Temporal proteomic profile of memory consolidation in the rat hippocampal dentate gyrus

Information storage in the brain depends on the ability of neurons to alter synaptic connectivity within key circuitries such as the hippocampus. Memory-associated synaptic plasticity is mediated by a temporal cascade of de novo protein synthesis and altered protein processing. Here, we have used two-dimensional difference in gel electrophoresis (2-D DIGE) to investigate memory-specific protein changes in the hippocampal dentate gyrus at increasing times following spatial learning. We identified 42 proteins that were significantly regulated in the first 24 h of spatial memory consolidation. Two distinct waves of protein expression regulation were evident, at 3 and 12 h post-learning and this is in agreement with studies employing inhibitors of global translation. Functional classification of the memory-associated proteins revealed that the majority of regulated proteins contributed either to cellular structure or cellular metabolism. For example, actins, tubulins and intermediate filament proteins, core proteins of the three major cytoskeletal components, were dynamically regulated at times that suggest a role in memory-associated synaptic reorganization. Increased proteasome-mediated protein degradation was evident in the early post-training period including the down-regulation of phosphoprotein enriched in astrocytes 15 kDa, a key inhibitor of extracellular signal-regulated kinase signaling. Some of the most substantial protein expression changes were observed for secreted carrier proteins including transthyretin and serum albumin at 6-12 h post-learning, regulations that could serve an important role in increasing the supply of retinoic acid and thyroid hormone, key synaptic plasticity-promoting signals in the adult brain. Together these observations provide further insight into protein level regulations occurring in the hippocampus during spatial memory consolidation.     

Amyloid precursor protein expression in the rat hippocampal dentate gyrus modulates during memory consolidation

Despite advances in our understanding of the basic biology of amyloid precursor protein (APP), the normal physiological function(s) of APP in learning and memory remains unclear. Here we show increased APP degradation in the hippocampus to be associated with the consolidation of a passive avoidance response. Neurone-specific APP695 expression became transiently reduced 2-4 h post-training through association with endosomal adaptin proteins and enhanced internalization. By contrast, internalization of glial-associated APP containing a Kunitz protease inhibitor-like domain (APP-KPI) was dependent on the low-density lipoprotein receptor-related protein (LRP). In addition, LRP expression and association with apolipoprotein E increased in the 2-4 h post-training period. The LRP antagonist receptor-associated protein prevented the APP-KPI internalization and LRP-apolipoprotein E association and this resulted in amnesia. Degradation of APP695 and APP-KPI did not appear to be related to alpha-secretase activity, as no learning-associated increase of secreted APP was observed in the CSF. Moreover, as internalization of APP isoforms was observed only in dentate gyrus, it probably relates to the learning-associated restructuring of the perforant path terminals. Memory-associated APP processing in both neuronal and glial compartments points to a role for glial unsheathing of synaptic connections, an event required for the synaptic restructuring that accompanies memory consolidation. These observations may have a direct relevance to understanding the pathophysiology of Alzheimer's disease as beta/gamma-secretase-derived beta-amyloid is formed following internalization of cell surface APP into the endosomal compartment.     

Eph receptor and ephrin signaling in developing and adult brain of the honeybee (Apis mellifera)

Roles for Eph receptor tyrosine kinase and ephrin signaling in vertebrate brain development are well established. Their involvement in the modulation of mammalian synaptic structure and physiology is also emerging. However, less is known of their effects on brain development and their function in adult invertebrate nervous systems. Here, we report on the characterization of Eph receptor and ephrin orthologs in the honeybee, Apis mellifera (Am), and their role in learning and memory. In situ hybridization for mRNA expression showed a uniform distribution of expression of both genes across the developing pupal and adult brain. However, in situ labeling with Fc fusion proteins indicated that the AmEphR and Amephrin proteins were differentially localized to cell body regions in the mushroom bodies and the developing neuropiles of the antennal and optic lobes. In adults, AmEphR protein was localized to regions of synaptic contacts in optic lobes, in the glomeruli of antennal lobes, and in the medial lobe of the mushroom body. The latter two regions are involved in olfactory learning and memory in the honeybee. Injections of EphR-Fc and ephrin-Fc proteins into the brains of adult bees, 1 h before olfactory conditioning of the proboscis extension reflex, significantly reduced memory 24 h later. Experimental amnesia in the group injected with ephrin-Fc was apparent 1 h post-training. Experimental amnesia was also induced by post-training injections with ephrin-Fc suggesting a role in recall. This is the first demonstration that Eph molecules function to regulate the formation of memory in insects.     

