The GFPp65 construct was also put into a PUC backbone under control of the neuronalspecific Thy-1 promoter (Thy-1 promoter was a kind gift from the laboratories of J.Sanes and P.Caroni) S1 . We chose the p65 NF-κB subunit for this construct because only p65 is capable of upregulating its own inhibitor, IκBα. This might alleviate potential problems that could be created if the fusion construct were over-expressed. A direct GFP-p65 fusion was chosen

SUMMARY Mutations that cause Intellectual Disability (ID) and Autism Spectrum Disorder (ASD) are commonly found in genes that encode for synaptic proteins. However, it remains unclear how mutations that disrupt synapse function impact intellectual ability. In the SYNGAP1 mouse model of ID/ASD, we found that dendritic spine synapses develop prematurely during the early postnatal period. Premature spine maturation dramatically enhanced excitability in the developing hippocampus, which corresponded with the emergence of behavioral abnormalities. Inducing SYNGAP1 mutations after critical developmental windows closed had minimal impact on spine synapse function, while repairing these pathogenic mutations in adulthood did not improve behavior and cognition. These data demonstrate that SynGAP protein acts as a critical developmental repressor of neural excitability that promotes the development of life-long cognitive abilities. We propose that the pace of dendritic spine synapse maturation in early life is a critical determinant of normal intellectual development.

Extracellular plaques of β-amyloid (Aβ) and intraneuronal neurofibrillary tangles made from tau are the histopathological signatures of Alzheimer's disease (AD). Plaques comprise Aβ fibrils that assemble from monomeric and oligomeric intermediates, and are prognostic indicators of AD. Despite the significance of plaques to AD, oligomers are considered to be the principal toxic forms of Aβ 1,2 . Interestingly, many adverse responses to Aβ, such as cytotoxicity 3 , microtubule loss 4 , impaired memory and learning 5 , and neuritic degeneration 6 , are greatly amplified by tau expression. N-terminally truncated, pyroglutamylated (pE) forms of Aβ 7,8 are strongly associated with AD, are more toxic than Aβ 1-42 and Aβ , and have been proposed as initiators of AD Users may view, print, copy, download and text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use: http://www.nature.com/authors/editorial_policies/license.html#terms * Correspondence: gsb4g@virginia.edu. **Correspondence: Hans-Ulrich.Demuth@probiodrug.de. J.M.N and S.S. contributed equally to the paper.Full Methods and relevant references will be available in the online Supplementary Information accompanying this paper at http:// www.nature.com/nature.Author Contributions: J.M.N. performed most of the biochemical and cell biological experiments; S.S. was the principal force behind the experiments involving hAPP SL /hQC and TBA2.1/tau KO mice, and was aided by B.H.-P., H.C.; A.S. and T.W. fractionated and analyzed human brain extracts; E.S., K.Y. and B.W. performed the peri-hippocampal injection experiments; A.H. and C.G.G. produced and characterized the M64 and M87 antibodies; R.R. and K.R. performed the electrophysiology experiments; A.A., W.J. and S.G. performed and analyzed the immunohistochemical experiments on TBA2.1 and Tau-KO/TBA2.1 mice; G.S.B. and H.-U.D. initiated and directed the project; G.S.B. was the principal writer of the paper; all of the authors participated in the design and analysis of experiments, and in editing of the paper. Fig. 2) to the oligomers. HHS Public AccessAt 5 μM peptide, 5% pE-Aβ aggregated faster than Aβ 3(pE)-42 or Aβ 1-42 alone based on thioflavin T fluorescence shifts 15 ( Supplementary Fig. 3). The OD 450 /OD 490 ratio for Aβ 3(pE)-42 rose and peaked more rapidly than for Aβ 1-42 , but peaked at an ~25% lower level. The fastest rise in the OD 450 /OD 490 ratio was for 5% pE-Aβ, which peaked similarly to Aβ 3(pE)-42 . Aβ 3(pE)-42 , Aβ 1-42 and 5% pE-Aβ thus oligomerized by different pathways.To test whether distinct biological activities were coupled to these oligomerization differences, we compared cytotoxicity of the peptides towards cultured neurons or glia using calcein-AM and fluorescence microscopy 16 . Twelve hours of Aβ 1-42 exposure had little effect on cell viability for wild type (WT) or tau knockout (KO) neurons, or WT glial cells (Fig. 1a). Contrastingly, most WT neurons died and detached from the substrate after exposur...

Lesions of the rodent hippocampus invariably abolish context fear memories formed in the recent past but do not always prevent new learning. To better understand this discrepancy, we thoroughly examined the acquisition of context fear in rats with pretraining excitotoxic lesions of the dorsal hippocampus. In the first experiment, animals received a shock immediately after placement in the context or after variable delays. Immediate shock produced no context fear learning in lesioned rats or controls. In contrast, delayed shock produced robust context fear learning in both groups. The absence of fear with immediate shock occurs because animals need time to form a representation of the context before shock is presented. The fact that it occurs in both sham and lesioned rats suggests that they learn about the context in a similar manner. However, despite learning about the context in the delay condition, lesioned rats did not acquire as much fear as controls. The second experiment showed that this lesion-induced deficit could be overcome by increasing the number of conditioning trials. Lesioned animals learned normally after multiple shocks, regardless of freezing level or trial spacing. The last experiment showed that animals with complete hippocampus lesions could also learn about the context, although the same lesions produced devastating retrograde amnesia. These results demonstrate that alternative systems can acquire context fear but do so less efficiently than the hippocampus.

