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The Journal of Neuroscience, October 25, 2006, 26(43):11034-11040; doi:10.1523/JNEUROSCI.3189-06.2006

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Behavioral/Systems/Cognitive
Central Administration of a Cytochrome P450-7B Product 7-Hydroxypregnenolone Improves Spatial Memory Retention in Cognitively Impaired Aged Rats

Joyce L. W. Yau, June Noble, Mags Graham, and Jonathan R. Seckl

Endocrinology Unit, The Queen's Medical Research Institute, University of Edinburgh, Edinburgh EH16 4TJ, United Kingdom

Correspondence should be addressed to Dr. Joyce L. W. Yau, Endocrinology Unit, The Queen's Medical Research Institute, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, UK. Email: joyce.yau{at}ed.ac.uk

Pregnenolone (PREG) and dehydroepiandrosterone (DHEA) have been reported to improve memory in aged rodents. In brain, these neurosteroids are transformed predominantly into 7-hydroxylated metabolites by the cytochrome P450-7B1 (CYP7B). The biological role of steroid B-ring hydroxylation is unclear. It has been proposed to generate bioactive derivatives that enhance cognition, immune, and other physiological processes. In support, 7-hydroxylated DHEA increases the immune response in mice with greater potency than the parent steroid. Whether the memory-enhancing effects of PREG in rats is mediated via its 7-hydroxylated metabolite 7-hydroxyPREG is not known. We investigated this by treating memory-impaired aged rats (identified by their spatial memory performances in the Morris water maze task compared with young controls) with 7-hydroxyPREG or PREG administered intracerebroventricularly using osmotic minipumps and then tested the rats during week 2 of steroid treatment in the eight-arm radial-arm version of the water maze (RAWM) that allows repeated assessment of learning. CYP7B bioactivity in hippocampal tissue (percentage conversion of [¹⁴C]DHEA to [¹⁴C]7-hydroxyDHEA) was decreased selectively in memory-impaired aged rats compared with both young and memory-intact aged rats. 7-hydroxyPREG (100 ng/h) but not PREG (100 ng/h) administration to memory-impaired aged rats for 11 d enhanced spatial memory retention (after a 30 min delay between an exposure trial 1 and test trial 2) in the RAWM. These data provide evidence for a biologically active enzyme product 7-hydroxyPREG and suggests that reduced CYP7B function in the hippocampus of memory-impaired aged rats may, in part, be overcome by administration of 7-hydroxyPREG.

Key words: neurosteroids; hippocampus; water maze; DHEA; pregnenolone; aging

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Received Dec. 8, 2005; revised Sept. 16, 2006; accepted Sept. 18, 2006.

Correspondence should be addressed to Dr. Joyce L. W. Yau, Endocrinology Unit, The Queen's Medical Research Institute, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, UK. Email: joyce.yau{at}ed.ac.uk

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