Age-related synapse loss in hippocampal CA3 is not reversed by caloric restriction

Caloric restriction (CR) is a reduction of total caloric intake without a decrease in micronutrients or a disproportionate reduction of any one dietary component. While CR attenuates age-related cognitive deficits in tasks of hippocampal-dependent memory, the cellular mechanisms by which CR improves this cognitive decline are poorly understood. Previously, we have reported age-related decreases in key synaptic proteins in the CA3 region of the hippocampus that are stabilized by lifelong CR. In the present study, we examined possible age-related changes in the functional microcircuitry of the synapses in the stratum lacunosum-moleculare (SL-M) of the CA3 region of the hippocampus, and whether lifelong CR might prevent these age-related alterations. We used serial electron microscopy to reconstruct and classify SL-M synapses and their postsynaptic spines. We analyzed synapse number and size as well as spine surface area and volume in young (10 months) and old (29 months) ad libitum fed rats and in old rats that were calorically restricted from 4 months of age. We limited our analysis to SL-M because previous work demonstrated age-related decreases in synaptophysin confined to this specific layer and region of the hippocampus. The results revealed an age-related decrease in macular axo-spinous synapses that was not reversed by CR that occurred in the absence of changes in the size of synapses or spines. Thus, the benefits of CR for CA3 function and synaptic plasticity may involve other biological effects including the stabilization of synaptic proteins levels in the face of age-related synapse loss.     

Effects of restraint stress on the expression of proteins involved in synaptic vesicle exocytosis in the hippocampus

Chronic restraint stress has been associated with induction of morphological changes in the hippocampus. Postsynaptically, these changes include decreased length and branching of apical dendrites from CA3 pyramidal neurons, while presynaptically, depletion and clustering of synaptic vesicles have been observed. However, the molecular correlates of these changes remain poorly defined; while some studies have identified changes in the levels of some presynaptic proteins, none have assessed the coordinate expression of components of the membrane fusion complex, including synaptobrevin, syntaxin, and synaptosomal-associated protein 25 kDa, and their major regulatory molecules synaptotagmin, synaptophysin, and synapsin. Therefore, we undertook to assess the immunoreactivity of these proteins in hippocampal slices obtained from rats subjected to either acute (one 6 h session) or chronic (21 days at 6 h per day) of restraint stress. Specifically, we observed a significant increase in synaptobrevin immunoreactivity in the inner molecular layer of the dentate gyrus (54.2%; P=0.005), the stratum radiatum in the CA1 subfield (55.5%; P=0.007), and a region including the stratum lucidum and the proximal portion of the stratum radiatum in the CA3 subfield (52.7%; P=0.002); we also observed a trend toward increased synaptophysin levels in the stratum lucidum/radiatum of the CA3 subfield (8.0%; P=0.051) following chronic, but not acute, restraint stress. In that synaptobrevin has been associated with replenishment of the "readily-releasable" pool of synaptic vesicles and the efficiency of neurotransmitter release, the present results suggest that stress-induced changes in synaptobrevin may at least in part underlie the previously observed changes in synaptic and neuronal morphology.     

Total number and distribution of inhibitory and excitatory synapses on hippocampal CA1 pyramidal cells

