Neuropeptides in fear and anxiety

Anxiety disorders have a high socio-economic impact on our society. Whereas anxiety is defined as a sustained state of apprehension of future potential danger, fear is a phasic emergency reaction to clearly identified and imminent threat. There is growing evidence that neuropeptides have important functions in regulating fear and anxiety. We are aiming to investigate the role of neuropeptides, in particular that of neuropeptide Y (NPY) in the central extended amygdala, including the central amygdala (CEA) and the bed nucleus of the stria terminalis (BNST) and in the basolateral amygdala (BLA). NPY has there an anxiolytic action mediated by Y1 receptors. On the other hand, presynaptic Y2 receptors suppressing NPY release mediate anxiogenic actions of NPY. Our previous experiments indicate that this anxiogenic-like action is mediated by Y2 receptors expressed in the CEA and BLA and involves Y2 receptors located on terminals of projection neurons arising from the CEA. Recent experiments of our group and from others suggest that NPY may have also a role in fear conditioning and fear extinction. 1) We will investigate, whether the anxiolytic effect of Y1 agonists is integrated in the central extended amygdala. We will approach this question by injecting locally a viral vector expressing the Y1 agonist Leu31Pro 34NPY into different parts of the central extended amygdala and by subsequent behavioral testing. These experiments will be performed in wild type and NPY-KO mice that expose a highly anxious phenotype. 2) We will investigate the effect of NPY, Y1, Y2 and Y4 receptor knockout on fear conditioning and fear extinction. By local site selective injections of rAAV-NPY and rAAV-Leu31Pro 34NPY we will attempt to rescue the accelerated fear learning of NPY-KO mice observed in preliminary experiments. These experiments will provide further insight into the brain sites involved in modulation of fear by NPY. 3) We will investigate the effect of NPY knockout and the effect of fear conditioning on the expression of different neuropeptides (e.g. neurokinin B, dynorphin, enkephalin, corticotropin-releasing factor) in the central extended amygdala. 4) We will attempt to locally delete e.g. neurokinin B in the CEA where it is highly expressed and investigate a role on anxiety and on fear conditioning and extinction. 5) We will also investigate effects on depression-like behaviors under the experimental settings described above. In summary our project aims to obtain further insight into the role of neuropeptides (in particular that of NPY and neurokinin B) in the integration of fear and anxiety aiming to identify novel drug targets for anxiolytic therapy.

While anxiety disorders are the brain disorders with the highest prevalence and constitute a major burden for the society, a considerable number of affected people are still treated insufficiently. Here, we identified two neuropeptide receptors in the mammalian brain that were able to inhibit fear expression and facilitate fear extinction. Targeting these receptors with specific drugs may support cognitive behavioral therapies for human anxiety disorders. More importantly, we also demonstrate a crucial interaction between food intake and fear, two life-sustaining survival circuits. Our data identifies thus, not only two novel drug targets for treating anxiety-related disorders but also provides a framework for the development of novel therapeutic approaches by linking energy homeostasis to fear-related behavior. Neuropeptide Y (NPY) is a highly conserved neuropeptide that is specifically expressed in fear-relevant brain areas. We demonstrated that NPY Y2 and Y4 receptors are crucially involved in the processing of fear memories. In particular, the synergistic action of Y1 and Y2 receptors was a novel finding that considerably changed established concepts. We further demonstrated that NPY, by acting on Y2 receptors in the amygdala (a center of emotional processing), promotes fear extinction and generates a long-term suppression of fear, two important preconditions that could support cognitive behavioral therapies in human patients. Electrophysiological characterizations of Y2 receptor activation in the central amygdala suggests that Y2 receptors inhibit also long-range amygdala output and input neurons and may thus serve as an essential modulator of neuronal fear pathways. Interestingly, we also identified a fear extinction-promoting effect after activation of Y4 receptors. These receptors are targeted not only by NPY but also by peripherally released pancreatic polypeptide and are generally known for their involvement in feeding. Since the NPY system is controlling both, emotional-affective behavior and energy homeostasis, it appears, from an evolutionary point of view, reasonable that fear and feeding circuits are in fact mutually influencing each other to produce an adaptive behavioral response. We investigated this putative interaction of survival circuits for fear and hunger and demonstrated that short-term fasting suppresses fear and promotes the extinction of fear by inhibiting excitability in an amygdala microcircuit. Thus, modulators of appetite, hunger and food intake may as well serve as potent fear-reducing drug-targets by interacting within distinct microcircuits in the mammalian brain. These data highlight the importance of integrating peripheral, hormonal signals with survival-dedicated brain circuits to modify and adapt fear-related emotional responses.