Sex differences in the dynamics of cue utilization and exploratory behavior

The purpose of the present study was to investigate the effects of sex and estrous cycle on exploratory behavior, as well as the degree to which reliance on environmental cues changes with training. Fischer 344 rats were placed three times in an open field box that contained three objects (two identical bottles and a cylinder). During the initial exposure to the environment all females showed higher activity levels and explored a larger region of the environment compared to males. However, upon subsequent exposure to the same environment, these sex differences disappeared. During the third and final session, the locations of the bottle and the cylinder were switched. The estrous females and to a lesser degree male rats, responded to the relocation of objects with a renewal of exploration and activity; proestrous females did not show this response. The rats were then trained on a four-arm radial maze reference memory task. The correct arm could be located by its relation to extra-room cues, a large distal white panel, or to local inserts on the maze. Once the animals consistently chose the goal arm, a probe session was conducted to determine which cues the animals were using to solve the task. During the probe trial both the white panel and the local inserts were rotated 90 degrees clockwise and counterclockwise respectively and the animals' choice of arm recorded. During the first probe, females tended to rely on all three types of cues in solving the task. With additional training there was a shift towards predominantly using the distal visual information. In contrast, male rats did not show this shift; by the first probe session the males were predominantly using the distal visual information to solve the task. The findings indicate: (1) sex differences in the initial use of environmental cues; (2) the usage of environmental information is dynamic and changes with additional exposures to the environment. The results are related to previous findings on sex differences and estrous cycle effects, with an emphasis on the implications for hippocampal processing.