Rapid effects of 17β-estradiol on male copulatory behaviors are not elicited by the novel membrane active estrogenic compound STX

Abstract

Estrogens have been shown to rapidly promote male copulatory behaviors with a time-course that suggests rapid signaling events are involved. The present study tested the hypothesis that estrogen acts through a novel Gq protein-coupled membrane estrogen receptor (ER). Thus, either estradiol (E2), STX (a diphenylacrylamide compound that selectively activates a membrane ER pathway), or vehicle were administered acutely to castrated male rats that bore subcutaneous (sc) dihydrotestosterone implants to maintain genital sensitivity. Appetitive (level changes, genital investigation) and consummatory (mounts, intromissions, ejaculations) components of male sexual behavior were measured in a bilevel testing apparatus. Testing showed that E2 treatment promoted olfactory and mounting behaviors, but had no effect on motivation as measured by anticipatory level changes. STX treatment showed no effect on either component of male sexual behavior. These results support previous results that showed that E2 can rapidly affect male sexual behaviors but fail to support a role for the specific membrane-initiated pathway activated by STX.

Figure 1

Experimental design and treatment time line. Adult stimulus female rats were ovariectomized prior to testing. Adult male rats were given sexual experience with estrus-induced females prior to training in the bilevel apparatus for 5 wk. The males were then castrated and given sc implants of DHT. Males were allowed to recover from surgery (2 wk) and then tested in the bilevel apparatus 15 min after receiving sc injections of E2 (4 trials); saline (2 trials); STX (2 trials); saline (1 trial), and E2 (final trial) over sequential weeks.

Figure 2

Short latency effects of E2 and STX on frequency of level changing behavior (A) and genital investigatory behavior (B). Values are mean ± SEM; n = 6–7 rats per group. Experimental groups are signified by different symbols and trials are labeled on the x-axis. The frequency of level changes showed a significant group difference but not a trial difference or interaction. Reanalysis of the data averaged by treatment showed a main effect of experimental group during the E2 trials only and indicated that E2 treated male exhibited significantly fewer levels changes than INT or VEH groups. The frequency of genital sniffs showed a main effect of trial and a trial by group interaction, but no effect of experimental group. Reanalysis of the results averaged by treatment showed that E2 treatment significantly increased genital sniffs compared to INT controls, while STX significantly lowered genital sniffs.

Figure 3

Short latency effects of E2 and STX on Mounts with thrust (A); Intromissions (B); and Ejaculations (C). Values are mean ± SEM; n = 6–7 rats per group. Experimental groups are signified by different symbols and trials are labeled on the x-axis. For all behaviors, INT males showed significantly higher behaviors than DHT+VEH and DHT+TX across all trials, indicating that E2 and STX had no effect.

Figure 4

Short latency effects of E2 and STX on frequency of thrustless mounts (A); mount latency (B); and % of males mounting during each trial (C). Values for A & B are mean ± SEM; n = 6–7 rats per all groups. Experimental groups are signified by different symbols and trials are labeled on the x-axis. For thrustless mounts (A) there was a significant effect of treatment and trial, and a trend for an interaction (p = 0.06). Reanalysis of the mean data per treatment period indicated that E2 treated males exhibited greater thrustless mount frequencies than INT or VEH groups. Mount latency (B) showed a significant effect of experimental group and trial and a significant interaction. Reanalysis of the mean data per treatment showed that E2 treatment, but not STX or VEH, maintained latency at a level equivalent to INT males.