Total Number Of Dendritic Spines Research Articles

Long-term voluntary exercise inhibited AGE/RAGE and microglial activation and reduced the loss of dendritic spines in the hippocampi of APP/PS1 transgenic mice

Alzheimer’s disease (AD) is closely related to hippocampal synapse loss, which can be alleviated by running exercise. However, further studies are needed to determine whether running exercise reduces synapse loss in the hippocampus in an AD model by regulating microglia. Ten-month-old male wild-type mice and APP/PS1 mice were randomly divided into control and running groups. All mice in the running groups were subjected to voluntary running exercise for four months. After the behavioral tests, immunohistochemistry, stereological methods, immunofluorescence staining, 3D reconstruction, western blotting and RNA-Seq were performed. Running exercise improved the spatial learning and memory abilities of APP/PS1 mice and increased the total number of dendritic spines, the levels of the PSD-95 and Synapsin Ia/b proteins, the colocalization of PSD-95 and neuronal dendrites (MAP-2) and the number of PSD-95-contacting astrocytes (GFAP) in the hippocampi of APP/PS1 mice. Moreover, running exercise reduced the relative expression of CD68 and Iba-1, the number of Iba-1+ microglia and the colocalization of PSD-95 and Iba-1+ microglia in the hippocampi of APP/PS1 mice. The RNA-Seq results showed that some differentially expressed genes (DEGs) related to the complement system (Cd59b, Serping1, Cfh, A2m, and Trem2) were upregulated in the hippocampi of APP/PS1 mice, while running exercise downregulated the C3 gene. At the protein level, running exercise also reduced the expression of advanced glycation end products (AGEs), receptor for advanced glycation end products (RAGE), C1q and C3 in the hippocampus and AGEs and RAGE in hippocampal microglia in APP/PS1 mice. Furthermore, the Col6a3, Scn5a, Cxcl5, Tdg and Clec4n genes were upregulated in the hippocampi of APP/PS1 mice but downregulated after running, and these genes were associated with the C3 and RAGE genes according to protein–protein interaction (PPI) analysis. These findings indicate that long-term voluntary exercise might protect hippocampal synapses and affect the function and activation of microglia, the AGE/RAGE signaling pathway in microglia and the C1q/C3 complement system in the hippocampus in APP/PS1 mice, and these effects may be related to the Col6a3, Scn5a, Cxcl5, Tdg and Clec4n genes. The current results provide an important basis for identifying targets for the prevention and treatment of AD.

Microglia and astrocytes mediate synapse engulfment in a MER tyrosine kinase-dependent manner after traumatic brain injury.

Recent studies have shown that microglia/macrophages and astrocytes can mediate synaptic phagocytosis through the MER proto-oncokinase in developmental or stroke models, but it is unclear whether the same mechanism is also active in traumatic brain injury. In this study, we established a mouse model of traumatic brain injury and found that both microglia/macrophages and astrocytes phagocytosed synapses and expression of the MER proto-oncokinase increased 14 days after injury. Specific knockout of MER in microglia/macrophages or astrocytes markedly reduced injury volume and greatly improved neurobehavioral function. In addition, in both microglia/macrophages-specific and astrocytes-specific MER knock-out mice, the number of microglia/macrophage and astrocyte phagocytosing synapses was markedly decreased, and the total number of dendritic spines was increased. Our study suggested that MER proto-oncokinase expression in microglia/macrophages and astrocytes may play an important role in synaptic phagocytosis, and inhibiting this process could be a new strategy for treating traumatic brain injury.

Optimisation of ketamine-xylazine anaesthetic dose and its association with changes in the dendritic spine of CA1 hippocampus in the young and old male and female Wistar rats.

