Seasonal variation of NGF in seminal plasma and expression of NGF and its cognate receptors NTRK1 and p75NTR in the sex organs of rams

•NGF system presence and gene expression were studied in the ram genital organs.•NGF was measured in seminal plasma to correlate it with ram reproductive seasonality.•NGF, NTRK1 and p75NTR mRNA and protein were detected in all male organs examined.•All gene transcripts were higher in the seminal vesicles than in other organs.•The concentration of the NGF seminal plasma was greater from January to May. Nerve growth factor (NGF) has long been known as the main ovulation-inducing factor in induced ovulation species, however, recent studies suggested the NGF role also in those with spontaneous ovulation. The first aim of this study was to evaluate the presence and gene expression of NGF and its cognate receptors, high-affinity neurotrophic tyrosine kinase 1 receptor (NTRK1) and low-affinity p75 nerve growth factor receptor (p75NTR), in the ram genital tract. Moreover, the annual trend of NGF seminal plasma values was investigated to evaluate the possible relationship between the NGF production variations and the ram reproductive seasonality. The presence and expression of the NGF/receptors system was evaluated in the testis, epididymis, vas deferens ampullae, seminal vesicles, prostate, and bulbourethral glands through immunohistochemistry and real-time PCR (qPCR), respectively. Genital tract samples were collected from 5 adult rams, regularly slaughtered at a local abattoir. Semen was collected during the whole year weekly, from 5 different adult rams, reared in a breeding facility, with an artificial vagina. NGF seminal plasma values were assessed through the ELISA method. NGF, NTRK1 and p75NTR immunoreactivity was detected in all male organs examined. NGF-positive immunostaining was observed in the spermatozoa of the germinal epithelium, in the epididymis and the cells of the secretory epithelium of annexed glands, NTRK1 receptor showed a localization pattern like that of NGF, whereas p75NTR immunopositivity was localized in the nerve fibers and ganglia. NGF gene transcript was highest (p < 0.01) in the seminal vesicles and lowest (p < 0.01) in the testis than in the other tissues. NTRK1 gene transcript was highest (p < 0.01) in the seminal vesicles and lowest (p < 0.05) in all the other tissues examined. Gene expression of p75NTR was highest (p < 0.01) in the seminal vesicles and lowest (p < 0.01) in the testis and bulbourethral glands. NGF seminal plasma concentration was greater from January to May (p < 0.01) than in the other months. This study highligh