The integrative properties of neurons depend strongly on the number, proportions and distribution of excitatory and inhibitory synaptic inputs they receive. In this study the three-dimensional geometry of dendritic trees and the density of symmetrical and asymmetrical synapses on different cellular compartments of rat hippocampal CA1 area pyramidal cells was measured to calculate the total number and distribution of excitatory and inhibitory inputs on a single cell.A single pyramidal cell has approximately 12,000 microm dendrites and receives around 30,000 excitatory and 1700 inhibitory inputs, of which 40 % are concentrated in the perisomatic region and 20 % on dendrites in the stratum lacunosum-moleculare. The pre- and post-synaptic features suggest that CA1 pyramidal cell dendrites are heterogeneous. Strata radiatum and oriens dendrites are similar and differ from stratum lacunosum-moleculare dendrites. Proximal apical and basal strata radiatum and oriens dendrites are spine-free or sparsely spiny. Distal strata radiatum and oriens dendrites (forming 68.5 % of the pyramidal cells' dendritic tree) are densely spiny; their excitatory inputs terminate exclusively on dendritic spines, while inhibitory inputs target only dendritic shafts. The proportion of inhibitory inputs on distal spiny strata radiatum and oriens dendrites is low ( approximately 3 %). In contrast, proximal dendritic segments receive mostly (70-100 %) inhibitory inputs. Only inhibitory inputs innervate the somata (77-103 per cell) and axon initial segments. Dendrites in the stratum lacunosum-moleculare possess moderate to small amounts of spines. Excitatory synapses on stratum lacunosum-moleculare dendrites are larger than the synapses in other layers, are frequently perforated ( approximately 40 %) and can be located on dendritic shafts. Inhibitory inputs, whose percentage is relatively high ( approximately 14-17 %), also terminate on dendritic spines.Our results indicate that: (i) the highly convergent excitation arriving onto the distal dendrites of pyramidal cells is primarily controlled by proximally located inhibition; (ii) the organization of excitatory and inhibitory inputs in layers receiving Schaffer collateral input (radiatum/oriens) versus perforant path input (lacunosum-moleculare) is significantly different.     

Different modes of synaptic and extrasynaptic NMDA receptor alteration in the hippocampus of P301S tau transgenic mice

N-methyl-d -aspartate receptors (NMDARs) are pivotal players in the synaptic transmission and synaptic plasticity underlying learning and memory. Accordingly, dysfunction of NMDARs has been implicated in the pathophysiology of Alzheimer disease (AD). Here, we used histoblot and sodium dodecylsulphate-digested freeze-fracture replica labelling (SDS-FRL) techniques to investigate the expression and subcellular localisation of GluN1, the obligatory subunit of NMDARs, in the hippocampus of P301S mice. Histoblots showed that GluN1 expression was significantly reduced in the hippocampus of P301S mice in a laminar-specific manner at 10 months of age but was unaltered at 3 months. Using the SDS-FRL technique, excitatory synapses and extrasynaptic sites on spines of pyramidal cells and interneuron dendrites were analysed throughout all dendritic layers in the CA1 field. Our ultrastructural approach revealed a high density of GluN1 in synaptic sites and a substantially lower density at extrasynaptic sites. Labelling density for GluN1 in excitatory synapses established on spines was significantly reduced in P301S mice, compared with age-matched wild-type mice, in the stratum oriens (so), stratum radiatum (sr) and stratum lacunosum-moleculare (slm). Density for synaptic GluN1 on interneuron dendrites was significantly reduced in P301S mice in the so and sr but unaltered in the slm. Labelling density for GluN1 at extrasynaptic sites showed no significant differences in pyramidal cells, and only increased density in the interneuron dendrites of the sr. This differential alteration of synaptic versus extrasynaptic NMDARs supports the notion that the progressive accumulation of phospho-tau is associated with changes in NMDARs, in the absence of amyloid-β pathology, and may be involved in the mechanisms causing abnormal network activity of the hippocampal circuit.     

Comparative Ultrastructural Analysis of Mitochondria in the CA1 and CA3 Hippocampal Pyramidal Cells Following Global Ischemia in Mongolian Gerbils

Post‐ischemic injury of the hippocampus unrolls at different levels and has both functional and structural implications. The deficiency in neuron energy metabolism is an initiating factor. We performed transmission electron microscopic (TEM) comparative analysis of mitochondria in excitatory spine synapses in CA1 stratum radiatum and CA3 hippocampal areas after 5 min of global cerebral ischemia in Mongolian gerbils, 4 and 7 days after reperfusion. Electron microscopy and unbiased morphometric methods were used to evaluate synaptic plasticity, and the number and size of mitochondria in synaptic terminals. We compared the morphological organization of mitochondria in presynaptic terminals between CA1 and CA3 areas in control and post‐ischemic condition according to the following morphometric parameters: mitochondrial volume fraction, mitochondrial frequency in CA1 and CA3 terminals, mean number of mitochondria per presynaptic terminal, frequency of damaged mitochondria in terminals, and density of presynaptic terminals. Our ultrastructural study revealed statistically significant differences in morphometric parameters between CA1 and CA3 areas in control conditions, as well as in post‐ischemic conditions. Also, we found temporal differences in measured parameters obtained 4 and 7 days after reperfusion. This study showed significant morphological differences in the organization of mitochondria in excitatory spine synapses between CA1 and CA3 areas, which corresponded with already known differences in functionality and sensitivity to the ischemic insult. Our conclusion is that revealed post‐ischemic changes in mitochondrial distribution in presynaptic CA1 and CA3 terminals could be an indicator of hippocampal metabolic dysfunction and synaptic plasticity. Anat Rec,, 2011. © 2011 Wiley‐Liss, Inc.     