The basolateral amygdala (BLA) is intimately involved in the development of conditional fear. Converging lines of evidence support a role for this region in the storage of fear memory but do not rule out a time-limited role in the memory consolidation. To examine this issue, we assessed the stability of BLA contribution to fear memories acquired across the adult lifetime of rats. Fear conditioning consisted of 10 tone-shock pairings in one context (remote memory), followed 16 months later by 10 additional tone-shock pairings with a novel tone in a novel context (recent memory). Twenty-four hours after recent training, rats were given NMDA or sham lesions of the BLA. Contextual and tone freezing were independently assessed in individual test sessions. Sham-lesioned rats showed high and comparable levels of freezing across all context and tone tests. In contrast, BLA-lesioned rats displayed robust freezing deficits across both recent and remote tests. Subsequent open-field testing revealed no effects of BLA lesions on activity patterns in a dark open field or during bright light exposure. Lesioned rats were able to reacquire normal levels of context-specific freezing after an overtraining procedure (76 unsignaled shocks). Together, these findings indicate that BLA lesions do not disrupt freezing behavior by producing hyperactivity, an inability to suppress behavior, or an inability to freeze. Rather, the consistent pattern of freezing deficits at both training-to-lesion intervals supports a role for the BLA in the permanent storage of fear memory.

Context memories initially require the hippocampus, but over time become independent of this structure. This shift reflects a consolidation process whereby memories are gradually stored in distributed regions of the cortex. The function of this process is thought to be the extraction of statistical regularities and general knowledge from specific experiences. The current study examined this idea in mice by measuring the specificity of context memories during consolidation. In the first experiment, separate groups of animals were trained with a single shock and tested in the training context or a novel environment 1, 14, 28, or 36 d later. We found a systematic increase in generalization over this period. Initially, mice froze more in the training context, but fear of the novel environment grew over time until animals eventually froze an equivalent amount in both contexts. The second experiment demonstrated that the increase in generalization was due to a loss of detailed information about the context and not fear incubation. In this experiment, mice were exposed to the context and then trained with an immediate shock 1 or 36 d later. Animals trained 1 d after exposure acquired robust context fear that did not generalize across environments. In contrast, mice trained 36 d after exposure froze an equivalent amount in the training context and the novel environment. The same profile was observed in H-ras mutants that exhibit enhanced hippocampal plasticity and learning. These results suggest that context memories are specific early after training when they require the hippocampus, and become more general as they are permanently stored in the cortex.The hippocampus plays a time-limited role in the retrieval of memory. Damage to this structure produces a loss of recently formed memories and leaves intact those acquired in the remote past (Anagnostaras et al. 1999;Squire et al. 2004;Bayley et al. 2005). As memory becomes independent of the hippocampus, it is thought to be permanently stored in distributed regions of the cortex (Squire and Alvarez 1995;Squire et al. 2004;Wiltgen et al. 2004;Frankland and Bontempi 2005). Consistent with this idea, recent animal studies showed activation of cortical sites and a concurrent deactivation of the hippocampus when old memories were retrieved. Pharmacological inactivation of these same cortical regions during retrieval produced a selective remote memory deficit (Bontempi et al. 1999;Frankland et al. 2004a;Maviel et al. 2004).Contemporary learning models suggest this reorganization of memory systems reflects an important process, the extraction of statistical regularities, and general knowledge from specific experiences (McClelland et al. 1995;O'Reilly and Rudy 2001). According to these models, the hippocampus rapidly encodes detailed memories (i.e., episodes) and then replays them so that the cortex can slowly extract features that are common across experiences (i.e., semantic memories). Consistent with this idea, episodic memory retrieval in humans includes a detailed reexperie...

The hippocampus is assumed to retrieve memory by reinstating patterns of cortical activity that were observed during learning. To test this idea, we monitored the activity of individual cortical neurons while simultaneously inactivating the hippocampus. Neurons that were active during context fear conditioning were tagged with the long-lasting fluorescent protein H2B-GFP and the light-activated proton pump ArchT. These proteins allowed us to identify encoding neurons several days after learning and silence them with laser stimulation. When tagged CA1 cells were silenced, we found that memory retrieval was impaired and representations in the cortex (entorhinal, retrosplenial, perirhinal) and the amygdala could not be reactivated. Importantly, hippocampal inactivation did not alter the total amount of activity in most brain regions. Instead, it selectively prevented neurons that were active during learning from being reactivated during retrieval. These data provide functional evidence that the hippocampus reactivates specific memory representations during retrieval.

Episodic memory reflects the ability to recollect the temporal and spatial context of past experiences. Episodic memories depend on the hippocampus, but have been proposed to undergo forgetting unless consolidated during off-line periods like sleep to neocortical areas for long-term storage. Here, we propose an alternative to systems consolidation theory -a contextual binding account -in which the hippocampus binds item-and context-related information. We compare this account with behavioral, lesion, neuroimaging and sleep studies of episodic memory, and contend that forgetting is largely due to contextual interference. Accordingly, episodic memory remains dependent on the hippocampus across time, contextual drift produces post-encoding activity, and sleep benefits memory by reducing contextual interference.