Suppression of Cofilin function in the somatosensory cortex alters social contact behavior in the BTBR mouse inbred line.

Sensory differences are a core feature of autism spectrum disorders (ASD) and are predictive of other ASD core symptoms such as social difficulties. However, the neurobiological substrate underlying the functional relationship between sensory and social functioning is poorly understood. Here, we examined whether misregulation of structural plasticity in the somatosensory cortex modulates aberrant social functioning in BTBR mice, a mouse model for autism spectrum disorder-like phenotypes. By locally expressing a dominant-negative form of Cofilin (CofilinS3D; a key regulator of synaptic structure) in the somatosensory cortex, we tested whether somatosensory suppression of Cofilin activity alters social functioning in BTBR mice. Somatosensory Cofilin suppression altered social contact and nest-hide behavior of BTBR mice in a social colony, assessed for seven consecutive days. Subsequent behavioral testing revealed that altered social functioning is related to altered tactile sensory perception; CofilinS3D-treated BTBR mice showed a time-dependent difference in the sensory bedding preference task. These findings show that Cofilin suppression in the somatosensory cortex alters social functioning in BTBR mice and that this is associated with tactile sensory processing, a critical indicator of somatosensory functioning.

Sleep deprivation reduces the density of individual spine subtypes in a branch-specific fashion in CA1 neurons.

Sleep deprivation has a negative impact on hippocampus-dependent memory, which is thought to depend on cellular plasticity. We previously found that 5 h of sleep deprivation robustly decreases dendritic spine density in the CA1 area of the hippocampus in adult male mice. However, recent work by others suggests that sleep deprivation increases the density of certain spine types on specific dendritic branches. Based on these recent findings and our previous work, we conducted a more in-depth analysis of different spine types on branches 1, 2 and 5 of both apical and basal dendrites to assess whether 5 h of sleep deprivation may have previously unrecognized spine-type and branch-specific effects. This analysis shows no spine-type specific changes on branch 1 and 2 of apical dendrites after sleep deprivation. In contrast, sleep deprivation decreases the number of mushroom and branched spines on branch 5. Likewise, sleep deprivation reduces thin, mushroom and filopodia spine density on branch 5 of the basal dendrites, without affecting spines on branch 1 and 2. Our findings indicate that sleep deprivation leads to local branch-specific reduction in the density of individual spine types, and that local effects might not reflect the overall impact of sleep deprivation on CA1 structural plasticity. Moreover, our analysis underscores that focusing on a subset of dendritic branches may lead to potential misinterpretation of the overall impact of, in this case, sleep deprivation on structural plasticity.

Elucidating the role of protein synthesis in hippocampus-dependent memory consolidation across the day and night.

It is widely acknowledged that de novo protein synthesis is crucial for the formation and consolidation of long-term memories. While the basal activity of many signaling cascades that modulate protein synthesis fluctuates in a circadian fashion, it is unclear whether the temporal dynamics of protein synthesis-dependent memory consolidation vary depending on the time of day. More specifically, it is unclear whether protein synthesis inhibition affects hippocampus-dependent memory consolidation in rodents differentially across the day (i.e., the inactive phase with an abundance of sleep) and night (i.e., the active phase with little sleep). To address this question, male and female C57Bl6/J mice were trained in a contextual fear conditioning task at the beginning or the end of the light phase. Animals received a single systemic injection with the protein synthesis inhibitor anisomycin or vehicle directly, 4, 8 hr, or 11.5 hr following training, and memory was assessed after 24 hr. Here, we show that protein synthesis inhibition impaired the consolidation of context-fear memories selectively when the protein synthesis inhibitor was administered at the first three time points, irrespective of timing of training. Even though the basal activity of signaling pathways regulating de novo protein synthesis may fluctuate across the 24-hr cycle, these results suggest that the temporal dynamics of protein synthesis-dependent memory consolidation are similar for day-time and night-time learning.

The contribution of Parkin, PINK1 and DJ-1 genes to selective neuronal degeneration in Parkinson's disease.

