Posttraining androgens' enhancement of cognitive performance is temporally distinct from androgens' increases in affective behavior.

Steroid hormone-induced variations in spatial learning and memory tasks have been reported. In this study, androgens' effects in various cognitive and affective tasks were investigated in order to determine whether any observed differences in cognitive performance could be due to affective changes produced by the hormones. Ovariectomized rats (N = 72) received 0.0, 3.0, or 7.5 mg/kg subcutaneously, of testosterone (T), dihydrotestosterone (DHT), or 5 alpha-androstane-3 alpha,17 beta-diol (3 alpha-Diol) suspended in 10% ethanol/sesame oil v/v. For the cognitive tasks (Y maze, inhibitory avoidance, and object recognition), subjects were injected after training trials. For the affective tasks (open field, elevated plus maze, and tailflick), subjects were injected 1 or 24 h before testing. Posttraining injections that produced physiological concentrations of androgens--T, DHT, and 3 alpha-Diol--1 h later increased the percentage of correct choices in the Y maze, the latencies to cross to the shock-associated side of the inhibitory avoidance chamber, and percentage of time exploring novel objects 24 h later, when androgen levels were no longer increased. Administration of T, DHT, and 3 alpha-Diol also increased the number of entries into the center squares of a brightly lit open field, open-arm time in the elevated plus maze, and tailflick latencies 1 but not 24 h following administration. These findings suggest that these androgens, when administered following training, can enhance cognitive performance in the tasks investigated 24 h later when androgen levels nadir, but overt changes in the affective behaviors examined occurred at the time of physiological concentrations 1 h but not 24 h following androgen administration. These findings suggest posttraining androgens can enhance consolidation and cognitive performance, independent of their anxiolytic actions.

The neurosteroids DHEA and DHEAS may influence cognitive performance by altering affective state.

The effects of Dehydroepiandrosterone (DHEA) and its sulfate ester, Dehydroepiandrosterone sulfate (DHEAS) on performance in various cognitive and affective tasks were investigated. Ovariectomized rats (n = 48) received 0.0, 3.0, or 7.5 mg/kg s.c. of DHEA or DHEAS suspended in 10% ethanol/sesame oil v/v. For the cognitive tasks (water maze, Y-maze, passive avoidance, and object recognition), subjects were injected after training trials. For the affective tasks (tail flick, open field, and elevated plus-maze), subjects were injected 1 or 24 h prior to testing. DHEA deceased latencies and trials to criterion in the water maze, and decreased motor activity in the open field at 24 h postinjection. DHEAS decreased latencies to the goal arm in the Y-maze and reduced motoricity and the number of entries into the center of a brightly lit open field, both 1 and 24 h after injection. These findings suggest that DHEA and DHEAS may alter performance on cognitive tasks due to motor or anxiety effects.

Elastic response of bilayers with intrinsic proteins.

Intrinsic membrane proteins affect the ordering of neighbouring lipid chains. We have used a model of protein-lipid interactions in bilayers proposed by Owicki et al. (Owicki, J.C., Springgate, M.W. and McConnell, H.M. (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 1616-1619) to show that near the lipid phase transition this effect may significantly increase the magnitude of a membrane's lateral compressibility (or correspondingly, decrease the magnitude of the membrane's elastic moduli).