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The zeta inhibitory peptide (ZIP) interferes with memory maintenance and long-term potentiation (LTP) 1 when administered to mice. However, mice lacking its putative target, protein kinase PKMζ, exhibit normal learning and memory as well as LTP 2,3 , making the mechanism of ZIP unclear. Here we show that ZIP disrupts LTP by removing surface AMPA receptors through its cationic charge alone. This effect requires endophilin-A2-mediated endocytosis and is fully blocked by drugs suppressing macropinocytosis. ZIP and other cationic peptides remove newly inserted AMPA receptor nanoclusters at potentiated synapses, providing a mechanism by which these peptides erase memories without altering basal synaptic function. When delivered in vivo, cationic peptides can modulate memories on local and brain-wide scales, and these mechanisms can be leveraged to prevent memory loss in a model of traumatic brain injury. Our findings uncover a previously unknown synaptic mechanism by which memories are maintained or lost., Competing Interests: Competing interests: The authors declare no competing interests., (© 2025. The Author(s), under exclusive licence to Springer Nature Limited.)

Tools for visualizing and manipulating protein dynamics in living cells are critical for understanding cellular function. Here we leverage recently available monoclonal antibody sequences to generate a set of affinity tags for labeling and manipulating AMPA-type glutamate receptors (AMPARs), which mediate nearly all excitatory neurotransmission in the central nervous system. These antibodies can be produced from heterologous cells for exogenous labeling applications or directly expressed in living neurons as intrabodies, where they bind their epitopes in the endoplasmic reticulum and co-traffic to the cell surface for visualization with cell impermeant fluorescent dyes. We show these reagents do not perturb AMPAR trafficking, function, mobility, or synaptic recruitment during plasticity and therefore can be used as probes for monitoring endogenous receptors in living neurons. We also adapt these reagents to deplete AMPARs from the cell surface by trapping them in the endoplasmic reticulum, providing a simple approach for loss of excitatory neurotransmission. The strategies outlined here serve as a template for generating similar reagents targeting diverse proteins as more antibody sequences become available., Competing Interests: Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

AMPA- and NMDA-type glutamate receptors mediate distinct postsynaptic signals that differ characteristically among synapses. How postsynaptic AMPA- and NMDA-receptor levels are regulated, however, remains unclear. Using newly generated conditional knockin mice that enable genetic control of neurexin alternative splicing, we show that in hippocampal synapses, alternative splicing of presynaptic neurexin-1 at splice site 4 (SS4) dramatically enhanced postsynaptic NMDA-receptor-mediated, but not AMPA-receptor-mediated, synaptic responses without altering synapse density. In contrast, alternative splicing of neurexin-3 at SS4 suppressed AMPA-receptor-mediated, but not NMDA-receptor-mediated, synaptic responses, while alternative splicing of neurexin-2 at SS4 had no effect on NMDA- or AMPA-receptor-mediated responses. Presynaptic overexpression of the neurexin-1β and neurexin-3β SS4+ splice variants, but not of their SS4- splice variants, replicated the respective SS4+ knockin phenotypes. Thus, different neurexins perform distinct nonoverlapping functions at hippocampal synapses that are independently regulated by alternative splicing. These functions transsynaptically control NMDA and AMPA receptors, thereby mediating presynaptic control of postsynaptic responses., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Ca 2+ -permeable AMPA-type glutamate receptors (CP-AMPARs) containing GluA1 but lacking GluA2 subunits contribute to multiple forms of synaptic plasticity, including long-term potentiation (LTP), but mechanisms regulating CP-AMPARs are poorly understood. A-kinase anchoring protein (AKAP) 150 scaffolds kinases and phosphatases to regulate GluA1 phosphorylation and trafficking, and trafficking of AKAP150 itself is modulated by palmitoylation on two Cys residues. Here, we developed a palmitoylation-deficient knockin mouse to show that AKAP150 palmitoylation regulates CP-AMPAR incorporation at hippocampal synapses. Using biochemical, super-resolution imaging, and electrophysiological approaches, we found that palmitoylation promotes AKAP150 localization to recycling endosomes and the postsynaptic density (PSD) to limit CP-AMPAR basal synaptic incorporation. In addition, we found that AKAP150 palmitoylation is required for LTP induced by weaker stimulation that recruits CP-AMPARs to synapses but not stronger stimulation that recruits GluA2-containing AMPARs. Thus, AKAP150 palmitoylation controls its subcellular localization to maintain proper basal and activity-dependent regulation of synaptic AMPAR subunit composition., (Copyright © 2018 The Author(s). Published by Elsevier Inc. All rights reserved.)

