The animals' reactivity and the levels of experimental anxiety during
pregnancy and lactation in female rats were studied using the burying
behavior test. The three main parameters analyzed in this test were: t
he cumulative burying behavior, the burying behavior latency, and the
number of shocks necessary for displaying the behavior. The burying be
havior was studied at the 7th, 14th, and 21st days of pregnancy and la
ctation. An additional group tested 12 h after parturition was also in
cluded. Simultaneously, in all animals, the ambulatory behavior was ev
aluated. All results were compared with those obtained in a control gr
oup of ovariectomized females. At the end of pregnancy a clear increas
e in burying behavior latency accompanied by a decrease in cumulative
burying behavior was observed. Similarly, a clear reduction in burying
behavior immediately after parturition was found. The number of shock
s necessary for displaying the burying behavior were not modified alon
g pregnancy and lactation with the exception of a clear decrease for t
he 7th lactation day. Changes in locomotor activity were observed at p
regnancy, but not along lactation. These changes do not account for th
e reduction in burying behavior observed at the 14th gestation day. Da
ta related to the reduction in burying behavior observed during gestat
ion are discussed on the possible participation of progestins, while t
hose found during lactation are discussed on the bases of the variatio
ns in serotonin and endorphins that normally occur during this period.