Reset of hippocampal-prefrontal circuitry facilitates learning.

The ability to rapidly adapt to novel situations is essential for survival, and this flexibility is impaired in many neuropsychiatric disorders1. Thus, understanding whether and how novelty prepares, or primes, brain circuitry to facilitate cognitive flexibility has important translational relevance. Exposure to novelty recruits the hippocampus and medial prefrontal cortex (mPFC)2 and may prime hippocampal-prefrontal circuitry for subsequent learning-associated plasticity. Here we show that novelty resets the neural circuits that link the ventral hippocampus (vHPC) and the mPFC, facilitating the ability to overcome an established strategy. Exposing mice to novelty disrupted a previously encoded strategy by reorganizing vHPC activity to local theta (4-12 Hz) oscillations and weakening existing vHPC-mPFC connectivity. As mice subsequently adapted to a new task, vHPC neurons developed new task-associated activity, vHPC-mPFC connectivity was strengthened, and mPFC neurons updated to encode the new rules. Without novelty, however, mice adhered to their established strategy. Blocking dopamine D1 receptors (D1Rs) or inhibiting novelty-tagged cells that express D1Rs in the vHPC prevented these behavioural and physiological effects of novelty. Furthermore, activation of D1Rs mimicked the effects of novelty. These results suggest that novelty promotes adaptive learning by D1R-mediated resetting of vHPC-mPFC circuitry, thereby enabling subsequent learning-associated circuit plasticity.

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.

Effects of sleep deprivation and aging on long-term and remote memory in mice.

Sleep deprivation (SD) following hippocampus-dependent learning in young mice impairs memory when tested the following day. Here, we examined the effects of SD on remote memory in both young and aged mice. In young mice, we found that memory is still impaired 1 mo after training. SD also impaired memory in aged mice 1 d after training, but, by a month after training, sleep-deprived and control aged animals performed similarly, primarily due to remote memory decay in the control aged animals. Gene expression analysis supported the finding that SD has similar effects on the hippocampus in young and aged mice.

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.

Genomic analysis of sleep deprivation reveals translational regulation in the hippocampus.

Sleep deprivation is a common problem of considerable health and economic impact in today's society. Sleep loss is associated with deleterious effects on cognitive functions such as memory and has a high comorbidity with many neurodegenerative and neuropsychiatric disorders. Therefore, it is crucial to understand the molecular basis of the effect of sleep deprivation in the brain. In this study, we combined genome-wide and traditional molecular biological approaches to determine the cellular and molecular impacts of sleep deprivation in the mouse hippocampus, a brain area crucial for many forms of memory. Microarray analysis examining the effects of 5 h of sleep deprivation on gene expression in the mouse hippocampus found 533 genes with altered expression. Bioinformatic analysis revealed that a prominent effect of sleep deprivation was to downregulate translation, potentially mediated through components of the insulin signaling pathway such as the mammalian target of rapamycin (mTOR), a key regulator of protein synthesis. Consistent with this analysis, sleep deprivation reduced levels of total and phosphorylated mTOR, and levels returned to baseline after 2.5 h of recovery sleep. Our findings represent the first genome-wide analysis of the effects of sleep deprivation on the mouse hippocampus, and they suggest that the detrimental effects of sleep deprivation may be mediated by reductions in protein synthesis via downregulation of mTOR. Because protein synthesis and mTOR activation are required for long-term memory formation, our study improves our understanding of the molecular mechanisms underlying the memory impairments induced by sleep deprivation.

Ventral tegmental area GABA neurons mediate stress-induced blunted reward-seeking in mice.

Decreased pleasure-seeking (anhedonia) forms a core symptom of depression. Stressful experiences precipitate depression and disrupt reward-seeking, but it remains unclear how stress causes anhedonia. We recorded simultaneous neural activity across limbic brain areas as mice underwent stress and discovered a stress-induced 4 Hz oscillation in the nucleus accumbens (NAc) that predicts the degree of subsequent blunted reward-seeking. Surprisingly, while previous studies on blunted reward-seeking focused on dopamine (DA) transmission from the ventral tegmental area (VTA) to the NAc, we found that VTA GABA, but not DA, neurons mediate stress-induced blunted reward-seeking. Inhibiting VTA GABA neurons disrupts stress-induced NAc oscillations and rescues reward-seeking. By contrast, mimicking this signature of stress by stimulating NAc-projecting VTA GABA neurons at 4 Hz reproduces both oscillations and blunted reward-seeking. Finally, we find that stress disrupts VTA GABA, but not DA, neural encoding of reward anticipation. Thus, stress elicits VTA-NAc GABAergic activity that induces VTA GABA mediated blunted reward-seeking.

Somatostatin Interneurons Facilitate Hippocampal-Prefrontal Synchrony and Prefrontal Spatial Encoding.

