Increase In Cell Body Size Research Articles

CGAS/STING signaling pathway-mediated microglial activation in the PFC underlies chronic ethanol exposure-induced anxiety-like behaviors in mice

Chronic ethanol consumption is a prevalent condition in contemporary society and exacerbates anxiety symptoms in healthy individuals. The activation of microglia, leading to neuroinflammatory responses, may serve as a significant precipitating factor; however, the precise molecular mechanisms underlying this phenomenon remain elusive. In this study, we initially confirmed that chronic ethanol exposure (CEE) induces anxiety-like behaviors in mice through open field test and elevated plus maze test. The cGAS/STING signaling pathway has been confirmed to exhibits a significant association with inflammatory signaling responses in both peripheral and central systems. Western blot analysis confirmed alterations in the cGAS/STING signaling pathway during CEE, including the upregulation of p-TBK1 and p-IRF3 proteins. Moreover, we observed microglial activation in the prefrontal cortex (PFC) of CEE mice, characterized by significant alterations in branching morphology and an increase in cell body size. Additionally, we observed that administration of CEE resulted in mitochondrial dysfunction within the PFC of mice, accompanied by a significant elevation in cytosolic mitochondrial DNA (mtDNA) levels. Furthermore, our findings revealed that the inhibition of STING by H-151 effectively alleviated anxiety-like behavior and suppressed microglial activation induced by CEE. Our study unveiled a significant association between anxiety-like behavior, microglial activation, inflammation, and mitochondria dysfunction during CEE.

Poloxamer 188-mediated anti-inflammatory effect rescues cognitive deficits in paraquat and maneb-induced mouse model of Parkinson’s disease

Mild cognitive impairment in Parkinson’s disease (PD-MCI) is considered as a nonmotor clinical symptom in Parkinson’s disease (PD). Microglia-mediated inflammation contributes to cognitive function impairment. Poloxamer 188 (P188) is an amphipathic polymer which has cytoprotective effect in 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-induced dopaminergic (DA) neurons degeneration in PD. But whether P188 could ameliorate cognitive impairment in PD is still illusive. In the present study, we showed in a mouse model that paraquat (10 mg/kg) and maneb (30 mg/kg) (P + M) treatment intraperitoneally twice a week for 6 consecutive weeks resulted in cognitive deficits and synapse loss in hippocampus, together with DA neuron damage in the substantia nigra pars compacta (SNpc). P188 (0.8 g/kg) injection via tail vein 30 min after P + M administration significantly restored DA neuron numbers in SNpc and synapse density in hippocampus, and alleviated P + M-mediated cognitive function impairment in novel object recognition task and morris water maze task (MWM). Pathological synapse loss might be attributed to increased microglial phagocytic activity and cell density, and P188 prevented P + M-induced phagocytic state changes of microglia, such as increase in cell body size and decrease in process length, and upregulated microglia abundance in hippocampus. Consistently, P188 attenuated P + M-mediated increased mRNA levels of microglia proliferation related CSF1r and CSF2ra, microglial engulfment associated CD68, ICAM1, and ICAM2, and pro-inflammatory IL-6, IL-1β, CD11b, and TNF-α in hippocampus. Together, these findings suggest that the biocompatible polymer P188 blunts microglia activation which may promote synaptic loss and exacerbate cognitive function in a mouse model of PD-MCI.

Hippocampal microglia modifications in C57Bl/6 Pahenu2 and BTBR Pahenu2 phenylketonuria (PKU) mice depend on the genetic background, irrespective of disturbed sleep patterns.