Alterations of perisomatic GABA synapses on hippocampal CA1 inhibitory interneurons and pyramidal cells in the kainate model of epilepsy.

In the kainate model of epilepsy, electrophysiological and anatomical modifications occur in inhibitory circuits of the CA1 region of the rat hippocampus. Using postembedding GABA immunocytochemistry and electron microscopy, we characterized perisomatic GABA and non-GABA synaptic contacts in CA pyramidal cells, and GABAergic interneurons of stratum oriens/alveus and stratum lacunosum-moleculare, and examined if changes occurred at these synapses at two weeks post-kainate treatment. We found that, in control rats, the number and total length of perisomatic GABA synapses were significantly smaller (approximately 40-50%) in lacunosum-moleculare interneurons than in oriens/alveus interneurons and pyramidal cells. Additionally, the number and total length of perisomatic non-GABA synapses were different among all cell types, with these parameters increasing significantly in the following order: pyramidal cells相似文献   

Changes in the synapses of rat hippocampus following pre- and postnatal alcohol exposure

Quantitative and qualitative changes in the synapses in stratum lacunosum-moleculare of rat hippocampus following pre- and postnatal alcohol exposure were studied. Dense and lamellar bodies, damaged mitochondria, autophagic vacuoles and dilatated cisterns of the smooth endoplasmic reticulum were seen in axons and dendrites. The enlarged glial processes were also found. The area and the vesicle number of presynaptic terminals were decreased in CA1 and CA3 hippocampal fields, while the vesicle number per area of synaptic contact zones (SCZ) was decreased only in field CA3. The relative and absolute lengths of the SCZ, the total length and total surface of the SCZ were quite differently changed in both fields. The synaptic density was insignificantly increased. The synaptic changes are thought to be due to the impaired development of the pyramidal cell dendrites in the hippocampus and their afferents.     

Membrane structure at synaptic junctions in area CA1 of the rat hippocampus

In tissue from area CA1 of the rat hippocampus prepared for electron microscopic study by thin-sectioning, asymmetric synaptic junctions were found on dendritic spines, spiny dendritic shafts, and non-spiny dendritic shafts. In freeze-fractured preparations, aggregates of large particles were found on the extracellular half of the postsynaptic membrane at each of these synaptic junctions. Particle aggregate areas were measured and particle packing densities were computed at dendritic spine synapses and dendritic shaft synapses in area CA1, and compared to similar measures of particle aggregates on dendritic spines of cerebellar Purkinje cells. All of these CA1 and cerebellar synapses are excitatory and are thought to use glutamate as a neurotransmitter. There was a tendency for the dispersion of particles within individual aggregates to be less uniform in larger aggregates in both area CA1 and cerebellar cortex. Distinct particle-free zones could be distinguished in the center of particle aggregates on large "mushroom-shaped" spines in area CA1. There was no statistically significant difference between the particle densities at CA1 dendritic spines (2848 +/- 863 particles/micron2) and CA1 dendritic shafts (2707 +/- 718 particles/micron2). However, the average density of particles at cerebellar dendritic spine synapses (3614 +/- 1081 particles/micron2) was significantly greater than at dendritic spine or shaft synapses found in area CA1. Symmetric synaptic junctions were observed on the CA1 pyramidal cell somas and dendritic shafts in thin-sectioned preparations. These synapses typically exert an inhibitory action mediated by gamma-aminobutyric acid. In freeze-fracture preparations, large varicosities were found apposed to the pyramidal somal and dendritic membranes, but there were no specializations of particle distribution on either the extracellular or the cytoplasmic half of the fractured postsynaptic membranes. This finding parallels observations from freeze-fracture preparations of other GABAergic synapses in the central nervous system.     