A combination of ketamine-xylazine (K-X) is frequently used for anaesthesia in rats. Sex and age affect this cocktail dosage. Ketamine causes a hypnotic effect by blocking NMDA receptors located on the dendritic spine of the CA1 region. The present study aimed to find the optimal dosage of K-X and its association with the changes in dendritic spine number of the CA1 region for aged and young rats of both sexes. We injected 150-4 mg/kg of K-X in young and 100-2 mg/kg in aged Wistar rats intraperitoneally and recorded the onset time and duration of anaesthesia and death percentage. Then, animals were sacrificed, brains removed, cut and after Golgi-Cox staining, the total number of dendritic spines on CA1 was estimated. The findings showed that the onset time of anaesthesia lasted longer and its duration lasted shorter, and the number of mature spines decreased with aging, but sex caused no significant effect. The death percentages in young groups comprise 20% and in the aged groups were lower: 5% in males and 0.0% in females. It seems 100-2 mg/kg of K-X is an optimal dose in aged rats and retains an association with reduction of the mature dendritic spine of CA1.

Exposure to RF-EMF Alters Postsynaptic Structure and Hinders Neurite Outgrowth in Developing Hippocampal Neurons of Early Postnatal Mice.

Exposure to radiofrequency electromagnetic fields (RF-EMFs) has increased rapidly in children, but information on the effects of RF-EMF exposure to the central nervous system in children is limited. In this study, pups and dams were exposed to whole-body RF-EMF at 4.0 W/kg specific absorption rate (SAR) for 5 h per day for 4 weeks (from postnatal day (P) 1 to P28). The effects of RF-EMF exposure on neurons were evaluated by using both pups’ hippocampus and primary cultured hippocampal neurons. The total number of dendritic spines showed statistically significant decreases in the dentate gyrus (DG) but was not altered in the cornu ammonis (CA1) in hippocampal neurons. In particular, the number of mushroom-type dendritic spines showed statistically significant decreases in the CA1 and DG. The expression of glutamate receptors was decreased in mushroom-type dendritic spines in the CA1 and DG of hippocampal neurons following RF-EMF exposure. The expression of brain-derived neurotrophic factor (BDNF) in the CA1 and DG was significantly lower statistically in RF-EMF-exposed mice. The number of post-synaptic density protein 95 (PSD95) puncta gradually increased over time but was significantly decreased statistically at days in vitro (DIV) 5, 7, and 9 following RF-EMF exposure. Decreased BDNF expression was restricted to the soma and was not observed in neurites of hippocampal neurons following RF-EMF exposure. The length of neurite outgrowth and number of branches showed statistically significant decreases, but no changes in the soma size of hippocampal neurons were observed. Further, the memory index showed statistically significant decreases in RF-EMF-exposed mice, suggesting that decreased synaptic density following RF-EMF exposure at early developmental stages may affect memory function. Collectively, these data suggest that hindered neuronal outgrowth following RF-EMF exposure may decrease overall synaptic density during early neurite development of hippocampal neurons.

Serum- and glucocorticoid-inducible kinase 1 activity reduces dendritic spines in dorsal hippocampus

The hippocampus has a well-known role in mediating learning and memory, and its function can be directly regulated by both stress and glucocorticoid receptor activation. Hippocampal contributions to learning are thought to be dependent on changes in the plasticity of synapses within specific subregions, and these functional changes are accompanied by morphological changes in the number and shape of dendritic spines, the physical correlates of these glutamatergic synapses. Serum- and glucocorticoid-inducible kinase 1 (SGK1) regulates dendritic spine morphology in the prefrontal cortex, and modulation of SGK1 expression in mouse hippocampus regulates learning. However, the role of SGK1 in dendritic spine morphology within the CA1 and dentate gyrus regions of the hippocampus are unknown. Thus, herpes simplex viral vectors expressing GFP and various SGK1 constructs, including wild type SGK1, a catalytically inactive version of SGK1 (K127Q), and a phospho-defective version of SGK1 (S78A), were infused into the hippocampus of adult mice and confocal fluorescent microscopy was used to visualize dendritic spines. We show that increasing expression of SGK1 in the dentate gyrus increased the total number of spines, driven primarily by an increase in mushroom spines, while decreasing SGK1 activity (K127Q) in the CA1 region increased the total number of dendritic spines, driven by a significant increase in mushroom and stubby spines. The differential effects of SGK1 in these regions may be mediated by the interactions of SGK1 with multiple pathways required for spine formation and stability. As the formation of mature synapses is a crucial component of learning and memory, this indicates that SGK1 is a potential target in the pathway underlying stress-associated changes in cognition and memory.

