Tiemo Friedrich

Due to phoenixin’s role in restraint stress and glucocorticoid stress, as well as its recently shown effects on the inflammasome, we aimed to investigate the effects of lipopolysaccharide (LPS)-induced inflammatory stress on the activity of brain nuclei-expressing phoenixin. Male Sprague Dawley rats (n = 6/group) were intraperitoneally injected with either LPS or control (saline). Brains were processed for c-Fos and phoenixin immunohistochemistry and the resulting slides were evaluated using ImageJ software. c-Fos was counted and phoenixin was evaluated using densitometry. LPS stress significantly increased c-Fos expression in the central amygdaloid nucleus (CeM, 7.2-fold), supraoptic nucleus (SON, 34.8 ± 17.3 vs. 0.0 ± 0.0), arcuate nucleus (Arc, 4.9-fold), raphe pallidus (RPa, 5.1-fold), bed nucleus of the stria terminalis (BSt, 5.9-fold), dorsal motor nucleus of the vagus nerve (DMN, 89-fold), and medial part of the nucleus of the solitary tract (mNTS, 121-fold) compared to the control-injected group (p < 0.05). Phoenixin expression also significantly increased in the CeM (1.2-fold), SON (1.5-fold), RPa (1.3-fold), DMN (1.3-fold), and mNTS (1.9-fold, p < 0.05), leading to a positive correlation between c-Fos and phoenixin in the RPa, BSt, and mNTS (p < 0.05). In conclusion, LPS stress induces a significant increase in activity in phoenixin immunoreactive brain nuclei that is distinctively different from restraint stress.

The novel peptide phoenixin was shown to be involved in several physiological processes ranging from reproduction to food intake. Interest in this protein has steadily increased over the last few years and its known implications have become much broader, playing a role in glucose homeostasis, anxiety, nociception, and pruritus. Phoenixin is expressed in a multitude of organs such as the small intestine, pancreas, and in the hypothalamus, as well as several other brain nuclei influencing numerous physiological functions. Its highly conserved amino-acid sequence amongst species leads to the assumption, that phoenixin might be involved in essential physiological functions. Its co-expression and opposing functionality to the extensively studied peptide nesfatin-1 has given rise to the idea of a possible counterbalancing role. Several recent publications focused on phoenixin’s role in stress reactions, namely restraint stress and lipopolysaccharide-induced inflammation response, in which also nesfatin-1 is known to be altered. This review provides an overview on the phoenixins and nesfatin-1 properties and putative effects, and especially highlights the recent developments on their role and interaction in the response to response.

Nesfatin-1 is a well-established anorexigenic peptide. Recent studies indicated an association between nesfatin-1 and anxiety/depression-like behavior. However, it is unclear whether this effect is retained in obesity. The aim was to investigate the effect of nesfatin-1_30-59—the active core of nesfatin-1—on anxiety and depression-like behavior in normal weight (NW) and diet-induced (DIO) obese rats. Male rats were intracerebroventricularly (ICV) cannulated and received nesfatin-1_30-59 (0.1, 0.3, or 0.9 nmol/rat) or vehicle 30 min before testing. Nesfatin-1_30-59 at a dose of 0.3 nmol reduced sucrose consumption in the sucrose preference test in NW rats compared to vehicle (–33%, p < 0.05), indicating depression-like/anhedonic behavior. This dose was used for all following experiments. Nesfatin-1_30-59 also reduced cookie intake during the novelty-induced hypophagia test (−62%, p < 0.05). Moreover, nesfatin-1_30-59 reduced the number of entries into the center zone in the open field test (−45%, p < 0.01) and the visits of open arms in the elevated zero maze test (−39%, p < 0.01) in NW rats indicating anxiety. Interestingly, DIO rats showed no behavioral alterations after the injection of nesfatin-1_30-59 (p > 0.05). These results indicate an implication of nesfatin-1_30-59 in the mediation of anxiety and depression-like behavior/anhedonia under normal weight conditions, while in DIO rats, a desensitization might occur.