Toxic levels of phenylalanine in blood and brain is a characteristic of (untreated) phenylketonuria (PKU), leading to cognitive deficits in PKU mice. In addition, our recent findings showed that PKU mice (as well as PKU patients) have a disturbed sleep/wake cycle. As a consequence, sleep loss may contribute to cognitive deficits in PKU. Sleep loss has been linked to increased activation of microglia in the hippocampus. In this study, we set out to examine morphological features of the microglia population in the hippocampus of the mouse PKU model, using both the C57Bl/6 and the BTBR strain and their wild-type controls (age 5.3 ± 0.5 months; n = 16 per group, both males and females; n = 8 each). Microglial activation is reflected by retraction and thickening of the dendritic branches and an increase in cell body size of a microglial cell. Such morphological changes of microglia were studied by way of immunohistochemical staining for Iba-1, a microglia-specific calcium binding protein. We measured the number of microglia in seven subregions of the dorsal hippocampus. The level of microglial activation was determined, based on the ratio between the soma size and total cell size (soma size plus the area covered by the dendritic branches). Results showed subtle but statistical significant activation of hippocampal microglia in the C57Bl6, but not in the BTBR, PKU mice when compared with their wild-type controls. Also the total number of microglia was higher in the C57Bl/6 PKU (compared to the wild-type) mouse, but not in the BTBR PKU mouse. It is concluded that the C57Bl/6 PKU mouse has mildly higher microglia activity, which may support rather than hamper hippocampal homeostasis. The results further indicate that high levels of phenylalanine or disturbed sleep patterns do not consequently cause hippocampal microglial activation in the PKU mouse. It is currently unknown why the two PKU mouse strains show these differences in number and activation level of their hippocampal microglia, and to what extent it influences hippocampal functioning. Further scrutinizing the role of microglia functioning in the context of PKU is therefore warranted.

Essential Role of Linx/Islr2 in the Development of the Forebrain Anterior Commissure

Linx is a member of the leucine-rich repeat and immunoglobulin family of membrane proteins which has critical roles in the development of the peripheral nervous system and forebrain connectivity. A previous study showed that Linx is expressed in projection neurons in the cortex and in cells that comprise the passage to the prethalamus that form the internal capsule, indicating the involvement of Linx in axon guidance and cell-cell communication. In this study, we found that Linx-deficient mice develop severe hydrocephalus and die perinatally by unknown mechanisms. Importantly, mice heterozygous for the linx gene exhibited defects in the development of the anterior commissure in addition to hydrocephalus, indicating haploinsufficiency of the linx gene in forebrain development. In N1E-115 neuroblastoma cells and primary cultured hippocampal neurons, Linx depletion led to impaired neurite extension and an increase in cell body size. Consistent with this, but of unknown significance, we found that Linx interacts with and upregulates the activity of Rho-kinase, a modulator of many cellular processes including cytoskeletal organization. These data suggest a role for Linx in the regulation of complex forebrain connectivity, and future identification of its extracellular ligand(s) will help clarify this function.

Brain inflammatory cytokines and microglia morphology changes throughout hibernation phases in Syrian hamster

Hibernators tolerate low metabolism, reduced cerebral blood flow and hypothermia during torpor without noticeable neuronal or synaptic dysfunction upon arousal. Previous studies found extensive changes in brain during torpor, including synaptic rearrangements, documented both morphologically and molecularly. As such adaptations may represent organ damage, we anticipated an inflammatory response in brain during specific hibernation phases. In this study, signs of inflammation in the brain were investigated in the Syrian hamster hippocampus (Mesocricetus Auratus) both during hibernation (torpor and arousal phases) and in summer and winter euthermic animals.mRNA expression of the pro-inflammatory cytokines TNF-α, IL-6 and IL-1β was quantified by RT-qPCR. Morphological changes of microglia were studied by immunohistochemistry staining for IBA-1. Activation of microglia based on retraction and thickening of the dendritic branches and an increase in cell body size was quantified by calculation of cell body size to total cell size ratio.Expression of pro-inflammatory cytokines was upregulated early in arousal (90 min), and normalized after 8 h of arousal. Substantial loss of microglia ramification was found throughout torpor and early arousal together with a 2-fold increase in the cell body size to total cell size ratio. Notably, microglia changes were fully reversed in late arousal (8 h) to euthermic levels.These results demonstrate an upregulation of inflammatory cytokines and signs of microglia activation during hibernation, which completely resolves by late arousal. Activation of this response may serve to prevent or offset brain damage resulting from the substantial physiological changes accompanying torpor and their rapid change during early arousal.

