The presence of endogenous opioids has been evidenced both in the male and
female reproductive tract, but less is still known on the role that they have on the reproductive
function. On the contrary lots of studies evidenced the role that calcium has on capacitation and
acrosome reaction, two important steps in the process that leads sperm cells to acquire the
ability of fertilizing the egg. In this study by means of immunostaining techniques the mu-opioid
receptor has been localized-on male cat germ cells and its presence and expression has been
studied during spermatogenesis
