The membrane actions of estrogens can potentiate their lordosis behavior-facilitating genomic actions

Abstract

The membrane actions of estrogens can facilitate their genomic actions. To determine whether this facilitation bears on CNS mechanisms for estrogen-dependent behaviors, ovariectomized rats were subjected to a two-pulse treatment of estrogen directly in the hypothalamic ventromedial nucleus. Two days later, each rat was given progesterone and then tested for lordosis behavior, the induction of which requires the genomic actions of estrogen. When estrogen was given in both pulses (15 min to 2 h duration, and 5 h apart) lordosis was induced. Based on results from studies on neuroblastoma cells, we hypothesized that the membrane actions of estrogen in the first pulse would potentiate the genomic actions of estrogen in the second. This hypothesis was confirmed with the use of a membrane-impermeable estrogen. However, surprisingly, the order of the pulses could be reversed and still achieve lordosis behavior induction. Finally, activators of protein kinase A or PKC were effective substitutes for the membrane-limited pulse of estrogen. Thus, estrogen-induced membrane actions in the hypothalamus can potentiate its lordosis-inducing genomic actions on behavior and may be mediated by signaling pathways involving the activation of protein kinase A and PKC.

Fig. 1.

Results of one- and two-pulse treatments of female rats with various combinations of E, E-BSA (E′, unfiltered; fE′, filtered), and control agents. Control group 1 (Ctrl 1) includes results from the following treatments: chol + E, O + E, BSA + E, and E + BSA. Control group 2 (Ctrl 2) includes chol + fE′ and fE′+ chol. As positive controls, in four rats each treated with E for 8 h or with E + E at 2 h each, very strong lordosis and full LQ were confirmed. For other groups, the number of rats ranges from 5 to 22. One-way ANOVA, compared with controls: a, P < 0.0005; b, P < 0.005; and c, P < 0.05; and compared with each other: d vs. d, P < 0.05. 0 (zero), no lordosis; Chol, cholesterol.

Fig. 2.

Results of dose–response experiments. E at 100% induced high levels of receptivity in all rats tested. It tended to be more effective than 40% E and is significantly more so than 10% E. With the two lower doses, there are large individual variations. Chol, cholesterol. *, P < 0.02, compared with E + E, one-way ANOVA.

Fig. 3.

Potentiation of the lordosis-inducing action of E by PK activators. V + E group includes control treatments of (saline + E), (DMSO + E), and (E + DMSO). All treatment groups are highly significantly different from the control group (P < 0.001, one-way ANOVA). There is no significant difference among the four experimental groups. V, vehicle; PDAc and PMA, PKC activators, both 333 μM in agar-saline; Sp-cAMP, 333 μM in agar-saline.