Abstract
The influence of NGF in male reproduction in some animal species and humans has already been assessed. Many of these effects are mediated by the distribution and abundance of tropomyosin receptor kinase A (TrKA) and p75 neurotrophin (p75NTR) receptors on sperm cells. The aim of this research was to investigate the role of NGF and its receptors, TrKA and p75NTR, in rabbit sperm outcomes during in vitro storage. Major semen traits (kinetic parameters, apoptotic, necrotic and live sperm) were recorded in rabbit semen samples from 0 to 12 h of storage (every 4 h). Three experimental hypotheses were formulated: i) sperm storage changes NGF receptor abundance in rabbit sperm; ii) TrKA and p75NTR differently modulate NGF signalling (assessed by the neutralisation of receptors); iii) NGF-receptor interactions show different responses during storage (evaluated by the addition of exogenous NGF). The results demonstrate that: (i) the receptor number changed in a time-dependent manner with a significant increase in p75NTR after 8-12 h of storage; ii) the neutralisation of NGF receptors largely affected VCL, apoptotic, necrotic and live cells during sperm storage, i.e. blockade of TrKA significantly increased speed, capacitation, necrosis and apoptosis, whereas blockade of p75NTR improved motility and live cells; iii) the addition of exogenous human NGF (100 ng/mL) at different time points of storage (0, 4, 8 h) differently influenced sperm traits i.e. NGF addition at time 0 positively affected all the pro-vital traits (kinetic, live cells) whereas, after 4-8 h, the effect of NGF was null or negative. In conclusion, NGF affects kinetic and other physiological traits (capacitation, apoptosis and necrosis) of rabbit sperm in a time-dependent manner. Most of these modifications are modulated by the receptors involved (TrKA or p75NTR), which changed considerably during sperm storage (increase of p75NTR).