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1. Adeno-associated viral overexpression of neuroligin 2 in the mouse hippocampus enhances GABAergic synapses and impairs hippocampal-dependent behaviors.

   https://doi.org/10.1016/j.bbr.2018.12.052  

   Van Zandt, M ; Weiss, E ; Almyasheva, A ; Lipior, S ; Maisel, S ; Naegele, J. ( January 2019 , Behavioural brain research)

   null (Ed.)

   The cell adhesion molecule neuroligin2 (NLGN2) regulates GABAergic synapse development, but its role inneural circuit function in the adult hippocampus is unclear. We investigated GABAergic synapses and hippo-campus-dependent behaviors following viral-vector-mediated overexpression of NLGN2. Transducing hippo-campal neurons with AAV-NLGN2 increased neuronal expression of NLGN2 and membrane localization ofGABAergic postsynaptic proteins gephyrin and GABAARγ2, and presynaptic vesicular GABA transporter protein(VGAT) suggesting trans-synaptic enhancement of GABAergic synapses. In contrast, glutamatergic postsynapticdensity protein-95 (PSD-95) and presynaptic vesicular glutamate transporter (VGLUT) protein were unaltered.Moreover, AAV-NLGN2 significantly increased parvalbumin immunoreactive (PV+) synaptic boutons co-loca-lized with postsynaptic gephyrin+puncta. Furthermore, these changes were demonstrated to lead to cognitiveimpairments as shown in a battery of hippocampal-dependent mnemonic tasks and social behaviors. 

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2. Aggression Results in the Phosphorylation of ERK1/2 in the Nucleus Accumbens and the Dephosphorylation of mTOR in the Medial Prefrontal Cortex in Female Syrian Hamsters

   https://doi.org/10.3390/ijms24021379  

   Borland, Johnathan M. ; Dempsey, Desarae A. ; Peyla, Anna C. ; Hall, Megan A. ; Kohut-Jackson, Abigail L. ; Mermelstein, Paul G. ; Meisel, Robert L. ( January 2023 , International Journal of Molecular Sciences)

   Like many social behaviors, aggression can be rewarding, leading to behavioral plasticity. One outcome of reward-induced aggression is the long-term increase in the speed in which future aggression-based encounters is initiated. This form of aggression impacts dendritic structure and excitatory synaptic neurotransmission in the nucleus accumbens, a brain region well known to regulate motivated behaviors. Yet, little is known about the intracellular signaling mechanisms that drive these structural/functional changes and long-term changes in aggressive behavior. This study set out to further elucidate the intracellular signaling mechanisms regulating the plasticity in neurophysiology and behavior that underlie the rewarding consequences of aggressive interactions. Female Syrian hamsters experienced zero, two or five aggressive interactions and the phosphorylation of proteins in reward-associated regions was analyzed. We report that aggressive interactions result in a transient increase in the phosphorylation of extracellular-signal related kinase 1/2 (ERK1/2) in the nucleus accumbens. We also report that aggressive interactions result in a transient decrease in the phosphorylation of mammalian target of rapamycin (mTOR) in the medial prefrontal cortex, a major input structure to the nucleus accumbens. Thus, this study identifies ERK1/2 and mTOR as potential signaling pathways for regulating the long-term rewarding consequences of aggressive interactions. Furthermore, the recruitment profile of the ERK1/2 and the mTOR pathways are distinct in different brain regions.

    

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3. Early life adversity promotes resilience to opioid addiction-related phenotypes in male rats and sex-specific transcriptional changes

   https://doi.org/10.1073/pnas.2020173118  

   Ordoñes Sanchez, Evelyn ; Bavley, Charlotte C. ; Deutschmann, Andre U. ; Carpenter, Rachel ; Peterson, Drew R. ; Karbalaei, Reza ; Flowers, II, James ; Rogers, Charleanne M. ; Langrehr, Miranda G. ; Ardekani, Cory S. ; et al ( February 2021 , Proceedings of the National Academy of Sciences)

   Experiencing some early life adversity can have an “inoculating” effect that promotes resilience in adulthood. However, the mechanisms underlying stress inoculation are unknown, and animal models are lacking. Here we used the limited bedding and nesting (LBN) model of adversity to evaluate stress inoculation of addiction-related phenotypes. In LBN, pups from postnatal days 2 to 9 and their dams were exposed to a low-resource environment. In adulthood, they were tested for addiction-like phenotypes and compared to rats raised in standard housing conditions. High levels of impulsivity are associated with substance abuse, but in males, LBN reduced impulsive choice compared to controls. LBN males also self-administered less morphine and had a lower breakpoint on a progressive ratio reinforcement schedule than controls. These effects of LBN on addiction-related behaviors were not found in females. Because the nucleus accumbens (NAc) mediates these behaviors, we tested whether LBN altered NAc physiology in drug-naïve and morphine-exposed rats. LBN reduced the frequency of spontaneous excitatory postsynaptic currents in males, but a similar effect was not observed in females. Only in males did LBN prevent a morphine-induced increase in the AMPA/NMDA ratio. RNA sequencing was performed to delineate the molecular signature in the NAc associated with LBN-derived phenotypes. LBN produced sex-specific changes in transcription, including in genes related to glutamate transmission. Collectively, these studies reveal that LBN causes a male-specific stress inoculation effect against addiction-related phenotypes. Identifying factors that promote resilience to addiction may reveal novel treatment options for patients.

