Manganese enhanced MRI detects mossy fiber sprouting rather than neurodegeneration, gliosis or seizure-activity in the epileptic rat hippocampus

We tested a hypothesis that manganese enhanced magnetic resonance imaging (MEMRI) after systemic injection of MnCl(2) could detect axonal sprouting in the hippocampus following kainate (KA) induced status epilepticus (SE). MEMRI was performed at 3 h, 25 h, 4 days, and 2 months post-SE. To assess the contribution of various cellular alterations that occur in parallel with sprouting to the MEMRI signal, we sacrificed animals for histology at 4 days and 2 months post-SE. Neurodegeneration was assessed from thionin and Fluoro-Jade B stained preparations, astrogliosis from GFAP (glial fibrillary acidic protein) and microgliosis from Ox-42 immunostained preparations. Sprouting of granule cells axons (mossy fibers) in the dentate gyrus was analyzed from Timm stained sections. Occurrence of spontaneous epileptic seizures was analyzed at 2 months post-SE using continuous video-EEG monitoring. Integrity of the blood-brain barrier (BBB) was studied using Gd-enhanced MRI. We found abnormal MEMRI hyperintensity in the CA1 and the dentate gyrus at 2 months post-SE but not at earlier time points. Based on histologic analysis of individual animals with MEMRI hyperintensity, hippocampal MEMRI changes could be attributed to increasing axonal density rather than to neurodegeneration, astrogliosis, or microgliosis. Moreover, MEMRI contrast was not affected by seizure activity, and we could not detect any leakage of the BBB that could have explained the observed MEMRI hyperintensity. Present data show that systemic MEMRI can reveal axonal sprouting, and thus, can potentially serve as a marker for neuroplasticity in preclinical studies.     

Magnetic resonance imaging of the mouse visual pathway for in vivo studies of degeneration and regeneration in the CNS

Traditionally, depiction of isolated CNS fiber tracts is achieved by histological post mortem studies. As a tracer-dependent strategy, the calcium analog manganese has proved valuable for in vivo imaging of CNS trajectories, particularly in rats. However, adequate protocols in mice are still rare. To take advantage of the numerous genetic mouse mutants that are available to study axonal de- and regeneration processes, a MnCl₂-based protocol for high-resolution contrast-enhanced MRI (MEMRI) of the visual pathway in mice acquired on a widely used clinical 3 Tesla scanner was established. Intravitreal application of MnCl₂ significantly enhanced T1-weighted contrast and signal intensity along the retino-petal projection enabling its reconstruction in a 3D mode from a maximum intensity projection (MIP) calculated dataset. In response to crush injury of the optic nerve, axonal transport of MnCl₂ was diminished and completely blocked proximal and distal to the lesion site, respectively. Conditions of Wallerian degeneration after acute optic nerve injury accelerated Mn²⁺-enhanced signal fading in axotomized projection areas between 12 and 24 h post-injury. In long-term regeneration studies 12 months after optic nerve injury, the MRI protocol proved highly sensitive and discriminated animals with rare spontaneous axonal regrowth from non-regenerating specimens. Also, structural MRI aspects shared high correlation with histological results in identical animals. Moreover, in a model of chronic neurodegeneration in p50/NF-κB-deficient mice, MnCl₂-based neuron-axonal tracing supported by heat map imaging indicated neuropathy of the visual pathway due to atrophy of optic nerve fiber projections. Toxic effects of MnCl₂ at MRI contrast-relevant dosages in repetitive administration protocols were ruled out by histological and optometric examinations. At higher dosages, photoreceptors, not retinal ganglion cells, turned out as most susceptible to the well-known toxicity of MnCl₂. Our data accentuate in vivo MEMRI of the murine visual system as a highly specific and sensitive strategy to uncover axonal degeneration and restoration processes, even in a functional latent state. We expect MEMRI to be promising for future applications in longitudinal studies on development, aging, or regeneration of CNS projections in mouse models mimicking human CNS pathologies.     