Re-structuring of synapses 24 hours after induction of long-term potentiation in the dentate gyrus of the rat hippocampus in vivo

In male rats, long-term potentiation was induced unilaterally in the dentate gyrus, either by high frequency (200Hz) or theta rhythm stimulation. Structural synaptic changes were examined 24h after induction using quantitative electron microscopy. A disector technique was employed in order to estimate the density of synapses (using 70-80-nm sections) and of granule cell nuclei (using 2-microm sections) in the middle, and inner molecular layer in both hemispheres. Synaptic height and total lateral areas of synaptic active zones per unit tissue volume were assessed via assumption-free stereological techniques coupled with image analysis. The results obtained indicated that both synaptic density and number (corrected per neuron) of axo-spinous, but not axo-dendritic, synapses were approximately 40% higher in the middle, but not inner molecular layer of the potentiated hemisphere compared to the contralateral (control hemisphere). No significant inter-hemispheric difference was found in the volume densities of lateral areas of active zones.These data suggest that 24h after long-term potentiation induction, active zones of existing axo-spinous synapses either split forming separate contacts, or decrease in size while new synapses are formed.     

Nitric oxide-containing pyramidal neurons of the subiculum innervate the CA1 area

Neurons and axon terminals containing neuron-specific nitric oxide synthase (nNOS) were examined in the rat subiculum and CA1 area of Ammon's horn. In the subiculum, a large subpopulation of the pyramidal neurons and non-pyramidal cells are immunoreactive for nNOS, whereas in the neighbouring CA1 area of Ammon's horn only non-pyramidal neurons are labelled with the antibody against nNOS. In the pyramidal layer of the subiculum, nNOS-positive axon terminals form both asymmetric and symmetric synapses. In the adjacent CA1 area the nNOS-positive terminals that form symmetric synapses are found in all layers, whereas those terminals that form asymmetric synapses are only in strata radiatum and oriens, but not in stratum lacunosum-moleculare. In both the subiculum and CA1 area, labelled terminals make symmetric synapses only on dendritic shafts, whereas asymmetric synapses are exclusively on dendritic spines. Previous observations demonstrated that all nNOS-positive non-pyramidal cells are GABAergic local circuit neurons, which form exclusively symmetric synapses. We suggest that nNOS-immunoreactive pyramidal cells of the subiculum may innervate neighbouring subicular pyramidal cells and, to a smaller extent, pyramidal cells of the adjacent CA1 area, forming a backward projection between the subicular and hippocampal principal neurons. Electronic Publication     

Long-term change in synaptic transmission in CA3 circuits followed by spontaneous rhythmic activity in rat hippocampal slices

The relevance of long-term potentiation (LTP) at excitatory synapses in CA3 circuits to generation of spontaneous epileptiform bursts in CA3 was investigated using rat hippocampal slices. CA3 pyramidal cells were antidromically stimulated through Schaffer collaterals. Evoked field potentials were extracellularly recorded from the stratum pyramidale and the stratum radiatum in CA3. Therefore, field potentials reflecting recurrent excitatory post-synaptic potentials (EPSPs) and inhibitory post-synaptic potentials (IPSPs) were positive at the stratum pyramidale and negative at the stratum radiatum. First, we tested how the amplitude of the evoked field potentials depends on a γ-aminobutyric acid (GABA_A) antagonist. Both of the positive and negative field potential peaks reduced in the medium containing penicillin (2 mM) or bicuculline (20 μM). This suggests that unmasked EPSPs due to suppression of IPSPs do not result in an increase in the evoked potentials. Second, CA3 pyramidal cells were antidromically stimulated by tetanic stimulation of Schaffer collaterals in order to induce LTP at synapses in CA3 circuits. Both of the positive and negative field potentials increased, suggesting that recurrent EPSPs were enhanced by tetanic stimulation. Induction of LTP at recurrent excitatory synapses was followed by spontaneous epileptiform bursts which persisted throughout experiments (1.5 h), while LTP of afferent synaptic potential evoked by hilar test stimulation was not induced. These results suggest that LTP at the afferent synapses is not necessary to spontaneous epileptiform bursts in CA3, but LTP at excitatory synapses between CA3 pyramidal cells contribute to spontaneous epileptiform bursts.     

