Exposure to Juvenile Stress Induces Epigenetic Alterations in the GABAergic System in Rats.

Epigenetics is a gene-environment interaction mechanism, manifested mostly through changes in regulatory gene expression. Stress is an established environmental factor known to induce epigenetic changes. This study aimed to assess the long-term effect of stress as juveniles, or juvenile and adult stress, on alterations in glutamic acid decarboxylase genes (GAD65, GAD67). We assessed DNA methylation and RNA expression in four rat groups: (1) control group, (2) juvenile stress group sacrificed two days following stress exposure (JSe) (RNA only), (3) juvenile stress group sacrificed as adults (JS), and (4) juvenile and adult stress group (JS + AS). Three different areas of the brain were examined in each group: the dorsal dentate gyrus (dDG), the dorsal CA1 (dCA1), and the basolateral amygdala (BLA). A significantly low methylation level of GAD65 in the BLA was observed among the JS group, followed by almost complete recovery among the JS + AS group. However, in dDG, an opposite trend was captured, and higher GAD65 methylation was found in JS. In addition, RNA levels were found to be decreased in JS compared to JSe and JS + AS. These findings can point to a possible mechanism: while juvenile stress may enhance a better coping strategy with life challenges, additional stress in adulthood may trigger a contradictory response, either beneficial or harmful.

Intra-amygdala metaplasticity modulation of fear extinction learning.

The amygdala is a key brain region involved in emotional memory formation. It is also responsible for memory modulation in other brain areas. Under extreme conditions, amygdala modulation may lead to the generation of abnormal plasticity and trauma-related psychopathologies. However, the amygdala itself is a dynamic brain region, which is amenable to long-term plasticity and is affected by emotional experiences. These alterations may modify the way the amygdala modulates activity and plasticity in other related brain regions, which in turn may alter the animal's response to subsequent challenges in what could be termed as "Behavioral metaplasticity."Because of the reciprocal interactions between the amygdala and other emotion processing regions, such as the medial prefrontal cortex (mPFC) or the hippocampus, experience-induced intra-amygdala metaplasticity could lead to alterations in mPFC-dependent or hippocampus-dependent behaviors. While initiated by alterations within the basolateral amygdala (BLA), such alterations in other brain regions may come to be independent of BLA modulation, thus establishing what may be termed "Trans-regional metaplasticity." In this article, we review evidence supporting the notions of intra-BLA metaplasticity and how this may develop into "Trans-regional metaplasticity." Future research is needed to understand how such dynamic metaplastic alterations contribute to developing psychopathologies, and how this knowledge may be translated into promoting novel interventions in psychopathologies associated with fear, stress, and trauma.

Network Neuromodulation of Opioid and GABAergic Receptors Following a Combination of "Juvenile" and "Adult Stress" in Rats.

Early life stress is suggested to alter behavioral responses during stressful challenges in adulthood and to exacerbate pathological symptoms that reminisce posttraumatic stress disorder (PTSD). These effects are often associated with changes in γ-Aminobutyric acid type A (GABAA) and κ opioid receptor expression and neuromodulation of the limbic system. Anxiety-like and stress coping behaviors were assessed in rats exposed to stress in adulthood on the background of previous exposure to stress in juvenility. Two weeks following behavioral assessment in adulthood, GABAAR α1 and α2 subunits and κ opioid receptor expression levels were measured in the medial prefrontal cortex (mPFC), nucleus accumbens (NAc), amygdala, and periaqueductal gray (PAG). To illustrate changes at the network level, an integrated expression profile was constructed. We found that exposure to juvenile stress affected rats' behavior during adult stress. The combination of juvenile and adult stress significantly affected rats' long term anxious-like behavior. Probabilities predicting model integrating the expression of GABAA α1-α2 and κ opioid receptors in different brain regions yielded highly successful classification rates. This study emphasizes the ability of exposure to stress in juvenility to exacerbate the impact of coping with stress in adulthood. Moreover, the use of integrated receptor expression network profiling was found to effectively characterize the discussed affective styles and their behavioral manifestations.