Role of neuronal activity and kinesin on tract tracing by manganese-enhanced MRI (MEMRI)

MEMRI offers the exciting possibility of tracing neuronal circuits in living animals by MRI. Here we use the power of mouse genetics and the simplicity of the visual system to test rigorously the parameters affecting Mn2+ uptake, transport and trans-synaptic tracing. By measuring electrical response to light before and after injection of Mn2+ into the eye, we determine the dose of Mn2+ with the least toxicity that can still be imaged by MR at 11.7 T. Using mice with genetic retinal blindness, we discover that electrical activity is not necessary for uptake and transport of Mn2+ in the optic nerve but is required for trans-synaptic transmission of this tracer to distal neurons in this pathway. Finally, using a kinesin light chain 1 knockout mouse, we find that conventional kinesin is a participant but not essential to neuronal transport of Mn2+ in the optic tract. This work provides a molecular and physiological framework for interpreting data acquired by MEMRI of circuitry in the brain.     

Reproducible imaging of rat corticothalamic pathway by longitudinal manganese-enhanced MRI (L-MEMRI)

Manganese-enhanced MRI (MEMRI) has been described as a powerful tool to depict the architecture of neuronal circuits. The aim of the present study was to optimize the experimental conditions of MEMRI that permits the study of insult-induced alterations of the somatosensory pathway in a longitudinal way, and to provide functional information on rat corticothalamic connectivity or disturbances thereof. A guidance screw was implanted in the skull of the rats, over the forelimb representation area of the primary somatosensory cortex (S1fl), allowing repetitive injections at the same stereotactic coordinates. MnCl2 (200 nL, 0.3 M) was injected 1.5 mm below the dura using a calibrated microcapillary. Animals received MnCl2 injections 3 times at 15 day intervals. Spatiotemporal patterns showed a significant hyperintensity on T1-weighted images induced by manganese transport in structures related to the somatosensory pathway, i.e. globus pallidus, caudate putamen, thalamus and substantia nigra. 7 days after MnCl2 injection hyperintensity was only evident at some points surrounding the injection site. Complete loss of manganese-induced contrast was achieved after 15 days after injection. Functional MRI (fMRI) experiments were performed under the same conditions, 24 h after MnCl2 injection. Activation of S1fl was observed showing that fMRI and MEMRI studies are compatible and can be performed in parallel in the same animals. The present study shows, for the first time, a robust and reproducible technique to perform longitudinal MEMRI (L-MEMRI) experiments and to study the time course of alterations of the corticothalamic connections following stroke in the rat.     

Axonal transport of recombinant baculovirus vectors.

Targeted gene delivery to neurons is crucial to effective gene therapy of neurodegenerative diseases. Several types of viral gene vectors may target neurons through retrograde axonal transport to somas of projection neurons after viral internalization at axon terminal fields. In this report we demonstrate for the first time that recombinant baculovirus vectors could migrate by axonal transport to cell bodies, resulting in transgene expression in projection neurons. After stereotaxic injection of Cy3-labeled baculovirus vectors into the rat striatum, retrograde axonal transport of the baculovirus vectors was observed along the corticostriatal pathway and nigrostriatal pathway. Furthermore, after intra-vitreous body injection, anterograde axonal transport and transsynaptic transport of the virus particles were observed in defined connections of the visual system, from the retina to the optic nerve, the lateral geniculate body, the superior colliculus, and the primary visual cortex. PCR analysis confirmed the existence of transported viral DNA in the tissue samples collected from projection fields. Driven by a neuron-specific promoter, transgene expression from the recombinant baculovirus vectors was detectable in target regions remote from injection sites. The attributes of baculovirus vectors in the bidirectional axonal transport and transneuronal transport in neural circuits of the central nervous system could be utilized for targeted gene delivery.     

