Perinatal exposure to low levels of the environmental antiandrogen vinclozolin alters sex-differentiated social play and sexual behaviors in the rat

Abstract

In this study we examined the effects of exposure to the antiandrogenic fungicide vinclozolin (Vz) on the development of two sex-differentiated behaviors that are organized by the perinatal actions of androgens. Pregnant Long-Evans rats were administered a daily oral dose of 0, 1.5, 3, 6, or 12 mg/kg Vz from the 14th day of gestation through postnatal day (PND)3. The social play behavior of juvenile offspring was examined on PND22 and again on PND34 during play sessions with a same-sex littermate. After they reached adulthood, the male offspring were examined with the ex copula penile reflex procedure to assess erectile function. Vz did not produce any gross maternal or neonatal toxicity, nor did it reduce the anogenital distance in male pups. We observed no effects of Vz on play behavior on PND22. However, the 12-mg/kg Vz dose significantly increased play behavior in the male offspring on PND34 compared with controls. The most dramatic increases were seen with the nape contact and pounce behavior components of play. The Vz effect was more pronounced in male than in female offspring. As adults, male offspring showed a significant reduction of erections at all dose levels during the ex copula penile reflex tests. The 12-mg/kg dose was also associated with an increase in seminal emissions. These effects demonstrate that perinatal Vz disrupts the development of androgen-mediated behavioral functions at exposure levels that do not produce obvious structural changes or weight reductions in androgen-sensitive reproductive organs.

Figure 1. Mean ± SEM total number of play behaviors per session on PND22 and PND34 for male offspring (A) and their female littermates (B). Males exposed to 6 mg/kg or 12 mg/kg Vz performed significantly more behaviors on PND34 than did same-sex controls; females were not significantly different on either day.

Figure 2. Mean ± SEM number of nape contacts per session on PND22 and PND34 for male offspring (A) and their female littermates (B). The male 12-mg/kg Vz group performed significantly more nape contacts on PND34 than did controls or the 3-mg/kg group.

Figure 3. Mean ± SEM number of pounces per session. Data have been averaged across sex and postnatal age groups. The 12-mg/kg Vz group produced pounced significantly more than did the control group. : *p < 0.05.

Figure 4. Mean ± SEM total number of erections during the ex copula penile reflex procedure. All four of the Vz exposure groups produced significantly fewer erections than did the control group. : *p < 0.01.

Figure 5. Mean ± SEM total number of reflex clusters during the ex copula penile reflex procedure. A cluster of reflexes is defined as a rapid sequence, where each behavior occurs within 15 sec of the previous behavior. The 3-, 6-, and 12-mg/kg Vz groups produced significantly fewer clusters of reflexes than did the control group. : *p < 0.01.

Figure 6. Mean ± SEM total number of seminal emissions during the ex copula penile reflex procedure. The 12-mg/kg Vz group produced significantly more emissions than did the control group. : *p = 0.02.

Figure 7. Polynomial model for ED₁₀ benchmark dose (BMD) value and 95% lower confidence level (BMDL) for the total erections per session variable.

Figure 8. Linear model for ED₁₀ benchmark dose (BMD) value and 95% lower confidence level (BMDL) for total play behavior in the male offspring on PND34.