Entorhinal cortex lesioning protects hippocampal CA3 neurons from stress-induced damage

The role of the entorhinal cortex (EC) in stress-induced damage in terms of dendritic branching points and intersections of hippocampal CA3 neurons has been investigated. Following bilateral electrolytic lesions of the EC, the rats were subjected to restraint stress, 6 h per day for 21 days. Chronic restraint stress resulted in the atrophy of hippocampal CA3 neurons and the lesioning of the EC prior to stress significantly (P<0.001) reduced this dendritic atrophy. These results show that the neuronal vulnerability to chronic stress can be attenuated by entorhinal glutamatergic denervation.     

慢性应激对大鼠海马CA3区锥体细胞顶树突及血清皮质酮浓度的影响

目的探讨慢性应激对大鼠海马CA3区锥体细胞结构和血清皮质酮浓度的影响。方法将20只雄性Sprague-Dawley大鼠按体质量随机分为应激组和对照组,每组10只。采用高尔基染色法及酶联免疫分析方法,观察慢性强迫游泳应激对大鼠海马CA3区锥体细胞顶树突和血清皮质酮浓度的影响。结果应激组大鼠海马CA3区锥体细胞顶树突的总长度[(112±10)μm]短于对照组[(168±34)μm],差异有统计学意义(P<0.01);一级树突直径[(9.0±1.1)μm]大于对照组[(5.7±0.9)μm],差异有统计学意义(P<0.01);血清皮质酮浓度[(13±14)μg/L]低于对照组[(30±16)μg/L],差异有统计学意义(P<0.05)。结论慢性强迫游泳可引起大鼠海马CA3区锥体细胞顶树突及血清皮质酮浓度的改变。     

Neuritic plaques in senile dementia of Alzheimer type: a Golgi analysis in the hippocampal region

Tissue sections from the hippocampal region of patients with senile dementia of Alzheimer type were examined in 75-100 microns thick vibratome sections impregnated by the Golgi-Cox method and counterstained with cresyl violet. The morphology of dendrites and axons with neuritic plaques was frequently abnormal. Abnormalities included pleomorphic outpouchings of terminal and preterminal dendritic and axonal segments, many of which contained filiform processes occurring singly and in tufts. The axon collaterals of some hippocampal neurons appeared to branch richly as they entered plaques. Impregnated neurites could occasionally be traced from a neuritic plaque to adjacent pyramidal and local circuit neurons. The findings confirm that local neurons of different types contribute dendrites and axons to plaques and that these processes may proliferate within the confines of the plaques.     

Early dendritic changes in hippocampal pyramidal neurones (field CA1) of rats subjected to acute soman intoxication: a light microscopic study

In rats poisoned with soman (s.c. 100 μg/kg), a potent inhibitor of cholinesterase (ChE), the numbers of dendritic spines of Golgi impregnated hippocampal pyramidal cells (CA1 sector) were evaluated within the first hour of the intoxication. Animals that experienced convulsions showed a rapid and striking decrease in the density of dendritic spines which could be reduced by nearly 80% of the controls in the basal dendrites 60 min post-soman exposure. Although the exact mechanisms cannot be determined from the present study, it is suggested that the spine loss may represent: (1) the first sign of the seizure-related neuronal changes which are known to occur later during soman intoxication; and (2) the expression of the ‘dendrotoxic’ effects produced by certain non-cholingergic excitatory transmitters such as glutamate.     

Efects of corticosterone on the electrophysiology of hippocampal CA1 pyramidal Cells in vitro

Modulation of CA1 field potential amplitudes by normal and stress concentrations of corticosterone (CT) was observed in hippocampal slice preparations from adrenalectomized rats. Slices exposed to CT levels characteristic of a morning (4 nM) or evening (7 nM) resting state showed increased population spike amplitudes in the CA1 pyramidal cell field within 10 min. A stress concentration (15 nM) also increased spike amplitudes, but only at the higher stimulus intensities. The effects of these doses were essentially the same 10 and 60 min after administration. The hormone facilitated responding more in morning resting concentrations than in concentrations characteristic of the evening resting state. This occurred, however, only for relatively low intensity stimuli. The data provide some support for the suggestion that circadian fluctuations in magnitude of long-term potentiation result from corresponding changes in CT level. The rapid onset of the observed changes is difficult to account for in terms of generally accepted mechanisms of receptor binding.     