GABAergic Transmission in the Basolateral Amygdala Differentially Modulates Plasticity in the Dentate Gyrus and the CA1 Areas.

The term "metaplasticity" is used to describe changes in synaptic plasticity sensitivity following an electrical, biochemical, or behavioral priming stimulus. For example, priming the basolateral amygdala (BLA) enhances long-term potentiation (LTP) in the dentate gyrus (DG) but decreases LTP in the CA1. However, the mechanisms underlying these metaplastic effects are only partly understood. Here, we examined whether the mechanism underlying these effects of BLA priming involves intra-BLA GABAergic neurotransmission. Low doses of muscimol, a GABAA receptor (GABAAR) agonist, were microinfused into the rat BLA before or after BLA priming. Our findings show that BLA GABAAR activation via muscimol mimicked the previously reported effects of electrical BLA priming on LTP in the perforant path and the ventral hippocampal commissure-CA1 pathways, decreasing CA1 LTP and increasing DG LTP. Furthermore, muscimol application before or after tetanic stimulation of the ventral hippocampal commissure-CA1 pathways attenuated the BLA priming-induced decrease in CA1 LTP. In contrast, muscimol application after tetanic stimulation of the perforant path attenuated the BLA priming-induced increase in DG LTP. The data indicate that GABAAR activation mediates metaplastic effects of the BLA on plasticity in the CA1 and the DG, but that the same GABAAR activation induces an intra-BLA form of metaplasticity, which alters the way BLA priming may modulate plasticity in other brain regions. These results emphasize the need for developing a dynamic model of BLA modulation of plasticity, a model that may better capture processes underlying memory alterations associated with emotional arousing or stressful events.

Juvenile stress leads to long-term immunological metaplasticity-like effects on inflammatory responses in adulthood.

Previous studies indicate that individuals exposed to stress in juvenility are more prone to suffer from stress-related psychopathologies in adulthood. Evidence suggests that exposure to enriched environment (EE) conditions alleviates juvenile stress (JVS) effects. Exposure to stress has been found to affect immune responses to challenges, but whether JVS has long-term effects on inflammatory processes remains unclear. Here, we examined the impact of JVS on inflammatory processes in adulthood, and the effects of exposure to EE conditions. Adult rats exposed to JVS showed elevated levels of blood monocytes after induction of peritoneal inflammation. This was associated with higher concentration of blood chemokine ligand type 2 (CCL2), but lower levels of its receptor, chemokine receptor type 2 (CCR2) on these monocytes, indicating reduced ability of these monocytes to be recruited to the inflammatory site. In accordance, JVS led to reduced levels of recruited macrophages at the peritoneal cavity, as well as a reduced activation ratio for the release of peritoneal interleukin-10 (IL-10) by lipopolysaccharide (LPS) activation. EE conditions, which fully reversed the anxiety-like behavior resulting from exposure to JVS, did not reverse JVS-induced alterations in blood concentration of monocytes or peritoneal macrophages, but affected IL-10 activation ratio. This effect was associated with a compensatory elevation of the peritoneal CCL2-CCR2 axis. Our results demonstrate long-term metaplasticity-like effects of JVS, which alter inflammatory processes in response to immune challenges in adulthood. Our results also raise the possibility that EE does not simply reverse the effects of JVS but rather indirectly modulates its impact.

Receptor tyrosine kinase EphA7 is required for interneuron connectivity at specific subcellular compartments of granule cells.

