Neuroestrogens rapidly regulate sexual motivation but not performance

Abstract

Estrogens exert pleiotropic effects on reproductive traits, which include differentiation and activation of reproductive behaviors and the control of the secretion of gonadotropins. Estrogens also profoundly affect non-reproductive traits, such as cognition and neuroprotection. These effects are usually attributed to nuclear receptor binding and subsequent regulation of target gene transcription. Estrogens also affect neuronal activity and cell-signaling pathways via faster, membrane-initiated events. How these two types of actions that operate in distinct timescales interact in the control of complex behavioral responses is poorly understood. Here, we show that the central administration of estradiol rapidly increases the expression of sexual motivation, as assessed by several measures of sexual motivation produced in response to the visual presentation of a female but not sexual performance in male Japanese quail. This effect is mimicked by membrane-impermeable analogs of estradiol, indicating that it is initiated at the cell membrane. Conversely, blocking the action of estrogens or their synthesis by a single intracerebroventricular injection of estrogen receptor antagonists or aromatase inhibitors, respectively, decreases sexual motivation within minutes without affecting performance. The same steroid has thus evolved complementary mechanisms to regulate different behavioral components (motivation vs performance) in distinct temporal domains (long- vs short-term) so that diverse reproductive activities can be properly coordinated to improve reproductive fitness. Given the pleiotropic effects exerted by estrogens, other responses controlled by these steroids might also depend on a slow genomic regulation of neuronal plasticity underlying behavioral activation and an acute control of motivation to engage in behavior.

Figure 1.

Experimental design used when comparing the effect of one (A) or two (B) experimental (Exp.) treatment(s) to their vehicle (Veh). Before the experiment, birds were divided into two or three subgroups (SG1–SG2 or SG1–SG3) depending on the number of conditions compared. Each experiment consisted in four or five tests: one pretest (Pre), two (A) or three (B) experimental tests, and a posttest (Post). In the pretest, all animals regardless of the their subgroup were tested for a given behavioral response after an acute intracerebroventricular injection of vehicle. Each subgroup was then tested on two (A) or three (B) different days for the two (A) or three (B) different treatments, but each subgroup received these treatments in different order such that, for example, in A, one half the animals would receive the experimental treatment on day 1 and the vehicle on day 2, whereas the other half received the vehicle first and experimental treatment second. In the posttest, all birds were tested again after an injection of vehicle. In these experiments, all tests were given either 2 d (group 1) or 3 d apart (groups 2 and 3).

Figure 2.

Chronic treatment with the aromatase inhibitor VOR almost completely eliminates CSB (group 1, preliminary phase). After the last pretest (Pre), CX males chronically treated with T were injected twice daily with VOR (1 mg/kg, i.m.; white bars, CX + T + VOR, n = 12) or its vehicle (PG; controls, black bars, CX + T, n = 4). Birds were then repeatedly tested every third day for the expression of CSB. CCM frequencies gradually decreased to almost zero within 9 d. Data were analyzed by two-way ANOVA with treatment as independent factor (F_(3,51) = 1230, p = 0.308) and successive tests as repeated factor (F_(1,17) = 17.532, p < 0.001; interaction, F_(3,51) = 3.758, p = 0.016). *p < 0.05 versus controls (CX + T); ^†p < 0.05 and ^††p < 0.01 versus Pre same treatment, by Tukey's post hoc test.

Figure 3.

E₂ rapidly facilitates appetitive (ASB) but not consummatory sexual behavior (CSB) in males chronically deprived males of estrogens by its action at the membrane level (group 1, experimental phase). CX males were chronically treated with T and the aromatase inhibitor VOR (CX + T + VOR, white bars) or with its vehicle (CX + T; black bars, n = 4). The estrogen-deprived males (CX + T + VOR) were then acutely injected with E₂ (50 μg, n = 12, A, C), the membrane-impermeant analog E₂–BSA (50 μg, n = 11, B), or the vehicle (Veh) and tested 15 min later for ASB (A, B) or CSB (C) assessed by the frequency of RCSM and of CCM, respectively. Data from CX + T males (black bars) are shown as reference of fully stimulated behavior but were not integrated in the final analyses. **p < 0.01 versus vehicle by Fisher's LSD post hoc test after identification of a significant treatment effect (repeated-measure) by two-way ANOVA.

