Charilaos Avrabos

Glutamatergic and Dopaminergic Neurons Mediate Anxiogenic and Anxiolytic Effects of CRHR1

An imbalance between CRHR1-controlled anxiogenic glutamatergic and anxiolytic dopaminergic systems might lead to emotional disturbances. The corticotropin-releasing hormone receptor 1 (CRHR1) critically controls behavioral adaptation to stress and is causally linked to emotional disorders. Using neurochemical and genetic tools, we determined that CRHR1 is expressed in forebrain glutamatergic and γ-aminobutyric acid–containing (GABAergic) neurons as well as in midbrain dopaminergic neurons. Via specific CRHR1 deletions in glutamatergic, GABAergic, dopaminergic, and serotonergic cells, we found that the lack of CRHR1 in forebrain glutamatergic circuits reduces anxiety and impairs neurotransmission in the amygdala and hippocampus. Selective deletion of CRHR1 in midbrain dopaminergic neurons increases anxiety-like behavior and reduces dopamine release in the prefrontal cortex. These results define a bidirectional model for the role of CRHR1 in anxiety and suggest that an imbalance between CRHR1-controlled anxiogenic glutamatergic and anxiolytic dopaminergic systems might lead to emotional disorders.

Nectin-3 links CRHR1 signaling to stress-induced memory deficits and spine loss

Stress impairs cognition via corticotropin-releasing hormone receptor 1 (CRHR1), but the molecular link between abnormal CRHR1 signaling and stress-induced cognitive impairments remains unclear. We investigated whether the cell adhesion molecule nectin-3 is required for the effects of CRHR1 on cognition and structural remodeling after early-life stress exposure. Postnatally stressed adult mice had decreased hippocampal nectin-3 levels, which could be attenuated by CRHR1 inactivation and mimicked by corticotropin-releasing hormone (CRH) overexpression in forebrain neurons. Acute stress dynamically reduced hippocampal nectin-3 levels, which involved CRH-CRHR1, but not glucocorticoid receptor, signaling. Suppression of hippocampal nectin-3 caused spatial memory deficits and dendritic spine loss, whereas enhancing hippocampal nectin-3 expression rescued the detrimental effects of early-life stress on memory and spine density in adulthood. Our findings suggest that hippocampal nectin-3 is necessary for the effects of stress on memory and structural plasticity and indicate that the CRH-CRHR1 system interacts with the nectin-afadin complex to mediate such effects.

Methylglyoxal-mediated anxiolysis involves increased protein modification and elevated expression of glyoxalase 1 in the brain.

J. Neurochem. (2010) 113, 1240–1251.

Tumor suppressor down-regulated in renal cell carcinoma 1 (DRR1) is a stress-induced actin bundling factor that modulates synaptic efficacy and cognition

Stress has been identified as a major causal factor for many mental disorders. However, our knowledge about the chain of molecular and cellular events translating stress experience into altered behavior is still rather scant. Here, we have characterized a murine ortholog of the putative tumor suppressor gene DRR1 as a unique stress-induced protein in brain. It binds to actin, promotes bundling and stabilization of actin filaments, and impacts on actin-dependent neurite outgrowth. Endogenous DRR1 localizes to some, but not all, synapses, with preference for the presynaptic region. Hippocampal virus-mediated enhancement of DRR1 expression reduced spine density, diminished the probability of synaptic glutamate release, and altered cognitive performance. DRR1 emerges as a protein to link stress with actin dynamics, which in addition is able to act on synaptic function and cognition.

