Effects of ovariectomy and calcium deficiency on learning and memory of eight-arm radial maze in middle-aged female rats

There is increasing evidence that estrogen and calcium ion are involved in learning and memory. In the present study, to examine the effect of estrogen deficiency and low-calcium diet on learning and memory, middle-aged female Wistar rats (50 weeks old) were fed either a low-calcium (0.02% Ca) or a normal-calcium (1.25% Ca) diet throughout the experiment. Rats were ovariectomized (OVX) or sham-operated (Sham). These animals were divided into four groups: 1) Sham group with normal-calcium diet [Sham-normal Ca group], 2) OVX group with normal-calcium diet [OVX-low Ca group], 3) Sham group with low-calcium diet [Sham-low Ca group], 4) OVX group with low-calcium diet [OVX-low Ca group]. Seventy-seven days after the OVX or Sham operation, the learning and memory abilities in the female rats were examined by using a radial maze task according to the method of Olton and Samuelson (regular trials) and using a delay-interposed task following regular trials. During regular trials and delay-interposed tasks, the OVX-low Ca group was inferior to all the other groups in accuracy of choice behavior. Both Sham-normal Ca and Sham-low Ca groups showed more accurate choices than the OVX-low Ca group, but were less accurate than the Sham-normal Ca group. In addition, there was no significant difference in locomotor activity between any of the groups. These results suggest that OVX or low-calcium diet may impair learning and memory, and that the combination of these factors impaired more markedly when the rats were tested in the eight-arm radial maze. These results may also imply the possibility that a woman in menopause or post-menopause suffers impairment of learning and/or memory when intakes low-calcium diet.