Cleavage of Hyaluronan and CD44 Adhesion Molecule Regulate Astrocyte Morphology via Rac1 Signalling.

Communication of cells with their extracellular environment is crucial to fulfill their function in physiological and pathophysiological conditions. The literature data provide evidence that such a communication is also important in case of astrocytes. Mechanisms that contribute to the interaction between astrocytes and extracellular matrix (ECM) proteins are still poorly understood. Hyaluronan is the main component of ECM in the brain, where its major receptor protein CD44 is expressed by a subset of astrocytes. Considering the fact that functions of astrocytes are tightly coupled with changes in their morphology (e.g.: glutamate clearance in the synaptic cleft, migration, astrogliosis), we investigated the influence of hyaluronan cleavage by hyaluronidase, knockdown of CD44 by specific shRNA and CD44 overexpression on astrocyte morphology. Our results show that hyaluronidase treatment, as well as knockdown of CD44, in astrocytes result in a “stellate”-like morphology, whereas overexpression of CD44 causes an increase in cell body size and changes the shape of astrocytes into flattened cells. Moreover, as a dynamic reorganization of the actin cytoskeleton is supposed to be responsible for morphological changes of cells, and this reorganization is controlled by small GTPases of the Rho family, we hypothesized that GTPase Rac1 acts as a downstream effector for hyaluronan and CD44 in astrocytes. We used FRET-based biosensor and a dominant negative mutant of Rac1 to investigate the involvement of Rac1 activity in hyaluronidase- and CD44-dependent morphological changes of astrocytes. Both, hyaluronidase treatment and knockdown of CD44, enhances Rac1 activity while overexpression of CD44 reduces the activity state in astrocytes. Furthermore, morphological changes were blocked by specific inhibition of Rac1 activity. These findings indicate for the first time that regulation of Rac1 activity is responsible for hyaluronidase and CD44-driven morphological changes of astrocytes.

Morphometric characterization of microglial phenotypes in human cerebral cortex

BackgroundMicroglia can adopt different morphologies, ranging from a highly ramified to an amoeboid-like phenotype. Although morphological properties of microglia have been described in rodents, little is known about their fine features in humans. The aim of this study was to characterize the morphometric properties of human microglia in gray and white matter of dorsal anterior cingulate cortex (dACC), a region implicated in behavioral adaptation to neuroinflammation. These properties were compared to those of murine microglia in order to gain a better appreciation of the differences displayed by these cells across species.MethodsPostmortem dACC samples were analyzed from 11 individuals having died suddenly without any history of neuroinflammatory, neurodegenerative, nor psychiatric illness. Tissues were sectioned and immunostained for the macrophage marker Ionized calcium binding adaptor molecule 1 (IBA1). Randomly selected IBA1-immunoreactive (IBA1-IR) cells displaying features corresponding to commonly accepted microglial phenotypes (ramified, primed, reactive, amoeboid) were reconstructed in 3D and all aspects of their morphologies quantified using the Neurolucida software. The relative abundance of each morphological phenotype was also assessed. Furthermore, adult mouse brains were similarly immunostained, and IBA1-IR cells in cingulate cortex were compared to those scrutinized in human dACC.ResultsIn human cortical gray and white matter, all microglial phenotypes were observed in significant proportions. Compared to ramified, primed microglia presented an average 2.5 fold increase in cell body size, with almost no differences in branching patterns. When compared to the primed microglia, which projected an average of six primary processes, the reactive and amoeboid phenotypes displayed fewer processes and branching points, or no processes at all. In contrast, the majority of microglial cells in adult mouse cortex were highly ramified. This was also the case following a postmortem interval of 43 hours. Interestingly, the morphology of ramified microglia was strikingly similar between species.ConclusionsThis study provides fundamental information on the morphological features of microglia in the normal adult human cerebral cortex. These morphometric data will be useful for future studies of microglial morphology in various illnesses. Furthermore, this first direct comparison of human and mouse microglia reveals that these brain cells are morphologically similar across species, suggesting highly conserved functions.

Hormonal control of cell death in a sexually dimorphic song nucleus in the zebra finch.

