Although NMDA receptor (NMDAR)-dependent long-term potentiation (LTP) and long-term depression (LTD) of glutamatergic transmission are candidate mechanisms for long-term spatial memory, the precise contributions of LTP and LTD remain poorly understood. Here, we report that LTP and LTD in the hippocampal CA1 region of freely moving adult rats were prevented by NMDAR 2A (GluN2A) and 2B subunit (GluN2B) preferential antagonists, respectively. These results strongly suggest that NMDAR subtype preferential antagonists are appropriate tools to probe the roles of LTP and LTD in spatial memory. Using a Morris water maze task, the LTP-blocking GluN2A antagonist had no significant effect on any aspect of performance, whereas the LTD-blocking GluN2B antagonist impaired spatial memory consolidation. Moreover, similar spatial memory deficits were induced by inhibiting the expression of LTD with intrahippocampal infusion of a short peptide that specifically interferes with AMPA receptor endocytosis. Taken together, our findings support a functional requirement of hippocampal CA1 LTD in the consolidation of long-term spatial memory.hippocampus | learning and memory | long-term potentiation | AMPA receptor endocytosis | Morris water maze T he hippocampus plays crucial roles in encoding and consolidating memory (1, 2). Activity-dependent plasticity of hippocampal glutamatergic synapses, particularly NMDA receptor (NMDAR)-dependent long-term potentiation (LTP) and longterm depression (LTD), has been proposed as the primary cellular substrate for fulfilling these cognitive functions (3, 4). Indeed, formation of long-term spatial memory in the Morris water maze (MWM) can be impaired by preventing NMDAR activation using either pharmacological or genetic approaches (5-7). However, blocking NMDARs affects both LTP and LTD (8, 9), making it hard to attribute the observed spatial memory deficits to selective disruption of either LTP or LTD. Recent attempts using transgenic mice with deficits in either LTP (10-12) or LTD (13-15) have achieved some success in delineating the contribution of these two opposing forms of plasticity in memory formation. However, results obtained from transgenic studies are equivocal, perhaps because of structural alterations and/or functional compensatory changes at synapses that often arise after prolonged genetic alterations (14). Thus, determining the exact roles of hippocampal LTP and/or LTD in spatial memory requires new experimental approaches that enable acute, selective inhibition of LTP or LTD in freely moving animals.Evidence accumulated from recent studies suggests that GluN2A-and GluN2B-containing NMDARs preferentially contribute to the induction of hippocampal LTP and LTD in vitro (12,16,17) and in vivo (18). For example, the GluN2A preferential antagonist NVP-AAM077 (NVP) (19) and the GluN2B-specific antagonist Ro25-6981 (Ro) (20) selectively inhibit LTP and LTD, respectively, in anesthetized rats (18,21). If such GluN2 subunitselective requirements for LTP and LTD can be shown in freely moving ...