DHCR24 exerts neuroprotection upon inflammation-induced neuronal death.

BackgroundDHCR24, involved in the de novo synthesis of cholesterol and protection of neuronal cells against different stress conditions, has been shown to be selectively downregulated in neurons of the affected brain areas in Alzheimer’s disease.MethodsHere, we investigated whether the overexpression of DHCR24 protects neurons against inflammation-induced neuronal death using co-cultures of mouse embryonic primary cortical neurons and BV2 microglial cells upon acute neuroinflammation. Moreover, the effects of DHCR24 overexpression on dendritic spine density and morphology in cultured mature mouse hippocampal neurons and on the outcome measures of ischemia-induced brain damage in vivo in mice were assessed.ResultsOverexpression of DHCR24 reduced the loss of neurons under inflammation elicited by LPS and IFN-γ treatment in co-cultures of mouse neurons and BV2 microglial cells but did not affect the production of neuroinflammatory mediators, total cellular cholesterol levels, or the activity of proteins linked with neuroprotective signaling. Conversely, the levels of post-synaptic cell adhesion protein neuroligin-1 were significantly increased upon the overexpression of DHCR24 in basal growth conditions. Augmentation of DHCR24 also increased the total number of dendritic spines and the proportion of mushroom spines in mature mouse hippocampal neurons. In vivo, overexpression of DHCR24 in striatum reduced the lesion size measured by MRI in a mouse model of transient focal ischemia.ConclusionsThese results suggest that the augmentation of DHCR24 levels provides neuroprotection in acute stress conditions, which lead to neuronal loss in vitro and in vivo.

Beta-hydroxy-beta-methylbutyrate ameliorates aging effects in the dendritic tree of pyramidal neurons in the medial prefrontal cortex of both male and female rats

Beta-hydroxy-beta-methylbutyrate (HMB), a supplement commonly used to maintain muscle in elderly and clinical populations, has been unexplored in the aging brain. In both healthy aging humans and rat models, there are cognitive deficits associated with age-related dendritic shrinkage within the prefrontal cortex. The present study explores the effects of relatively short- and long-term (7 and 31 weeks) oral HMB supplementation starting at 12 months of age in male and female rats on the dendritic tree of layer 5 pyramidal neurons in the medial prefrontal cortex. Since female rats continue to secrete ovarian hormones after reaching reproductive senescence, middle-aged female rats were ovariectomized to model humans. As expected, there were fewer spines and a retraction of dendritic material in the apical and basilar trees in old age controls of both sexes compared with their middle-aged counterparts. However, these losses did not occur in the HMB-treated rats in either dendrites or the total number of dendritic spines. Thus, HMB forestalled the effects of aging on the dendritic tree of this population of neurons.

Nebracetam Inhibited Hippocampus Neurons Injury Induced by Aβ25-35 in MRTF-A-CArG Manner via ERK1/2 Pathway

Nebracetam has been recently proposed to have a neuroprotective action and cognitive enhancing effect being characteristic of a nootropic drug, while the mechanisms remained ambiguity. In this study, we investigated the protective effects of nebracetam on hippocampus neurons injury-induced by β-amyloid protein(Aβ25-35)and its mechanisms. Hippocampus neurons were treated with nebracetam (0.05 mM, 0.2 mM or 0.8 mM) or Aβ25-35 (20 uM/L). We found that Nebracetam significantly reduced apoptotic induced by Aβ25-35 and increase in the total number of dendritic spines and dendritic spine density in a dose-dependent manner. RT-PCR assay and Western blotting analysis revealed that nebracetam increased the expressions of myeloid cell leukemia-1 (Mcl-1), B-cell lymphoma-2 (Bcl-2) and activity regulated cytoskeleton associated protein (Arc) in Aβ25-35-treated hippocampus neurons. Cotreatment nebracetam with MRTF-A (Myocardin-related transcription factor-A) siRNA reversed Mcl-1, Bcl-2 and Arc mRNA and protein levels. What’s more, the luciferase assays indicated that the transcriptional activities of Mcl-1, Bcl-2 and Arc genes were significantly abolished by MRTF-A siRNA while it showed no changes on activities of mut Mcl- 1-promoter-luc, mut Bcl-2-promoter-luc and mut Arc-promoter-luc. Additionally, the up-regulation of Mcl-1, Bcl-2 and Arc protein expressions in nebracetam-treated group was inhibited by extracellular signal regulated protein kinase 1/2 (ERK1/2) inhibitor PH98059. These results demonstrated that nebracetam inhibited Aβ25-35-induced hippocampus neurons injury by enhancing the transactivity of Mcl-1, Bcl-2 and Arc, which may actively based in MRTF-A-CArGdependent manner by thwarting the ERK1/2 pathway.

