PRL and hyperprolactinemia: We can consider that the dose of prolactin adopted was high, since the serological level of prolactin was around 6.5 ng/mL in the female gerbil in the pre-oestrus phase and 3.7 ng/mL in the male gerbil, according to our measurements; the pathological condition of hyperprolactinemia is defined as circulating PRL levels above the normal range, occurring in conditions other than pregnancy and lactation, when physiological hyperprolactinemia occurs.