Will they ever stop? Andersen et. co. were not satisfied with tormenting young rats with cocaine and sleep-deprivation in order to see how that affects their ability to get-it-up, now they want to find out the same in old rats...

Does paradoxical sleep deprivation and cocaine induce penile erection and ejaculation in old rats? [link]
Andersen ML, Bignotto M, Machado RB, Tufik S
Addict Biol. 2002 Jul ; 7(3): 285-90

To discover whether the same effects occurred in old animals ..."

...we administered cocaine (15 mg/kg) to young (3-month) and old (22-month) male rats after a 4-day period of PSD [paradoxical sleep deprivation] ...

...we then evaluated erections and ejaculations."

..in conclusion, our results suggest that although genital reflexes usually decrease with age, testosterone levels alone cannot account for these changes..."