The song control nuclei of the brain of the male zebra finch (Poephila guttata) contain more neurons of larger cross-sectional area and more extensive innervation than those in the female. The sexual dimorphism of nucleus robustus archistriatalis (RA), one of the song nuclei, arises from neuronal atrophy and death in the female brain as well as from an increase in cell-body size and afferent terminals from other forebrain nuclei in the male. Subcutaneous implantation of a slow-release pellet of oestrogen in a female chick not only prevents her RA neurons from dying but also promotes their growth and innervation. The masculinizing effects of oestrogen on RA appear to be limited to a period of 35-40 days after hatching. Oestrogen may act on RA neurons indirectly by promoting their innervation from other forebrain song nuclei.

Evidence for the direct role of acetylcholinesterase in neurite outgrowth in primary dorsal root ganglion neurons

Dorsal root ganglion (DRG) neurons show a transient peak expression of acetylcholinesterase (AChE) during periods of axonal outgrowth prior to synaptogenesis, suggesting that AChE has a non-enzymatic role during development. We have previously shown that perturbation of cell surface AChE in cultured embryonic rat DRG neurons results in decreased neurite outgrowth and neurite detachment. In this report, we demonstrate a direct correlation between endogenous AChE content and neurite outgrowth in primary DRG neurons. Adenoviral vectors were constructed using full-length rat AChE T cDNA in either the sense or antisense orientations to overexpress or knock down AChE expression, respectively. Treatment with the sense-expressing vector produced a 2.5-fold increase in AChE expression and a 2-fold increase in neurite length compared with either untreated or null virus-treated control cells. Conversely, treatment with the antisense-expressing vector reduced AChE expression by 40% and resulted in a reduction in neurite length of similar magnitude. We also observed that overexpression of AChE resulted in greater branching at the distal tips of each primary neurite as well as an increase in cell body size. These findings further indicate that AChE expressed on the axonal surface of developing DRG neurons may modulate their adhesive properties and thereby support axonal development.

Aspects of early postnatal development of cortical neurons that proceed independently of normally present extrinsic influences.

To examine the contribution of local versus extrinsic influences on postnatal development of cortical neurons, we compared the maturation of deep (infragranular) layer neurons in isolated slices of neocortex grown in organotypic culture to a similar population of neurons developing in vivo. All slice cultures were prepared from sensorimotor cortices of newborn mice (P0) and neurons in these cultures were examined at daily intervals during the first 9 days in vitro (DIV). The maturational state of neurons developing in vivo over this same time period was assessed in acute slices prepared from animals of equivalent postnatal age, P1-P9. Electrophysiological recordings were obtained from neurons in both cultured and acute slices, using Lucifer yellow filled whole-cell recording electrodes, enabling subsequent morphometric analysis of the labeled cells. We report significant changes in both cellular morphology and electrical membrane properties of these deep layer cortical neurons during the first week in culture. Morphological maturation over this time period was characterized by a two- to three-fold increase in cell body size and total process length, and an increase in dendritic complexity. In this same population of cells a three-fold decrease in input resistance and changes in the action potential waveform, including a two-fold decrease in the AP duration, also occur. The degree of morphological and electrophysiological differentiation of individual neurons was highly correlated across developmental ages, suggesting that the maturational state of a cell is reflected in both cellular morphology and intrinsic membrane properties. A remarkably similar pattern of neuronal maturation was observed in neurons in layers V, VI/SP examined in acute slices prepared from animals between P1-P9. Because our culture system preserves many aspects of the local cortical environment while eliminating normal extrinsic influences (including thalamic, brainstem, and callosal connections), our findings argue that this early phase of neuronal differentiation, including the rate and extent of dendritic growth and development of AP waveform, results from instructive and/or permissive local influences, and appears to proceed independently of the many normally present extrinsic factors.

Changes in size and dendritic arborization patterns of adult cat spinal alpha-motoneurons following permanent axotomy.