Parkinson's disease (PD) is characterised by selective and severe degeneration of the substantia nigra pars compacta and the locus coeruleus (LC), which underlies the most prominent symptoms. Although α-synuclein accumulation has long been established to play a causal role in the disease, it alone cannot explain the selective degenerative pattern. Recent evidence shows that the selective vulnerability could arise due to the large presence of cytosolic catecholamines and Ca2+ ions in the substantia nigra pars compacta and LC specifically that can be aberrantly affected by α-synuclein accumulation. Moreover, each has its own toxic potential, and disturbance of one can exacerbate the toxic effects of the others. This presents a mechanism unique to these areas that can lead to a vicious degenerative cycle. Interestingly, in familial variants of PD, the exact same brain areas are affected, implying the underlying process is likely the same. However, the exact disease mechanisms of many of these genetic variants remain unclear. Here, we review the effects of the PD-related genes Parkin, PINK1 and DJ-1. We establish that these mutant varieties can set in motion the same degenerative process involving α-synuclein, cytosolic catecholamines and Ca2+ . Additionally, we show indications that model organisms might not accurately represent all components of this central mechanism, explaining why Parkin, PINK1 and DJ-1 model organisms often lack a convincing PD-like phenotype.

A brief period of sleep deprivation negatively impacts the acquisition, consolidation, and retrieval of object-location memories.

Memory is a cognitive concept and refers to the storage of information over a longer time period. It exists of a series of complementary processes; acquisition, consolidation, and retrieval. Each of these processes has its own partly unique neurobiological signature. Sleep deprivation is known to impair hippocampus-dependent long-term memories. Many studies have used extended periods of wakefulness, affecting all three memory processes, thereby making it unable to determine how each of the processes is affected by sleep loss, separately. Others have extensively examined the effects on memory consolidation, showing the detrimental effect of sleep deprivation during the consolidation process on memory formation. Few studies have investigated how memory acquisition and its retrieval are affected by sleep loss. In the present study, we therefore assessed in mice how sleep deprivation negatively impacts memory acquisition, consolidation, and retrieval, in the Object Location Memory task. Mice were sleep deprived for six hours at the beginning of the light phase using the gentle handling method, 1) directly preceding the learning trial (acquisition), 2) immediately after the learning trial (consolidation), or 3) directly preceding the test trial (retrieval). Memory was assessed at either a 24-h or 1-h interval. Using this approach, we show for the first time that six hours of sleep deprivation attenuates the acquisition, consolidation, and retrieval of object-location memories in mice.

Phosphodiesterase inhibitors roflumilast and vardenafil prevent sleep deprivation-induced deficits in spatial pattern separation.

Sleep deprivation (SD) is known to impair hippocampus-dependent memory processes, in part by stimulating the phosphodiesterase (PDE) activity. In the present study, we assessed in mice whether SD also affects spatial pattern separation, a cognitive process that specifically requires the dentate gyrus (DG) subregion of the hippocampus. Adult male mice were trained in an object pattern separation (OPS) task in the middle of the light phase and then tested 24 hr thereafter. In total, we conducted three studies using the OPS task. In the first study, we validated the occurrence of pattern separation and tested the effects of SD. We found that 6 hr of SD during the first half of the light phase directly preceding the test trial impaired the spatial pattern separation performance. As a next step, we assessed in two consecutive studies whether the observed SD-induced performance deficits could be prevented by the systemic application of two different PDE inhibitors that are approved for human use. Both the PDE4 inhibitor roflumilast and PDE5 inhibitor vardenafil successfully prevented SD-induced deficits in spatial pattern separation. As a result, these PDE inhibitors have clinical potential for the prevention of memory deficits associated with loss of sleep.

A brief period of sleep deprivation leads to subtle changes in mouse gut microbiota.

Not getting enough sleep is a common problem in our society and contributes to numerous health problems, including high blood pressure, diabetes and obesity. Related to these observations, a wealth of studies has underscored the negative impact of both acute and chronic sleep deprivation on cognitive function. More recently it has become apparent that the gut microbiota composition can be rapidly altered, modulates brain function and is affected by the aforementioned health problems. As such, changes in the microbiota composition may contribute to the behavioural and physiological phenotypes associated with sleep deprivation. It is unclear, however, whether a brief period of sleep deprivation can also negatively impact the gut microbiota. Here, we examined the impact of 5 hr of sleep deprivation on gut microbiota composition of male C57Bl6/J mice. Despite the fact that the overall microbial composition did not change between the control- and sleep-deprived groups, the relative abundance of the Clostridiaceae and Lachnospiraceae were slightly altered in sleep-deprived animals compared to controls. Together, these data suggest that depriving mice of sleep for 5 hr leads to subtle changes in the gut microbiota composition.