Voltage-sensitive dye imaging demonstrates an enhancing effect of corticotropin- releasing hormone on neuronal activity propagation through the hippocampal formation

Corticotropin-releasing hormone (CRH) is thought to play an important role in the pathophysiology of stress-related psychiatric disorders, such as major depressive disorder (MDD) and post-traumatic stress disorder (PTSD). However, knowledge about the actions of CRH at the neuronal network level is only scarce. Here, we examined whether CRH affects neuronal activity propagation through the hippocampal formation (HF), a brain region which is likely to be involved in MDD and PTSD. For this purpose, we applied voltage-sensitive dye imaging (VSDI) to specifically cut hippocampal brain slices obtained from adult mice. This approach allowed us to investigate evoked neuronal activity propagation through the HF with micrometer spatial and millisecond temporal resolution. Application of CRH (50 nM) to slices increased neuronal activity propagation from the dentate gyrus (DG) to the CA1 subfield. This effect of CRH was caused by amplification of neuronal excitation on its passage through the HF and absent in mice lacking the CRH receptor type 1 (CRHR1). In conclusion, our study presents a VSDI assay for the investigation of neuronal activity propagation through the HF and demonstrates that CRH, via CRHR1, enhances this activity propagation. This effect of CRH might contribute to alterations of memory formation seen in MDD and PTSD. Moreover, it could influence hippocampal regulation of hypothalamic-pituitary-adrenal axis (HPA-axis) activity.

Real-Time Imaging of Amygdalar Network Dynamics In Vitro Reveals a Neurophysiological Link to Behavior in a Mouse Model of Extremes in Trait Anxiety

In humans and numerous other mammalian species, individuals considerably vary in their level of trait anxiety. This well known phenomenon is closely related to the etiology of several psychiatric disorders, but its neurophysiological basis remains poorly understood. Here, we applied voltage-sensitive dye imaging to brain slices from animals of the high (HAB), normal (NAB), and low (LAB) trait anxiety mouse model and investigated whether evoked neuronal activity propagations from the lateral (LA) to the central (CeA) amygdala differ in their relative strength among HAB, NAB, and LAB mice. For this purpose, we divided a real-time measure of neuronal population activity in the CeA by a respective measure obtained for the LA. This calculation yielded the metric “CeA/LA activity.” Our data clearly demonstrate a positive correlation between trait anxiety levels evaluated by the elevated plus-maze test and CeA/LA activity. Moreover, we found reduced CeA/LA activity in HAB mice, which responded with decreased anxiety levels to an environmental enrichment and, inversely, detected increased anxiety levels and CeA/LA activity in LAB mice that experienced chronic mild stress. We did not observe differences in the spread of neuronal activity in the motor and visual cortex among HAB, NAB, and LAB animals. Collectively, these findings provide evidence that, in mammals, interindividual variability in trait anxiety is causally linked to individual variations in the physiological constitution of the LA-to-CeA circuitry that give rise to a differential regulation of neuronal signal flow through this fundamental input–output network of the amygdala.

Intranasally Applied Neuropeptide S Shifts a High-Anxiety Electrophysiological Endophenotype in the Ventral Hippocampus towards a "Normal"-Anxiety One

The neurobiological basis of pathological anxiety and the improvement of its pharmacological treatment are a matter of intensive investigation. Here, using electrophysiological techniques in brain slices from animals of the high anxiety-related behavior (HAB) and normal anxiety-related behavior (NAB) mouse model, we show that basal neurotransmission at ventral hippocampal CA3-CA1 synapses is weaker in HAB compared to NAB mice. We further demonstrate that paired-pulse facilitation (PPF) and long-term potentiation (LTP) at these synapses are more pronounced in slices from HAB animals. Based on previous findings, we also examined whether intranasal delivery of neuropeptide S (NPS), which increasingly emerges as a potential novel treatment option for anxiety symptoms occurring in a variety of diseases like anxiety disorders, posttraumatic stress disorder, and major depression, impacts on the high-anxiety electrophysiological endophenotype in HAB mice. Strikingly, we detected enhanced basal neurotransmission and reduced PPF and LTP in slices from NPS-treated HAB animals. Collectively, our study uncovers a multifaceted high-anxiety neurophysiological endophenotype in the murine ventral hippocampus and provides the first evidence that an intranasally applied neuropeptide can shift such an endophenotype in an anxiety-regulating brain structure towards a “normal”-anxiety one.