Gonadal hormones are responsible for maintaining the integrity of spine synapses in the CA1 hippocampal subfield of female nonhuman primates

It is well established that gonadal hormonal manipulation results in morphologic changes in the rat hippocampus. The great similarities in the hippocampal formation between nonhuman primates and humans, as well as the differences in this structure between humans and rats, led to this investigation of whether hormonal manipulation in female subhuman primates influences pyramidal cell spine density in the CA1 hippocampal subfield, as it does in rats. African green monkeys (Cercopithecus aethiops sabaeus) were ovariectomized, and half of the animals received estrogen replacement therapy. One month later, the monkeys were killed. In the first group of experiments, pyramidal cell spines were analyzed on Golgi-impregnated material taken from the CA1 hippocampal subfield. In the second experiment, unbiased electron microscopic stereologic calculations were performed to estimate the volumetric density of spine synapses in the same hippocampal subfield. Analysis of the Golgi-impregnated material showed that the spine density of CA1 pyramidal cells is much lower in the ovariectomized animals than in ovariectomized and estrogen-replaced monkeys. The unbiased, electron microscopic, stereologic calculation confirmed the light microscopic observation. The volumetric density (number of spine synapses/microm(3)) of spine synapses was significantly lower (43.33%) in the ovariectomized animals than in ovariectomized and estrogen-replaced monkeys. Because the hippocampus is involved in specific mnemonic functions, this observation highlights the importance of hormone replacement therapy in postmenopausal conditions.     

慢性应激对大鼠海马CA3区长时程增强的影响

目的　探讨慢性应激对大鼠海马CA3区长时程增强 (LTP)的影响及机制。方法　将 34只Wistar大鼠随机分成应激组 (8只 )、应激 +盐水组 (8只 )、应激 +MK 80 1组 (8只 )及空白对照组 (1 0只 ) ,应激刺激为饮水冲突模型 ,分别于实验初和LTP检测前 1天评定大鼠情绪性行为 ,在应激 1 5天后检测大鼠强直性LTP ,测量强直后 1 ,5 ,1 0 ,30 ,60 ,90 ,1 2 0minLTP群体峰电位幅度及峰潜期。结果(1 )应激前各组情绪性行为评分的差异均无显著性 ;应激后 ,应激 +盐水组 [(4 33± 0 50 )分 ]、应激 +MK 80 1组 [(3 60± 0 55)分 ]及应激组 [(2 90± 0 74)分 ]的评分均高于对照组 [(2 0 2± 1 1 6)分 ] ,差异有显著性 (P =0 0 0 0 ) ;(2 )应激组测试刺激阈值较对照组高 (45V∶30V) ;(3)在强直后第 1 ,90min时的LTP群体峰电位变化率应激组 [分别为 (2 1 1± 58) %和 (2 4 3± 69) % ]、应激 +盐水组 [分别为 (1 69±92 ) %和 (1 82± 1 61 ) % ]低于对照组 [分别为 (30 2± 2 1 0 ) %和 (30 3± 1 4 1 ) % ]和应激 +MK 80 1组 [分别为(375± 99) %和 (489± 2 36) % ] ,差异有显著性 (P <0 0 5) ,应激 +MK 80 1组与对照组的差异无显著性 ;(4)各应激组于各时点LTP峰潜期均较对照组长 ,但差异未呈显著性。结论　慢性     

Synaptic potentiation in the hippocampal CA1 region induced by application of N-methyl-D-aspartate

The effect of local pressure application of N-methyl-D-aspartate (NMDA) in the synaptic layer of CA1 pyramidal cells was investigated in the guinea pig hippocampal slice preparation using extracellular recording technique. Application of NMDA produced a transient depression and a subsequent 30-60 min potentiation of the field excitatory postsynaptic potential (EPSP) seen as an increase of the initial slope and amplitude of the EPSP. The increase in amplitude was consistently greater than that of the initial slope. Prior tetanization that caused saturation of long-term potentiation prevented the generation of an NMDA-induced potentiation of the initial slope for more than 1-2 h, but not the generation of an increase of the amplitude.     

