The Endogenous Neuregulin In The Bed Nucleus Of The Stria Terminalis Regulates The Anxiety-like Behavior

Among these, the generalized anxiety disorder (GAD) is the most common one. In the worldwide, the life time prevalence of the GAD in adults is estimated at 4.1%-6.6%. However, its pathogenesis is yet unknown until now.According to the animal experiments and imaging studies, scientists come up with the basic neural pathways of the anxiety and fears moods. Amygdala is the critical neural structures to regulate alertness and fear response. Moreover, the hippocampus is related with learning and memory and information processing. Hippocampal dysfunction may lead to over-evaluation of the potential threat information, which can lead to pathological anxiety. Animal experiments found that the damage of the ventral prefrontal will affect the normal acquisition of fear dissipated. Therefore we speculate that the dysfunction of the ventral prefrontal cortex may affect the innocuous stimuli and the adjustment of past experience of threat-related stimulus, thereby it may cause some pathological anxiety.The study on the anxiety-related neurotransmitters demonstrates that the CNS noradrenalin-ergic pathway, dopamin-ergic pathway, serotonin-ergic pathway and gamma-aminobutyric acid (GABA) may be related to the pathogenesis of the anxiety disorders. Noradrenalin-ergic system plays the role of aposdatism in the locus coeruleus, and can cause vigilance to dangerous and expectation. The dopamin-ergic pathway in the cerebral cortex is related to emotional behavior and emotional expression. Serotoni-ergic pathway can inhibit anxiety-related behavior in the dorsal raphe nucleus. The action of CNS 5-HT has an important role in maintaining vigilance and control of anxiety. GAB A is the main inhibitory neurotransmitter. These types of neurotransmitters interact between different parts of the brain. The neurotransmitters integrate at the subcellular level by means of cAMP and calcium ions, and it can lead to different functional variations in various parts of the brain and body. Thereby, various clinical manifestations of anxiety appear. Accordingly, we believe that the GABA-energy system plays an important role in the pathogenesis of the GAD.Neuregulin (NRG) is a trophic factor that contains an epidermal growth factor (EGF)-like domain signals by stimulating ErbB receptor tyrosine kinases. It belongs to a family of growth factors that are encoded by four individual genes (NRGl-4), of which NRG1 is the best characterized. Each of the protein types has a distinct amino terminal region. The EGF-like domain is located in the membrane-proximal region of the extracellular domain that is necessary and sufficient for activation of the ErbB receptor tyrosine kinases. The different NRG1 isoforms have different functions. NRG1 acts by stimulating a family of single-transmembrane receptor tyrosine kinases called ErbB proteins. ErbB proteins have homology with the EGF receptor. ErbB4 is the only autonomous NRGl-specific ErbB that can both interact with the ligand and become activated by it as a tyrosine kinase. EGFR does not bind to NRG1, but it can form heterodimers with ErbB4. Among the ErbB proteins, ErbB4 is the best-characterized for its function in the CNS. Unlike ErbB4-mutant mice, mice that carried mutations in ErbB2 and ErbB3 did not produce behaviours that were characteristic of mood disorders. In canonical forward signalling, NRG1-induced ErbB dimerization activates the ErbB kinase domain, resulting in auto-and transphosphorylation of the intracellular domains. The Raf-MEK-ERK and PI3K-Akt-S6K pathways are frequently activated by the NRG1-induced stimulation of ErbB receptor homo-or heterodimers. NRG1 signalling is mediated by heterodimers of ErbB2-ErbB3, ErbB2-ErbB4 and ErbB3-ErbB4 and by the homodimer ErbB4-ErbB4. NRG1 and ErbB proteins are expressed in regions of both the developing and the adult brain which undergo proliferation or neurogenesis. NRG1 increases the proliferation of neuronal progenitors from embryonic neural stem cells. The ancient document has shown that ErbB4 receptors exist in the presynaptic terminals of the GABA-ergic neurons. NRG1 can enhance the activity-dependent GABA release by activating presynaptic ErbB4 receptorsThe bed nucleus of the stria terminalis (BNST) is a heterogeneous nucleus defined as part of the extended amygdala. Anatomically, the extended amygdala arises from both the central and the medial nuclei, with the central nucleus giving rise to the lateral BNST and the medial nucleus projecting to the medial BNST. Furthermore, the BNST has extensive connections with the different nuclei of the amygdala, the hypothalamus and other limbic structures, suggesting a role for this structure in a variety of cognitive and emotional behaviors. The function of the BNST is regulated by an extensive network of internal GABA-ergic neurons. Several studies have shown that the BNST is involved in the generation of anxiety-like responses. In addition, BNST appears to play a critical role in unconditioned responses as compared with the central nucleus of the amygdala which is involved in conditioned fear behaviors. Thus an intact GABAergic response within the BNST appears to be critical for normal regulation of anxiety behaviors and, based on the findings reviewed above, may not induce panic-like states.According to the above information, we embed a stainless steel cannula into the brain of mice using the stereotactic technique, and then injected related drugs precisely to the BNST. With this method, we can study whether the changes of the GABA-ergic pathway can influence the GAD.The mice are anaesthetized with 10% chloral hydrate and fixed on the stereotaxic injection apparatus. Then, we embed a stainless steel cannula with a plastic hose to the position of BNST (bregma 1.8mm, sagittal 0.4mm, ventral 4.6mm). The cannula is fixed on the skull with the reinforced glass ionomer cement. After one week for recovery, we insert the microsyringe into the steel cannula and inject the control drugs, the GABA receptor antagonist bicuculine, the ErbB4 specific inhibitor ecto-ErbB4, the boiled ecto-ErbB4 and NRG1 into the BNST, then some related animal behavior experiments are carried out to test the anxiety condition. The results showed that ecto-ErbB4 can significantly lead to the occurrence of the anxiety-like behavior in the elevated plus maze test, open field test, the novelty suppressed feeding test and the social interaction test. These results suggest that blocking the NRG1-ErbB4 pathway can influence GABA release in the BNST, and then lead to the anxiety-like behavior. So we consider that the BNST may play an important role in the pathogenesis of the GAD.