Detection of amyloid plaques targeted by USPIO-Aβ1-42 in Alzheimer's disease transgenic mice using magnetic resonance microimaging

Amyloid plaques are one of the pathological hallmarks of Alzheimer's disease (AD). The visualization of amyloid plaques in the brain is important to monitor AD progression and to evaluate the efficacy of therapeutic interventions. Our group has developed several contrast agents to detect amyloid plaques in vivo using magnetic resonance microimaging (μMRI) in AD transgenic mice, where we used intra-carotid mannitol to enhance blood-brain barrier (BBB) permeability. In the present study, we used ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles, chemically coupled with Aβ1-42 peptide to detect amyloid deposition along with mannitol for in vivo μMRI by femoral intravenous injection. A 3D gradient multi-echo sequence was used for imaging with a 100μm isotropic resolution. The amyloid plaques detected by T2*-weighted μMRI were confirmed with matched histological sections. Furthermore, two different quantitative analyses were used. The region of interest-based quantitative measurement of T2* values showed contrast-injected APP/PS1 mice had significantly reduced T2* values compared to wild-type mice. In addition, the scans were examined with voxel-based morphometry (VBM) using statistical parametric mapping (SPM) for comparison of contrast-injected AD transgenic and wild-type mice. The regional differences seen in VBM comparing USPIO-Aβ1-42 injected APP/PS1 and wild-type mice correlated with the amyloid plaque distribution histologically, contrasting with no differences between the two groups of mice without contrast agent injection in regions of the brain with amyloid deposition. Our results demonstrated that both approaches were able to identify the differences between AD transgenic mice and wild-type mice, after injected with USPIO-Aβ1-42. The feasibility of using less invasive intravenous femoral injections for amyloid plaque detection in AD transgenic mice facilitates using this method for longitudinal studies in the pathogenesis of AD.     

丹参大黄合剂对拟老年痴呆大鼠学习记忆能力及海马β淀粉样前体蛋白、早老素1mRNA表达的影响

目的探讨丹参大黄合剂对拟老年性痴呆（AD）大鼠学习记忆能力的影响及其机制。方法用D-半乳糖和三氯化铝联合用药制备拟AD动物模型。从造模的第20天开始,丹参大黄组灌胃给予丹参大黄合剂,连续70d。给药结束后,通过方形水迷宫、逆转录聚合酶链反应来观察丹参大黄合剂对拟AD模型大鼠学习记忆和海马β淀粉样前体蛋白（APP）、早老素1（PS1）基因表达的影响。结果丹参大黄合剂可以缩短拟AD模型大鼠水迷宫测试的潜伏期（P〈0.05）,减少其错误次数（P〈0.05）,同时降低海马APP、PS1 mRNA的表达（P〈0.05）。结论丹参大黄合剂能提高拟AD大鼠学习、记忆能力,可能与降低APP、PS1 mRNA的表达有关。     

锰离子增强磁共振成像在动物神经系统研究中的应用

以二价锰离子(Mn2 )为探针的锰离子增强磁共振成像(MEMRI)是近年来发展迅速的一种脑成像新技术。Mn2 作为强顺磁性钙离子竞争剂,可以通过钙离子通道进入神经细胞,并可通过轴突、突触运输,减少含Mn2 组织的T1值,从而增强区域T1加权MRI信号。目前,MEMRI主要用于三方面的研究:活动诱导观察脑的功能活动,在体、动态地追踪神经传导通路,并可以精细观察脑部形态学。MEMRI在多领域的研究结果表明它是探测生物体内的分子过程和大脑功能活动的重要工具和手段。本文综述了MEMRI的原理及其在动物中枢神经系统研究中的应用。     

Imaging unconditioned fear response with manganese-enhanced MRI (MEMRI)

Recent use of manganese-enhanced MRI (MEMRI) to assess the neural circuitry involved in autonomic and somatosensory paradigms has been promising. The current study addresses the feasibility of utilizing this technique to assess more complex cognitive and emotional processes. Since olfactory cues are particularly salient to animals, we utilized odorless air, novel/arousing and novel/fear-inducing scents to assess the neural circuitry sub-serving novelty and unconditioned fear. The present imaging data clearly indicate that animals with no prior exposure to a threat-inducing emotional stimulus selectively activated the unconditional fear neuronal pathway, specifically with heightened amygdala and hypothalamic activation. While animals exposed to the novel/arousing compared to fear-inducing odor demonstrated enhanced uptake in the cingulated and prefrontal cortices. In addition, as expected the hippocampus showed significantly enhanced manganese contrast after novelty exposure. Therefore the current study support the validity of MEMRI in the exploration of highly relevant complex neural circuitries associated with cognition and emotion.     

