Dendritic Surface Area Research Articles

Impact of a pyridazine derivative on tripartite synapse ultrastructure in hippocampus: a three-dimensional analysis.

We previously discovered a pyridazine derivative compound series that can improve cognitive functions in mouse models of Alzheimer's disease. One of the advanced compounds from this series, LDN/OSU-0215111-M3, was selected as the preclinical development candidate. This compound activates local protein translation at the perisynaptic astrocytic process (PAP) and enhances synaptic plasticity sequentially. While biochemical evidence supports the hypothesis that the compound enhances the structural plasticity of the tripartite synapse, its direct structural impact has not been investigated. Volume electron microscopy was used to study the hippocampal tripartite synapse three-dimensional structure in 3-month-old wild-type FVB/NJ mice after LDN/OSU-0215111-M3 treatment. LDN/OSU-0215111-M3 increased the size of tertiary apical dendrites, the volume of mushroom spines, the proportion of mushroom spines containing spine apparatus, and alterations in the spine distribution across the surface area of tertiary dendrites. Compound also increased the number of the PAP interacting with the mushroom spines as well as the size of the PAP in contact with the spines. Furthermore, proteomic analysis of the isolated synaptic terminals indicated an increase in dendritic and synaptic proteins as well as suggested a possible involvement of the phospholipase D signaling pathway. To further validate that LDN/OSU-0215111-M3 altered synaptic function, electrophysiological studies showed increased long-term potentiation following compound treatment. This study provides direct evidence that pyridazine derivatives enhance the structural and functional plasticity of the tripartite synapse.

Chronic glial activation causes cholinergic cell loss in the basal forebrain during pathological aging

AbstractBackgroundNeuroinflammation, described by chronic glial reactivation lead to gradual neurodegeneration during pathological aging, contributing to disorders like Alzheimer’s disease (AD). Cholinergic cell loss in the basal forebrain (BF) including the medial septum (MS) is associated with AD; however the underlying mechanism is still unknown. Hence, this study investigated the effects of aging and chronic neuroinflammation on the MS cholinergic cell numbers and morphology.MethodAged, 12 and 24 months WT and GFAP‐IL6 mice (presenting IL‐6 overexpression under the GFAP promoter, resulting in chronic glial activation) were used. Immunohistochemistry combined with unbiased stereology and 3D morphology analysis were used to estimate the number and morphology of Iba1+ microglia and ChAT+ cholinergic cells in the MS. Transcriptomic analysis of the MS was performed using qPCR.ResultStereological estimation of MS microglia number displayed a significant 25% increase in GFAP‐IL6 mice compared to control WT (12M). A significant 30% increase was obtained for GFAP‐IL6 (24M) mice compared to control (24M). Furthermore, a significant 23% increase in microglia was described for GFAP‐IL6 (24M) compared to the GFAP‐IL6 (12M) mice. A significant 28% and 38% decrease in microglial 3D surface area, and volume respectively were observed between WT and GFAP‐IL (12M) mice, as well as 26% and 34% decrease respectively between WT (12M) and (24M), resembling reactive microglial morphology. Meanwhile, cholinergic cell number displayed a significant 31% decrease in GFAP‐IL6 (12M) mice compared to WT (12M). While a significant 30% decrease was displayed in GFAP‐IL6 (24M) mice compared to WT (24M) mice. There was a tendency for the cholinergic cell number to decrease with ageing among control and GFAP‐IL6 cohorts. Cholinergic cell morphology displayed significant 58% and 67% reduction in the 3D dendritic field surface area, and volume respectively between WT (12M) and GFAP‐IL (12M) mice, as well as 41% and 46% decrease respectively between WT (12M) and (24M), displaying patterns like neuronal degeneration.ConclusionThese findings demonstrate a significant impact of both aging and chronic glial activation alone on cholinergic cell number and morphology in the MS, resembling the cholinergic cell loss in AD, which can exacerbate throughout ageing leading to neurodegenerative impairments.