Sleep deprivation-induced impairment of memory consolidation is not mediated by glucocorticoid stress hormones.

The general consensus is that sleep promotes neuronal recovery and plasticity, whereas sleep deprivation (SD) impairs brain function, including cognitive processes. Indeed, a wealth of data has shown a negative impact of SD on learning and memory processes, particularly those that involve the hippocampus. The mechanisms underlying these negative effects of sleep loss are only partly understood, but a reoccurring question is whether they are in part caused by stress hormones that may be released during SD. The purpose of the present study is therefore to examine the role of glucocorticoid stress hormones in SD-induced memory impairment. Male C57BL/6J mice were trained in an object-location memory paradigm, followed by 6 hr of SD by mild stimulation. At the beginning of the SD mice were injected with the corticosterone synthesis inhibitor metyrapone. Memory was tested 24 hr after training. Blood samples taken in a separate group of mice showed that SD resulted in a mild but significant increase in plasma corticosterone levels, which was prevented by metyrapone. However, the SD-induced impairment in object-location memory was not prevented by metyrapone treatment. This indicates that glucocorticoids play no role in causing the memory impairments seen after a short period of SD.

A brief period of sleep deprivation causes spine loss in the dentate gyrus of mice.

Sleep and sleep loss have a profound impact on hippocampal function, leading to memory impairments. Modifications in the strength of synaptic connections directly influences neuronal communication, which is vital for normal brain function, as well as the processing and storage of information. In a recently published study, we found that as little as five hours of sleep deprivation impaired hippocampus-dependent memory consolidation, which was accompanied by a reduction in dendritic spine numbers in hippocampal area CA1. Surprisingly, loss of sleep did not alter the spine density of CA3 neurons. Although sleep deprivation has been reported to affect the function of the dentate gyrus, it is unclear whether a brief period of sleep deprivation impacts spine density in this region. Here, we investigated the impact of a brief period of sleep deprivation on dendritic structure in the dentate gyrus of the dorsal hippocampus. We found that five hours of sleep loss reduces spine density in the dentate gyrus with a prominent effect on branched spines. Interestingly, the inferior blade of the dentate gyrus seems to be more vulnerable in terms of spine loss than the superior blade. This decrease in spine density predominantly in the inferior blade of the dentate gyrus may contribute to the memory deficits observed after sleep loss, as structural reorganization of synaptic networks in this subregion is fundamental for cognitive processes.

Mutation of neuron-specific chromatin remodeling subunit BAF53b: rescue of plasticity and memory by manipulating actin remodeling.

Recent human exome-sequencing studies have implicated polymorphic Brg1-associated factor (BAF) complexes (mammalian SWI/SNF chromatin remodeling complexes) in several intellectual disabilities and cognitive disorders, including autism. However, it remains unclear how mutations in BAF complexes result in impaired cognitive function. Post-mitotic neurons express a neuron-specific assembly, nBAF, characterized by the neuron-specific subunit BAF53b. Subdomain 2 of BAF53b is essential for the differentiation of neuronal precursor cells into neurons. We generated transgenic mice lacking subdomain 2 of Baf53b (BAF53bΔSB2). Long-term synaptic potentiation (LTP) and long-term memory, both of which are associated with phosphorylation of the actin severing protein cofilin, were assessed in these animals. A phosphorylation mimic of cofilin was stereotaxically delivered into the hippocampus of BAF53bΔSB2 mice in an effort to rescue LTP and memory. BAF53bΔSB2 mutant mice show impairments in phosphorylation of synaptic cofilin, LTP, and memory. Both the synaptic plasticity and memory deficits are rescued by overexpression of a phosphorylation mimetic of cofilin. Baseline physiology and behavior were not affected by the mutation or the experimental treatment. This study suggests a potential link between nBAF function, actin cytoskeletal remodeling at the dendritic spine, and memory formation. This work shows that a targeted manipulation of synaptic function can rescue adult plasticity and memory deficits caused by manipulations of nBAF, and thereby provides potential novel avenues for therapeutic development for multiple intellectual disability disorders.