Synaptic modifications at the CA3–CA1 synapse after chronic AMPA receptor blockade in rat hippocampal slices

Maintenance of dendritic spines, the postsynaptic elements of most glutamatergic synapses in the central nervous system, requires continued activation of AMPA receptors. In organotypic hippocampal slice cultures, chronic blockade of AMPA receptors for 14 days induces a substantial loss of dendritic spines on CA1 pyramidal neurons. Here, using serial section electron microscopy, we show that loss of dendritic spines is paralleled by a significant reduction in synapse density. In contrast, we observed an increased number of asymmetric synapses onto the dendritic shaft, suggesting that spine retraction does not inevitably lead to synapse elimination. Functional analysis of the remaining synapses revealed that hippocampal circuitry compensates for the anatomical loss of synapses by increasing synaptic efficacy. Moreover, we found that the observed morphological and functional changes were associated with altered bidirectional synaptic plasticity. We conclude that continued activation of AMPA receptors is necessary for maintaining structure and function of central glutamatergic synapses.     

Postsynaptic-GABAergic inhibition of non-pyramidal neurons in the guinea-pig hippocampus

Intracellular recording and staining was applied to study non-pyramidal neurons in the guinea-pig hippocampus. To avoid accidental impalement of pyramidal or granule cells, two hippocampal regions known to be devoid of pyramidal or granule cells were chosen. In transverse and longitudinal slices, neurons of the deep hilar region (zone 4 of Amaral3), and in transverse slices, neurons of the stratum lacunosum-moleculare (CA3) were impaled. The intracellular staining with Lucifer Yellow revealed that of 20 neurons stained in these zones all were non-pyramidal neurons. Hilar neurons, situated just below the granular layer, differed from granule cells and CA3 neurons with respect to their action potential waveform and their current/voltage relationship. In contrast to granule cells, hilar neurons exhibited spontaneous bursts in the presence of bicuculline (25 microM). In all neurons impaled in the hilar region and the stratum lacunosum-moleculare (n = 42), inhibitory postsynaptic potentials could be elicited. These inhibitory postsynaptic potentials were blocked by bicuculline. In transverse slices, perforant path stimulation elicited inhibition preceding excitation in hilar neurons and excitation preceding inhibition in granule cells. Since non-pyramidal neurons are likely to be inhibitory neurons, our data suggest that GABAergic neurons in the hilus or in the stratum lacunosum-moleculare are controlled by inhibitory GABAergic synapses. This was verified by immunocytochemistry using antibodies against glutamate decarboxylase, the gamma-aminobutyric acid synthetizing enzyme. In both hippocampal regions studied, glutamate decarboxylase-positive synaptic terminals on glutamate decarboxylase-positive cells were observed. It is concluded that disinhibition is an important feature of information processing in the hippocampus, and that disinhibition is mediated by GABAergic synapses on GABAergic neurons.     

Chronic stress and a cyclic regimen of estradiol administration separately facilitate spatial memory: relationship with hippocampal CA1 spine density and dendritic complexity

This study investigated the effects of chronic restraint stress and repeated cyclic estradiol pulses on hippocampal CA3 and CA1 dendritic and/or spine morphology and spatial memory in female rats. Sprague-Dawley adult female rats were ovariectomized and then injected over 2 days with 17β-estradiol (10 μg, s.c.), which was repeated every 4-5 days. While all rats received similar estradiol injection histories, half of the rats were chronically restrained and/or given a final cyclic pulse of estradiol prior to testing on a hippocampal-dependent object placement (OP) task to assess spatial memory. OP testing was performed 2 days after the last restraint session, as well as when the last 2 estradiol pulses best captured the maximal effect on hippocampal CA1 spine density. The data revealed several novel findings: (a) chronic stress or estradiol separately facilitated spatial memory, but did not have the same effects when coadministered, (b) CA1 spine densities negatively correlated with spatial memory, and (c) repeated estradiol pulses failed to prevent stress-induced CA3 dendritic retraction. We also corroborated previous studies showing increased CA1 spine density following estradiol, chronic stress, and behavioral manipulations. The present study uniquely combined chronic stress, repeated estradiol pulses, hippocampal morphology, and behavior within the same animals, allowing for correlational analyses to be performed between CA1 spine morphology and spatial memory. We demonstrate novel findings that chronic stress or estradiol pulses independently facilitate spatial memory, but not when coadministered, and that these effects may involve a balance of CA1 apical spine expression that is independent of CA3 dendritic complexity.     