Postnatal Inhibition of TrkB Kinase Reduces the Number of Phrenic Motor Neurons

During embryonic development, the number of phrenic motor neurons (PhMNs) declines precipitously during the final trimester and continues into the early postnatal period. When BDNF/TrkB signaling is absent in utero, animals do not survive after birth, most likely due to excessive loss of vital motor neurons (e.g., PhMNs). Far less is known about the early postnatal effect of BDNF/TrkB signaling. We have shown that BDNF/TrkB signaling is important in promoting PhMN neuroplasticity in mature rodents. Taken together, we hypothesized that inhibition of BDNF/TrkB signaling during early postnatal development results in fewer PhMNs. Chemo-genetic TrkBF616A mutant mice were used to induce inhibition of TrkB kinase activity in response to oral administration (via drinking water) of a phosphoprotein phosphatase 1 inhibitor derivative (1NMPP1). 1NMPP1-induced TrkB kinase inhibition was initiated at P0 and continued until P21 and compared to untreated control mice. At P28, PhMNs were retrogradely labeled via rhodamine phrenic nerve dip. One day later, mice were euthanized, perfused with 4% paraformaldehyde, and the cervical spinal cord was excised and processed for longitudinal cryosectioning (70 μm). Labeled PhMNs were imaged by 3D high resolution confocal microscopy. The number of PhMNs were counted. PhMN somal surface area and number of primary dendrites were also determined. 1NMPP1-induced inhibition of TrkB kinase resulted in 24% fewer PhMNs (P=0.01) and 21% more primary dendrites (P=0.0002) than control mice. The distribution of PhMN somal surface areas was not affected. We conclude that BDNF/TrkB signaling is essential in promoting survival of PhMNs in the early postnatal period. BDNF/TrkB signaling during postnatal development also plays a role in paring primary dendrites. While inhibition of TrkB kinase did not significantly alter the distribution of PhMN somal surface areas at P28, it is possible that further growth of PhMNs into maturity might have been altered as larger PhMNs emerge as a result of disproportionate growth beyond this age in mice. Supported by National Institutes of Health grants R01-AG044615 (GCS), R01-HL96750 (GCS). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Motor neuron loss and neuromuscular transmission failure following chemogenetic inhibition of BDNF/TrkB signaling in adult rats

Brain derived neurotrophic factor (BDNF) signaling through its high-affinity tropomyosin receptor kinase B (TrkB) is known to have potent effects on motor neuron survival and morphology during development and in neurodegenerative diseases. However, the specific effects of reduced BDNF/TrkB signaling on neuromuscular structure and function in adult mammals are not as well known. In this study, we employed a novel 1NMPP1 sensitive TrkBF616 rat model to evaluate the effect of 14 days inhibition of BDNF/TrkB signaling on the number and morphology of phrenic motor neurons (PhMNs) and diaphragm muscle (DIAm) neurotransmission in adult animals. We hypothesized that reduced BDNF/TrkB signaling results in PhMN loss and impaired DIAm neuromuscular transmission. Adult female and male TrkBF616 rats were divided into 1NMPP1 or vehicle treated groups. Three days prior to treatment, PhMNs in both groups were labeled via intrapleural injection of Alexa-Fluor647 cholera toxin B (CTB). After 11 days of treatment, retrograde axonal transport was assessed by secondary labeling of PhMNs by intrapleural injection of Alexa-Fluor488 CTB. After 14 days of treatment, the spinal cord was excised and 100 μm thick spinal sections containing PhMNs were imaged in 3D using two-channel confocal microscopy. Phrenic nerve and DIAm was excised en bloc, and the extent of neuromuscular transmission failure (NMTF) was assessed by comparing DIAm isometric forces evoked by nerve (40 Hz in 330 ms duration trains repeated each s) compared to direct muscle stimulation (40 Hz 330 ms duration train) superimposed every 15 s. Presynaptic (synaptophysin immunoreactivity) and postsynaptic (α-Bungarotoxin) compartments of neuromuscular junctions (NMJs) were labeled and imaged in 3D by confocal microscopy and the extent of pre- and postsynaptic apposition assessed. 1NMPP1-induced BDNF/TrkB inhibition reduced the total number of PhMNs by ~16%, reduced the mean PhMN somal surface areas by ~25%, reduced PhMN dendritic surface area by ~38%, impaired secondary CTB uptake by 2.5-fold and impaired neuromuscular transmission by ~33%, with no overt evidence of NMJ derangement. We conclude that inhibition of BDNF/TrkB signaling in adult TrkBF616 rats is sufficient to lead to PhMN loss, morphological degeneration, deficits in retrograde axonal transport and impaired DIAm neurotransmission. Supported by NIH: R01-AG44615 and R01-HL146114 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Chemogenetic inhibition of TrkB signalling reduces phrenic motor neuron survival and size