Acute stress impairs memory retrieval and facilitates the induction of long-term depression (LTD) in the hippocampal CA1 region of the adult rodent brain. However, whether such alterations in synaptic plasticity cause the behavioral effects of stress is not known. Here, we report that two selective inhibitors of the induction or expression of stress-enabled, N-methyl-D-aspartate receptor-dependent hippocampal LTD also block spatial memory retrieval impairments caused by acute stress. Additionally, we demonstrate that facilitating the induction of hippocampal LTD in vivo by blockade of glutamate transport mimics the behavioral effects of acute stress by impairing spatial memory retrieval. Thus, the present study demonstrates that hippocampal LTD is both necessary and sufficient to cause acute stressinduced impairment of spatial memory retrieval and provides a new perspective from which to consider the nature of cognitive deficits in disorders whose symptoms are aggravated by stress.glutamate transporter ͉ interference peptide ͉ synaptic plasticity ͉ water maze ͉ corticosterone C ognitive functions such as learning and memory are greatly affected by stress. Memory retrieval in humans is especially vulnerable to acute psychological stress (1) or cortisol treatment (2), effects caused in part by alterations in medial temporal lobe function (3). In rodents, acute stress or administration of glucocorticoids disrupts the retrieval of hippocampal-dependent spatial memory (4). Furthermore, stress and glucocorticoids have a profound influence on the physiology of the hippocampal CA1 region by inhibiting long-term potentiation (LTP) (5-7) and enabling long-term depression (LTD) (7,8), the two most well characterized forms of synaptic plasticity and proposed cellular substrates for learning and memory (9, 10). However, it remains to be established whether the alterations in either LTP or LTD caused by stress contribute to the stress-induced impairment of spatial memory retrieval.Considerable experimental evidence supports the role of hippocampal LTP in spatial memory (11)(12)(13)(14), and theoretical accounts of associative memory, based on neural network models, suggest that a balance between LTP and LTD may underlie efficient memory storage (10, 15). By using two recently developed specific inhibitors of LTD (16, 17), the present experiments assess the role of LTD in the spatial memory retrieval deficits induced by acute stress and provide strong evidence for a role of hippocampal LTD in mediating this aspect of acute stress-induced impairment of cognitive function in adult rats. ResultsBlocking the Induction of LTD Prevents the Stress-Induced Impairment of Spatial Memory Retrieval. It is well accepted that the induction of hippocampal CA1 homosynaptic LTD depends on the N-methyl-D-aspartate subtype of glutamate receptors (NMDARs) (10), which are heteromeric complexes of NR1 subunits and at least one type of NR2 subunit (NR2A-D) (18). Converging evidence supports the hypothesis that the subunit composition of NMDARs may c...

SummarySynapses are fundamental units of communication in the brain. The prototypical synapse-organizing complex neurexin-neuroligin mediates synapse development and function and is central to a shared genetic risk pathway in autism and schizophrenia. Neurexin’s role in synapse development is thought to be mediated purely by its protein domains, but we reveal a requirement for a rare glycan modification. Mice lacking heparan sulfate (HS) on neurexin-1 show reduced survival, as well as structural and functional deficits at central synapses. HS directly binds postsynaptic partners neuroligins and LRRTMs, revealing a dual binding mode involving intrinsic glycan and protein domains for canonical synapse-organizing complexes. Neurexin HS chains also bind novel ligands, potentially expanding the neurexin interactome to hundreds of HS-binding proteins. Because HS structure is heterogeneous, our findings indicate an additional dimension to neurexin diversity, provide a molecular basis for fine-tuning synaptic function, and open therapeutic directions targeting glycan-binding motifs critical for brain development.

The extent of conservation in the programmed cell death pathways that are activated in species belonging to different kingdoms is not clear. Caspases are key components of animal apoptosis; caspase activities are detected in both animal and plant cells. Yet, while animals have caspase genes, plants do not have orthologous sequences in their genomes. It is 10 years since the first caspase activity was reported in plants, and there are now at least eight caspase activities that have been measured in plant extracts using caspase substrates. Various caspase inhibitors can block many forms of plant programmed cell death, suggesting that caspase-like activities are required for completion of the process. Since plant metacaspases do not have caspase activities, a major challenge is to identify the plant proteases that are responsible for the caspase-like activities and to understand how they relate, if at all, to animal caspases. The protease vacuolar processing enzyme, a legumain, is responsible for the cleavage of caspase-1 synthetic substrate in plant extracts. Saspase, a serine protease, cleaves caspase-8 and some caspase-6 synthetic substrates. Possible scenarios that could explain why plants have caspase activities without caspases are discussed.

Selective suppression of inhibitory synapses—with no effect on excitatory synapses—results from interaction of the autism- and schizophrenia-associated proteins MDGA1 and neuroligin-2 through effects on the neuroligin–neurexin pathway.