Stress suppresses and learning induces plasticity in CA3 of rat hippocampus: a three-dimensional ultrastructural study of thorny excrescences and their postsynaptic densities

Chronic stress and spatial training have been proposed to affect hippocampal structure and function in opposite ways. Previous morphological studies that addressed structural changes after chronic restraint stress and spatial training were based on two-dimensional morphometry which does not allow a complete morphometric characterisation of synaptic features. Here, for the first time in such studies, we examined these issues by using three-dimensional (3-D) reconstructions of electron microscope images taken from thorny excrescences of hippocampal CA3 pyramidal cells. Ultrastructural alterations in postsynaptic densities (PSDs) of thorny excrescences receiving input from mossy fibre boutons were also determined, as were changes in numbers of multivesicular bodies (endosome-like structures) within thorny excrescences and dendrites. Quantitative 3-D data demonstrated retraction of thorny excrescences after chronic restraint stress which was reversed after water maze training, whilst water maze training alone increased thorny excrescence volume and number of thorns per thorny excrescence. PSD surface area was unaffected by restraint stress but water maze training increased both number and area of PSDs per thorny excrescence. In restrained rats that were water maze trained PSD volume and surface area increased significantly. The proportion of perforated PSDs almost doubled after water maze training and restraint stress. Numbers of endosome-like structures in thorny excrescences decreased after restraint stress and increased after water maze training. These findings demonstrate that circuits involving contacts between mossy fibre terminals and CA3 pyramidal cells at stratum lucidum level are affected conversely by water maze training and chronic stress, confirming the remarkable plasticity of CA3 dendrites. They provide a clear illustration of the structural modifications that occur after life experiences noted for their different impact on hippocampal function.     

Theta rhythmic stimulation of stratum lacunosum-moleculare in rat hippocampus contributes to associative LTP at a phase offset in stratum radiatum

Computational modeling demonstrates that encoding and context-dependent retrieval of memories in region CA1 of the hippocampus will be most effective when the phase of strongest entorhinal input (to stratum lacunosum-moleculare) is offset from the phase of maximal induction of long-term potentiation at Schaffer collateral synapses (in s. radiatum). This would allow entorhinal input to play a role in both retrieval and encoding without engaging long-term potentiation (LTP) during retrieval. Experiments in brain slice preparations of the hippocampal formation tested the relationship between rhythmic input to s. lacunosum-moleculare and the time of maximal LTP induction at Schaffer collateral synapses in s. radiatum. Analysis of the data demonstrates a statistically significant difference in the induction of LTP for different time intervals between the end of each four-pulse train in s. lacunosum-moleculare and the single pulse s. radiatum stimulation. The time of maximal LTP induction was found to be approximately 30 ms after the end of lacunosum-moleculare stimulation, consistent with the requirements of the model.     

Synaptic reorganization in the rabbit hippocampus after lesion of commissural afferents

Summary The degeneration of commissural afferents to the hippocampus in the rabbit was studied by using the Fink-Heimer degeneration method, electron microscopy, and the combined Golgi/EM technique. The stratum oriens (CA3) was selected for quantitative electron microscopic evaluation of postlesional changes since the degeneration of commissural fibers as seen in Fink-Heimer preparations was dense throughout the width of that layer. Accordingly, in electron micrographs of stratum oriens many electron-dense degenerating boutons were found after short survival times (3 and 6 days, respectively), most of them (96%) in synaptic contact with dendritic spines. In the fine structural analysis of Golgi-impregnated CA3 pyramidal cells, spines of basal dendrites were identified as postsynaptic elements of degenerating commissural afferents in stratum oriens.Three days after the lesion, the number of intact synapses/unit area was reduced in stratum oriens of CA3 to 64% of the control; 20% of the synapses were degenerating. Thus, part of the degenerated synapses had disappeared. Evidence is provided that phagocytosis of degenerated boutons still attached to fragments of dendritic spines played a role in this process.Seven weeks after the lesion, the number of intact synapses had returned to control level, suggesting reactive growth of synaptic structures. When the ratio of spine synapses versus shaft synapses was compared with controls, no change had occurred. Thus, after an initial loss of spine synapses after short survival times, new spines have been formed in parallel with ingrowth (sprouting) of neighbouring nonlesioned afferents.     