CpG-C immunotherapeutic efficacy is jeopardized by ongoing exposure to stress: Potential implications for clinical use

Bi-directional influences between stress hormones and immune responses have been repeatedly documented, however, in the clinical setting they are rarely considered when immunotherapeutic approaches are used or studied in patients. As some immunotherapeutic treatments have shown great potential in animal models but have had limited success in patients, we hypothesize that ongoing psychological and physiological stress responses in patients, which do not characterize the setting of animal studies, contribute to this discrepancy. In the current study we examined the interaction between ongoing water stress and CpG-C immunotherapy to determine whether stress that precedes immunotherapy can modulate the efficacy of CpG-C immunostimulation. C57BL/6 mice were exposed to water stress or served as controls. Two hours following the commencement of the stress protocol animals were injected with CpG-C, non-CpG, or PBS, and sacrificed 1, 4 or 12 h thereafter. We found that in CpG-C-treated animals stress eliminated the elevation of plasma IL-12, and synergistically elevated corticosterone levels. Furthermore, stress markedly reduced the total number of myeloid (33D1⁺), plasmacytoid (mPDCA-1⁺) and plasmacytoid-derived (33D1⁺mPDCA-1⁺) dendritic cells in CpG-C-treated animals, as well as the numbers of these cell sub-types expressing CD11b, CD80 and CD69. These changes were more dramatic in the blood than in the spleen. Overall, these findings indicate that under no-stress conditions CpG-C induces a robust immune response, which is significantly diminished when immunostimulation is attempted during ongoing stress. If these findings hold in humans, potential prophylactic treatments should be found to limit the deleterious effects of ongoing stress on the efficacy of immunotherapy.     

Role of adrenal steroid mineralocorticoid and glucocorticoid receptors in long-term potentiation in the CA1 field of hippocampal slices

We previously demonstrated in the dentate gyrus (DG) of anesthetized and freely behaving rats that both acute as well as chronic administration of corticosterone produces a suppression in long-term potentiation (LTP). In subsequent studies we showed, again in the DG, that activation of the two types of adrenal steroid receptors (mineralocorticoid (MR) and glucocorticoid (GR)) produce biphasic effects on synaptic plasticity; activation of MR produces an enhancement while activation of GR produces a suppression in LTP. In a separate study, we further demonstrated in rats administered the specific GR agonist RU 28362 that high-frequency stimulation, which normally produces LTP, instead produced long-term depression (LTD) in these animals. In the present study we investigated the effects of MR and GR activation by adrenal steroids on synaptic plasticity of the hippocampal CA1 field, but we studied this ex vivo, in a slice preparation. The results indicate that, as in our studies in the DG, adrenal steroids produce biphasic effects: in ADX rats, aldosterone (a specific MR agonist) enhanced while RU 28362 suppressed synaptic plasticity. Unlike the in vivo preparation, however, rarely was LTD observed in the animals receiving RU 28362. Also, ADX itself did not produce noticeable effects on synaptic plasticity. The present results are in agreement with previous studies showing that elevations in corticosterone or an acute episode of experimentally induced stress in vivo causes a suppression in LTP in the hippocampal CA1 field, in vitro.     

Long-lasting structural changes in CA3 hippocampal and layer V motor cortical pyramidal neurons associated with self-stimulation rewarding experience: a quantitative Golgi study

Self-stimulation (SS) rewarding experience induced structural changes in CA3 hippocampal and layer V motor cortical pyramidal neurons in adult male Wistar rats has been demonstrated. In the present study, whether these structural changes are transient or of a permanent nature was evaluated. Self-stimulation experience was provided for 1 h daily over a period of 10 days through bilaterally implanted bipolar electrodes in the lateral hypothalamus and the substantia nigra-ventral tegmental area. Following 10 days of SS experience, the rats were sacrificed after an interval of 30 and 60 days for the quantitative analysis of the dendritic morphology in Golgi stained CA3 hippocampal and layer V motor cortical pyramidal neurons. The results revealed a significant increase in the dendritic branching points and intersections in apical and basal dendrites in both types of neurons in 30 days post-SS group compared to sham control. The total number of apical and basal dendrites were significantly increased in both 30 and 60 days post-SS groups of rats. This study suggests that SS experience induced structural changes are sustainable, even in the absence of rewarding experience.     

Morphological variability is a characteristic feature of granule cells in the primate fascia dentata: A combined Golgi/electron microscope study