    

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4. Transient Enhanced GluA2 Expression in Young Hippocampal Neurons of a Fragile X Mouse Model

   https://doi.org/10.3389/fnsyn.2020.588295  

   Banke, Tue G. ; Barria, Andres ( December 2020 , Frontiers in Synaptic Neuroscience)

   AMPA-type glutamate receptors (AMPARs) are tetrameric ligand-gated channels made up of combinations of GluA1-4 subunits and play important roles in synaptic transmission and plasticity. Here, we have investigated the development of AMPAR-mediated synaptic transmission in the hippocampus of the Fmr1 knock-out (KO) mouse, a widely used model of Fragile X syndrome (FXS). FXS is the leading monogenic cause of intellectual disability and autism spectrum disorders (ASD) and it is considered a neurodevelopmental disorder. For that reason, we investigated synaptic properties and dendritic development in animals from an early stage when synapses are starting to form up to adulthood. We found that hippocampal CA1 pyramidal neurons in the Fmr1-KO mouse exhibit a higher AMPAR-NMDAR ratio early in development but reverses to normal values after P13. This increase was accompanied by a larger presence of the GluA2-subunit in synaptic AMPARs that will lead to altered Ca 2+ permeability of AMPARs that could have a profound impact upon neural circuits, learning, and diseases. Following this, we found that young KO animals lack Long-term potentiation (LTP), a well-understood model of synaptic plasticity necessary for proper development of circuits, and exhibit an increased frequency of spontaneous miniature excitatory postsynaptic currents, a measure of synaptic density. Furthermore, post hoc morphological analysis of recorded neurons revealed altered dendritic branching in the KO group. Interestingly, all these anomalies are transitory and revert to normal values in older animals. Our data suggest that loss of FMRP during early development leads to temporary upregulation of the GluA2 subunit and this impacts synaptic plasticity and altering morphological dendritic branching. 

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5. Imbalanced post- and extrasynaptic SHANK2A functions during development affect social behavior in SHANK2-mediated neuropsychiatric disorders

   https://doi.org/10.1038/s41380-021-01140-y  

   Eltokhi, Ahmed ; Gonzalez-Lozano, Miguel A. ; Oettl, Lars-Lennart ; Rozov, Andrey ; Pitzer, Claudia ; Röth, Ralph ; Berkel, Simone ; Hüser, Markus ; Harten, Aliona ; Kelsch, Wolfgang ; et al ( November 2021 , Molecular Psychiatry)

   Abstract Mutations in SHANK genes play an undisputed role in neuropsychiatric disorders. Until now, research has focused on the postsynaptic function of SHANKs, and prominent postsynaptic alterations in glutamatergic signal transmission have been reported in Shank KO mouse models. Recent studies have also suggested a possible presynaptic function of SHANK proteins, but these remain poorly defined. In this study, we examined how SHANK2 can mediate electrophysiological, molecular, and behavioral effects by conditionally overexpressing either wild-type SHANK2A or the extrasynaptic SHANK2A(R462X) variant. SHANK2A overexpression affected pre- and postsynaptic targets and revealed a reversible, development-dependent autism spectrum disorder-like behavior. SHANK2A also mediated redistribution of Ca 2+ -permeable AMPA receptors between apical and basal hippocampal CA1 dendrites, leading to impaired synaptic plasticity in the basal dendrites. Moreover, SHANK2A overexpression reduced social interaction and increased the excitatory noise in the olfactory cortex during odor processing. In contrast, overexpression of the extrasynaptic SHANK2A(R462X) variant did not impair hippocampal synaptic plasticity, but still altered the expression of presynaptic/axonal signaling proteins. We also observed an attention-deficit/hyperactivity-like behavior and improved social interaction along with enhanced signal-to-noise ratio in cortical odor processing. Our results suggest that the disruption of pre- and postsynaptic SHANK2 functions caused by SHANK2 mutations has a strong impact on social behavior. These findings indicate that pre- and postsynaptic SHANK2 actions cooperate for normal neuronal function, and that an imbalance between these functions may lead to different neuropsychiatric disorders. 

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