Brain derived neurotrophic factor (BDNF) signalling through its high-affinity tropomyosin receptor kinase B (TrkB) is known to have potent effects on motor neuron survival and morphology during development and in neurodegenerative diseases. Here, we employed a novel 1NMPP1 sensitive TrkBF616 rat model to evaluate the effect of 14 days inhibition of TrkB signalling on phrenic motor neurons (PhMNs). Adult female and male TrkBF616 rats were divided into 1NMPP1 or vehicle treated groups. Three days prior to treatment, PhMNs in both groups were initially labeled via intrapleural injection of Alexa-Fluor-647 cholera toxin B (CTB). After 11 days of treatment, retrograde axonal uptake/transport was assessed by secondary labeling of PhMNs by intrapleural injection of Alexa-Fluor-488 CTB. After 14 days of treatment, the spinal cord was excised 100 μm thick spinal sections containing PhMNs were imaged using two-channel confocal microscopy. TrkB inhibition reduced the total number of PhMNs by ∼16 %, reduced the mean PhMN somal surface areas by ∼25 %, impaired CTB uptake 2.5-fold and reduced the estimated PhMN dendritic surface area by ∼38 %. We conclude that inhibition of TrkB signalling alone in adult TrkBF616 rats is sufficient to lead to PhMN loss, morphological degeneration and deficits in retrograde axonal uptake/transport.

The adenosine A2A receptor antagonist KW6002 distinctly regulates retinal ganglion cell morphology during postnatal development and neonatal inflammation.

Adenosine A2A receptors (A2ARs) appear early in the retina during postnatal development, but the roles of the A2ARs in the morphogenesis of distinct types of retinal ganglion cells (RGCs) during postnatal development and neonatal inflammatory response remain undetermined. As the RGCs are rather heterogeneous in morphology and functions in the retina, here we resorted to the Thy1-YFPH transgenic mice and three-dimensional (3D) neuron reconstruction to investigate how A2ARs regulate the morphogenesis of three morphologically distinct types of RGCs (namely Type I, II, III) during postnatal development and neonatal inflammation. We found that the A2AR antagonist KW6002 did not change the proportion of the three RGC types during retinal development, but exerted a bidirectional effect on dendritic complexity of Type I and III RGCs and cell type-specifically altered their morphologies with decreased dendrite density of Type I, decreased the dendritic field area of Type II and III, increased dendrite density of Type III RGCs. Moreover, under neonatal inflammation condition, KW6002 specifically increased the proportion of Type I RGCs with enhanced the dendrite surface area and volume and the proportion of Type II RGCs with enlarged the soma area and perimeter. Thus, A2ARs exert distinct control of RGC morphologies to cell type-specifically fine-tune the RGC dendrites during normal development but to mainly suppress RGC soma and dendrite volume under neonatal inflammation.

Form, synapses and orientation topography of a new cell type in layer 6 of the cat’s primary visual cortex

Here we report the morpho-functional features of a novel type of deep-layer neuron. The neuron was selected from a large pool of intracellularly labelled cells based on the large cell body, numerous spine-free dendrites with an overall interneuron morphology. However, the axon gave off long-range axons up to 2.8 mm from the parent soma in layers 5/6 before entering the white matter. The boutons were uniformly distributed along the axon without forming distinct clusters. Dendritic length, surface area and volume values were at least 3 times larger than any known cortical neuron types with the exception of giant pyramidal cells of layer 5. Electron microscopy of the boutons revealed that they targeted dendritic spines (78%) and less frequently dendritic shafts (22%). Nearly half of the postsynaptic dendrites were immunopositive to GABA. Superimposing the axonal field on the orientation map obtained with optical imaging showed a preponderance of boutons to cross-orientations (38%) and an equal representation of iso- and oblique orientations (31%). The results suggest an integrating role for the layer 6 stellate neuron which projects to a functionally broad range of neurons in the deep cortical layers and to other cortical and/or subcortical regions.

