus after mice were fed with valganciclovir chow for 4 consecutive weeks (40x). (C) Quantification of CldU-labeled cells in the dentate gyrus of nestin-HSV-TK mice demonstrated that neurogenesis was efficiently inhibited in all the experimental groups. One-way ANOVA with Fisher’s LSD multiple comparisons was used in C, * <i>p</i><0.05, ** <i>p</i><0.01, ***p<0.001, **** <i>p</i><0.0001. Sham: <i>sham-injured</i>, CCI: <i>controlled cortical injury</i>, Veh: <i>vehicle</i>, Don: <i>donepezil</i>. Nor: <i>normal chow</i>, Valgan: <i>valganciclovir</i>. Number of mice used was 4 (Sham, Veh, Nor), 5 (Sham, Veh, Valgan) 6 (Sham, Don, Nor), 5 (Sham, Don, Valgan), 3 (CCI, Veh, Nor), 3 (CCI, Veh, Valgan), 4 (CCI, Don, Nor), and 5 (CCI, Don, Valgan). Scale bar in B is 50μm.</p

Donepezil treatment enhanced adult neurogenesis in the dentate gyrus in sham-operated but not injured mice.

<p>(A) Surgery was performed on 8-week old mice (D0). Starting from D3, vehicle or donepezil was given for 5 days a week, for 2 weeks. CldU was also injected for 3 days to label the dividing cells. Mice were perfused for further analysis 4 weeks after surgery. (B, C) Representative pictures show that more newly born neurons (arrows) were observed in CCI-operated mice after being treated with donepezil when compared to control. (D) Unbiased stereology quantification revealed that donepezil treatment resulted in a significant increase in CldU-labeled cells in the dentate gyrus in sham-operated but not injured mice. (E) Treatment with donepezil led to a significant increase in number of newborn neurons in sham-operated mice. One-way ANOVA with Fisher’s multiple comparisons post-hoc analysis in D and E with * <i>p</i><0.05, ** <i>p</i><0.01, *** <i>p</i><0.001, **** <i>p</i><0.0001. Sham: <i>sham-injured</i>, CCI: <i>controlled cortical injury</i>, Veh: <i>vehicle</i>, Don: <i>donepezil</i>, Ipsi: <i>ipsilateral</i>, Contra: <i>contralateral</i>. Number of mice used was 9 (Sham, Veh), 6 (Sham, Don) 6 (Sham, Don), 5 (CCI, Veh), 5 (CCI, Don), Scale bar in C is 50μm.</p

The effect of donepezil in spatial learning and memory in injured mice is independent from neurogenesis.

<p>(A) As depicted in the scheme, sham- and injured mice received either vehicle or donepezil for two weeks. Four weeks after surgery, mice were habituated for the Morris water maze. Mice were trained to find the platform for 11 consecutive days and a probe test was performed at day 12 Mice were fed with valganciclovir chow immediately after surgery until the end of all experiments. (B) Swimming speed in injured mice without neurogenesis and treatment was slower than controls. Donepezil treatment was able to overcome the impairment even in the absence of neurogenesis. (C) Consistent with previous observations, in the absence of neurogenesis the injured mice took the longest path to locate the hidden platform if no treatment was given. However, the performance improved after injured mice were treated with donepezil even while neurogenesis was inhibited. (D) Injured mice without neurogenesis and donepezil treatment spent significantly less time in the target zone when compared with the summation of time spent in other zones (open blue bars). However, treatment with donepezil reversed this deficit (open red bars). Two-way ANOVA with Fisher’s LSD post-hoc analysis was used in A and B. One-way ANOVA with Fisher’s LSD analysis was used in C. * <i>p</i><0.05, **** <i>p</i><0.001. Sham: <i>sham-injured</i>, CCI: <i>controlled cortical injury</i>, Veh: <i>vehicle</i>, Don: <i>donepezil</i>. Nor: <i>normal chow</i>, Valgan: <i>valganciclovir</i>. Number of mice used was 10 (Sham, Veh, Valgan), 12 (Sham, Don, Valgan), 11 (CCI, Veh, Valgan), and 10 (CCI, Don, Valgan).</p

Depletion of adult neurogenesis exacerbates cognitive deficits in Alzheimer’s disease by compromising hippocampal inhibition

Abstract Background The molecular mechanism underlying progressive memory loss in Alzheimer’s disease is poorly understood. Neurogenesis in the adult hippocampus is a dynamic process that continuously changes the dentate gyrus and is important for hippocampal plasticity, learning and memory. However, whether impairments in neurogenesis affect the hippocampal circuitry in a way that leads to memory deficits characteristic of Alzheimer’s disease is unknown. Controversial results in that regard were reported in transgenic mouse models of amyloidosis. Methods Here, we conditionally ablated adult neurogenesis in APPswe/PS1ΔE9 mice by crossing these with mice expressing nestin-driven thymidine kinase (δ-HSV-TK). Results These animals show impairment in performance in contextual conditioning and pattern separation tasks following depletion of neurogenesis. Importantly, these deficits were not observed in age-matched APPswe/PS1ΔE9 or δ-HSV-TK mice alone. Furthermore, we show that cognitive deficits were accompanied by the upregulation of hyperphosphorylated tau in the hippocampus and in immature neurons specifically. Interestingly, we observed upregulation of the immediate early gene Zif268 (Egr-1) in the dentate gyrus, CA1 and CA3 regions of the hippocampus following learning in the neurogenesis-depleted δ-HSV-TK mice. This may suggest overactivation of hippocampal neurons in these areas following depletion of neurogenesis. Conclusions These results imply that neurogenesis plays an important role in the regulation of inhibitory circuitry of the hippocampus. This study suggests that deficits in adult neurogenesis may contribute to cognitive impairments, tau hyperphosphorylation in new neurons and compromised hippocampal circuitry in Alzheimer’s disease

Endogenous Neural Stem/Progenitor Cells Stabilize the Cortical Microenvironment after Traumatic Brain Injury

Although a myriad of pathological responses contribute to traumatic brain injury (TBI), cerebral dysfunction has been closely linked to cell death mechanisms. A number of therapeutic strategies have been studied in an attempt to minimize or ameliorate tissue damage; however, few studies have evaluated the inherent protective capacity of the brain. Endogenous neural stem/progenitor cells (NSPCs) reside in distinct brain regions and have been shown to respond to tissue damage by migrating to regions of injury. Until now, it remained unknown whether these cells have the capacity to promote endogenous repair. We ablated NSPCs in the subventricular zone to examine their contribution to the injury microenvironment after controlled cortical impact (CCI) injury. Studies were performed in transgenic mice expressing the herpes simplex virus thymidine kinase gene under the control of the nestin δ promoter exposed to CCI injury. Two weeks after CCI injury, mice deficient in NSPCs had reduced neuronal survival in the perilesional cortex and fewer Iba-1-positive and glial fibrillary acidic protein-positive glial cells but increased glial hypertrophy at the injury site. These findings suggest that the presence of NSPCs play a supportive role in the cortex to promote neuronal survival and glial cell expansion after TBI injury, which corresponds with improvements in motor function. We conclude that enhancing this endogenous response may have acute protective roles after TBI