Beta-catenin is required for memory consolidation

AKT/GSK-3beta/beta-catenin signalling within hippocampus and amygdala reflects genetically determined differences in posttraumatic stress disorder like symptoms

Only a small percentage of individuals develop posttraumatic stress disorder (PTSD) in the aftermath of a trauma. It is still largely unknown to what extent gene-environment interactions contribute to the inter-individual differences in PTSD susceptibility and resilience and what cellular processes may underlie long-term maintenance of the disorder. Here we employed a mouse model of PTSD to unravel the contribution of genetic background and maternal influences on long-lasting changes in kinase and transcription factor activities in PTSD-susceptible C57BL/6NCrl (B6N) and resilient C57BL/6JOlaHsd (B6JOla) mice. Mice received an inescapable foot shock and were tested for activity changes in the AKT/GSK-3beta/beta-catenin-pathway in specific brain structures 42 days later. To control for prenatal and postnatal environmental (i.e. maternal) factors part of the experiments were performed with animals originating from within-strain and between-strain embryo transfers. In PTSD-susceptible B6N mice, long-term maintenance of contextual and sensitized fear was accompanied by (i) increased levels of phosphorylated AKT within the dorsal hippocampus and (ii) higher levels of phosphorylated AKT and GSK-3beta and increased beta-catenin levels within the basolateral amygdala. In animals originating from embryo transfers, levels of phosphorylated GSK-3beta and of beta-catenin were decreased in the dorsal hippocampus, but increased in the basolateral amygdala of shocked B6N mice compared to shocked B6JOla mice. This was independent of the genotype of the recipient mothers. At the behavioural level, these differences coincided with sustained sensitized and more pronounced contextual fear of B6N compared to B6JOla mice. Taken together our study identifies lasting changes in the AKT/GSK-3beta/beta-catenin cascade within the hippocampus and amygdala as molecular correlates of genetically determined differences in the severity of PTSD-like symptoms.

Cholinergic hypofunction impairs memory acquisition possibly through hippocampal Arc and BDNF downregulation

Recent evidence suggests that activity-regulated cytoskeleton associated protein (Arc) and brain-derived neurotrophic factor (BDNF) are key players in the cellular mechanisms that trigger synaptic changes and memory consolidation. Cholinergic deafferentiation of hippocampus has been largely shown to induce memory impairments in different behavioral tasks. However, the mechanisms underlying cholinergic-induced memory formation remain unclear. The role of hippocampal cholinergic denervation on synaptic consolidation and further acquisition of spatial memory was hereby examined by analyzing Arc and BDNF in standard environment and after behavioral training in Morris water maze (MWM). In standard environment, a cholinergic hypofunction induced by the toxin (192) IgG-saporin led to significant decreases in Arc protein and mRNA as well as in BDNF. Lesioned rats subjected to MWM showed a worse acquisition performance that was reversed after galantamine treatment. Recovery of memory acquisition was accompanied by normalization of Arc and BDNF levels in hippocampus. Stimulation of muscarinic, but not nicotinic receptors, in hippocampal primary neurons caused a rapid induction of Arc production. These data suggest that cholinergic denervation of hippocampus leads to deficits in muscarinic-dependent induction of Arc and a subsequent impairment of spatial memory acquisition.

How the neurocircuitry and genetics of fear inhibition may inform our understanding of PTSD

Exposure to traumatic events that produce extreme fear and horror is all too common in both military and civilian populations, but not all individuals develop posttraumatic stress disorder (PTSD) as a result of the exposure. What mediates risk and resilience in the development of PTSD and other stress-related psychopathology is of paramount importance to our further understanding of trauma-related psychopathology as well as the development of new treatment approaches. Biological factors, such as genotype and neurobiology, interact with environmental factors, such as childhood background and trauma load, to affect vulnerability and resilience in the aftermath of trauma exposure. One of the core symptoms of PTSD is the inability to control fear, which has led some investigators and clinicians to conceptualize PTSD as a disorder of fear or, more importantly, its inhibition. This review focuses on translational methods that have been used to examine fear conditioning and inhibition of fear in PTSD and summarizes genetic and neurobiological factors related to fear inhibition. The authors also discuss different pharmacological approaches that enhance fear inhibition and may improve treatment outcomes for patients with PTSD.

Linkage analysis of Tourette syndrome in a large Utah pedigree

Tourette syndrome (TS) is a neuropsychiatric disorder characterized by multiple motor and phonic tics. The heritability of TS has been well established, yet there is a lack of consensus in genome-wide linkage studies. The purpose of this study was to conduct a genome-wide linkage analysis on a unique, large, high-risk TS Utah pedigree. We examined a qualitative trait (TS1) where cases had a definitive diagnosis of TS as observed by a clinical interviewer (n = 66) and a quantitative phenotype based on the total Yale global motor and phonic tic severity scores (n = 102). Both parametric and non-parametric multipoint linkage analyses based on MCMC methods were performed using a 10 cM spaced micro-satellite autosomal marker set. Two regions of interest were identified under affecteds-only recessive models; a LOD score of 3.3 on chromosome 1p for Yale tic severity and a LOD score of 3.1 on chromosome 3p for the TS1 phenotype. Twenty-seven individuals shared linked segregating haplotypes for the 1p region. They had significantly higher Yale tic phonic scores than non-sharers (P = 0.01). There were 46 haplotype sharers on chromosome 3p with significantly higher percentage of females among these individuals compared to the non-sharers (P = 0.03). The significant linkage peaks on chromosomes 1p and 3p are in new areas of the genome for TS, and replication of these findings is necessary.

Prelimbic cortical BDNF is required for memory of learned fear but not extinction or innate fear

In the medial prefrontal cortex, the prelimbic area is emerging as a major modulator of fear behavior, but the mechanisms remain unclear. Using a selective neocortical knockout mouse, virally mediated prelimbic cortical-specific gene deletion, and pharmacological rescue with a TrkB agonist, we examined the role of a primary candidate mechanism, BDNF, in conditioned fear. We found consistently robust deficits in consolidation of cued fear but no effects on acquisition, expression of unlearned fear, sensorimotor function, and spatial learning. This deficit in learned fear in the BDNF knockout mice was rescued with systemic administration of a TrkB receptor agonist, 7,8-dihydroxyflavone. These data indicate that prelimbic BDNF is critical for consolidation of learned fear memories, but it is not required for innate fear or extinction of fear. Moreover, use of site-specific, inducible BDNF deletions shows a powerful mechanism that may further our understanding of the pathophysiology of fear-related disorders.

Regulation of dendrite and spine morphogenesis and plasticity by catenins

The appropriate regulation of dendrite, spine, and synapse morphogenesis in neurons both during and after development is critical for the formation and maintenance of neural circuits. It is becomingly increasingly clear that the cadherin-catenin cell adhesion complex, a complex that has been widely studied in epithelia, regulates neuronal morphogenesis. More interestingly, the catenins, cytosolic proteins that bind to cadherins, regulate multiple aspects of neuronal morphogenesis including dendrite, spine, and synapse morphogenesis and plasticity, both independent of and dependent on their ability to bind cadherins. In this review, we examine some of the more recent and exciting studies that implicate individual catenins in various aspects of neuronal morphogenesis and plasticity.