Effects of membrane androgen receptor binding on synaptic plasticity in primary hippocampal neurons

Androgens play an important role in the regulation of hippocampal synaptic plasticity. While the classical molecular mechanism of androgen's genomic activity is their binding to intracellular androgen receptors (iARs), they can also induce rapid non-genomic effects through specific membrane androgen receptors (mARs). In this study, we aimed to localize and characterize these mARs in primary rat hippocampal neurons. Specific punctate fluorescent signals on the cell surface, observed by testosterone-fetal bovine serum albumin conjugated fluorescein isothiocyanate (T-BSA-FITC), indicated the presence of mARs in hippocampal neurons. T-BSA-FITC binding to the cell membrane was incompletely blocked by the iAR-antagonist flutamide, and mAR binding site was competitively bound by free testosterone (T). Most neurons expressing androgen membrane binding sites are glutamatergic (excitatory), although several are γ-aminobutyric acid (GABA)ergic (inhibitory). Confocal microscopy and live-cell imaging techniques were used to observe the real-time rapid effects of androgens on hippocampal dendritic spine morphology. Immunofluorescence cell staining was used to observe their effects on the postsynaptic density protein 95 (PSD95) and synapsin (SYN) synaptic markers. While androgens did not cause a short-term increase in dendritic spine density of rat primary hippocampal neurons, they promoted the transformation of dendritic spines from thin to mushroom, promoted dendritic spine maturation, increased dendritic spine surface area, and rapidly increased PSD95 and SYN expression in the primary hippocampal neurons. Hippocampal synaptosomes were prepared using the Optiprep and Percoll density gradient two-step centrifuge methods, and the gene expression profiles of the synaptosomes and hippocampus were compared using a gene chip; PSD95 mRNA expression was detected by reverse transcription-polymerase chain reaction. Several mRNAs were detected at the synaptic site, including PSD95. Finally, the Venus-PSD95 plasmid was constructed and transfected into HT22 cells, which is a mouse hippocampal neuronal cell line. The real-time effect of androgen on synaptic protein PSD95 was observed by fluorescence recovery after photobleaching experiments, which involved the translation process of PSD95 mRNA. In conclusion, our findings increased our understanding of how androgens exert the neuroprotective mechanisms on synaptic plasticity.

Direct Detection of Lithium Exchange across the Solid Electrolyte Interphase by 7Li Chemical Exchange Saturation Transfer.

Lithium metal anodes offer a huge leap in the energy density of batteries, yet their implementation is limited by solid electrolyte interphase (SEI) formation and dendrite deposition. A key challenge in developing electrolytes leading to the SEI with beneficial properties is the lack of experimental approaches for directly probing the ionic permeability of the SEI. Here, we introduce lithium chemical exchange saturation transfer (Li-CEST) as an efficient nuclear magnetic resonance (NMR) approach for detecting the otherwise invisible process of Li exchange across the metal–SEI interface. In Li-CEST, the properties of the undetectable SEI are encoded in the NMR signal of the metal resonance through their exchange process. We benefit from the high surface area of lithium dendrites and are able, for the first time, to detect exchange across solid phases through CEST. Analytical Bloch-McConnell models allow us to compare the SEI permeability formed in different electrolytes, making the presented Li-CEST approach a powerful tool for designing electrolytes for metal-based batteries.

Modulating the Pore Architecture of Ice-Templated Dextran Microparticles Using Molecular Weight and Concentration.

Spray freeze drying (SFD) is an ice templating method used to produce highly porous particles with complex pore architectures governed by ice nucleation and growth. SFD particles have been advanced as drug carrier systems, but the quantitative description of the morphology formation in the SFD process is still challenging. Here, the pore space dimensions of SFD particles prepared from aqueous dextran solutions of varying molecular weights (40-200 kDa) and concentrations (5-20%) are analyzed using scanning electron microscopy. Coexisting morphologies composed of cellular and dendritic motifs are obtained, which are attributed to variations in the ice growth mechanism determined by the SFD system and modulation of these mechanisms by given precursor solution properties leading to changes in their pore dimensions. Particles with low-aspect ratio cellular pores showing variation of around 0.5-1 μm in diameter with precursor composition but roughly constant with particle diameter are ascribed to a rapid growth regime with high nucleation site density. Image analysis suggests that the pore volume decreases with dextran solid content. Dendritic pores (≈2-20 μm in diameter) with often a central cellular region are identified with surface nucleation and growth followed by a slower growth regime, leading to the overall dendrite surface area scaling approximately linearly with the particle diameter. The dendrite lamellar spacing depends on the concentration according to an inverse power law but is not significantly influenced by molecular weight. Particles with highly elongated cellular pores without lamellar formation show intermediate pore dimensions between the above two limiting morphological types. Analysis of variance and post hoc tests indicate that dextran concentration is the most significant factor in affecting the pore dimensions. The SFD dextran particles herein described could find use in pulmonary drug delivery due to their high porosity and biocompatibility of the matrix material.