The first step in the generation of the amyloid-beta peptide (Abeta) deposited in the brains of patients with Alzheimer's disease (AD) is the processing of the larger Abeta precursor protein (APP) by an integral membrane aspartyl protease named the beta-site APP-cleaving enzyme (BACE). We present the genomic organization of the BACE gene. BACE mRNAs are synthesized as nine exons and eight introns from a 30.6 kb region of chromosome 11q23.2-11q23.3. Regulation of BACE may play an important role in regulating the levels of Abeta produced and is therefore likely to play an important role in AD. Herein, we report the cloning and detailed analysis of 3765 nucleotides of the promoter region of BACE and 364 nucleotides of the 5' untranslated region of the BACE mRNA (5' UTR). Characteristic "CAAT" and "TATA" boxes are absent within 1.5 kb of the transcription start site (TSS). The promoter region and 5' UTR contain multiple transcription factor binding sites, such as activator protein (AP)1, AP2, cAMP response element binding protein (CREB), estrogen responsive element (ERE), glucocorticoid responsive element (GRE), "GC" box, nuclear factor (NF)-kappaB, signal transducer and activator of transcription (STAT)1, stimulating protein (SP)1, metal-regulatory elements, and possible Zeste binding sites. Limited interspecies similarity was observed between the human sequence and corresponding genomic DNA from the rat and mouse sequences, but several transcription factor-binding sites are conserved. Thus, the BACE gene contains basal regulatory elements, inducible features and sites for regulated activity by various transcription factors. These results identify the important regions for functional analysis of the binding domains and neuron-specific expression (1). Such a study will allow us to further examine the possible role of changes in the promoter of BACE in AD pathogenesis.

Mutations in a synaptic organizing pathway contribute to autism. Autism-associated mutations in MDGA2 (MAM domain containing glycosylphosphatidylinositol anchor 2) are thought to reduce excitatory/inhibitory transmission. However, we show that mutation of Mdga2 elevates excitatory transmission, and that MDGA2 blocks neuroligin-1 interaction with neurexins and suppresses excitatory synapse development. Mdga2(+/-) mice, modeling autism mutations, demonstrated increased asymmetric synapse density, mEPSC frequency and amplitude, and altered LTP, with no change in measures of inhibitory synapses. Behavioral assays revealed an autism-like phenotype including stereotypy, aberrant social interactions, and impaired memory. In vivo voltage-sensitive dye imaging, facilitating comparison with fMRI studies in autism, revealed widespread increases in cortical spontaneous activity and intracortical functional connectivity. These results suggest that mutations in MDGA2 contribute to altered cortical processing through the dual disadvantages of elevated excitation and hyperconnectivity, and indicate that perturbations of the NRXN-NLGN pathway in either direction from the norm increase risk for autism.

Age-related changes in levels of melatonin and 6-hydroxymelatonin sulfate and effects of dietary melatonin on their levels in different tissues were determined in mice. Levels of melatonin were highest in the serum followed by liver, kidney, cerebral cortex and heart as measured by a quantitative and sensitive enzyme-labeled immunosorbent assay (ELISA). Serum melatonin levels decreased with age, and were reduced by 80% in 27-month old mice relative to 12-month old mice. Levels of 6-hydroxymelatonin sulfate were measured independently in various tissues. Levels of the melatonin metabolite, 6-hydroxymelatonin sulfate were significantly higher than free melatonin in all tissues tested. Levels of 6-hydroxymelatonin sulfate were highest in the cerebral cortex followed by the serum, heart, kidney, and liver. In 12-month old mice 6-hydroxymelatonin sulfate concentration was approximately 1000-fold greater than that of melatonin in the cerebral cortex, it was only 3-fold greater than melatonin levels in the serum. Thus only 0.1% of total melatonin in the brain was present in the free and unconjugated form but the corresponding value for serum was 27.4%. The cerebral cortex had the highest levels of combined melatonin and 6-hydroxymelatonin sulfate than other tissue tested in control mice. There was no significant change in 6-hydroxymelatonin sulfate levels between young and old mice. There was also no age-dependent change in levels of serotonin or cortisol in the serum samples. Dietary supplementation with melatonin resulted in a significant increase in levels of melatonin in the serum and all other tissue samples tested. Thus, any age-related decline of tissue melatonin can be reversed by supplementation with dietary melatonin.