The novel neuropeptide phoenixin is highly co-expressed with nesfatin-1 in the rat hypothalamus, an immunohistochemical study

• Phoenixin and nesfatin-1 have similar patterns of distribution throughout the rat hypothalamus.
• Phoenixin-immunoreactive cells are present in the arcuate nucleus, paraventricular nucleus, ventromedial and lateral hypothalamus.
• In the rat hypothalamus 70–86% of phoenixin-immunoreactive cells colocalize with nesfatin-1.

The hypothalamus regulates a number of autonomic functions essential for homeostasis; therefore, investigations concerning hypothalamic neuropeptides and their functions and distribution are of great importance in contemporary neuroscience. Recently, novel regulatory factors expressed in the hypothalamus have been discovered, of which nesfatin-1 and phoenixin (PNX), show intriguing similarities in their brain distributions.There are currently few studies characterizing PNX expression, so it is imperative to accurately trace its localization, with particular attention to the hypothalamic nuclei and nesfatin-1 co-expression. Using fluorescence and classical immunohistochemical stainings on adult rat brain, we visualized the potential co-expression of nesfatin-1 and PNX immunoreactive cells.We have demonstrated a distinct PNX-immunoreactivity in 21–32% of cells in the arcuate nucleus, paraventricular nucleus, ventromedial and lateral hypothalamus. Nesfatin-1 expression reached 45–68% of all neurons in the same sites, while co-expression was strikingly seen in the vast majority (70–86%) of PNX-immunoreactive neurons in the rat hypothalamic nuclei.Our results demonstrate for the first time, a wide distribution of PNX in the hypothalamus which could implicate a potential functional relationship with nesfatin-1, possibly in the regulation of the hypothalamic–pituitary–gonadal axis or other autonomic functions, which require further study.