Sa. Farr et al., EFFECT OF OVARIAN-STEROIDS ON FOOTSHOCK AVOIDANCE-LEARNING AND RETENTION IN FEMALE MICE, Physiology & behavior, 58(4), 1995, pp. 715-723
Mice were trained to avoid footshock in a T-maze, with retention teste
d one week later. Adult male CD-1 mice made their first avoidance duri
ng acquisition after fewer trials than random cycling females and with
less variability. Female mice in diestrus, when plasma levels of prog
esterone are low, learned to avoid footshock faster than females in es
trus. Ovariectomized (OVX) mice learned in fewer trials than intact ra
ndom cycling mice. Similar differences, though of a smaller magnitude,
were found on the retention tests (i.e. males had better retention th
an females, mice in diestrus showed better retention 8 days later when
in the same part of the estrous cycle than those in estrus, and OVX m
ice had better retention than cycling females). OVX mice with estrogen
implants learned faster than those with progesterone implants or prog
esterone plus estrogen implants. Hormonal status did not affect sensit
ivity to acoustic or footshock stimuli as measured by a startle reflex
, nor did it affect activity. Pretraining administration of amphetamin
e, picrotoxin and strychnine attenuated the impairing effect of proges
terone on acquisition. The possibility that progesterone may impair le
arning and to some extent, retention by facilitating the GABAergic act
ivity and thereby reducing arousal level is discussed.