Steven A. Kushner

Selective Erasure of a Fear Memory

Memories are thought to be encoded by sparsely distributed groups of neurons. However, identifying the precise neurons supporting a given memory (the memory trace) has been a long-standing challenge. We have shown previously that lateral amygdala (LA) neurons with increased cyclic adenosine monophosphate response element–binding protein (CREB) are preferentially activated by fear memory expression, which suggests that they are selectively recruited into the memory trace. We used an inducible diphtheria-toxin strategy to specifically ablate these neurons. Selectively deleting neurons overexpressing CREB (but not a similar portion of random LA neurons) after learning blocked expression of that fear memory. The resulting memory loss was robust and persistent, which suggests that the memory was permanently erased. These results establish a causal link between a specific neuronal subpopulation and memory expression, thereby identifying critical neurons within the memory trace.

The HMG-CoA reductase inhibitor lovastatin reverses the learning and attention deficits in a mouse model of neurofibromatosis type 1.

Neurofibromatosis Type 1 (NF1) is a common neurological disorder caused by mutations in the gene encoding Neurofibromin, a p21Ras GTPase Activating Protein (GAP). Importantly, NF1 causes learning disabilities and attention deficits. A previous study showed that the learning and memory deficits of a mouse model of NF1 (nf1+/-) appear to be caused by excessive p21Ras activity leading to impairments in long-term potentiation (LTP), a cellular mechanism of learning and memory. Here, we identify lovastatin as a potent inhibitor of p21Ras/Mitogen Activated Protein Kinase (MAPK) activity in the brain. Lovastatin is a specific inhibitor of three-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, used commonly for the treatment of hypercholesterolemia. We report that lovastatin decreased the enhanced brain p21Ras-MAPK activity of the nf1+/- mice, rescued their LTP deficits, and reversed their spatial learning and attention impairments. Therefore, these results demonstrate that lovastatin may prove useful in the treatment of Neurofibromatosis Type 1.

Modulation of Presynaptic Plasticity and Learning by the H-ras/Extracellular Signal-Regulated Kinase/Synapsin I Signaling Pathway

Molecular and cellular studies of the mechanisms underlying mammalian learning and memory have focused almost exclusively on postsynaptic function. We now reveal an experience-dependent presynaptic mechanism that modulates learning and synaptic plasticity in mice. Consistent with a presynaptic function for endogenous H-ras/extracellular signal-regulated kinase (ERK) signaling, we observed that, under normal physiologic conditions in wild-type mice, hippocampus-dependent learning stimulated the ERK-dependent phosphorylation of synapsin I, and MEK (MAP kinase kinase)/ERK inhibition selectively decreased the frequency of miniature EPSCs. By generating transgenic mice expressing a constitutively active form of H-ras (H-rasG12V), which is abundantly localized in axon terminals, we were able to increase the ERK-dependent phosphorylation of synapsin I. This resulted in several presynaptic changes, including a higher density of docked neurotransmitter vesicles in glutamatergic terminals, an increased frequency of miniature EPSCs, and increased paired-pulse facilitation. In addition, we observed facilitated neurotransmitter release selectively during high-frequency activity with consequent increases in long-term potentiation. Moreover, these mice showed dramatic enhancements in hippocampus-dependent learning. Importantly, deletion of synapsin I, an exclusively presynaptic protein, blocked the enhancements of learning, presynaptic plasticity, and long-term potentiation. Together with previous invertebrate studies, these results demonstrate that presynaptic plasticity represents an important evolutionarily conserved mechanism for modulating learning and memory.

Effect of Simvastatin on Cognitive Functioning in Children With Neurofibromatosis Type 1: A Randomized Controlled Trial