Compartmentalized PDE4A5 Signaling Impairs Hippocampal Synaptic Plasticity and Long-Term Memory.

UNLABELLED: Alterations in cAMP signaling are thought to contribute to neurocognitive and neuropsychiatric disorders. Members of the cAMP-specific phosphodiesterase 4 (PDE4) family, which contains >25 different isoforms, play a key role in determining spatial cAMP degradation so as to orchestrate compartmentalized cAMP signaling in cells. Each isoform binds to a different set of protein complexes through its unique N-terminal domain, thereby leading to targeted degradation of cAMP in specific intracellular compartments. However, the functional role of specific compartmentalized PDE4 isoforms has not been examined in vivo Here, we show that increasing protein levels of the PDE4A5 isoform in mouse hippocampal excitatory neurons impairs a long-lasting form of hippocampal synaptic plasticity and attenuates hippocampus-dependent long-term memories without affecting anxiety. In contrast, viral expression of a truncated version of PDE4A5, which lacks the unique N-terminal targeting domain, does not affect long-term memory. Further, overexpression of the PDE4A1 isoform, which targets a different subset of signalosomes, leaves memory undisturbed. Fluorescence resonance energy transfer sensor-based cAMP measurements reveal that the full-length PDE4A5, in contrast to the truncated form, hampers forskolin-mediated increases in neuronal cAMP levels. Our study indicates that the unique N-terminal localization domain of PDE4A5 is essential for the targeting of specific cAMP-dependent signaling underlying synaptic plasticity and memory. The development of compounds to disrupt the compartmentalization of individual PDE4 isoforms by targeting their unique N-terminal domains may provide a fruitful approach to prevent cognitive deficits in neuropsychiatric and neurocognitive disorders that are associated with alterations in cAMP signaling. SIGNIFICANCE STATEMENT: Neurons exhibit localized signaling processes that enable biochemical cascades to be activated selectively in specific subcellular compartments. The phosphodiesterase 4 (PDE4) family coordinates the degradation of cAMP, leading to the local attenuation of cAMP-dependent signaling pathways. Sleep deprivation leads to increased hippocampal expression of the PDE4A5 isoform. Here, we explored whether PDE4A5 overexpression mimics behavioral and synaptic plasticity phenotypes associated with sleep deprivation. Viral expression of PDE4A5 in hippocampal neurons impairs long-term potentiation and attenuates the formation of hippocampus-dependent long-term memories. Our findings suggest that PDE4A5 is a molecular constraint on cognitive processes and may contribute to the development of novel therapeutic approaches to prevent cognitive deficits in neuropsychiatric and neurocognitive disorders that are associated with alterations in cAMP signaling.

Transiently increasing cAMP levels selectively in hippocampal excitatory neurons during sleep deprivation prevents memory deficits caused by sleep loss.

The hippocampus is particularly sensitive to sleep loss. Although previous work has indicated that sleep deprivation impairs hippocampal cAMP signaling, it remains to be determined whether the cognitive deficits associated with sleep deprivation are caused by attenuated cAMP signaling in the hippocampus. Further, it is unclear which cell types are responsible for the memory impairments associated with sleep deprivation. Transgenic approaches lack the spatial resolution to manipulate specific signaling pathways selectively in the hippocampus, while pharmacological strategies are limited in terms of cell-type specificity. Therefore, we used a pharmacogenetic approach based on a virus-mediated expression of a Gαs-coupled Drosophila octopamine receptor selectively in mouse hippocampal excitatory neurons in vivo. With this approach, a systemic injection with the receptor ligand octopamine leads to increased cAMP levels in this specific set of hippocampal neurons. We assessed whether transiently increasing cAMP levels during sleep deprivation prevents memory consolidation deficits associated with sleep loss in an object-location task. Five hours of total sleep deprivation directly following training impaired the formation of object-location memories. Transiently increasing cAMP levels in hippocampal neurons during the course of sleep deprivation prevented these memory consolidation deficits. These findings demonstrate that attenuated cAMP signaling in hippocampal excitatory neurons is a critical component underlying the memory deficits in hippocampus-dependent learning tasks associated with sleep deprivation.

