SPATIAL-LEARNING AND HIPPOCAMPAL VOLUME IN MALE DEER MICE - RELATIONSTO AGE, TESTOSTERONE AND ADRENAL-GLAND WEIGHT

Spatial learning and various physiological parameters were examined in old (57 month), middle aged (38 month), adult (18 month) and young (3 -3.5 month) male deer mice (Peromyscus maniculatus). Performance durin g acquisition of a water maze task was not significantly reduced for m iddle aged and adult mice relative to young reproductively active (bre eding) mice. Performance was deteriorated in old mice relative to youn g breeding mice on block 4 of training. Retention of this spatial task , however, was reduced in all three older groups relative to young bre eding mice. Corrected hippocampal volume (corrected for brain weight) was reduced only in old mice relative to young breeding mice although absolute volumes of hippocampus were lower in all groups relative to y oung breeding mice. Old mice also were shown to have lower levels of p lasma testosterone and lighter brains relative to young breeding mice. Spatial retention was not deficient in old, middle aged and adult mic e relative to a group of young reproductively quiescent male (non-bree ding) mice. Young breeding mice displayed better spatial performance a nd had significantly higher plasma testosterone levels, corrected hipp ocampal volume and brain weight relative to young non-breeding mice. T hese results indicate that retention of a spatial task is more sensiti ve to the age of male deer mice than acquisition of the task. Hippocam pal volume, although a gross morphological feature, appears to be sens itive to the effects of ageing in male deer mice. Plasma testosterone levels do not appear to be a crucial factor underlying age-related def icits in retention of a spatial task. (C) 1998 IBRO. Published by Else vier Science Ltd.