Neonatal agonism of ERβ impairs male reproductive behavior and attractiveness

Abstract

The organization of the developing male rodent brain is profoundly influenced by endogenous steroids, most notably estrogen. This process may be disrupted by estrogenic endocrine disrupting compounds (EDCs) resulting in altered sex behavior and the capacity to attract a mate in adulthood. To better understand the relative role each estrogen receptor (ER) subtype (ERα and ERβ) plays in mediating these effects, we exposed male Long Evans rats to estradiol benzoate (EB, 10 μg), vehicle, or agonists specific for ERβ (DPN, 1 mg/kg) or ERα (PPT, 1 mg/kg) daily for the first four days of life, and then assessed adult male reproductive behavior and attractiveness via a partner preference paradigm. DPN had a greater adverse impact than PPT on reproductive behavior, suggesting a functional role for ERβ in the organization of these male-specific behaviors. Therefore the impact of neonatal ERβ agonism was further investigated by repeating the experiment using vehicle, EB and additional DPN doses (0.5 mg/kg, 1 mg/kg, and 2 mg/kg bw). Exposure to DPN suppressed male reproductive behavior and attractiveness in a dose dependent manner. Finally, males were exposed to EB or an environmentally relevant dose of genistein (GEN, 10 mg/kg), a naturally occurring xenoestrogen, which has a higher relative binding affinity for ERβ than ERα. Sexual performance was impaired by GEN but not attractiveness. In addition to suppressing reproductive behavior and attractiveness, EB exposure significantly lowered the testis to body weight ratio, and circulating testosterone levels. DPN and GEN exposure only impaired behavior, suggesting that disrupted androgen secretion does not underlie the impairment.

Fig. 1

Experiment 1 sexual behavior and partner preference results. (A – C) Only behavior from the fifth round of testing was analyzed and no significant differences between groups emerged for any endpoint, but the outcome suggested an emasculating effect of neonatal EB or DPN exposure. (A) EB and DPN exposed males had fewer intromissions compared to vehicle exposed (OIL) males. (B) EB and DPN exposed males had longer intromission latencies compared to vehicle exposed males. (C) Females selected against the EB exposed males by spending significantly more time in the chamber containing the vehicle exposed (control) males. Partner preference was unaffected in the other groups (Mean ± SEM; * P ≤ 0.05)

Fig. 2

Experiment 2 sexual behavior and partner preference results. (A) The number of intromissions did not differ between groups in either round but the 1 mg/kg DPN exposed group was the only group that did not display increased numbers of intromissions in Round 4 compared to Round 3. (B) Intromission latency did not initially differ between groups, but significantly dropped over time in all groups except the 1 mg/kg DPN exposed group resulting in significantly longer latencies within this group compared to the vehicle (OIL) exposed controls. (C) Females significantly preferred vehicle exposed (Control) males over 2 mg/kg DPN exposed males but showed no preference between 1 mg/kg DPN exposed males and control males. (Mean ± SEM; * P ≤ 0.05; a = significant difference between rounds, b = significant difference from OIL controls)

Fig. 3

Experiment 3 sexual behavior and partner preference results. (A) The number of intromissions did not significantly differ between groups in either round. The vehicle exposed group was the only group that had significantly more intromissions over time. (B) Intromission latency was similar across exposure groups in Round 2 but by Round 3, the EB and GEN exposed males had significantly longer latencies compared to controls, with only the controls having shorter latencies in Round 3 compared to Round 2. (C) Females significantly preferred vehicle exposed (Control) males over EB exposed males but showed no preference between GEN exposed and control males. (Mean ± SEM; * P ≤ 0.05; a = significant difference between rounds, b = significant difference from OIL controls)

Fig. 4

Experiment 4 sexual behavior and partner preference results. (A) Number of intromissions was significantly lower in the EB and GEN exposed groups compared to the OIL control males in both rounds of testing. Numbers did not significantly increase over time in any group. (B) Latency to intromit was significantly longer in the EB exposed groups compared to the OIL group in Round 3 but this difference was lost in Round 4. (C, D) Partner preference results differed between rounds. In both cases, females significantly preferred control males over EB exposed males. However, females displayed a significant preference for GEN exposed males compared to OIL control males in the first round of partner preference testing (Experiment 4a) but not the second (Experiment 4b). (Mean ± SEM; * P ≤ 0.05; b = significant difference from OIL controls)