BACKGROUND AND AIMS: Phoenixin (PNX) is one of the last revealed peptide in the rat hypothalamus. PNX so called a satiety molecule, takes part in such processes as the regulation of energy metabolism and also in reproduction. The aim of the study was to examine PNX immunoreactive structures (PNX-ir) and their distribution in the neuroendocrine part of the pig (Sus scrofa domestica) hypothalamus, because PNX was examined only in rodent brains. METHODS: Hypothalamic tissue was prepared by immunohistochemical techniques (immunofluorescence and DAB methods) with using Phoenixin-14 amide (H-079-01; Phoenix). RESULTS: PNX was immunodetected in neurons of the paraventricular (PVN) and supraoptic (SON) nuclei and also in neighbouring areas. PNX-ir cells had oval or multipolar perikarya with 1 to 4 visible primary dendrites. PNX-ir cells in the PVN were situated loosely at dorsal and ventral parts close to the third ventricle, whereas between these parts PNX-ir cells were numbered and clustered. PNX-ir structures with morphology like dendrites and also single fibres covered with varicosities resembled axons were observed in the neuropil of the PVN. PNX-ir cells in the SON were clustered on the medial side of the SON from which narrow band of the PNX-ir perikarya was directed to the lateral side, along the optic tract. PNX-ir perikarya in the SON have similar shapes as in the PVN, but some of them possess short protoplasmic irregular processes, what gives them irregular shapes. In the SON there was not observed immunoreactive structures in neuropil, as above described in the PVN. CONCLUSIONS: This is the first study which demonstrates the presence of PNX in axons. These results suggest that PNX in the PVN and SON may differ in signaling mechanism or acting as molecule-regulated neuroendocrine factor, but multidirectional functions of PNX complicate the understanding of the role played by this neuropeptide and further studies are needed.
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