Structural changes in AMPA-receptive neurons in the nucleus of the solitary tract of spontaneously hypertensive rats.

The baroreceptor reflex is critical for homeostatic regulation of blood pressure and is initiated centrally by glutamate release from baroreceptive afferents onto neurons in the nucleus of the solitary tract that activates AMPA-type glutamate receptors. The GluR1 subunit of the AMPA receptor is located at postsynaptic sites within the nucleus of the solitary tract, particularly in dendritic spines, which are important sites for synaptic plasticity. We tested whether the distribution of GluR1 changes after sustained hypertension, which alters baroreceptor afferent activity. We examined the distribution of GluR1 in the nucleus of the solitary tract of both hypertensive (spontaneously hypertensive) and normotensive (Wistar-Kyoto) rats at the light microscopic and electron microscopic levels. There were more GluR1-containing dendritic spines in the nucleus of the solitary tract of hypertensive rats compared with normotensive rats, which was attributable to an increase in the proportion of dendritic spines containing GluR1 as well as an increase in the total number of dendritic spines. The differences were only seen after the development of hypertension and were not seen in rostral regions of the nucleus of the solitary tract. In the spontaneously hypertensive rat, many synapses on GluR1-containing dendrites had the morphological features of synapses undergoing dynamic changes, including the presence of perforated synapses. These results suggest that changes in afferent activity to the nucleus of the solitary tract during sustained hypertension alter both the dendritic structure and AMPA receptor content of some neurons. These structural changes may be a substrate for central resetting of the baroreceptor reflex.

Experience- and Age-Related Outgrowth of Intrinsic Neurons in the Mushroom Bodies of the Adult Worker Honeybee

A worker honeybee performs tasks within the hive for approximately the first 3 weeks of adult life. After this time, it becomes a forager, flying repeatedly to collect food outside of the hive for the remainder of its 5-6 week life. Previous studies have shown that foragers have an increased volume of neuropil associated with the mushroom bodies, a brain region involved in learning, memory, and sensory integration. We report here that growth of the mushroom body neuropil in adult bees occurs throughout adult life and continues after bees begin to forage. Studies using Golgi impregnation asked whether the growth of the collar region of the mushroom body neuropil was a result of growth of the dendritic processes of the mushroom body intrinsic neurons, the Kenyon cells. Branching and length of dendrites in the collar region of the calyces were strongly correlated with worker age, but when age-matched bees were directly compared, those with foraging experience had longer, more branched dendrites than bees that had foraged less or not at all. The density of Kenyon cell dendritic spines remained constant regardless of age or behavioral state. Older and more experienced foragers therefore have a greater total number of dendritic spines in the mushroom body neuropil. Our findings indicate that, under natural conditions, the cytoarchitectural complexity of neurons in the mushroom bodies of adult honeybees increases as a function of increasing age, but that foraging experience promotes additional dendritic branching and growth.

Interlaminar differences in the pyramidal cell phenotype in cortical areas 7 m and STP (the superior temporal polysensory area) of the macaque monkey.