This study was performed to analyse quantitatively the changes in dimensions and dendritic branching patterns of adult cat spinal alpha-motoneurons following permanent axotomy, i.e., in a situation in which the transected motoraxons are prevented from reinnervating their peripheral target muscle. After transection and ligation of the medial gastrocnemius nerve of adult cats, homonymous alpha-motoneurons were intracellularly labelled with horseradish peroxidase and subjected to quantitative light microscopic analyses. The cell bodies and proximal dendrites were studied at 3, 6, and 12 weeks after the axotomy. An initial increase in cell body size at 3 weeks was followed by a gradual return towards normal values. The mean diameter of the stem dendrites was decreased at all time periods studied, and the combined diameter of the stem dendrites was reduced at 12 weeks after the axotomy. Entire dendritic trees were reconstructed at 12 weeks postoperatively, and the regression equations describing the correlations between dendritic stem diameter, on one hand, and the size of the entire dendrite, on the other, were used to calculate the total dendritic length, volume, and membrane area of whole axotomized motoneurons. The dendritic branching patterns were also analysed. In comparison with normal medial gastrocnemius alpha-motoneurons, the dendritic membrane area and volume of the axotomized cells had decreased by 36% and 29%, respectively, at 12 weeks after the axotomy. This reduction in dendritic size was due to a loss of preterminal and terminal dendritic segments. Abnormal dendritic elongations were observed in 2 of 16 completely reconstructed dendrites.

Axonal sprouting after botulinum toxin does not elicit a histological axon reaction

In an attempt to determine which elements of the axon reaction are essential for early axonal outgrowth, axonal sprouting was induced with botulinum toxin (BoTx) and the nerve cell body changes compared with those accompanying axonal growth after nerve trauma. Anterior horn cells of mice were examined histologically at times ranging from 3 days to 3 weeks after either BoTx hindlimb injection or sciatic nerve crush. After sciatic nerve crush there was dispersion of Nissl substance, increase in cell body size, and an increase in neurofilament protein staining. None of these changes were found after BoTx-induced terminal axonal sprouting, suggesting that these morphological features of the axon reaction are not essential for early axonal outgrowth.

Starburst amacrine cells: morphological constancy and systematic variation in the anisotropic field of rabbit retinal neurons

Starburst amacrine cells of rabbit retina have been characterized previously in terms of their highly distinctive and regular dendritic geometry. They have been identified as probable cholinergic neurons of the retina and have been shown to direct output solely to ganglion cells. The objectives of this paper are to chart the variation of starburst amacrine cells across the retina, to register the morphological features which are held constant for individual cells, and to examine factors which may remain invariant for the population with change in retinal position. Starburst amacrine cells occur as two completely segregated mirror-symmetrical populations, type a and type b cells, separately serving OFF and ON pathways, respectively. They are treated here as two distinct subpopulations with very similar features. A characteristic morphological feature of both types, related to branching pattern and best seen in flat view, is the location of boutons in the distal annular zone. This is the effective zone of synaptic output, which is constant at 50 to 60% of dendritic field area, regardless of the cell's retinal location. Both type a and type b cells exhibit systematic increase in cell body size and dendritic field diameter, and systematic decrease in frequency of branching and of synaptic boutons with perpendicular distance from the visual streak. These rates of increase or decrease fall off considerably at distances greater than about 1.5 mm dorsal and ventral to the visual streak, but at this distance, the dendritic field diameters of cells in dorsal retina are about 65% larger than the diameters of cells in ventral retina. When type a and type b cells are closely compared, they are seen to differ in several respects. Branching patterns of type a and type b cells differ slightly, the latter being more highly branched, and the normalized branching frequency histograms, characteristic for each type, remain constant with changing retinal position. At the same retinal location type a cells always have larger dendritic field diameters than type b cells. This difference is significant in ventral retina, out to a distance of at least 4.5 mm from the streak. The maximum percentage difference in size occurs not at mid-visual streak, but about 1.5 mm ventral to the streak. The population statistics of dendritic field overlap and areal dendritic coverage have been calculated using published data on cell densities. It is concluded that overlap is extraordinarily high (k greater than 25), more than 10 times that calculated for retinal ganglion cells.(ABSTRACT TRUNCATED AT 400 WORDS)