Neuronal transmission is regulated by the local circuitry which is composed of principal neurons targeted at different subcellular compartments by a variety of interneurons. However, mechanisms that contribute to the subcellular localisation and maintenance of GABAergic interneuron terminals are poorly understood. Stabilization of GABAergic synapses depends on clustering of the postsynaptic scaffolding protein gephyrin and its interaction with the guanine nucleotide exchange factor collybistin. Lentiviral knockdown experiments in adult rats indicated that the receptor tyrosine kinase EphA7 is required for the stabilisation of basket cell terminals on proximal dendritic and somatic compartments of granular cells of the dentate gyrus. EphA7 deficiency and concomitant destabilisation of GABAergic synapses correlated with impaired long-term potentiation and reduced hippocampal learning. Reduced GABAergic innervation may be explained by an impact of EphA7 on gephyrin clustering. Overexpression or ephrin stimulation of EphA7 induced gephyrin clustering dependent on the mechanistic target of rapamycin (mTOR) which is an interaction partner of gephyrin. Gephyrin interactions with mTOR become released after mTOR activation while enhanced interaction with the guanine nucleotide exchange factor collybistin was observed in parallel. In conclusion, EphA7 regulates gephyrin clustering and the maintenance of inhibitory synaptic connectivity via mTOR signalling.

Magnesium sulfate prevents maternal inflammation-induced impairment of learning ability and memory in rat offspring.

OBJECTIVE: Maternal chorioamnionitis is associated with newborn neurologic injury. Recent evidence suggests that maternal administration of magnesium sulphate (MG) may protect fetuses from white matter injury. Previously we demonstrated evidence by magnetic resonance imaging that MG may prevent maternal inflammation-induced gray matter injury of offspring. Thus, we sought to determine the potential of maternal inflammation to induce fetal neurological/behavioral deficits and assess whether maternal MG attenuates these effects. STUDY DESIGN: Pregnant rats at day 18 received injections of intraperitoneal lipopolysaccharide (LPS) or saline. Dams were treated with subcutaneous saline/MG (270 mg/kg followed by 27 mg/kg every 20 minutes) for 2 hours before and following LPS/saline injections. Pups were delivered spontaneously. At 1 and 3 months of age, 11-12 offspring of each group (saline, LPS, MG, LPS-MG) underwent a 2-way shuttle box avoidance testing. The shuttle box is divided in half and the animal moves between compartments to avoid an electric shock in response to an auditory stimulus. RESULTS: Control offspring demonstrated significantly improved learning and memory abilities from age 1 to 3 months. At 1 month, LPS-treated dams' offspring were similar to controls with no improvement in learning abilities at 3 months. MG treatment of LPS dams significantly improved offspring learning at 3 months, to equal or better than that of controls. CONCLUSION: LPS-stimulated inflammation during pregnancy impairs offspring learning ability and memory, which is ameliorated by maternal MG treatment. These results suggest that maternal MG therapy may prevent white and gray matter injuries associated with maternal infection/inflammation.

Long-term effects of controllability or the lack of it on coping abilities and stress resilience in the rat.

Findings suggest that stress-induced impaired learning and coping abilities may be attributed more to the psychological nature of the stressor, rather than its physical properties. It has been proposed that establishing controllability over stressors can ameliorate some of its effects on cognition and behavior. Gaining controllability was suggested to be associated with the development of stress resilience. Based on repeated exposure to the two-way shuttle avoidance task, we previously developed and validated a behavioral task that leads to a strict dissociation between gaining controllability (to the level that the associated fear is significantly reduced) and a fearful state of uncontrollability. Employing this protocol, we investigated here the impact of gaining or failing to gain emotional controllability on indices of anxiety and depression and on subsequent abilities to cope with positively or negatively reinforcing learning experiences. In agreement with previous studies, rats exposed to the uncontrollable protocol demonstrated high concentration of sera corticosterone, increased immobility, reduced duration of struggling in the forced swim test and impaired ability to acquire subsequent learning tasks. Achieving emotional controllability resulted in resilience to stress as was indicated by longer duration of struggling in the forced swim test, and enhanced learning abilities. Our prolonged training protocol, with the demonstrated ability of rats to gain emotional controllability, is proposed as a useful tool to study the neurobiological mechanisms of stress resilience.