Pyramidal neurones were injected with Lucifer Yellow in slices cut tangential to the surface of area 7 m and the superior temporal polysensory area (STP) of the macaque monkey. Comparison of the basal dendritic arbors of supra- and infragranular pyramidal neurones (n = 139) that were injected in the same putative modules in the different cortical areas revealed variation in their structure. Moreover, there were relative differences in dendritic morphology of supra- and infragranular pyramidal neurones in the two cortical areas. Sholl analyses revealed that layer III pyramidal neurones in area STP had considerably higher peak complexity (maximum number of dendritic intersections per Sholl circle) than those in layer V, whereas peak complexities were similar for supra- and infragranular pyramidal neurones in area 7 m. In both cortical areas, the basal dendritic trees of layer III pyramidal neurones were characterized by a higher spine density than those in layer V. Calculations of the total number of dendritic spines in the "average" basal dendritic arbor revealed that layer V pyramidal neurones in area 7 m had twice as many spines as cells in layer III (4535 and 2294, respectively). A similar calculation for neurones in area STP revealed that layer III pyramidal neurones had approximately the same number of spines as cells in layer V (3585 and 3850 spines, respectively). Relative differences in the branching patterns of, and the number of spines in, the basal dendritic arbors of supra- and infragranular pyramidal neurones in the different cortical areas may allow for integration of different numbers of inputs, and different degrees of dendritic processing. These results support the thesis that intra-areal circuitry differs in different cortical areas.

Aging reverts to juvenile conditions the synaptic connectivity of cerebral cortical pyramidal shafts

Quantitative analysis of the total number and distribution of dendritic spines along the apical shafts of layer V cerebral cortical pyramids has been performed on aging rats (90–120 to 1,135 days old) and on rats during the period of early and late development (10–80 days). As expected from previous works, present results show that the total number of dendritic spines along the shafts increase from 10 to 80 days, after which it starts to gradually decrease until the last age studied (1,135 days). The quantitative analysis of the effect of aging on the relative decrease of dendritic spines shows that this decrease starts being homogeneous along the whole length of the apical shafts and that from a certain age onwards, estimated according to present results in 400 days, this effect is significantly more pronounced in layers IV and III-II than in deep layers. Furthermore, the comparison made between the distribution of dendritic spines along the apical shafts of pyramidal neurons of old and young animals has shown that aging produces a regression of this distribution to juvenile conditions.

The effects of intrauterine growth retardation on the development of the Purkinje cell dendritic tree in the cerebellar cortex of fetal sheep: A note on the ontogeny of the Purkinje cell

The development of the fetal sheep cerebellum at 80, 100, 120 and 140 days gestation (term = 146 days) and 3 months postnatally was studied using Nissl stained sections and rapid Golgi preparations. The most rapid expansion of the Purkinje cell dendritic tree occurred between 100 and 120 days of gestation (5–6 fold increase in area). By 140 days it had acquired its adult form after which time growth continued mainly in the vertical direction. The effects of intrauterine growth retardation on the growth of granule and Purkinje cell dendrites in the cerebellar cortex of fetal sheep (140 days) were investigated in Golgi preparations. Compared with control cerebella the length (but not the number) of granule cell dendrites was reduced by 14% (P<0.01); the area of the Purkinje cell dendritic field was reduced by 20% (P<0.01); the branching density was reduced by 8% (P<0.01); the total branch length was reduced by 27% (P<0.002); the density of dendritic spines per row was not affected. These factors resulted in a decrease of 26% (P<0.002) in the total number of dendritic spines per row per Purkinje cell.These findings show that the growth of granule cell dendrites and the Purkinje cell dendritic tree have been significantly affected by chronic intrauterine deprivation. Such structural abnormalities could affect the pattern of neuronal connectivity and could be associated with functional deficits.

Differentiation of granule cell dendrites in the dentate gyrus of the rhesus monkey: a quantitative Golgi study.

The differentiation of granule cell dendrites in the dentate gyrus of the hippocampal region was studied in a series of developing fetal and postnatal rhesus monkeys whose brains were processed by the rapid Golgi method. The total combined lengths of dendrites, the total number of dendritic spines, and their density on the proximal, middle, and distal thirds of the dendritic shafts were determined at embryonic days 58, 95, 120, 153, term (165), postnatal days 3, 20, 60, 150, 365, and adults. At all ages examined, granule cells exhibited various levels of maturation with the more differentiated cells being situated in the superficial strata of the granular layer and the less mature cells lying in progressively deeper positions, thus conforming to the outside-to-inside spatiotemporal gradient of their genesis. Quantitative analysis shows that, in this primate, hippocampal granule cells differentiate mainly in the second half of gestation with all measured parameters attaining mature values by the time of birth. However, the analysis also reveals a transient phase of exuberant postnatal development which involves excessive dendritic branching, regional changes in dendritic length, overproduction of dendritic spines, and redistribution of spines within the molecular layer. After reaching peak values around the middle of the first year of life, these parameters decrease and in adult monkeys fall back to the neonatal level.