Effects of testosterone on hippocampal CA1 spine synaptic density in the male rat are inhibited by fimbria/fornix transection

This study investigated the contribution of sub-cortical afferent input to the effects of testosterone (T) on spine synapse density in the CA1 subfield of the hippocampus, in adult male rats. Gonadectomized (GDX) male rats exhibited a considerably lower density of spine synapses in the CA1 region than control, intact males. The effects of GDX were reversed by treatment with testosterone propionate (TP; 500 microg/day, for 2 days). Transection of the fimbria/fornix (FF) had no significant effect on the synaptic density in non-GDX males. However, FF transection partially inhibited the responses to TP in GDX animals. These data suggest that the effects of T on spine synapse density in the CA1 region of the male rat hippocampus are partially, but not completely, dependent on afferent sub-cortical input.     

人脐带间充质干细胞移植对慢性应激模型小鼠抑郁行为的改善作用

目的 探讨人脐带间充质干细胞(hUCMSCs)尾静脉移植对慢性不可预测性温和应激(CUMS)模型小鼠抑郁行为的改善作用.方法 获得第3代hUCMSCs;将60只C57BL/6雄性小鼠随机分为正常组、模型组(给予生理盐水)、细胞组(移植hUCMSCs)、氟西汀(flu)给药组(给予flu),每组15只.构建6周CUMS小...     

A quantitative analysis of the synaptic development of the lobus parolfactorius of the chick (Gallus domesticus)

Summary The lobus parolfactorius (LPO) of the chick has been shown to undergo an increase in the mean synaptic numerical density (Nv _syn) in response to one-trial passive avoidance learning (Stewart et al. 1987). The present study was undertaken in order to describe the pattern of normal development of synapses in the LPO, to further investigate the significance of this plastic response. The LPO's from each hemisphere of pre-hatch (16 days), and post-hatch (1 day, 9 day and 22 day old) chicks were processed for electron microscopy. Synapses were classified into asymmetric spine, asymmetric shaft, symmetric spine, and symmetric shaft synapses, on the basis of the density of the post-synaptic thickening and the nature of the post-synaptic target. A 3-dimensional stereological probe was used (the disector) to calculate Nv _syp, and mean projected height (H _syp) of the post-synaptic density (PSD). Mean values for each age and hemisphere were compared with a 2-way analysis of variance test using paired samples. A six-fold increase in Nv _syp was seen between 16 days in ovo, and 9 days post-hatch. There was a hemispheric asymmetry at 9 days post-hatch, with the left hemisphere LPO containing 1.6 times as many synapses per m^-3. There was a subsequent period of reduction in synaptic density in the left hemisphere LPO between 9 and 22 days post-hatch. The Nv of all classes of synapse increased with age, but the proportions of the symmetrical synapses with respect to the total number of synapses, decreased with age. This decrease was of a similar magnitude for each hemisphere. A hemispheric difference was seen in post-hatch asymmetric synapses, with a greater proportion of asymmetric spine synapses in the left hemisphere. The magnitude of the hemispheric asymmetry was constant throughout the 3 week period of post-hatch development, but was not present in pre-hatch chicks. The PSD increased in length in each hemisphere by approximately 40% between post-hatch day 1 and post-hatch day 9. These data show that the LPO contains a synaptic population which undergoes substantial modification during the first week post-hatch. An asymmetry exists at post-hatch day 9 which is not present at the earlier ages investigated, nor indeed after 22 days post-hatch. This may have significance with regard to studies of passive avoidance learning in the one-day old chick, where an increase in both the size and number of synapses in the LPO has been demonstrated (Stewart et al. 1987). It is possible that training, in this situation, may simply enhance the timing of synaptic events that result as a consequence of normal development.