Additivity in murine circadian phototransduction.

Additivity in the circadian phototransduction system of the mouse has not been tested directly. Because of this, accurate prediction of circadian phase shifts elicited by polychromatic light stimuli cannot be derived from the results of studies using monochromatic light stimuli. This limitation also makes it impossible to deduce the relative contributions of the photoreceptive mechanisms (rods, cones and melanopsin-containing retinal ganglion cells) underlying circadian phototransduction in the mouse. Using nearly monochromatic light stimuli of different spectral composition, and combinations thereof, we demonstrated that murine circadian phototransduction exhibits additivity. Based on the locomotor activity phase shifts elicited by these stimuli, we developed the first quantitative assessment of the relative contributions of conventional and novel photoreceptive mechanisms for circadian functioning in the mouse.

Effects of withdrawal from anabolic androgenic steroids on aggression in adult male rats.

In gonadally intact male rats, chronic exposure to high levels of testosterone propionate (TP) increases aggression, nandrolone (ND) has little effect and stanozolol (ST) suppresses aggression. The present experiment tested whether the effects of TP, ND and ST on aggression and reproductive tissues are reversed following anabolic androgenic steroid (AAS) withdrawal. Gonadally intact males received TP, ND, ST or vehicle for 12 weeks. Injections were then discontinued. Aggression was tested 3 weeks (short term) and 12 weeks (long term) after withdrawal of AAS treatment, with either a gonadally intact or a castrated opponent in three different environments (home, opponent's and neutral cage). After short-term withdrawal, some parameters of aggression were significantly above control levels in TP males. There were no significant differences between ND or ST males and controls, though ST males showed the lowest levels of aggression. No significant differences between any of the groups were found after long-term withdrawal. Eighteen weeks after AAS withdrawal, serum testosterone (T) and LH levels were comparable to controls in all groups. Testes weights were at control levels in ST males, but significantly higher than controls in TP and ND males. Seminal vesicle weights were significantly elevated in TP males, but similar to controls in both ND and ST males. None of the prostate weights were significantly different from controls. These results suggest that aggression gradually returns to normal following withdrawal from AAS. Some, if not all, hormone levels and tissue weights return to normal, suggesting possible long-lasting effects of chronic AAS exposure.