Recent studies have shown different relationships between hormones and
personality in humans, including a relationship between prolactin lev
els and impulsivity. The aim of the present work was to study the rela
tionships between basal levels of prolactin and some measures of activ
ity and emotional reactivity in rats. One of the most consistent resul
ts showed a negative correlation between basal prolactin levels and ac
tivity. This finding is in line with the serotonergic theories of impu
lsive behavior and with the effects of dopamine upon activity.