Distribution and Neurochemical Characterization of Dorsal Root Ganglia (DRG) Neurons Containing Phoenixin (PNX) and Supplying the Porcine Uterine Cervix

One of most important parts of the female genital tract is the uterine cervix, both from the anatomical as well as physiological points of view. As there is currently a lack of detailed information on the presence, distribution pattern(s), and the chemical coding of phoenixin (PNX)-containing dorsal root ganglia (DRG) neurons supplying the porcine uterine cervix, this study, using combined retrograde tracing and double-immunofluorescence techniques, was aimed at analyzing (i) the distribution pattern of uterine cervix-supplying sensory neurons (UC-SNs) at the particular spinal cord levels, (ii) their intraganglionic distribution, and (iii) the patterns of PNX co-expression with other biologically active substances. UC-SNs were identified by the presence of deposits of Fast Blue (FB), in DRG of thoracic (Th10-Th15), lumbar (L1-L5) and sacral (S2-S4) spinal cord segments. FB⁺/PNX⁺ neurons constitute approximately 33% of all UC-SNs, 73% at the L, and 27% at the S neuromeres. These neurons were mainly small sized (52%), with a slightly smaller population of medium-sized cells (40%), while large-diameter cells made up the least numerous population (8%). The vast majority of FB⁺/PNX⁺ neurons simultaneously contained calcitonin gene-related peptide (CGRP; 80.9%) or substance P (SP; 77.9%); one-third of them showed immunoreactivity toward neuronal nitric oxide synthase (nNOS; 34%), while PNX⁺ UC-SNs containing pituitary adenylate cyclase-activating polypeptide (PACAP), galanin (GAL), calretinin (CRT), or somatostatin (SOM) formed significantly smaller populations (21.4%, 7.4%, 3.1%, and 0.7%, respectively). The results of the present study demonstrate the presence of PNX in DRG UC-SNs, and its co-occurrence with numerous neurotransmitters suggesting a putative role for this neuropeptide in the transmission of various types of sensory information and possible effects on the functioning of this organ in the body.