Influence of hexagonal to orthorhombic phase transformation on diffusion-controlled dendrite evolution in directionally solidified Sn–Ni peritectic alloy

The hexagonal to orthorhombic (HO) transformation from β-Ni3Sn2 (hexagonal) phase to α’-Ni3Sn2 (orthorhombic) phase was confirmed in directionally solidified Sn–Ni peritectic alloys. It is shown that the remelting/resolidification process which is caused by both the temperature gradient zone melting (TGZM) and Gibbs−Thomson (G−T) effects can take place on secondary dendrites. Besides, the intersection angle between the primary dendrite stem and secondary branch (θ) is found to increase from π/3 to π/2 as the solidification proceeds. This is the morphological feature of the HO transformation, which can change the diffusion distance of the remelting/ resolidification process. Thus, a diffusion-based analytical model is established to describe this process through the specific surface area (SV) of dendrites. The theoretical prediction demonstrates that the remelting/resolidification process is restricted when the HO transformation occurs during peritectic solidification. In addition, the slope of the prediction curves is changed, indicating the variation of the local remelting/resolidification rates.

Phrenic motor neuron loss in an animal model of early onset hypertonia.

Phrenic motor neuron (PhMN) development in early onset hypertonia is poorly understood. Respiratory disorders are one of the leading causes of morbidity and mortality in individuals with early onset hypertonia, such as cerebral palsy (CP), but they are largely overshadowed by a focus on physical function in this condition. Furthermore, while the brain is the focus of CP research, motor neurons, via the motor unit and neurotransmitter signaling, are the targets in clinical interventions for hypertonia. Furthermore, critical periods of spinal cord and motor unit development also coincide with the timing that the supposed brain injury occurs in CP. Using an animal model of early-onset spasticity (spa mouse [B6.Cg-Glrbspa/J] with a glycine receptor mutation), we hypothesized that removal of effective glycinergic neurotransmitter inputs to PhMNs during development will result in fewer PhMNs and reduced PhMN somal size at maturity. Adult spa (Glrb-/-), and wild-type (Glrb+/+) mice underwent unilateral retrograde labeling of PhMNs via phrenic nerve dip in tetramethylrhodamine. After three days, mice were euthanized, perfused with 4% paraformaldehyde, and the spinal cord excised and processed for confocal imaging. Spa mice had ~30% fewer PhMNs (P = 0.005), disproportionately affecting larger PhMNs. Additionally, a ~22% reduction in PhMN somal surface area (P = 0.019), an 18% increase in primary dendrites (P < 0.0001), and 24% decrease in dendritic surface area (P = 0.014) were observed. Thus, there are fewer larger PhMNs in spa mice. Fewer and smaller PhMNs may contribute to impaired diaphragm neuromotor control and contribute to respiratory morbidity and mortality in conditions of early onset hypertonia.NEW & NOTEWORTHY Phrenic motor neuron (PhMN) development in early-onset hypertonia is poorly understood. Yet, respiratory disorders are a common cause of morbidity and mortality. In spa mice, an animal model of early-onset hypertonia, we found ~30% fewer PhMNs, compared with controls. This PhMN loss disproportionately affected larger PhMNs. Thus, the number and heterogeneity of the PhMN pool are decreased in spa mice, likely contributing to the hypertonia, impaired neuromotor control, and respiratory disorders.