This study analyzes the structural variability of granule cells in the monkey fascia dentata. The hippocampi of three adult rhesus monkeys (Macaca mulatta) and two 1-year-old female baboons (Papio anubis) were used for a combined Golgi/electron microscope (EM) study. The results were compared with other Golgi/EM studies on dentate granule cells in small laboratory animals. Whereas the granule cells in small rodents form a relatively uniform population of neurons, we observed a much greater variability of granule cell morphology in monkeys. This variability concerned the size of the cell body, the length and thickness of apical dendrites, the spine density, and the occasional occurrence of basal dendrites. The dendritic length of individual granule cells largely depended on their position in the highly convoluted granular layer. These convolutions caused significant variations in the thickness of the molecular layer and consequently in the length of individual granule cell dendrites. Granule cells with thick dendrites densely covered with spines could be differentiated from those exhibiting much thinner dendritic processes and moderate spine numbers. About 10% of granule cells in the monkey fascia dentata exhibited basal dendrites. Occasionally in the hilus ectopic granule cells were observed that gave rise to long apical dendrites traversing the granular layer. The axons of granule cells, the mossy fibers, entered the hilus, where they gave off several collaterals. In contrast to the light microscopic variability, subtypes of granule cells revealed similar fine structural characteristics, i. e., a round nucleus lacking indentations, a thin rim of cytoplasm, and characteristic spine formations. Large complex spines and smaller, “stubby” spines were observed on apical as well as basal dendrites. This suggests that characteristic spine formations were not induced by specific afferent fibers. All synaptic contacts on spines were of the asymmetric type, whereas both symmetric and asymmetric synapses occured on cell bodies and dendritic shafts. Unlike in rodents, we found a large variability of granule cells in the primate fascia dentata. This variability has to be considered in neropathological studies of this cell type.     

The influence of electric fields on the epileptiform bursts induced by high potassium in CA3 region of rat hippocampal slice

Abstract

The effects of pulsed direct current (de) electric fields on the frequency of spontaneous bursting in a model epileptic focus were studied. The high potassium hippocampal slice model was used to generate spontaneous burst firing activity similar to interictal spikes in the pyramidal cell layer of CA3. Electric fields were generated from platinum subdural electrodes placed in the perfusion bath. Three hundred and seventy-eight experimental trials were performed on 10 hippocampal slices from 10 rats and the effects of field polarity, field strength and duration of stimuli on firing frequency was examined. Hippocampal slices were oriented horizontally with the CA3 layer towards the positive electrodel the average interburst interval did not correlate significantly with polarity of the delivering pulses (one-way ANOVA, p = 0.96). Average interburst interval showed a significant correlation with pulse duration of200 and 400msec (p = 0.030 and p = 0.004, respectively). As a function of field strength, there were significant average interval changes for fields of 33, 46, and 73 mV/mm (p = 0.024, P = 0.001 and p = 0.001, respectively). In conclusion, CA3 burst firing activity in high potassium concentration can therefore be altered by electric fields. [Neural Res 1998; 20: 542-548]     

Deficit in long-term contextual fear memory induced by blockade of beta-adrenoceptors in hippocampal CA1 region

The present study investigated the effects of intra-CA1 infusion of d,l-propranolol, the beta-adrenergic antagonist, on memory for contextual fear conditioning. d,l-Propranolol administered 5 min ('0 h') postconditioning impaired long-term but not short-term contextual fear memory, while it was ineffective when administered 6 h postconditioning, suggesting that there is a time window for beta-adrenoceptors to play a role. Thus, we conclude that beta-adrenoceptors in area CA1 are involved in regulating consolidation of contextual fear memory, with '0 h' but not 6 h post-training, a sensitive time point for the beta-adrenergic involvement.     

Effect of protein malnutrition on CA3 hippocampal pyramidal cells in rats of three ages

Prenatal and postnatal protein deprivation effect on CA3 hippocamapal pyramidal pyramidal cells were investigated in 30-, and 90- and 220-day old rats Female rats were fed either a 6% or a 25% casein diet 5 wk before conception and the litters were maintained on their respective diet until sacrificed. In 216 rapid Golgi-impregnatd cells, we measured somal size, length and diameter of apical dendrite, number of apical dendrites intersecting 10 concentric rings 38 μm apart, thorny excrescence area and length, head diameter and density of synaptic spines on 50-μm segments of apical dendrite. The present experiments showed that malnutrition produced significant reductions of somal size in animals at 220 days of age. There were significant reductions of apical dendrite diameters in animals of 30 and 90 days, and of density and head diameter of synaptic spines at the three ages studied, and significant decrease of the thorny excrescence area at 220 days of age. At this latter age, dendritic branching was significantly decreased in the last four rings representing the area into which the perforant pathway projects. In 30-day malnourished rats, dendritic branching showed a significant increase in rings 4–6 representing the area in which the Schaffer collaterals synapse. The location of the deficit spines corresponds to the sites where mossy fibers synapse on the apical dendrites of CA3 neurons. Age-related changes normally observed in control rats (e.g., the 30-day-old control group showed the smallest somal size and 220-day-old controls the largest size) failed to occur in the malnourished rats. The deficits in spine density and dendritic branching (in animals of 220 days old) were similar to those found in our previous studies on fascia dentata.     