Decreased hippocampal-prefrontal synchrony may mediate cognitive deficits in schizophrenia, but it remains unclear which cells orchestrate this long-range synchrony. Parvalbumin (PV)- and somatostatin (SOM)-expressing interneurons show histological abnormalities in individuals with schizophrenia and are hypothesized to regulate oscillatory synchrony within the prefrontal cortex. To examine the relationship between interneuron function, long-range hippocampal-prefrontal synchrony, and cognition, we optogenetically inhibited SOM and PV neurons in the medial prefrontal cortex (mPFC) of mice performing a spatial working memory task while simultaneously recording neural activity in the mPFC and the hippocampus (HPC). We found that inhibiting SOM, but not PV, interneurons during the encoding phase of the task impaired working memory accuracy. This behavioral impairment was associated with decreased hippocampal-prefrontal synchrony and impaired spatial encoding in mPFC neurons. These findings suggest that interneuron dysfunction may contribute to cognitive deficits associated with schizophrenia by disrupting long-range synchrony between the HPC and PFC.

Cytosolic Accumulation of L-Proline Disrupts GABA-Ergic Transmission through GAD Blockade.

Proline dehydrogenase (PRODH), which degrades L-proline, resides within the schizophrenia-linked 22q11.2 deletion suggesting a role in disease. Supporting this, elevated L-proline levels have been shown to increase risk for psychotic disorders. Despite the strength of data linking PRODH and L-proline to neuropsychiatric diseases, targets of disease-relevant concentrations of L-proline have not been convincingly described. Here, we show that Prodh-deficient mice with elevated CNS L-proline display specific deficits in high-frequency GABA-ergic transmission and gamma-band oscillations. We find that L-proline is a GABA-mimetic and can act at multiple GABA-ergic targets. However, at disease-relevant concentrations, GABA-mimesis is limited to competitive blockade of glutamate decarboxylase leading to reduced GABA production. Significantly, deficits in GABA-ergic transmission are reversed by enhancing net GABA production with the clinically relevant compound vigabatrin. These findings indicate that accumulation of a neuroactive metabolite can lead to molecular and synaptic dysfunction and help to understand mechanisms underlying neuropsychiatric disease.

Sleep deprivation impairs memory by attenuating mTORC1-dependent protein synthesis.

Sleep deprivation is a public health epidemic that causes wide-ranging deleterious consequences, including impaired memory and cognition. Protein synthesis in hippocampal neurons promotes memory and cognition. The kinase complex mammalian target of rapamycin complex 1 (mTORC1) stimulates protein synthesis by phosphorylating and inhibiting the eukaryotic translation initiation factor 4E-binding protein 2 (4EBP2). We investigated the involvement of the mTORC1-4EBP2 axis in the molecular mechanisms mediating the cognitive deficits caused by sleep deprivation in mice. Using an in vivo protein translation assay, we found that loss of sleep impaired protein synthesis in the hippocampus. Five hours of sleep loss attenuated both mTORC1-mediated phosphorylation of 4EBP2 and the interaction between eukaryotic initiation factor 4E (eIF4E) and eIF4G in the hippocampi of sleep-deprived mice. Increasing the abundance of 4EBP2 in hippocampal excitatory neurons before sleep deprivation increased the abundance of phosphorylated 4EBP2, restored the amount of eIF4E-eIF4G interaction and hippocampal protein synthesis to that seen in mice that were not sleep-deprived, and prevented the hippocampus-dependent memory deficits associated with sleep loss. These findings collectively demonstrate that 4EBP2-regulated protein synthesis is a critical mediator of the memory deficits caused by sleep deprivation.

Sleep deprivation causes memory deficits by negatively impacting neuronal connectivity in hippocampal area CA1.

Brief periods of sleep loss have long-lasting consequences such as impaired memory consolidation. Structural changes in synaptic connectivity have been proposed as a substrate of memory storage. Here, we examine the impact of brief periods of sleep deprivation on dendritic structure. In mice, we find that five hours of sleep deprivation decreases dendritic spine numbers selectively in hippocampal area CA1 and increased activity of the filamentous actin severing protein cofilin. Recovery sleep normalizes these structural alterations. Suppression of cofilin function prevents spine loss, deficits in hippocampal synaptic plasticity, and impairments in long-term memory caused by sleep deprivation. The elevated cofilin activity is caused by cAMP-degrading phosphodiesterase-4A5 (PDE4A5), which hampers cAMP-PKA-LIMK signaling. Attenuating PDE4A5 function prevents changes in cAMP-PKA-LIMK-cofilin signaling and cognitive deficits associated with sleep deprivation. Our work demonstrates the necessity of an intact cAMP-PDE4-PKA-LIMK-cofilin activation-signaling pathway for sleep deprivation-induced memory disruption and reduction in hippocampal spine density.

Daily acclimation handling does not affect hippocampal long-term potentiation or cause chronic sleep deprivation in mice.