Region-specific effects of copulation on dendritic spine morphology and gene expression related to spinogenesis in the medial preoptic nucleus of male rats

The medial preoptic nucleus (MPN) plays an essential role in the control of male sexual behavior. In rats, the central part of the MPN (MPNc) contains a sexually dimorphic nucleus exhibiting male-biased morphological sex differences. Although it has been suggested that the MPNc of male rats functions to induce sexual arousal, the mechanisms by which male rats are sexually aroused to successfully achieve copulation are poorly understood. We recently showed that increased neuronal activity in the MPNc of male rats during copulation is higher at their first copulation compared with later copulations, indicating that a plastic change in excitatory synaptic transmission occurs with copulatory experience. In this study, we tested the hypothesis that changes to dendritic spines at structural and molecular levels occur following copulatory experience. First, we examined the effects of at least two copulations on the morphology of dendrites and spines in the MPNc and in the lateral and medial parts of the MPN (MPNlm) of male rats. In the MPNc, the total number of dendrites and their branches, and the surface area of dendrites were not significantly affected by copulation. However, the copulatory experience, specifically experience of ejaculation, significantly reduced the density of mushroom spines but not of filopodia, thin or stubby spines in the MPNc. In the MPNlm, the copulatory experience, specifically experience of ejaculation, significantly increased the surface area of dendrites, although there was no significant effect of copulation on spine density. Next, we measured the mRNA levels of genes encoding actin-binding proteins related to spinogenesis after male rats had copulated for their first and second times. Copulatory stimuli, especially stimuli from ejaculation, significantly reduced the mRNA levels of drebrin A and spinophilin in the MPNc but not in the MPNlm. These results indicate that copulatory experiences, especially experience of ejaculation, reduce spine density in the MPNc of male rats, which may result, in part, from downregulation of genes encoding actin-binding proteins.

Neuronal plasticity affects correlation between the size of dendritic spine and its postsynaptic density

Structural plasticity of dendritic spines is thought to underlie memory formation. Size of a dendritic spine is considered proportional to the size of its postsynaptic density (PSD), number of glutamate receptors and synaptic strength. However, whether this correlation is true for all dendritic spine volumes, and remains stable during synaptic plasticity, is largely unknown. In this study, we take advantage of 3D electron microscopy and reconstruct dendritic spines and cores of PSDs from the stratum radiatum of the area CA1 of organotypic hippocampal slices. We observe that approximately 1/3 of dendritic spines, in a range of medium sizes, fail to reach significant correlation between dendritic spine volume and PSD surface area or PSD-core volume. During NMDA receptor-dependent chemical long-term potentiation (NMDAR-cLTP) dendritic spines and their PSD not only grow, but also PSD area and PSD-core volume to spine volume ratio is increased, and the correlation between the sizes of these two is tightened. Further analysis specified that only spines that contain smooth endoplasmic reticulum (SER) grow during cLTP, while PSD-cores grow irrespectively of the presence of SER in the spine. Dendritic spines with SER also show higher correlation of the volumetric parameters than spines without SER, and this correlation is further increased during cLTP only in the spines that contain SER. Overall, we found that correlation between PSD surface area and spine volume is not consistent across all spine volumes, is modified and tightened during synaptic plasticity and regulated by SER.

Maternal stress during pregnancy predicts methylation of the glucocorticoid receptor gene (NR3C1) in borderline personality disorder

The medial preoptic nucleus (MPN) plays an essential role in the control of male sexual behavior. In rats, the central part of the MPN (MPNc) contains a sexually dimorphic nucleus exhibiting male-biased morphological sex differences. Although it has been suggested that the MPNc of male rats functions to induce sexual arousal, the mechanisms by which male rats are sexually aroused to successfully achieve copulation are poorly understood. We recently showed that increased neuronal activity in the MPNc of male rats during copulation is higher at their first copulation compared with later copulations, indicating that a plastic change in excitatory synaptic transmission occurs with copulatory experience. In this study, we tested the hypothesis that changes to dendritic spines at structural and molecular levels occur following copulatory experience. First, we examined the effects of at least two copulations on the morphology of dendrites and spines in the MPNc and in the lateral and medial parts of the MPN (MPNlm) of male rats. In the MPNc, the total number of dendrites and their branches, and the surface area of dendrites were not significantly affected by copulation. However, the copulatory experience, specifically experience of ejaculation, significantly reduced the density of mushroom spines but not of filopodia, thin or stubby spines in the MPNc. In the MPNlm, the copulatory experience, specifically experience of ejaculation, significantly increased the surface area of dendrites, although there was no significant effect of copulation on spine density. Next, we measured the mRNA levels of genes encoding actin-binding proteins related to spinogenesis after male rats had copulated for their first and second times. Copulatory stimuli, especially stimuli from ejaculation, significantly reduced the mRNA levels of drebrin A and spinophilin in the MPNc but not in the MPNlm. These results indicate that copulatory experiences, especially experience of ejaculation, reduce spine density in the MPNc of male rats, which may result, in part, from downregulation of genes encoding actin-binding proteins.