CONTEXT Neurofibromatosis type 1 (NF1) is among the most common genetic disorders that cause learning disabilities. Recently, it was shown that statin-mediated inhibition of 3-hydroxy-3-methylglutaryl coenzyme A reductase restores the cognitive deficits in an NF1 mouse model. OBJECTIVE To determine the effect of simvastatin on neuropsychological, neurophysiological, and neuroradiological outcome measures in children with NF1. DESIGN, SETTING, AND PARTICIPANTS Sixty-two of 114 eligible children (54%) with NF1 participated in a randomized, double-blind, placebo-controlled trial conducted between January 20, 2006, and February 8, 2007, at an NF1 referral center at a Dutch university hospital. INTERVENTION Simvastatin or placebo treatment once daily for 12 weeks. MAIN OUTCOME MEASURES Primary outcomes were scores on a Rey complex figure test (delayed recall), cancellation test (speed), prism adaptation, and the mean brain apparent diffusion coefficient based on magnetic resonance imaging. Secondary outcome measures were scores on the cancellation test (standard deviation), Stroop color word test, block design, object assembly, Rey complex figure test (copy), Beery developmental test of visual-motor integration, and judgment of line orientation. Scores were corrected for baseline performance, age, and sex. RESULTS No significant differences were observed between the simvastatin and placebo groups on any primary outcome measure: Rey complex figure test (beta = 0.10; 95% confidence interval [CI], -0.36 to 0.56); cancellation test (beta = -0.19; 95% CI, -0.67 to 0.29); prism adaptation (odds ratio = 2.0; 95% CI, 0.55 to 7.37); and mean brain apparent diffusion coefficient (beta = 0.06; 95% CI, -0.07 to 0.20). In the secondary outcome measures, we found a significant improvement in the simvastatin group in object assembly scores (beta = 0.54; 95% CI, 0.08 to 1.01), which was specifically observed in children with poor baseline performance (beta = 0.80; 95% CI, 0.29 to 1.30). Other secondary outcome measures revealed no significant effect of simvastatin treatment. CONCLUSION In this 12-week trial, simvastatin did not improve cognitive function in children with NF1. Trial Registration isrctn.org Identifier: ISRCTN14965707.

Neurons Are Recruited to a Memory Trace Based on Relative Neuronal Excitability Immediately before Training

Memories are thought to be sparsely encoded in neuronal networks, but little is known about why a given neuron is recruited or allocated to a particular memory trace. Previous research shows that in the lateral amygdala (LA), neurons with increased CREB are selectively recruited to a fear memory trace. CREB is a ubiquitous transcription factor implicated in many cellular processes. Which process mediates neuronal memory allocation? One hypothesis is that CREB increases neuronal excitability to bias neuronal recruitment, although this has not been shown experimentally. Here we use several methods to increase neuronal excitability and show this both biases recruitment into the memory trace and enhances memory formation. Moreover, artificial activation of these neurons alone is a sufficient retrieval cue for fear memory expression, showing that these neurons are critical components of the memory trace. These results indicate that neuronal memory allocation is based on relative neuronal excitability immediately before training.

|[beta]|CaMKII controls the direction of plasticity at parallel fiber|[ndash]|Purkinje cell synapses

We found that βCaMKII, the predominant CaMKII isoform of the cerebellum, is important for controlling the direction of plasticity at the parallel fiber–Purkinje cell synapse; a protocol that induced synaptic depression in wild-type mice resulted in synaptic potentiation in Camk2b knockout mice and vice versa. These findings provide us with unique experimental insight into the mechanisms that transduce graded calcium signals into either synaptic depression or potentiation.

Risk of Postpartum Relapse in Bipolar Disorder and Postpartum Psychosis: A Systematic Review and Meta-Analysis

OBJECTIVE Women with a history of bipolar disorder, postpartum psychosis, or both are at high risk for postpartum relapse. The aim of this meta-analysis was to estimate the risk of postpartum relapse in these three patient groups. METHOD A systematic literature search was conducted in all public medical electronic databases, adhering to the PRISMA guidelines. Studies were included if they reported postpartum relapse in patients diagnosed with bipolar disorder and/or a history of postpartum psychosis or mania according to DSM or ICD criteria or the Research Diagnostic Criteria. RESULTS Thirty-seven articles describing 5,700 deliveries in 4,023 patients were included in the quantitative analyses. The overall postpartum relapse risk was 35% (95% CI=29, 41). Patients with bipolar disorder were significantly less likely to experience severe episodes postpartum (17%, 95% CI=13, 21) than patients with a history of postpartum psychosis (29%, 95% CI=20, 41). Insufficient information was available to determine relapse rates for patients with bipolar disorder and a history of postpartum episodes. In women with bipolar disorder, postpartum relapse rates were significantly higher among those who were medication free during pregnancy (66%, 95% CI=57, 75) than those who used prophylactic medication (23%, 95% CI=14, 37). CONCLUSIONS One-third of women at high risk experience a postpartum relapse. In women with bipolar disorder, continuation of prophylactic medication during pregnancy appears highly protective for maintaining mood stability postpartum. In women with a history of isolated postpartum psychosis, initiation of prophylaxis immediately after delivery offers the opportunity to minimize the risk of relapse while avoiding in utero medication exposure.