MGluR5 mediates the interaction between late-LTP, network activity, and learning

Hippocampal synaptic plasticity and learning are strongly regulated by metabotropic glutamate receptors (mGluRs) and particularly by mGluR5. Here, we investigated the mechanisms underlying mGluR5-modulation of these phenomena. Prolonged pharmacological blockade of mGluR5 with MPEP produced a profound impairment of spatial memory. Effects were associated with 1) a reduction of mGluR1a-expression in the dentate gyrus; 2) impaired dentate gyrus LTP; 3) enhanced CA1-LTP and 4) suppressed theta (5-10 Hz) and gamma (30-100 Hz) oscillations in the dentate gyrus. Allosteric potentiation of mGluR1 after mGluR5 blockade significantly ameliorated dentate gyrus LTP, as well as suppression of gamma oscillatory activity. CA3-lesioning prevented MPEP effects on CA1-LTP, suggesting that plasticity levels in CA1 are driven by mGluR5-dependent synaptic and network activity in the dentate gyrus. These data support the hypothesis that prolonged mGluR5-inactivation causes altered hippocampal LTP levels and network activity, which is mediated in part by impaired mGluR1-expression in the dentate gyrus. The consequence is impairment of long-term learning.     

Early natural stimulation through environmental enrichment accelerates neuronal development in the mouse dentate gyrus

The dentate gyrus is the primary afferent into the hippocampal formation, with important functions in learning and memory. Granule cells, the principle neuronal type in the dentate gyrus, are mostly formed postnatally, in a process that continues into adulthood. External stimuli, including environmental enrichment, voluntary exercise and learning, have been shown to significantly accelerate the generation and maturation of dentate granule cells in adult rodents. Whether, and to what extent, such environmental stimuli regulate the development and maturation of dentate granule cells during early postnatal development is largely unknown. Furthermore, whether natural stimuli affect the synaptic properties of granule cells had been investigated neither in newborn neurons of the adult nor during early development. To examine the effect of natural sensory stimulation on the dentate gyrus, we reared newborn mice in an enriched environment (EE). Using immunohistochemistry, we showed that dentate granule cells from EE-reared mice exhibited earlier morphological maturation, manifested as faster peaking of doublecortin expression and elevated expression of mature neuronal markers (including NeuN, calbindin and MAP2) at the end of the second postnatal week. Also at the end of the second postnatal week, we found increased density of dendritic spines across the entire dentate gyrus, together with elevated levels of postsynaptic scaffold (post-synaptic density 95) and receptor proteins (GluR2 and GABA(A)Rγ2) of excitatory and inhibitory synapses. Furthermore, dentate granule cells of P14 EE-reared mice had lower input resistances and increased glutamatergic and GABAergic synaptic inputs. Together, our results demonstrate that EE-rearing promotes morphological and electrophysiological maturation of dentate granule cells, underscoring the importance of natural environmental stimulation on development of the dentate gyrus.     

慢性应激对大鼠学习记忆能力和海马LTP的影响

目的和方法：本研究采用一种多因素的２１ｄ慢性应激动物模型,以Ｙ迷宫和ＬＴＰ为指标,探讨慢性应激对运动学习记忆能力和海马神经突触可塑性的影响。结果：长期慢性应激使大鼠空间学习记忆能力下降,而且,使中枢海马齿状回ＬＴＰ的诱生受到抑制。结论：慢性应激可能使大鼠海马齿状回神经突触可塑性降低,并进一步影响到学习记忆的功能。     

Neuritin Attenuates Cognitive Function Impairments in Tg2576 Mouse Model of Alzheimer's Disease

Neuritin, also known as CPG15, is a neurotrophic factor that was initially discovered in a screen to identify genes involved in activity-dependent synaptic plasticity. Neuritin plays multiple roles in the process of neural development and synaptic plasticity, although its binding receptor(s) and downstream signaling effectors remain unclear. In this study, we found that the cortical and hippocampal expression of neuritin is reduced in the brains of Alzheimer''s disease (AD) patients and demonstrated that viral-mediated expression of neuritin in the dentate gyrus of 13-month-old Tg2576 mice, an AD animal model, attenuated a deficit in learning and memory as assessed by a Morris water maze test. We also found that neuritin restored the reduction in dendritic spine density and the maturity of individual spines in primary hippocampal neuron cultures prepared from Tg2576 mice. It was also shown that viral-mediated expression of neuritin in the dentate gyrus of 7-week-old Sprague-Dawley rats increased neurogenesis in the hippocampus. Taken together, our results demonstrate that neuritin restores the reduction in dendritic spine density and the maturity of individual spines in primary hippocampal neurons from Tg2576 neurons, and also attenuates cognitive function deficits in Tg2576 mouse model of AD, suggesting that neuritin possesses a therapeutic potential for AD.     

