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The major adrenal steroid dehydroepiandrosterone (DHEA) enhances memory and immune function but has no known dedicated receptor; local metabolism may govern its activity. We described a cytochrome P450 expressed in brain and other tissues, CYP7B, that catalyzes the 7␣-hydroxylation of oxysterols and 3␤-hydroxysteroids including DHEA. We report here that CYP7B mRNA and 7␣-hydroxylation activity are widespread in rat tissues. However, steroids related to DHEA are reported to be modified at positions other than 7␣, exemplified by prominent 6␣-hydroxylation of 5␣-androstane-3␤,17␤-diol (A/anediol) in some rodent tissues including brain. To determine whether CYP7B is responsible for these and other activities we disrupted the mouse Cyp7b gene by targeted insertion of an IRES-lacZ reporter cassette, placing reporter enzyme activity (␤-galactosidase) under Cyp7b promoter control. In heterozygous mouse brain, chromogenic detection of reporter activity was strikingly restricted to the dentate gyrus. Staining did not exactly reproduce the in situ hybridization expression pattern; post-transcriptional control is inferred. Lower level staining was detected in cerebellum, liver, and kidney, and which largely paralleled mRNA distribution. Liver and kidney expression was sexually dimorphic. Mice homozygous for the insertion are viable and superficially normal, but ex vivo metabolism of DHEA to 7␣-hydroxy-DHEA was abolished in brain, spleen, thymus, heart, lung, prostate, uterus, and mammary gland; lower abundance metabolites were also eliminated. 7␣-Hydroxylation of 25-hydroxycholesterol and related substrates was also abolished, as was presumed 6␣-hydroxylation of A/anediol. These different enzyme activities therefore derive from the Cyp7b gene. CYP7B is thus a major extrahepatic steroid and oxysterol hydroxylase and provides the predominant route for local metabolism of DHEA and related molecules in brain and other tissues.Brain function is subject to hormonal control, notably by steroids synthesized from the adrenal glands and gonads. Accumulating evidence also points to local steroid synthesis and metabolism in brain; a growing field of investigation focuses on the biological role of brain-active steroids, or "neurosteroids" (1-5). Attention has focused on the major adrenal steroid in primates, dehydroepiandrosterone (DHEA), 1 in view of a possible link with cognitive aging and immunosenescence. DHEA and related steroids, including pregnenolone, have memoryenhancing properties in rodents (6 -8) as well as immunostimulatory effects (9 -11). In primates, levels of DHEA and its sulfate (DHEAS) decline asymptotically with age (12-14). A causal relationship with age-related physiological impairments has been debated (15, 16). Because DHEA replacement therapy has brought mixed results (15,(17)(18)(19), and no dedicated receptor has been described for DHEA, its bioactivity may require local metabolism.B-ring hydroxylation is a major metabolic route for 3␤-hydroxysteroids, including DHEA and pregnenolone, in diverse tissues includ...

The eects of the endogenous cannabinoid anandamide were studied on peripheral, polymodal nociceptors recorded from normal and chronically in¯amed (Freund's adjuvant) knee joint aerents in rats anaesthetized with pentobarbitone. Anandamide (860 nmol) caused a rapid, short lasting excitation of a sub-population of capsaicin-sensitive nociceptive aerents in normal knee joints (7.2+2.3 impulses s 71; n=15 units from ®ve animals). In arthritic joints there were 9.7+3.0 impulses s 71 (n=11 from six animals), which was not signi®cantly dierent from normal joints. The excitation was dose dependent (8.6 ± 2900 nmol) and mediated by activation of the vanilloid receptor (VR 1 ) as it was abolished by the VR1 antagonist capsazepine (1 mg kg 71). Our results show that anandamide, at high doses, can activate nociceptive aerents innervating the rat knee joints, in contrast with its widely described analgesic actions.

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