The diffusion-controlled remelting/resolidification process in directionally solidified Sn-Mn peritectic alloy

The Sn-40at.%Mn peritectic alloy were directionally solidified in a temperature gradient at different growth velocities. It was demonstrated that the diffusion-controlled remelting/resolidification process occurred on the secondary dendrite arms in the mushy zone of Sn-40at.%Mn peritectic alloy. Theoretical analysis has shown that the diffusion-controlled solute transport which occurred between secondary dendrite arms was produced by both the temperature gradient zone melting (TGZM) and the Gibbs-Thomson effects (capillary effect). An analytical model was established to describe the diffusion-controlled solute transport during the remelting/resolidification process. The coupling influences of the TGZM and Gibbs-Thomson effects on the remelting/resolidification process during peritectic solidification was analyzed in terms of the specific surface area (SV) of dendrites. It was found that the remelting/resolidification process by the Gibbs-Thomson effect was retarded by peritectic reaction, while that by the TGZM effect was accelerated by peritectic reaction. Since the diffusion-controlled solute transport by the TGZM effect is dominant as compared with that by the Gibbs-Thomson effect in this work, the diffusion-controlled remelting/resolidification process of dendrites is accelerated during peritectic solidification in a temperature gradient.

Phrenic motoneuron structural plasticity across models of diaphragm muscle paralysis.

Structural plasticity in motoneurons may be influenced by activation history and motoneuron-muscle fiber interactions. The goal of this study was to examine the morphological adaptations of phrenic motoneurons following imposed motoneuron inactivity while controlling for diaphragm muscle inactivity. Well-characterized rat models were used including unilateral C2 spinal hemisection (SH; ipsilateral phrenic motoneurons and diaphragm muscle are inactive) and tetrodotoxin phrenic nerve blockade (TTX; ipsilateral diaphragm muscle is paralyzed while phrenic motoneuron activity is preserved). We hypothesized that inactivity of phrenic motoneurons would result in a decrease in motoneuron size, consistent with a homeostatic increase in excitability. Phrenic motoneurons were retrogradely labeled by ipsilateral diaphragm muscle injection of fluorescent dextrans or cholera toxin subunit B. Following 2 weeks of diaphragm muscle paralysis, morphological parameters of labeled ipsilateral phrenic motoneurons were assessed quantitatively using fluorescence confocal microscopy. Compared to controls, phrenic motoneuron somal volumes and surface areas decreased with SH, but increased with TTX. Total phrenic motoneuron surface area was unchanged by SH, but increased with TTX. Dendritic surface area was estimated from primary dendrite diameter using a power equation obtained from three-dimensional reconstructed phrenic motoneurons. Estimated dendritic surface area was not significantly different between control and SH, but increased with TTX. Similarly, TTX significantly increased total phrenic motoneuron surface area. These results suggest that ipsilateral phrenic motoneuron morphological adaptations are consistent with a normalization of motoneuron excitability following prolonged alterations in motoneuron activity. Phrenic motoneuron structural plasticity is likely more dependent on motoneuron activity (or descending input) than muscle fiber activity.