α- and β-neurexins are presynaptic cell-adhesion molecules whose general importance for synaptic transmission is well documented. The specific functions of neurexins, however, remain largely unknown because no conditional neurexin knockouts are available and targeting all α- and β-neurexins produced by a particular gene is challenging. Using newly generated constitutive and conditional knockout mice that target all neurexin-3α and neurexin-3β isoforms, we found that neurexin-3 was differentially required for distinct synaptic functions in different brain regions. Specifically, we found that, in cultured neurons and acute slices of the hippocampus, extracellular sequences of presynaptic neurexin-3 mediated trans-synaptic regulation of postsynaptic AMPA receptors. In cultured neurons and acute slices of the olfactory bulb, however, intracellular sequences of presynaptic neurexin-3 were selectively required for GABA release. Thus, our data indicate that neurexin-3 performs distinct essential pre- or postsynaptic functions in different brain regions by distinct mechanisms.

Neurexins are essential presynaptic cell adhesion molecules that are linked to schizophrenia and autism and are subject to extensive alternative splicing. Here, we used a genetic approach to test the physiological significance of neurexin alternative splicing. We generated knockin mice in which alternatively spliced sequence #4 (SS4) of neuexin-3 is constitutively included but can be selectively excised by cre-recombination. SS4 of neurexin-3 was chosen because it is highly regulated and controls neurexin binding to neuroligins, LRRTMs, and other ligands. Unexpectedly, constitutive inclusion of SS4 in presynaptic neurexin-3 decreased postsynaptic AMPA, but not NMDA receptor levels, and enhanced postsynaptic AMPA receptor endocytosis. Moreover, constitutive inclusion of SS4 in presynaptic neurexin-3 abrogated postsynaptic AMPA receptor recruitment during NMDA receptor-dependent LTP. These phenotypes were fully rescued by constitutive excision of SS4 in neurexin-3. Thus, alternative splicing of presynaptic neurexin-3 controls postsynaptic AMPA receptor trafficking, revealing an unanticipated alternative splicing mechanism for trans-synaptic regulation of synaptic strength and long-term plasticity., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Normal brain function requires that the overall synaptic activity in neural circuits be kept constant. Long-term alterations of neural activity lead to homeostatic regulation of synaptic strength by a process known as synaptic scaling. The molecular mechanisms underlying synaptic scaling are largely unknown. Here, we report that all-trans retinoic acid (RA), a well-known developmental morphogen, unexpectedly mediates synaptic scaling in response to activity blockade. We show that activity blockade increases RA synthesis in neurons and that acute RA treatment enhances synaptic transmission. The RA-induced increase in synaptic strength is occluded by activity blockade-induced synaptic scaling. Suppression of RA synthesis prevents synaptic scaling. This form of RA signaling operates via a translation-dependent but transcription-independent mechanism, causes an upregulation of postsynaptic glutamate receptor levels, and requires RARalpha receptors. Together, our data suggest that RA functions in homeostatic plasticity as a signaling molecule that increases synaptic strength by a protein synthesis-dependent mechanism.

Homeostatic plasticity is thought to play an important role in maintaining the stability of neuronal circuits. During one form of homeostatic plasticity, referred to as synaptic scaling, activity blockade leads to a compensatory increase in synaptic transmission by stimulating in dendrites the local translation and synaptic insertion of the AMPA receptor subunit GluR1. We have previously shown that all-trans retinoic acid (RA) mediates activity blockade-induced synaptic scaling by activating dendritic GluR1 synthesis and that this process requires RARalpha, a member of the nuclear RA receptor family. This result raised the question of where RARalpha is localized in dendrites and whether its localization is regulated by RA and/or activity blockade. Here, we show that activity blockade or RA treatment in neurons enhances the concentration of RARalpha in the dendritic RNA granules and activates local GluR1 synthesis in these RNA granules. Importantly, the same RNA granules that contain RARalpha also exhibit an accumulation of GluR1 protein but with a much slower time course than that of RARalpha, suggesting that the former regulates the latter. Taken together, our results provide a direct link between dendritically localized RARalpha and local GluR1 synthesis in RNA granules during RA-mediated synaptic signaling in homeostatic synaptic plasticity.