Estrogen and progesterone improve scopolamine-induced impairment of spatial memory

This study was conducted to investigate the effects of estrogen and progesterone on spatial memory in ovariectomized female rats, specifically, on memory impaired by the cholinergic antagonist scopolamine. Forty-one female rats were divided into five groups: ovariectomized (OVX), estrogen-treated after ovariectomy (OE), progesterone-treated after ovariectomy (OP), estrogen-progesterone-treated after ovariectomy (OEP), and the sham control group (Control). The animals were trained on an eight-arm radial maze with four arms baited to assess both working and reference memory performances. The OE and OEP groups showed significant improvement in the ability to perform a spatial memory task over the OVX group (P<0.05). Spatial memory in the OP group did not differ from that in the OVX group. After thirty-two trials were conducted and all rats learned the eight-radial maze task, scopolamine hydrobromide (0.2 mg/kg i.p.) was administered prior to retesting. After scopolamine injection, the OVX group showed an increased number of working memory errors, reference memory errors than the other groups (P<0.05). The OE, OEP and OP groups showed significant improvement in spatial impairment induced by scopolamine. These findings suggest progesterone alone or in combination with estrogen, improved scopolamine-induced impairment of working memory and reference memory as effectively as estrogen supplementation.