Stress modulation of hippocampal activity--spotlight on the dentate gyrus.

The effects of stress on learning and memory are diverse, ranging from impairment to facilitation. Many studies emphasize the major role of the hippocampus, mainly its CA1 and CA3 areas, in the process of memory formation under emotional and stressful conditions. In the current review, we summarize work which suggests that the dentate gyrus (DG) of the hippocampus is likely to play a pivotal role in defining the impact of stress on hippocampal functioning. We describethe effects of stress on long term potentiation (LTP) and local circuit activity in the DG and the role of the amygdala in mediating these effects. As one of the brain regions known to have a high rate of adult neurogenesis, the effects of stress on DG neurogenesis will also be reviewed. Finally, we discuss exposure to stress during juvenility and its influence on the adult DG. The DG is a dynamic structure which is susceptible to stress. Under stressful conditions, its response is variable and complex, much like the behavioral outcomes of such circumstances. It is likely to significantly contribute to the diverse effects of stress on memory formation.

A novel recombinant fusion protein encoding a 20-amino acid residue of the third extracellular (E3) domain of CCR2 neutralizes the biological activity of CCL2.

CCL2 is a key CC chemokine that has been implicated in a variety of inflammatory autoimmune diseases and in tumor progression and it is therefore an important target for therapeutic intervention in these diseases. Soluble receptor-based therapy is a known approach for neutralizing the in vivo functions of soluble mediators. Owing to the complexity of seven-transmembrane G protein-coupled receptors, efforts to generate neutralizing soluble chemokine receptors have so far failed. We developed a strategy that is based on the generation of short recombinant proteins encoding different segments of a G protein-coupled receptor, and tested the ability of each of them to bind and neutralize its target chemokine. We show that a fusion protein comprised of as few as 20 aa of the third extracellular (E3) domain of the CCL2 receptor, stabilized by the IgG H chain Fc domain (E3-IgG or BL-2030), selectively binds CCL2 and CCL16 and effectively neutralizes their biological activities. More importantly, E3-IgG (BL-2030) could effectively suppress the in vivo biological activity of CCL2, attenuating ongoing experimental autoimmune encephalomyelitis, as well as the development of human prostate tumor in SCID mice.

CXCL12 (SDF-1alpha) suppresses ongoing experimental autoimmune encephalomyelitis by selecting antigen-specific regulatory T cells.

Experimental autoimmune encephalomyelitis (EAE) is a T cell-mediated autoimmune disease of the central nervous system induced by antigen-specific effector Th17 and Th1 cells. We show that a key chemokine, CXCL12 (stromal cell-derived factor 1alpha), redirects the polarization of effector Th1 cells into CD4(+)CD25(-)Foxp3(-)interleukin (IL) 10(high) antigen-specific regulatory T cells in a CXCR4-dependent manner, and by doing so acts as a regulatory mediator restraining the autoimmune inflammatory process. In an attempt to explore the therapeutic implication of these findings, we have generated a CXCL12-immunoglobulin (Ig) fusion protein that, when administered during ongoing EAE, rapidly suppresses the disease in wild-type but not IL-10-deficient mice. Anti-IL-10 neutralizing antibodies could reverse this suppression. The beneficial effect included selection of antigen-specific T cells that were CD4(+)CD25(-)Foxp3(-)IL-10(high), which could adoptively transfer disease resistance, and suppression of Th17 selection. However, in vitro functional analysis of these cells suggested that, even though CXCL12-Ig-induced tolerance is IL-10 dependent, IL-10-independent mechanisms may also contribute to their regulatory function. Collectively, our results not only demonstrate, for the first time, that a chemokine functions as a regulatory mediator, but also suggest a novel way for treating multiple sclerosis and possibly other inflammatory autoimmune diseases.