Capillary changes in hippocampal CA1 and CA3 areas of the aging rhesus monkey

The rhesus monkey is considered a useful animal model for studying human aging, because non-human primates show many of the neurobiological alterations that have been reported in aging humans. Cognitive impairment that accompanies normal aging may, at least partially, originate from capillary changes in the hippocampus, known to be involved in learning and memory. Age-related effects on the cerebral capillaries in the non-human primate hippocampus have not yet been studied. Therefore, we investigated age-related microvascular changes in the hippocampus of the aged non-human primate. We examined by electron microscopy the microvascular ultrastructure in the CA1 and CA3 areas of 14 male rhesus monkeys (Macaca mulatta), ranging from 1 to 31 years of age. The percentages of capillaries showing basement membrane thickening and deposits of collagen in the basement membrane were determined semiquantitatively in 4 young (1–6 years), 6 middle-aged (17– 24 years), and 4 aged (29–31 years) monkeys. Aberrations in the basement membrane are few in young subjects (28 ± 6% of capillaries), and occur with increasing frequency during the aging process in rhesus monkeys (aged animals: 71 ± 5% of capillaries). This could be ascribed to an aging-associated increasing number of capillaries showing depositions of collagen fibrils, rather than local thickenings of the basement membrane. The observed changes in microvascular integrity are very similar to those seen in humans, supporting the view of rhesus monkeys as a model for human aging. The slow but steady progression of these changes could be detrimental for an efficient nutrient supply of the neuropil, and might therefore contribute to decreased cognitive functioning during normal aging. Received: 30 August 1999 / Revised: 21 January 2000 / Accepted: 22 February 2000     

Dendritic changes in the hippocampal formation of AIDS patients: a quantitative Golgi study

We have previously shown that in the hippocampal formation of patients with acquired immunodeficiency syndrome (AIDS) there is neuronal atrophy, without cell loss. Because reductions in neuronal size are suggestive of associated neuritic alterations, we decided to study the dendritic trees of the main neuronal populations in the hippocampal formation. Material was obtained in five male AIDS patients and five male controls. After Golgi impregnation, the dendritic arborizations of dentate granule and hilar basket cells, and of CA3 and CA1 pyramidal cells, were hand traced, and their segments classified, counted and measured. We found an impoverishment of the dendritic trees in all neuronal populations in the AIDS group, which was more striking in the hilus and CA3 field. Specifically, hilar neurons had fewer dendritic segments, and reduced branching density and dendritic extent; in CA3 pyramids there was a decrease in the number of terminal segments in the basal trees, and a reduction in the total number of segments, number of medium order terminals, dendritic branching density and dendritic extent in the apical trees. In CA1 pyramids, the terminals were shorter in the apical trees and the dendritic spine density decreased in the basal trees, whereas in granule cells only the dendritic spine density was reduced in AIDS patients. Subtle signs suggestive of dendritic reorganization were observed. These results point to a regional vulnerability of the hippocampal formation to HIV infection, and might contribute to explaining the occurrence of dementia, as a consequence of overall reduction in the hippocampal neuronal receptive surface.     

Chaotic responses of the hippocampal CA3 region to a mossy fiber stimulation in vitro

Undoubted evidence of chaotic activity of a biological neural network are given. Spontaneous epileptiform bursts of a neuron population in the CA3 region of rat hippocampal slices were caused in a perfusing medium with 2 mM penicillin and 8 mM K⁺ ions, and responses of field potential in the CA3 region to a periodic mossy fiber stimulation were investigated. Phase-locked and chaotic responses occur depending on stimulus parameters; for example, when the frequency of the stimulation increases, 1:1 phase-locking bifurcates to chaos through 1:2 phase-locking. The chaotic responses show a broad-band spectrum, and their trajectories in the three-dimensional phase space (V(t), V(t + τ), V(t + 2τ)) reconstruct a strange attractor. Lyapunov exponents of the strange attractors estimated by the Wolf's algorithm are positive. Moreover, one-dimensional strobomaps obtained from the chaotic responses show a non-invertible function. Since the slope of each strobomap at their fixed point is more negative than −1, the fixed points are unstable. These are undoubted evidences for chaotic responses of the CA3 region in hippocampal slices maintained in vitro. Cross-correlation functions between field potential responses which were simultaneously observed at different sites show that the responses are spatially coherent throughout the CA3 region even when the responses are chaotic.