STUDY OBJECTIVES: Gentle handling is commonly used to perform brief sleep deprivation in rodents. It was recently reported that daily acclimation handling, which is often used before behavioral assays, causes alterations in sleep, stress, and levels of N-methyl-D-aspartate receptor subunits prior to the actual period of sleep deprivation. It was therefore suggested that acclimation handling could mediate some of the observed effects of subsequent sleep deprivation. Here, we examine whether acclimation handling, performed as in our sleep deprivation studies, alters sleep/wake behavior, stress, or forms of hippocampal synaptic plasticity that are impaired by sleep deprivation. DESIGN: Adult C57BL/6J mice were either handled daily for 6 days or were left undisturbed in their home cages. On the day after the 6(th) day of handling, long-term potentiation (LTP) was induced in hippocampal slices with spaced four-train stimulation, which we previously demonstrated to be impaired by brief sleep deprivation. Basal synaptic properties were also assessed. In three other sets of animals, activity monitoring, polysomnography, and stress hormone measurements were performed during the 6 days of handling. RESULTS: Daily gentle handling alone does not alter LTP, rest/activity patterns, or sleep/wake architecture. Handling initially induces a minimal stress response, but by the 6(th) day, stress hormone levels are unaltered by handling. CONCLUSION: It is possible to handle mice daily to accustom them to the researcher without causing alterations in sleep, stress, or synaptic plasticity in the hippocampus. Therefore, effects of acclimation handling cannot explain the impairments in signaling mechanisms, synaptic plasticity, and memory that result from brief sleep deprivation.

Hypospadias surgery in plastic surgery: a snapshot of today with an eye on tomorrow.

The current provision of hypospadias correctional surgery lies across the specialities of paediatric surgery, general surgery, urology and plastic surgery. This study aimed to look at how this provision is structured within plastic surgery, what plastic surgeons are currently doing and how this impacts on training. All plastic surgery units within the UK were contacted via letter and telephone in order to ascertain their current practice with regard to hypospadias surgery. Specialist registrars in the West Midlands Deanery were also questioned on their training in this area. The results indicate that 42 plastic surgeons in the UK carry out hypospadias surgery. The majority of clinicians use the Bracka two-stage repair (88%), with Snodgrass (45%) and MAGPI (43%) widely used. Operations are being carried out across the age spectrum from birth, with 51% favouring intervention at 3 years or more. Approximately two-thirds of plastic surgeons treat less than 25 patients per year. One-third treat 26 to 50, with only two clinicians claiming to treat more than 50 patients per year. Of the specialist registrars questioned in the West Midlands Deanery the majority (74%) were confident with the assessment of new cases and in obtaining consent. One-quarter of registrars (28%) only wished to carry out hypospadias surgery once they were consultants, with only one feeling that they had the necessary training to achieve this now. Plastic surgeons represent about half (52%) of the consultants currently identified in the UK as carrying out hypospadias surgery. If this provision is to be maintained then a greater opportunity for development of skills and experience needs to be created within plastic surgery training. The authors advocate the formulation of a coordinated national framework for the provision of this service, promoting a regional focus for skills and governance.

Mastectomy scars following breast reconstruction: should routine histologic analysis be performed?

BACKGROUND: There is some debate in the recent literature regarding the routine submission of mastectomy scars for histologic analysis when performing delayed breast reconstructions. The aim of this study was to review the relevant publications and evaluate the practice of routine histologic examination of mastectomy scars. METHODS: The authors conducted a retrospective review, across three regional plastic and reconstructive surgery units, of 433 patients who had 455 scars routinely sent for histologic examination following delayed breast reconstruction between January of 2000 and December of 2006. Patients with clinical evidence of recurrent carcinoma were excluded. RESULTS: Data from 433 patients revealed an average age at reconstruction of 49.9 years (range, 25 to 77 years). The mean interval from primary breast surgery to reconstruction was 3.9 years (range, 2 months to 32 years), and the average length of patient follow-up, from primary surgery, was 6.4 years (range, 1 to 40 years). The majority of the initial operations were carried out for invasive carcinoma (89 percent). Four mastectomy scars in three patients were positive for carcinoma recurrence. CONCLUSIONS: The publications related to the practice of routine histologic analysis of mastectomy scars provide conflicting conclusions. As a proportion of patients may benefit from the early detection and treatment of locoregional recurrence, the authors suggest that the routine submission of mastectomy scars will allow for the earlier detection of soft-tissue recurrences that may affect long-term outcome. In keeping with cancer surgery principles, the authors recommend routine histologic examination of mastectomy scars following delayed breast reconstruction.

Intraoperative findings of cancer in delayed breast reconstruction: a dilemma?

Recurrence of breast cancer discovered at the time of reconstruction is rare. However, with increasing numbers of delayed postmastectomy reconstructions being performed, this scenario may become more common. There are no guidelines on how to manage this dilemma. There are two main issues: the effect on the patient and the effect on the reconstruction itself. The authors present two cases and discuss the factors involved in this difficult decision, along with their recommendations.