Neonatal inflammation induces reorganization in dendritic morphology of retinal ganglion cells but not their retinogeniculate projection in mice

Perinatal inflammatory insult in preterm babies is associated with vision impairment, but the underlying cellular mechanism is still unknown. In this study, we set out to explore whether systemic inflammatory stress affects the development of retinal ganglion cells (RGCs). Neonatal inflammation was induced by single and systemic injection of lipopolysaccharide (LPS, 1 mg/kg) at postnatal day 4 (P4). Morphological changes of RGCs were investigated by using 3D neuron reconstruction technique in Thy-1 YFPH transgenic mice at P21, of which a fraction of RGCs selectively expresses the yellow fluorescent protein (YFP). Three types (Type I, II, III) of RGCs were distinguished and classified according to the characteristic features in their dendritic field area and dendrite density. Neonatal exposure to LPS did not alter the composition of the three RGC types but induced a reorganization of dendritic architecture in the RGC Type I and II (but not Type III). The average diameter, surface area and volume of dendrites in both RGC Type I and II were increased after systemic inflammation compared with those in the control group. However, soma sizes of all three RGC types were not affected by neonatal inflammation. Meanwhile, using anterograde labeling of the retinal cells, we found that neonatal exposure to LPS also did not affect the pattern of RGC projections in the dorsal lateral geniculate nucleus of the thalamus (dLGN). These results indicate that RGC dendrite reorganization induced by neonatal inflammation may contribute to the retinal cell dysfunctions associated with systemic inflammation in premature babies.

Phrenic motor neuron loss in aged rats.

Sarcopenia is the age-related reduction of muscle mass and specific force. In previous studies, we found that sarcopenia of the diaphragm muscle (DIAm) is evident by 24 mo of age in both rats and mice and is associated with selective atrophy of type IIx and IIb muscle fibers and a decrease in maximum specific force. These fiber type-specific effects of sarcopenia resemble those induced by DIAm denervation, leading us to hypothesize that sarcopenia is due to an age-related loss of phrenic motor neurons (PhMNs). To address this hypothesis, we determined the number of PhMNs in young (6 mo old) and old (24 mo old) Fischer 344 rats. Moreover, we determined age-related changes in the size of PhMNs, since larger PhMNs innervate type IIx and IIb DIAm fibers. The PhMN pool was retrogradely labeled and imaged with confocal microscopy to assess the number of PhMNs and the morphometry of PhMN soma and proximal dendrites. In older animals, there were 22% fewer PhMNs, a 19% decrease in somal surface area, and a 21% decrease in dendritic surface area compared with young Fischer 344 rats. The age-associated loss of PhMNs involved predominantly larger PhMNs. These results are consistent with an age-related denervation of larger, more fatigable DIAm motor units, which are required primarily for high-force airway clearance behaviors. NEW & NOTEWORTHY Diaphragm muscle sarcopenia in rodent models is well described in the literature; however, the relationship between sarcopenia and frank phrenic motor neuron (MN) loss is unexplored in these models. We quantify a 22% loss of phrenic MNs in old (24 mo) compared with young (6 mo) Fischer 344 rats. We also report reductions in phrenic MN somal and proximal dendritic morphology that relate to decreased MN heterogeneity in old compared with young Fischer 344 rats.

Comprehensive Morpho-Electrotonic Analysis Shows 2 Distinct Classes of L2 and L3 Pyramidal Neurons in Human Temporal Cortex.

There have been few quantitative characterizations of the morphological, biophysical, and cable properties of neurons in the human neocortex. We employed feature-based statistical methods on a rare data set of 60 3D reconstructed pyramidal neurons from L2 and L3 in the human temporal cortex (HL2/L3 PCs) removed after brain surgery. Of these cells, 25 neurons were also characterized physiologically. Thirty-two morphological features were analyzed (e.g., dendritic surface area, 36 333 ± 18 157 μm2; number of basal trees, 5.55 ± 1.47; dendritic diameter, 0.76 ± 0.28 μm). Eighteen features showed a significant gradual increase with depth from the pia (e.g., dendritic length and soma radius). The other features showed weak or no correlation with depth (e.g., dendritic diameter). The basal dendritic terminals in HL2/L3 PCs are particularly elongated, enabling multiple nonlinear processing units in these dendrites. Unlike the morphological features, the active biophysical features (e.g., spike shapes and rates) and passive/cable features (e.g., somatic input resistance, 47.68 ± 15.26 MΩ, membrane time constant, 12.03 ± 1.79 ms, average dendritic cable length, 0.99 ± 0.24) were depth-independent. A novel descriptor for apical dendritic topology yielded 2 distinct classes, termed hereby as “slim-tufted” and “profuse-tufted” HL2/L3 PCs; the latter class tends to fire at higher rates. Thus, our morpho-electrotonic analysis shows 2 distinct classes of HL2/L3 PCs.