Neuroanatomical and functional characterization of CRF neurons of the amygdala using a novel transgenic mouse model

Abstract

The corticotrophin releasing factor (CRF)-producing neurons of the amygdala have been implicated in behavioral and physiological responses associated with fear, anxiety, stress, food intake and reward. To overcome the difficulties in identifying CRF neurons within the amygdala, a novel transgenic mouse line, in which the humanized Renilla reniformis green fluorescent protein (hrGFP) is under the control of the CRF promoter (CRF-hrGFP mice), was developed. First, the CRF-hrGFP mouse model was validated and the localization of CRF neurons within the amygdala was systematically mapped. Amygdalar hrGFP-expressing neurons were located primarily in the interstitial nucleus of the posterior limb of the anterior commissure, but also present in the central amygdala. Secondly, the marker of neuronal activation c-Fos was used to explore the response of amygdalar CRF neurons in CRF-hrGFP mice under different experimental paradigms. C-Fos induction was observed in CRF neurons of CRF-hrGFP mice exposed to an acute social defeat stress event, a fasting/refeeding paradigm or LPS administration. In contrast, no c-Fos induction was detected in CRF neurons of CRF-hrGFP mice exposed to restraint stress, forced swimming test, 48 h fasting, acute high fat diet (HFD) consumption, intermittent HFD consumption, ad libitum HFD consumption, HFD withdrawal, conditioned HFD aversion, ghrelin administration or melanocortin 4 receptor agonist administration. Thus, this study fully characterizes the distribution of amygdala CRF neurons in mice and suggests that they are involved in some, but not all, stress or food intake-related behaviors recruiting the amygdala.

Contribution of amygdala CRF neurons to chronic pain

“…The viral expression was almost completely limited to the CeAmy with only a few scattered cells in the medial amygdala. This expression pattern matches the previously described pattern of CRF immunoreactivity in rats [43, 44] and mice [45]. We also performed antibody labeling.…”

Ghrelin activates hypophysiotropic corticotropin-releasing factor neurons independently of the arcuate nucleus

“…However, such behaviors are likely mediated by non-PVN CRF systems since the vast majority of PVN CRF neurons are hypophysiotropic (Wamsteeker Cusulin et al, 2013). In line with this possibility, it has been shown that some stress-related fear-modulating effects of ghrelin do not involve the HPA axis activity but rather the amygdala (Meyer et al, 2014), where CRF neurons are also present (De Francesco et al, 2015). Thus, future studies are required to understand the interplay between the neuronal circuits mediating the effects of ghrelin on stress-related behavioral and neuroendocrine responses.…”

Activation of corticotropin releasing factor-containing neurons in the rat central amygdala and bed nucleus of the stria terminalis following exposure to two different anxiogenic stressors

“…First, exposure to both predator stress and EPM induced neuronal activation in the BNST, but not the central amygdala, and similar levels of neuronal activation were seen in both the high and low anxiety groups in the BNST after EPM exposure. CRF-positive neurons in the CEA project to regions such as the periaqueductal gray [18, 19] and have recently been demonstrated to be activated following acute social defeat stress [24]. Dual-labeled immunohistochemistry showed that rats which were exposed to butyric acid, ferret odor, or exposure to the EPM displayed no change in co-localization of CRF with c-Fos in any subdivision of the CEA compared to controls.…”

“…However, recent studies have demonstrated that the central amygdala does mediate unconditioned anxiety to the EPM [45]. In addition, CRF-containing neurons of the central amygdala displayed increased co-localization with c-Fos in a number of acute behavior paradigms including acute social defeat stress, a fasting/feeding paradigm, and lipopolysaccharide administration [24]. Furthermore, a previous study determined that the CEA mediates unconditioned anxiety in the EPM test through enkephalin-dependent mechanisms [46] which supported our own previous studies which demonstrated a role of opioids and the μ-opioid receptor in the CEA in mediating anxiety-related behaviors and the actions of anxiolytics in the EPM and defensive burying task [25, 47–49].…”

“…We have demonstrated that the pattern of activation of phenotypically-distinct neurons in the central amygdala is different following exposure to noxious odor, predator odor, or the elevated plus maze [1, 2]. A recent study by De Francesco et al [24] demonstrated increased co-localization of the immediate early gene c-Fos in CRF neurons of the central amygdala following acute social defeat stress. However, no studies to date have directly compared the activation of CRF-containing neurons in the central amygdala and BNST following predator odor and EPM exposure.…”