SPATIAL-LEARNING IN DEER MICE - SEX-DIFFERENCES AND THE EFFECTS OF ENDOGENOUS OPIOIDS AND 60 HZ MAGNETIC-FIELDS

We examined the effects of brief exposure to weak 60 Hz extremely low frequency (ELF) magnetic fields and opioid systems on spatial behavior and learning in reproductive adult male and female deer mice, Peromys cus maniculatus. Sex differences were evident in spatial performance, with male deer mice displaying significantly better performance than f emale mice in the Morris water maze, whereby animals had to acquire an d retain the location of a submerged hidden platform. Brief (maximum 5 min) exposure to weak (100 mu T) 60 Hz magnetic fields during task ac quisition significantly improved female performance, eliminating the s ex differences in acquisition. The opiate antagonist, naltrexone, also improved female acquisition, though significantly less than the magne tic fields. These facilitatory effects involved alterations of ''non-s patial'' (task familiarization and reduction of related anxiety/aversi ve related behaviors) and possibly ''spatial'' aspects of the task. En hancement of enkephalin activity with the enkephalinase inhibitor, SCH 34826, significantly reduced task performance by male deer mice. Both naltrexone and the 60 Hz magnetic fields attenuated the enkephalin me diated reductions of spatial performance. These findings indicate that brief exposure to 60 Hz magnetic fields can enhance water maze task a cquisition by deer mice and suggest that these facilitatory effects on spatial performance involve alterations in opioid activity.