Sleep deprivation impairs cAMP signalling in the hippocampus.

Millions of people regularly obtain insufficient sleep. Given the effect of sleep deprivation on our lives, understanding the cellular and molecular pathways affected by sleep deprivation is clearly of social and clinical importance. One of the major effects of sleep deprivation on the brain is to produce memory deficits in learning models that are dependent on the hippocampus. Here we have identified a molecular mechanism by which brief sleep deprivation alters hippocampal function. Sleep deprivation selectively impaired 3', 5'-cyclic AMP (cAMP)- and protein kinase A (PKA)-dependent forms of synaptic plasticity in the mouse hippocampus, reduced cAMP signalling, and increased activity and protein levels of phosphodiesterase 4 (PDE4), an enzyme that degrades cAMP. Treatment of mice with phosphodiesterase inhibitors rescued the sleep-deprivation-induced deficits in cAMP signalling, synaptic plasticity and hippocampus-dependent memory. These findings demonstrate that brief sleep deprivation disrupts hippocampal function by interfering with cAMP signalling through increased PDE4 activity. Thus, drugs that enhance cAMP signalling may provide a new therapeutic approach to counteract the cognitive effects of sleep deprivation.

Sleep deprivation during a specific 3-hour time window post-training impairs hippocampal synaptic plasticity and memory.

Sleep deprivation disrupts hippocampal function and plasticity. In particular, long-term memory consolidation is impaired by sleep deprivation, suggesting that a specific critical period exists following learning during which sleep is necessary. To elucidate the impact of sleep deprivation on long-term memory consolidation and synaptic plasticity, long-term memory was assessed when mice were sleep deprived following training in the hippocampus-dependent object place recognition task. We found that 3h of sleep deprivation significantly impaired memory when deprivation began 1h after training. In contrast, 3 h of deprivation beginning immediately post-training did not impair spatial memory. Furthermore, a 3-h sleep deprivation beginning 1h after training impaired hippocampal long-term potentiation (LTP), whereas sleep deprivation immediately after training did not affect LTP. Together, our findings define a specific 3-h critical period, extending from 1 to 4h after training, during which sleep deprivation impairs hippocampal function.

A presynaptic role for PKA in synaptic tagging and memory.

Protein kinase A (PKA) and other signaling molecules are spatially restricted within neurons by A-kinase anchoring proteins (AKAPs). Although studies on compartmentalized PKA signaling have focused on postsynaptic mechanisms, presynaptically anchored PKA may contribute to synaptic plasticity and memory because PKA also regulates presynaptic transmitter release. Here, we examine this issue using genetic and pharmacological application of Ht31, a PKA anchoring disrupting peptide. At the hippocampal Schaffer collateral CA3-CA1 synapse, Ht31 treatment elicits a rapid decay of synaptic responses to repetitive stimuli, indicating a fast depletion of the readily releasable pool of synaptic vesicles. The interaction between PKA and proteins involved in producing this pool of synaptic vesicles is supported by biochemical assays showing that synaptic vesicle protein 2 (SV2), Rim1, and SNAP25 are components of a complex that interacts with cAMP. Moreover, acute treatment with Ht31 reduces the levels of SV2. Finally, experiments with transgenic mouse lines, which express Ht31 in excitatory neurons at the Schaffer collateral CA3-CA1 synapse, highlight a requirement for presynaptically anchored PKA in pathway-specific synaptic tagging and long-term contextual fear memory. These results suggest that a presynaptically compartmentalized PKA is critical for synaptic plasticity and memory by regulating the readily releasable pool of synaptic vesicles.

Treatment with the selective PDE4B inhibitor A-33 or PDE4D inhibitor zatolmilast prevents sleep deprivation-induced deficits in spatial pattern separation.