Quantitative in vivo measurement of early axonal transport deficits in a triple transgenic mouse model of Alzheimer's disease using manganese-enhanced MRI

Impaired axonal transport has been linked to the pathogenic processes of Alzheimer's disease (AD) in which axonal swelling and degeneration are prevalent. The development of non-invasive neuroimaging methods to quantitatively assess in vivo axonal transport deficits would be enormously valuable to visualize early, yet subtle, changes in the AD brain, to monitor the disease progression and to quantify the effect of drug intervention. A triple transgenic mouse model of AD closely resembles human AD neuropathology. In this study, we investigated age-dependent alterations of the axonal transport rate in the triple transgenic mouse olfactory system, using fast multi-sliced T(1) mapping with manganese-enhanced MRI. The data show that impairment in axonal transport is a very early event in AD pathology in these mice, preceding both deposition of Aβ plaques and formation of Tau fibrils.     

Allele-specific RNAi Mitigates Phenotypic Progression in a Transgenic Model of Alzheimer's Disease

Despite recent advances suggesting new therapeutic targets, Alzheimer''s disease (AD) remains incurable. Aberrant production and accumulation of the Aβ peptide resulting from altered processing of the amyloid precursor protein (APP) is central to the pathogenesis of disease, particularly in dominantly inherited forms of AD. Thus, modulating the production of APP is a potential route to effective AD therapy. Here, we describe the successful use of an allele-specific RNA interference (RNAi) approach targeting the Swedish variant of APP (APPsw) in a transgenic mouse model of AD. Using recombinant adeno-associated virus (rAAV), we delivered an anti-APPsw short-hairpin RNA (shRNA) to the hippocampus of AD transgenic mice (APP/PS1). In short- and long-term transduction experiments, reduced levels of APPsw transprotein were observed throughout targeted regions of the hippocampus while levels of wild-type murine APP remained unaltered. Moreover, intracellular production of transfer RNA (tRNA)-valine promoter–driven shRNAs did not lead to detectable neuronal toxicity. Finally, long-term bilateral hippocampal expression of anti-APPsw shRNA mitigated abnormal behaviors in this mouse model of AD. The difference in phenotype progression was associated with reduced levels of soluble Aβ but not with a reduced number of amyloid plaques. Our results support the development of allele-specific RNAi strategies to treat familial AD and other dominantly inherited neurodegenerative diseases.     

Changes in hippocampal connectivity in the early stages of Alzheimer's disease: evidence from resting state fMRI

A selective distribution of Alzheimer's disease (AD) pathological lesions in specific cortical layers isolates the hippocampus from the rest of the brain. However, functional connectivity between the hippocampus and other brain regions remains unclear in AD. Here, we employ a resting state functional MRI (fMRI) to examine changes in hippocampal connectivity comparing 13 patients with mild AD versus 13 healthy age-matched controls. Hippocampal connectivity was investigated by examination of the correlation between low frequency fMRI signal fluctuations in the hippocampus and those in all other brain regions. We found that functional connectivity between the right hippocampus and a set of regions was disrupted in AD; these regions are: medial prefrontal cortex (MPFC), ventral anterior cingulate cortex (vACC), right inferotemporal cortex, right cuneus extending into precuneus, left cuneus, right superior and middle temporal gyrus and posterior cingulate cortex (PCC). We also found increased functional connectivity between the left hippocampus and the right lateral prefrontal cortex in AD. In addition, rightward asymmetry of hippocampal connectivity observed in elderly controls was diminished in AD patients. The disrupted hippocampal connectivity to the MPFC, vACC and PCC provides further support for decreased activity in "default mode network" previously shown in AD. The decreased connectivity between the hippocampus and the visual cortices might indicate reduced integrity of hippocampus-related cortical networks in AD. Moreover, these findings suggest that resting-state fMRI might be an appropriate approach for studying pathophysiological changes in early AD.     

