Inducible forebrain-specific ablation of the transcription factor Creb during adulthood induces anxiety but no spatial/contextual learning deficits

The cyclic AMP (cAMP)-response element binding protein (CREB) is an activity-dependent transcription factor playing a role in synaptic plasticity, learning and memory, and emotional behavior. However, the impact of Creb ablation on rodent behavior is vague as e.g. memory performance of different Creb mutant mice depends on the specific type of mutation per se but additionally on the background and learning protocol differences. Here we present the first targeted ablation of CREB induced during adulthood selectively in principal forebrain neurons in a pure background strain of C57BL/6 mice. All hippocampal principal neurons exhibited lack of CREB expression. Mutant mice showed a severe anxiety phenotype in the openfield and novel object exploration test as well as in the Dark-Light Box Test, but unaltered hippocampus-dependent long-term memory in the Morris water maze and in context dependent fear conditioning. On the molecular level, CREB ablation led to CREM up regulation in the hippocampus and frontal cortex which may at least in part compensate for the loss of CREB. BDNF, a postulated CREB target gene, was down regulated in the frontal lobe but not in the hippocampus; neurogenesis remained unaltered. Our data indicate that in the adult mouse forebrain the late onset of CREB ablation can, in case of memory functionality, be compensated for and is not essential for memory consolidation and retrieval during adulthood. In contrast, the presence of CREB protein during adulthood seems to be pivotal for the regulation of emotional behavior

Gene Expression Analysis of In Vivo Fluorescent Cells

BACKGROUND: The analysis of gene expression for tissue homogenates is of limited value because of the considerable cell heterogeneity in tissues. However, several methods are available to isolate a cell type of interest from a complex tissue, the most reliable one being Laser Microdissection (LMD). Cells may be distinguished by their morphology or by specific antigens, but the obligatory staining often results in RNA degradation. Alternatively, particular cell types can be detected in vivo by expression of fluorescent proteins from cell type-specific promoters. METHODOLOGY/PRINCIPAL FINDINGS: We developed a technique for fixing in vivo fluorescence in brain cells and isolating them by LMD followed by an optimized RNA isolation procedure. RNA isolated from these cells was of equal quality as from unfixed frozen tissue, with clear 28S and 18S rRNA bands of a mass ratio of approximately 2ratio1. We confirmed the specificity of the amplified RNA from the microdissected fluorescent cells as well as its usefulness and reproducibility for microarray hybridization and quantitative real-time PCR (qRT-PCR). CONCLUSIONS/SIGNIFICANCE: Our technique guarantees the isolation of sufficient high quality RNA obtained from specific cell populations of the brain expressing soluble fluorescent marker, which is a critical prerequisite for subsequent gene expression studies by microarray analysis or qRT-PCR

Perinatal Hypoxia and Ischemia in Animal Models of Schizophrenia

Intrauterine or perinatal complications constitute a major risk for psychiatric diseases. Infants who suffered from hypoxia–ischemia (HI) are at twofold risk to develop schizophrenia in later life. Several animal models attempt to reproduce these complications to study the yet unknown steps between an insult in early life and outbreak of the disease decades later. However, it is very challenging to find the right type and severity of insult leading to a disease-like phenotype in the animal, but not causing necrosis and focal neurological deficits. By contrast, too mild, repetitive insults may even be protective via conditioning effects. Thus, it is not surprising that animal models of hypoxia lead to mixed results. To achieve clinically translatable findings, better protocols are urgently needed. Therefore, we compare widely used models of hypoxia and HI and propose future directions for the field

Fluoxetine Enhances Synaptic Vesicle Trafficking and Energy Metabolism in the Hippocampus of Socially Isolated Rats

Chronic social isolation (CSIS)–induced alternation in synaptic and mitochondrial function of specific brain regions is associated with major depressive disorder (MDD). Despite the wide number of available medications, treating MDD remains an important challenge. Although fluoxetine (Flx) is the most frequently prescribed antidepressant, its mode of action is still unknown. To delineate affected molecular pathways of depressive-like behavior and identify potential targets upon Flx treatment, we performed a comparative proteomic analysis of hippocampal purified synaptic terminals (synaptosomes) of rats exposed to six weeks of CSIS, an animal model of depression, and/or followed by Flx treatment (lasting three weeks of six-week CSIS) to explore synaptic protein profile changes. Results showed that Flx in controls mainly induced decreased expression of proteins involved in energy metabolism and the redox system. CSIS led to increased expression of proteins that mainly participate in Ca2+/calmodulin-dependent protein kinase II (Camk2)-related neurotransmission, vesicle transport, and ubiquitination. Flx treatment of CSIS rats predominantly increased expression of proteins involved in synaptic vesicle trafficking (exocytosis and endocytosis), and energy metabolism (glycolytic and mitochondrial respiration). Overall, these Flx-regulated changes in synaptic and mitochondrial proteins of CSIS rats might be critical targets for new therapeutic development for the treatment of MDD

The Differential Effects of Acute Vs. Chronic Stress and Their Combination on Hippocampal Parvalbumin and Inducible Heat Shock Protein 70 Expression

The hippocampus plays a central role in stress-related mood disorders. The effects of acute vs. chronic stress on the integrity of hippocampal circuitry in influencing the vulnerability to, or resiliency against, neuronal injury are poorly understood. Here we investigated whether acute vs. chronic psychosocial isolation stress or a combination of the two (chronic stress followed by acute stress) influences the expression of the interneuronal marker parvalbumin (PV) and the chaperone-inducible heat shock protein 70 (Hsp70i) in different subregions of the hippocampus. Low levels of the Ca2+-binding protein (PV) may increase the vulnerability to neuronal injury, and Hsp70i represents an indicator of intense excitation-induced neuronal stress. Adult male Wistar rats were exposed to 2 h of immobilization (IM) or cold (4 degrees C) (acute stressors), 21 d of social isolation (chronic stress), or a combination of both acute and chronic stress. Both chronic isolation and the combined stressors strongly decreased the PV-Immunoreactive cells in the CA1, CA3 and dentate gyrus (DG) region of the hippocampus, while acute stress did not affect PV expression. The combination of acute and chronic stress induced a dramatic increase in Hsp70i expression in the DG, but Hsp70i expression was unaffected in acute and chronic stress alone. We also monitored serum corticosterone (CORT) levels as a neuroendocrine marker of the stress response. Acute stress increased CORT levels, while chronic isolation stress compromised hypothalamic pituitary adrenocortical (HPA) axis activity such that the normal stress response was impaired following subsequent acute stress. These results indicate that in contrast to acute stress, chronic isolation compromises the HPA axis and generates a considerable reduction in PV expression, representing a decrease in the calcium-buffering capacity and a putatively higher vulnerability of specific hippocampal interneurons to excitotoxic injury. The induction of Hsp70i expression in response to acute and chronic isolation reveals that neurons in the DG are particularly vulnerable to an acute stressor following a chronic perturbation of HPA activity. (C) 2013 IBRO. Published by Elsevier Ltd. All rights reserved