Effects of climbing fiber destruction on large dendrite spines of Purkinje cells.

The number and freeze-fracture membrane organization of spines on Purkinje cell dendrites were studied in rats after destruction, by intraperitoneal injection of 3-acetyl-pyridine (3-AP), of the climbing fiber afferents to the cerebellum. The results obtained show that: (1) there is a 1.6 fold increase in the total number of dendritic spines in the 3-AP-treated animals as compared to controls, but no change in the total number of spine synaptic profiles; (2) the spines from main dendrites in both control and 3-AP-treated animals have more than 1,000 IMP/micron 2 of P-face membrane; and, (3) the spines formed on Purkinje cell dendrites in the absence of their presynaptic axons have the same P-face membrane organization (i.e. more than 1,000 IMP/micron 2) as spines normally innervated by afferent climbing fibers. These data suggest that each type of Purkinje cell spine has a specific P-face membrane organization which does not appear to be influenced by presynaptic terminals.

A comparison of dendritic spine number and type on pyramidal neurons of the visual cortex of old adult rats from social or isolated environments.

The present study determined the effect of the housing condition experienced by old adult male rats on the appearance and number of dendritic spines. Specifically, 20-month-old rats were killed following 6 months of living in either a social environment (three to a cage) or living alone. The total number of dendritic spines per unit length was examined along segments of oblique, basal, and apical dendritic branches of pyramidal cells from layers II, III, Va, and Vb of the visual cortex. In addition to determining the total spine number, the spines were differentiated into two topographical categories: those with a lollipop configuration (type L) and those with a nubbin configuration (type N). Our results show that neither the total spine density nor the type L spine density were generally influenced by the two housing conditions. However, the density of type N spines was almost always greater on neurons from rats which had been living alone irrespective of the cortical layer or the dendritic segment counted. Some differences in total spine density and type L spine density were noted when neurons from the same environment but different cortical layers were compared, and these findings are discussed. However, the major focus of this paper was to extend our previous report of a selective increase in type N spines with age. We now show that in addition to increasing with age, type N spine density is also selectively increased by the condition of social deprivation.

Evidence for loss of Purkinje cell dendrites during late development: A morphometric Golgi analysis in the mouse

The late postnatal development of the Purkinje cell dendritic tree in mouse cerebellar vermis was investigated in Golgi preparations by morphometric techniques in order to determine at what age adult characteristics of the Purkinje cell are achieved in the rodent brain which grows continuously throughout adult life. B 6D 2F 1 hybrid mice were sacrificed at 9, 15, 20, 35 and 250 days of age. ‘Hindbrain’ weights (by direct weighing) and vermis volume (determined histometrically from Golgi sections), both increased rapidly from 9 to 20 days of age and continued to increase steadily with advancing age. The growth of Purkinje dendritic field areas, determined by planimetric measurements from Golgi sections, paralleled the growth curves for vermis cross-sectional area, vermis volume and ‘hindbrain’ weight. However, stereological determinations revealed an unexpected disparity between the growth of the Purkinje dendritic field areas and changes in the total length of dendrites of Purkinje cells. The total dendritic branch length per Purkinje cell increased sharply up to 20 days of age but thereafter declined with advancing age. Dendritic spine counts on Purkinje cells revealed no change in the number of dendritic spines per unit length of dendrites between 20 and 250 days of age, however, since the Purkinje cell total branch length declined — calculations suggest that the total number of spines per cell declined after 20 days of age. Thus, the size of the cerebellum and the Purkinje cell dendritic tree continued to enlarge during late postnatal development; however, the total dendritic surface area and the total number of dendritic spines on each Purkinje cell, after reaching a peak at 20 days of age, declined with advancing age. The data suggest that the late postnatal development of the Purkinje cell dendritic tree is characterized by resorption as well as dendritic growth. The functional significance of such developmental remodelling is unknown.