In vivo axonal transport rates decrease in a mouse model of Alzheimer's disease

Axonopathy is a pronounced attribute of many neurodegenerative diseases. In Alzheimer's disease (AD), axonal swellings and degeneration are prevalent and may contribute to the symptoms of AD senile dementia. Current limitations in identifying the contribution of axonal damage to AD include the inability to detect when this damage occurs in relation to other identifiers of AD because of the invasiveness of existing methods. To overcome this, we further developed the MRI methodology Manganese Enhanced MRI (MEMRI) to assess in vivo axonal transport rates. Prior to amyloid-beta (Abeta) deposition, the axonal transport rates in the Tg2576 mouse model of AD were normal. As Abeta levels increased and before plaque formation, we observed a significant decrease in axonal transport rates of the Tg2576 mice compared to controls. After plaque formation, the decline in the transport rate in the Tg2576 mice became even more pronounced. These data indicate that in vivo axonal transport rates decrease prior to plaque formation in the Tg2576 mouse model of AD.     

Manganese-enhanced magnetic resonance imaging of mossy fiber plasticity in vivo

Mn(2+)-enhanced magnetic resonance imaging (MEMRI) was used to characterize activity-dependent plasticity in the mossy fiber pathway after intraperitoneal kainic acid (KA) injection. Enhancement of the MEMRI signal in the dentate gyrus and the CA3 subregion of the hippocampus was evident 3 to 5 days after injection of MnCl(2) into the entorhinal cortex both in control and KA-injected rats. In volume-rendered three-dimensional reconstructions, Mn(2+)-induced signal enhancement revealed the extent of the mossy fiber pathway throughout the septotemporal axis of the dentate gyrus. An increase in the number of Mn(2+)-enhanced pixels in the dentate gyrus and CA3 subfield of rats with KA injection correlated (P < 0.05) with histologically verified mossy fiber sprouting. These data demonstrate that MEMRI can be used to detect specific changes at the cellular level during activity-dependent plasticity in vivo. The present findings also suggest that MEMRI signal changes can serve as an imaging marker of epileptogenesis.     

Tracing of noradrenergic projections using manganese-enhanced MRI

We examined the applicability of manganese-enhanced MRI (MEMRI) to the in vivo tracing of diffuse neuromodulatory projections by means of simultaneous iontophoretic injections of an extremely low, non-toxic concentration of MnCl₂ (10 mM) and fluorescent dextran in the locus coeruleus (LC) in the rat. We validated the use of the iontophoretic injection by reproducing previously reported results from pressure injections of MnCl₂ in primary somatosensory cortex. Twenty four hours after injection in LC, Mn^2 + labeling was detected in major cortical and subcortical targets of LC projections including predominantly ipsilateral primary motor and somatosensory cortices, hippocampus and amygdala. Although the injections were in most cases centered in the core of LC, the pattern of Mn^2 + labeling greatly varied across rats. In addition, despite a certain degree of overlap of the labeling obtained with both MEMRI and classical tracing, MEMRI tracing consistently failed to reliably label not only several minor but also major targets of LC, notably the thalamus. The lack of Mn^2 + labeling in thalamus possibly reflected a weaker functional connectivity within coeruleothalamic projections that could not be predicted by anatomical tracing. Inversely, a number of brain regions, particularly contralateral motor cortex, that were not or only sparsely labeled with fluorescent dextran were strongly labeled by Mn^2 +. This discrepancy could be partly due to both the activity-dependent and transsynaptic nature of Mn^2 + transport. The overall labeling produced using MEMRI with iontophoretic injections in LC indicates that the Mn^2 + imaging of highly diffuse projections is in principle feasible. However, the labeling pattern of each individual case needs to be carefully interpreted particularly before submitting data for group analysis or in the case of longitudinal examination of discrete changes in functional connectivity under various physiological or behavioral conditions.     

