Standardization of the Whitten Effect to induce susceptibility to Neisseria gonorrhoeae in female mice.

Female mice (Mus musculus) frequently are used to study hormonally related differences in susceptibility to infectious organisms or response to pharmaceutical agents. Cyclical variation in hormone levels within a group of mice, however, challenges the experimental design of such studies in that it is often difficult to obtain sufficient numbers of mice in the desired phase of the estrous cycle at the time of treatment. The purpose of this work is to provide investigators with a standardized protocol for inducing estrus in mice through exposure to male urine (Whitten Effect). In addition, we demonstrate how the Whitten Effect can be used to induce susceptibility of mice to Neisseria gonorrhoeae infection. Female BALB/c mice were exposed to male urine via soiled bedding for 0, 24, 48, 72, or 96 h. The effect of exposure on the reproductive cycle was monitored by cytologic examination of vaginal smears and measurement of serum 17-b estradiol levels by using a nonradioactive immunoassay kit. In a separate experiment, mice were exposed to male-urine-soaked bedding for 0, 24, 72, or 96 h prior to intravaginal inoculation with Neisseria gonorrhoeae. Infection was monitored by using vaginal culture for 5 consecutive days. We found that the highest percentage of mice in estrus occurred among mice that were exposed to male-urine-soaked bedding for 96 h. Consistent with this finding was the demonstration that mice were more susceptible to gonococcal infection after exposure to male urine for 3 to 4 days. We conclude that exploitation of this natural murine behavioral response is a simple and inexpensive method by which estrus can be synchronized in a group of mice within a defined period of time. In addition, this protocol can be used to increase mouse susceptibility to experimental gonococcal infection.