EFFECT OF OVARIAN-STEROIDS ON FOOTSHOCK AVOIDANCE-LEARNING AND RETENTION IN FEMALE MICE

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.