Arc/Arg3.1 is essential for the consolidation of synaptic plasticity and memories

Arc/Arg3.1 is robustly induced by plasticity-producing stimulation and specifically targeted to stimulated synaptic areas. To investigate the role of Arc/Arg3.1 in synaptic plasticity and learning and memory, we generated Arc/Arg3.1 knockout mice. These animals fail to form long-lasting memories for implicit and explicit learning tasks, despite intact short-term memory. Moreover, they exhibit a biphasic alteration of hippocampal long-term potentiation in the dentate gyrus and area CA1 with an enhanced early and absent late phase. In addition, long-term depression is significantly impaired. Together, these results demonstrate a critical role for Arc/Arg3.1 in the consolidation of enduring synaptic plasticity and memory storage.     

The timing of differentiation of adult hippocampal neurons is crucial for spatial memory

Adult neurogenesis in the dentate gyrus plays a critical role in hippocampus-dependent spatial learning. It remains unknown, however, how new neurons become functionally integrated into spatial circuits and contribute to hippocampus-mediated forms of learning and memory. To investigate these issues, we used a mouse model in which the differentiation of adult-generated dentate gyrus neurons can be anticipated by conditionally expressing the pro-differentiative gene PC3 (Tis21/BTG2) in nestin-positive progenitor cells. In contrast to previous studies that affected the number of newly generated neurons, this strategy selectively changes their timing of differentiation. New, adult-generated dentate gyrus progenitors, in which the PC3 transgene was expressed, showed accelerated differentiation and significantly reduced dendritic arborization and spine density. Functionally, this genetic manipulation specifically affected different hippocampus-dependent learning and memory tasks, including contextual fear conditioning, and selectively reduced synaptic plasticity in the dentate gyrus. Morphological and functional analyses of hippocampal neurons at different stages of differentiation, following transgene activation within defined time-windows, revealed that the new, adult-generated neurons up to 3–4 weeks of age are required not only to acquire new spatial information but also to use previously consolidated memories. Thus, the correct unwinding of these key memory functions, which can be an expression of the ability of adult-generated neurons to link subsequent events in memory circuits, is critically dependent on the correct timing of the initial stages of neuron maturation and connection to existing circuits.     

寡聚体Aβ1-42对大鼠海马突触可塑性的慢性影响

突触传递的长时程抑制(long-term depression,LTD)和长时程增强(longterm-potentiation,LTP)是突触可塑性的两种重要形式,并且与学习记忆密切相关.本文探讨Sprague-Dawley(SD)大鼠在海马齿状回区(dentate gyrus,DG)注射36 h孵育形成的寡聚体Aβ...     

Cell adhesion molecules and the transition from short- to long-term memory

Training chicks on a one-trial passive avoidance task results in a cascade of molecular and cellular processes in two forebrain regions, culminating within 60–90 min in post-translational glycosylation of synaptic membrane proteins and expression of immediate early genes c-fos and c-jun. We have now found a second window of vulnerability of memory to the protein synthesis inhibitor anisomycin, 4 h downstream of training. By 5.5 h post-training this window closes, to be replaced by a window of sensitivity to blockade of glycoprotein synthesis, presumably representing post-translational modification of the newly synthesised proteins. Amongst the pre- and post-synaptic membrane glycoproteins involved at both first and second time windows are the cell adhesion molecules, L1 (at both times) and NCAM (at the later). Molecular dissection of the external membrane domains of L1 distinguishes between a requirement for the IgG domain at the early time, the fibronectin-like domain at the later. The second time window only occurs if the animal is trained on a stimulus strong enough to be remembered for a long period. Weak memories do not persist beyond 6–8 h and the second wave of glycoprotein synthesis does not occur. Thus the second wave may represent the molecular processes required for the alterations in synaptic configuration, by way of the adhesion molecules amongst others, required for the morphological changes in neuronal connectivity hypothesised to encode memory.