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Show 8 HPA axis triggers a series of behavioral and physiological changes that improve an individual's chance of survival, such as increased cognition, awareness, analgesia, respiratory and heart-beating rate, along with inhibition of general behaviors including feeding and reproduction (Smith and Vale, 2006). The HPA axis is highly modulated, for example, by a glucocorticoid negative feedback and CRH-binding protein (CRHBP) as CRH's inhibitor (Smith and Vale, 2006). In fish, this axis is called hypothalamic-pituitaryinterrenal (HPI) axis because of anatomical differences between mammalian adrenal gland and fish interrenal gland (Löhr and Hammerschmidt, 2011). Despite these differences, the development and function of the HPA axis in mammals and the HPI axis in fish are well conserved (Löhr and Hammerschmidt, 2011). Specifically for zebrafish, all components of the HPI axis are expressed by 2 dpf, but the response to stressors does not occur before 4 dpf (Löhr and Hammerschmidt, 2011). 1.3.2 Embryonic neurogenesis in the hypothalamus 1.3.2.1 Mouse Mouse hypothalamic embryonic neurogenesis happens between embryonic day 10 (E10) and E16 with a typical "outside-in" pattern: earlier-born neurons are located more laterally than later-born neurons (Shimada and Nakamura, 1973). However, this typical pattern does not apply to all the hypothalamic neuroendocrine cells (Markakis, 2002; Markakis and Swanson, 1997). Most hypothalamic neuropeptides involved in behavioral circuitry in the adult are already made before E16, such as the proopiomelanocortin (POMC) and neuropeptide Y (NPY) (Padilla et al., 2010). Whereas adult POMC and NPY neurons display antagonistic functions in food intake, embryonic POMC and NPY neurons |
