Journal of Neuroscience, Vol 13, 2582-2590, Copyright © 1993 by Society for Neuroscience
Selective loss of hippocampal granule cells following adrenalectomy: implications for spatial memory
CD Conrad and EJ Roy
Neuroscience Program, University of Illinois, Champaign 61820.
We examined the effects of long-term adrenalectomy (ADX) on hippocampal
anatomy and behavioral learning in two spatial memory tasks. We assessed
damage throughout the hippocampus by stereological analysis of the dentate
gyrus and Ammon's horn. Rats were ADX or sham operated, and then tested in
the Morris water maze 12 weeks after surgery, followed by testing on an
eight-arm, alternating-baited radial maze at 22 weeks postsurgery. Animals
were killed 7 1/2 months after surgery. ADX rats had selective volume
reduction in the dentate gyrus with no changes in pyramidal regions CA1,
CA2, CA3, or CA4. Dentate gyrus damage in some cases occurred throughout
the entire rostrocaudal extent of the hippocampus. Analysis of
corticosterone serum levels, serum Na+/K+ ratios, and body weight gain
suggested that individual differences in dentate gyrus damage appear to be
due to incomplete adrenalectomies or remaining ectopic tissue. ADX rats
were able to learn in both the Morris water maze and eight-arm radial maze,
even when the dentate gyrus was severely damaged (80% volume reduction).
However, in the Morris water maze, the ADX rats' learning rate was
significantly slower compared to controls. There was no difference between
ADX and controls during reversal in either task. These data indicate that
damage to the dentate gyrus following long-term ADX is severe enough to
cause learning impairment in selected learning tasks. Such damage is
restricted to the dentate gyrus and can occur throughout the rostrocaudal
regions of the hippocampus.
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