Abstract
Survival in a natural environment forces an individual into constantly adapting purposive behavior. Specified interoceptive neurons monitor metabolic and physiological balance and activate dedicated brain circuits to satisfy essential needs, such as hunger, thirst, thermoregulation, fear, or anxiety. Neuropeptides are multifaceted, central components within such life‐sustaining programs. For instance, nutritional depletion results in a drop in glucose levels, release of hormones, and activation of hypothalamic and brainstem neurons. These neurons, in turn, release several neuropeptides that increase food‐seeking behavior and promote food intake. Similarly, internal and external threats activate neuronal pathways of avoidance and defensive behavior. Interestingly, specific nuclei of the hypothalamus and extended amygdala are activated by both hunger and fear. Here, we introduce the relevant neuropeptides and describe their function in feeding and emotional‐affective behaviors. We further highlight specific pathways and microcircuits, where neuropeptides may interact to identify prevailing homeostatic needs and direct respective compensatory behaviors. A specific focus will be on neuropeptide Y, since it is known for its pivotal role in metabolic and emotional pathways. We hypothesize that the orexigenic and anorexigenic properties of specific neuropeptides are related to their ability to inhibit fear and anxiety.
Highlights
Changing environmental conditions and the necessity to maintain an endogenous homeostatic balance force an individual into constantly adapting purposive behaviors.[1]
It has been long known that fear and anxiety can reduce appetite; recent evidence demonstrates that the opposite is true, that hunger can suppress fear and anxiety
An individual encounters continuous challenges and has to adapt purposive behaviors according to the most urgent needs to ensure survival. It appears that evolutionarily conserved neuropeptides are central elements controlling homeostatic balance and related emotional-affective behaviors
Summary
Changing environmental conditions and the necessity to maintain an endogenous homeostatic balance force an individual into constantly adapting purposive behaviors.[1]. The vBNST has the strongest noradrenergic inputs in the brain,[168] which often corelease NPY, and it receives dense innervation from hypothalamic, brainstem, and cortical areas, such as the insula, mPFC, and BLA It may coordinate valence surveillance, which integrates stimuli of different modalities and priorities to generate a specific purposive behavior.[165] For instance, stimulation of beta-adrenoreceptors in the ventral BNST has been shown to reduce food intake while increasing anxiety.[169] On the other hand, recent evidence demonstrates that NPY acting on vBNST Y2R reduces fear expression and promotes fear extinction.[63,64] Interestingly, the activation of vBNST Y2R was able to induce long-term suppression of conditioned fear even in the absence of extinction training. This may include CRH in CeL neurons[161] or in PVH secretagogues.[172,173]
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