Functional activity mapping of rat auditory pathway after intratympanic manganese administration

In the present study, we report a new method of manganese enhanced magnetic resonance imaging (MEMRI) using intratympanic (IT) manganese administration. We explore Mn2? uptake from the middle ear cavity into the cochlea through mechanically gated ion channels of the hair cell and also functional auditory tract tracing without the use of excessive auditory stimuli for a long time period outside the scanner. After manganese administration in animals with normal hearing and unilateral deafness, T1-weighted MR images were obtained for up to 48 h with a 3.0 T MR imager. In normal rats, the mean signal-to-noise ratio (SNR) at each region of interest on the auditory pathway was significantly higher in the IT injection group than in the intraperitoneal (IP) injection group (P<0.05). Furthermore, the cochlea showed Mn2? signal enhancement only in the IT injection group. In unilateral deafness rats, the IT injection of Mn2? into the deaf-side middle ear cavity demonstrated signal enhancement in the cochlea but not in other auditory structures without axonal transport of Mn2? along the auditory pathway. On the other hand, the IT injection of Mn2? into the normal-side middle ear cavity demonstrated that the mean SNRs at the cochlea, cochlear nucleus, superior olivary complex, lateral lemniscus and inferior colliculus were significantly higher in the ipsilateral auditory pathway than in the contralateral pathway (P<0.05). For the IP injection group, the mean SNRs at each auditory structure, except the cochlea, increased bilaterally. In conclusion, the present work demonstrated the potential advantages of a new IT MEMRI over conventional systemic injection strategies in that (i) the functional auditory tract tracing initiated by the hair cell function is possible and (ii) the axonal transport of Mn2? ions by trans-synaptic activity is possible without auditory stimulation for a long time period outside MR scanner.     

Live imaging of neuronal connections by magnetic resonance: Robust transport in the hippocampal-septal memory circuit in a mouse model of Down syndrome

Connections from hippocampus to septal nuclei have been implicated in memory loss and the cognitive impairment in Down syndrome (DS). We trace these connections in living mice by Mn(2+) enhanced 3D MRI and compare normal with a trisomic mouse model of DS, Ts65Dn. After injection of 4 nl of 200 mM Mn(2+) into the right hippocampus, Mn(2+) enhanced circuitry was imaged at 0.5, 6, and 24 h in each of 13 different mice by high resolution MRI to detect dynamic changes in signal over time. The pattern of Mn(2+) enhanced signal in vivo correlated with the histologic pattern in fixed brains of co-injected 3kD rhodamine-dextran-amine, a classic tracer. Statistical parametric mapping comparing intensity changes between different time points revealed that the dynamics of Mn(2+) transport in this pathway were surprisingly more robust in DS mice than in littermate controls, with statistically significant intensity changes in DS appearing at earlier time points along expected pathways. This supports reciprocal alterations of transport in the hippocampal-forebrain circuit as being implicated in DS and argues against a general failure of transport. This is the first examination of in vivo transport dynamics in this pathway and the first report of elevated transport in DS.     

