Steve Warren David and Dr. Reuben Ward Rhees, Zoology
Sexual differentiation of the brain is dependent on the presence or absence of androgen (testosterone) during prenatal development. Exposure to testosterone is essential for masculinization and defeminization of sexual behavior, and brain structural development. Present evidence suggests that the action of testosterone during brain development involves the metabolic conversion of testosterone in one of two ways. Testosterone is either converted to estradiol by the enzyme aromatase or to dihydrotestosterone by the enzyme 5 alpha reductase. Testosterone and these two metabolites interact to regulate sexual differentiation of the brain. This project monitored the activity of both aromatase and 5 alpha reductase in stressed pregnant rats and their offspring. We determined the significance of stress on the activity of these two enzymes.
We hypothesized that the activity of 5 alpha reductase and aromatase would significantly decrease in pregnant rats and in their unborn offspring when subjected to a scientifically controllable stress treatment.
Eighteen adult Sprague-Dawley female rats were purchased from Sasco, Inc.and mated with male rats already in the laboratory. The presence of sperm in vaginal smears constituted day 1 of pregnancy. Upon impregnation, these rats were divided into two groups: 1) 9 control, and 2) 9 stress treated. Both groups were subjected to ample food and water and other normal treatment of laboratory animals. The two groups were then subjected to the following treatment and testing timetable.
Day 1 – day of pregnancy.
Day 14 – experimental group received first stress treatment.
Day 15 – experimental group received second stress treatment.
Day 16 – experimental group received third stress treatment.
Day 17 – three experimental and three control animals were sacrificed by decapitation Mothers: trunk blood collected, pituitary removed, and brain removed and the frontal cortex and medial hypothalamus isolated. Pups: pooled by sex, three males and three females isolated. Trunk blood collected and similar isolation of the above brain areas. – remaining experimental group received fourth stress treatment.
Day 18 – experimental group received fifth stress treatment.
Day 19 – three additional experimental and control animals were sacrificed by decapitation and identical collection procedures were followed for both mothers and pups as day 17 group. – remaining experimental group received sixth stress treatment.
Day 20 – experimental group received seventh and final stress treatment.
Day 21 – remaining experimental and control animals were sacrificed and collections made.
Pregnant females in the experimental group were subjected to a heat-light-restraint stress 3 times daily for 45 minute sessions. The animals were placed in a 13 x 6 x 8 cm semicircular transparent Plexiglas chamber. These chambers restricted the movement of the animals to provide the restraint stress. The chambers were placed under two 150-watt flood lamps during the 45 minutes to provide the heat and light stress.
The blood hormones were measured by pretested radioimmunoassays. Maternal and fetal brain 5 alpha reductase and aromatase activity was measured by thin-layer chromatography and quantified by liquid scintillation.
As hypothesized, fetal brain aromatase activity was significantly reduced in stressed animals and their offspring throughout the last four days of pregnancy. In the mothers the brain aromatase activity reduced from 90.1 fmol/hr/mg protein (control) to 61 fmol/hr/mg protein (stress). However, a comparison in 5 alpha reductase activity showed no significant difference between stressed and control animals in both the mothers and the pups. Likewise, there was no difference between the male and female offspring. These results indicate that 5 alpha reductase activity in maternal or fetal brain is not significantly altered by prenatal stress, whereas, aromatase activity is significantly reduced in the maternal and fetal brains1.
References
- Davis, S. W. and R. W. Rhees. 1996. Spring Meeting Utah Academy of Sciences, Arts, and Letters. Utah Valley State College.