Figure 4.

Effects of acute blockade of estrogen receptors on the ASB and CSB of fully active males (group 2). The blockade of estrogen action by the estrogen receptor antagonists ICI (50 μg) and TMX (50 μg) acutely inhibits RCSM frequency (A, B, n = 15) but not CCM frequency (C, D, n = 13 and 15, respectively) within 15 or 30 min compared with vehicle (Veh) injection (white bars). The “Pre” and “Post” black bars provide reference behavior frequencies after vehicle intracerebroventricular injections performed before and after the acute treatments, but these data are not included in the statistical analyses. ***p < 0.001 versus vehicle; ^†p < 0.05 versus ICI by Newman–Keuls post hoc tests after identification of a significant treatment effect (repeated-measure) by two-way ANOVA.

Figure 5.

Effects of acute deprivation in brain-derived estrogens on the ASB and CSB of fully active males (group 2). Blockade of local estrogen synthesis by the aromatase inhibitors ATD (50 μg) or VOR (50 μg) inhibits RCSM frequency (A, C, D) but not CCM frequency (B) within 30 min. E₂ (50 μg; C) or its membrane-impermeant analog E₂–biotin (E₂-BIO, 50 μg E₂ equivalent; D) injected 15 min after VOR counteracts its effect on RCSM. The “Pre” and “Post” black bars provide reference behavior frequencies after vehicle intracerebroventricular injections performed before and after the acute treatments, but these data are not included in the statistical analyses. **p < 0.01 and ***p < 0.001 versus vehicle (Veh); ^†††p < 0.001 vs VOR by Newman–Keuls post hoc tests after identification of a significant treatment effect (repeated measure, n = 12 in each case) by two-way ANOVA.

Figure 6.

Effects of acute blockade of estrogen action or synthesis on copulatory behavior of behaviorally active males tested in large test chambers (group 2). The acute blockade of estrogen action by general estrogen antagonists (A, n = 14) or synthesis by aromatase inhibitors (B, n = 12) profoundly inhibits CSB when measured in a large test arena (90 × 90 × 50 cm) 30 min after injection compared with control vehicle (Veh) injection. The “Pre” and “Post” black bars provide reference behavior frequencies after vehicle intracerebroventricular injections performed before and after the acute treatments, but these data are not included in the statistical analyses. **p < 0.01 and ***p < 0.001 versus vehicle (Veh) by Newman–Keuls post hoc tests after identification of a significant treatment effect (repeated measure) by two-way ANOVA.

Figure 7.

Effects of acute blockade of brain estrogen synthesis associated or not with an acute E₂ injection on appetitive and consummatory aspects of male sexual behavior in sexually active males (group 3). Blockade of local estrogen synthesis by the aromatase inhibitor VOR (50 μg) acutely reduces whereas E₂ (50 μg) restores the time spent near the window (A) and looking at the female (B) in the learned social proximity test (n = 16). Similar effects are observed on RCSM frequency (C, n = 9) and copulatory behavior assessed by the frequency of CCM measured in the large arena (D, n = 9). However, no such effects were detected on copulatory behavior measured in the small arena (E, n = 9). The “Pre” and “Post” black bars provide reference behavior frequencies after vehicle intracerebroventricular injections performed before and after the acute treatments. **p < 0.01 and ***p < 0.001 versus vehicle (Veh); ^(†)p < 0.10, ^†p < 0.05, ^††p < 0.01 versus VOR by Newman–Keuls post hoc tests after identification of a significant treatment effect (repeated measure) by two-way ANOVA.