Ube3a reinstatement identifies distinct developmental windows in a murine Angelman syndrome model

Angelman syndrome (AS) is a severe neurodevelopmental disorder that results from loss of function of the maternal ubiquitin protein ligase E3A (UBE3A) allele. Due to neuron-specific imprinting, the paternal UBE3A copy is silenced. Previous studies in murine models have demonstrated that strategies to activate the paternal Ube3a allele are feasible; however, a recent study showed that pharmacological Ube3a gene reactivation in adulthood failed to rescue the majority of neurocognitive phenotypes in a murine AS model. Here, we performed a systematic study to investigate the possibility that neurocognitive rescue can be achieved by reinstating Ube3a during earlier neurodevelopmental windows. We developed an AS model that allows for temporally controlled Cre-dependent induction of the maternal Ube3a allele and determined that there are distinct neurodevelopmental windows during which Ube3a restoration can rescue AS-relevant phenotypes. Motor deficits were rescued by Ube3a reinstatement in adolescent mice, whereas anxiety, repetitive behavior, and epilepsy were only rescued when Ube3a was reinstated during early development. In contrast, hippocampal synaptic plasticity could be restored at any age. Together, these findings suggest that Ube3a reinstatement early in development may be necessary to prevent or rescue most AS-associated phenotypes and should be considered in future clinical trial design.

Immune system dysregulation in first-onset postpartum psychosis

BACKGROUND Accumulating evidence suggests that dysregulation of the immune system represents an important vulnerability factor for mood disorders. Postpartum psychosis (PP) is a severe mood disorder occurring within 4 weeks after delivery, a period of heightened immune responsiveness and an altered endocrine set point. Therefore, the aim of this study was to examine immune activation in patients with first-onset PP at the level of monocytes, T cells, and serum cytokines/chemokines. METHODS We included 63 women admitted with first-onset PP. Control groups included healthy postpartum (n = 56) and nonpostpartum (n = 136) women. A quantitative-polymerase chain reaction monocyte gene expression analysis was performed with 43 genes previously identified as abnormally regulated in nonpostpartum mood disorder patients including the isoforms of the glucocorticoid receptor. Peripheral blood mononuclear cells percentages were measured by fluorescence-activated cell sorter analysis, whereas serum cytokines/chemokines were determined with a cytometric bead array. RESULTS In healthy women, postpartum T cell levels were significantly elevated compared with nonpostpartum. Patients with PP failed to show the normal postpartum T cell elevation. In contrast, these patients showed a significant elevation of monocyte levels and a significant upregulation of several immune-related monocyte genes compared with control subjects postpartum and nonpostpartum. Furthermore, the glucocorticoid receptor α/β gene expression ratio was decreased in monocytes of PP patients, strongly correlating with their immune activation. CONCLUSIONS This study demonstrates a robust dysregulation of the immuno-neuro-endocrine set point in PP, with a notable over-activation of the monocyte/macrophage arm of the immune system.

Dysfunctional cerebellar Purkinje cells contribute to autism-like behaviour in Shank2 -deficient mice

Loss-of-function mutations in the gene encoding the postsynaptic scaffolding protein SHANK2 are a highly penetrant cause of autism spectrum disorders (ASD) involving cerebellum-related motor problems. Recent studies have implicated cerebellar pathology in the aetiology of ASD. Here we evaluate the possibility that cerebellar Purkinje cells (PCs) represent a critical locus of ASD-like pathophysiology in mice lacking Shank2. Absence of Shank2 impairs both PC intrinsic plasticity and induction of long-term potentiation at the parallel fibre to PC synapse. Moreover, inhibitory input onto PCs is significantly enhanced, most prominently in the posterior lobe where simple spike (SS) regularity is most affected. Using PC-specific Shank2 knockouts, we replicate alterations of SS regularity in vivo and establish cerebellar dependence of ASD-like behavioural phenotypes in motor learning and social interaction. These data highlight the importance of Shank2 for PC function, and support a model by which cerebellar pathology is prominent in certain forms of ASD.