强化训练通过调节海马蛋白酶体活性对阿尔茨海默症小鼠认知障碍的影响

目的探究强化训练通过调节海马蛋白酶体活性对阿尔兹海默症(AD)小鼠认知障碍的影响。方法选取雄性无特定病原级的KM小鼠30只,将其按随机数字表法分为对照组、AD模型组和强化训练组,每组各10只。AD模型组和强化训练组小鼠给予腹腔注射D-半乳糖和苯甲酸钠构建AD模型,对照组无特殊处理。强化训练组在给药后1 h,将其放置于含自由转轮的鼠笼中进行强化训练。实验结束前1周内,通过水迷宫实验、定位航行实验和空间探索实验研究强化训练对AD小鼠的学习记忆和认知能力的影响;通过免疫组织化学实验研究小鼠脑组织切片后DCX、Ki67的阳性表达数和小鼠大脑皮层、海马CAI区内Aβ-42表达情况;通过蛋白酶体活性检测试剂盒检测各组小鼠海马区蛋白酶体活性情况;并利用蛋白质印迹(Western blotting)法检测海马蛋白酶体表达水平。结果与AD模型组相比,强化训练组小鼠的逃避潜伏期延长,在目标象限内的穿越次数和停留时间缩短,且小鼠脑内DCX和Ki67阳性细胞数增多,平均神经元突起的长度也增长(P <0.05),同时大脑皮层和海马CAI区Aβ-42阳性神经元的面积也小于AD模型组,而其海马蛋白酶体活性升高,运动皮层和小脑部位蛋白酶活性也均出现升高的现象(P <0.05);Western blotting结果显示,强化训练后AD小鼠海马区蛋白酶体表达和其亚基PSMB5表达均较AD模型组小鼠表达增强(P <0.05)。结论强化训练可通过调节阿尔兹海默症小鼠海马蛋白酶体活性,降低小鼠Aβ沉积水平,达到增强小鼠学习和记忆能力的目的,改善小鼠的认知功能障碍现象。     

黄连解毒汤对APP/PS1双转基因AD小鼠海马区病理形态学及脑内β-APP基因mRNA的影响

目的:探讨黄连解毒汤(HLJDD)对APP/PS1双转基因阿尔茨海默病(AD)模型小鼠海马CA1区的病理形态学及脑内β-淀粉样前体蛋白(β-APP)基因mRNA的影响。方法:选用3月龄的APP/PS1双转基因AD小鼠模型50只,随机分为对照组、安理申组、HLJDD大剂量组、HLJDD中剂量组、HLJDD小剂量组各10只,分别给予安理申或不同剂量HLJDD灌胃治疗6个月,对照组不予治疗,记录并比较各组死亡率;分别于6月龄和10月龄时采用HE染色观察各组海马CA1区神经细胞形态,采用改良甲醇刚果红染色观察各组老年斑形成情况;于末次灌胃治疗后,通过实时荧光定量PCR检测各组脑内β-APPmRNA水平。结果:各组小鼠死亡率差异无统计学意义;10月龄HLJDD各剂量组海马CA1区神经损伤情况较对照组明显减轻,老年斑数量少于对照组(P0.05);HLJDD各剂量组β-APPmRNA水平低于对照组(P0.05),其中以中剂量组水平降低最明显(P0.01)。结论:HLJDD能保护海马神经细胞。     

Layer specific tracing of corticocortical and thalamocortical connectivity in the rodent using manganese enhanced MRI

Information about layer specific connections in the brain comes mainly from classical neuronal tracers that rely on histology. Manganese Enhanced MRI (MEMRI) has mapped connectivity along a number of brain pathways in several animal models. It is not clear at what level of specificity neuronal connectivity measured using MEMRI tracing can resolve. The goal of this work was to determine if neural tracing using MEMRI could distinguish layer inputs of major pathways of the cortex. To accomplish this, tracing was performed between hemispheres of the somatosensory (S1) cortex and between the thalamus and S1 cortex. T(1) mapping and T(1) weighted pulse sequences detected layer specific tracing after local injection of MnCl(2). Approximately 12 h following injections into S1 cortex, maximal T(1) reductions were observed at 0.6+/-0.07 and 1.1+/-0.12 mm from the brain surface in the contralateral S1. These distances correspond to the positions of layer 3 and 5 consistent with the known callosal inputs along this pathway. Four to six hours following injection of MnCl(2) into the thalamus there were maximal T(1) reductions between 0.7+/-0.08 and 0.8+/-0.08 mm from the surface of the brain, which corresponds to layer 4. This is consistent with terminations of the known thalamocortical projections. In order to observe the first synapse projection, it was critical to perform MRI at the right time after injections to detect layer specificity with MEMRI. At later time points, tracing through the cortical network led to more uniform contrast throughout the cortex due to its complex neuronal connections. These results are consistent with well established neuronal pathways within the somatosensory cortex and demonstrate that layer specific somatosensory connections can be detected in vivo using MEMRI.