Sleep deprivation (SD) disrupts hippocampus-dependent memory, particularly in the dentate gyrus (DG) region, an area crucial for pattern separation. Previous research showed that non-selective phosphodiesterase type 4 (PDE4) inhibitors like roflumilast can alleviate these deficits. However, it remains unclear whether these outcomes are specific to a particular subfamily of PDE4. Hence, this study examined the specific impact of PDE4B inhibitor (A-33) and PDE4D inhibitor (zatolmilast) on spatial pattern separation in sleep deprived mice. Results demonstrated that SD impairs pattern separation, but both zatolmilast and A-33 alleviate these effects. However, A-33 impaired pattern separation in non-sleep deprived animals. The cognitive benefits of these inhibitors after SD may arise from alterations in relevant signaling pathways in the DG. This study provides initial evidence that inhibiting PDE4B or PDE4D holds promise for mitigating memory deficits due to SD.

Gravin orchestrates protein kinase A and ß2-adrenergic receptor signaling critical for synaptic plasticity and memory.

A kinase-anchoring proteins (AKAPs) organize compartmentalized pools of protein kinase A (PKA) to enable localized signaling events within neurons. However, it is unclear which of the many expressed AKAPs in neurons target PKA to signaling complexes important for long-lasting forms of synaptic plasticity and memory storage. In the forebrain, the anchoring protein gravin recruits a signaling complex containing PKA, PKC, calmodulin, and PDE4D (phosphodiesterase 4D) to the ß2-adrenergic receptor. Here, we show that mice lacking the α-isoform of gravin have deficits in PKA-dependent long-lasting forms of hippocampal synaptic plasticity including ß2-adrenergic receptor-mediated plasticity, and selective impairments of long-term memory storage. Furthermore, both hippocampal ß2-adrenergic receptor phosphorylation by PKA, and learning-induced activation of ERK in the CA1 region of the hippocampus are attenuated in mice lacking gravin-α. We conclude that gravin compartmentalizes a significant pool of PKA that regulates learning-induced ß2-adrenergic receptor signaling and ERK activation in the hippocampus in vivo, thereby organizing molecular interactions between glutamatergic and noradrenergic signaling pathways for long-lasting synaptic plasticity, and memory storage.

Molecular fingerprints in the hippocampus of alcohol seeking during withdrawal.

Alcohol use disorder (AUD) is characterized by excessive alcohol seeking and use. Here, we investigated the molecular correlates of impaired extinction of alcohol seeking using a multidimentional mouse model of AUD. We distinguished AUD-prone and AUD-resistant mice, based on the presence of ≥ 2 or < 2 criteria of AUD and utilized RNA sequencing to identify genes that were differentially expressed in the hippocampus and amygdala of mice meeting ≥ 2 or < 2 criteria, as these brain regions are implicated in alcohol motivation, seeking, consumption and the cognitive inflexibility characteristic of AUD. Our findings revealed dysregulation of the genes associated with the actin cytoskeleton, including actin binding molecule cofilin, and impaired synaptic transmission in the hippocampi of mice meeting ≥ 2 criteria. Overexpression of cofilin in the polymorphic layer of the dentate gyrus (PoDG) inhibited ML-DG synapses, increased motivation to seek alcohol and impaired extinction of alcohol seeking, resembling the phenotype observed in mice meeting ≥ 2 criteria. Overall, our study uncovers a novel mechanism linking increased hippocampal cofilin expression with the AUD phenotype.

Cofilin overactivation improves hippocampus-dependent short-term memory.

Many living organisms of the animal kingdom have the fundamental ability to form and retrieve memories. Most information is initially stored as short-term memory, which is then converted to a more stable long-term memory through a process called memory consolidation. At the neuronal level, synaptic plasticity is crucial for memory storage. It includes the formation of new spines, as well as the modification of existing spines, thereby tuning and shaping synaptic efficacy. Cofilin critically contributes to memory processes as upon activation, it regulates the shape of dendritic spines by targeting actin filaments. We previously found that prolonged activation of cofilin in hippocampal neurons attenuated the formation of long-term object-location memories. Because the modification of spine shape and structure is also essential for short-term memory formation, we determined whether overactivation of hippocampal cofilin also influences the formation of short-term memories. To this end, mice were either injected with an adeno-associated virus expressing catalytically active cofilin, or an eGFP control, in the hippocampus. We show for the first time that cofilin overactivation improves short-term memory formation in the object-location memory task, without affecting anxiety-like behavior. Surprisingly, we found no effect of cofilin overactivation on AMPA receptor expression levels. Altogether, while cofilin overactivation might negatively impact the formation of long-lasting memories, it may benefit short-term plasticity.