Harvey H. Feder

Cytoplasmic progestin-receptors in guinea pig brain: characteristics and relationship to the induction of sexual behavior.

The synthetic progestin, R 5020, was used to measure cytoplasmic progestin receptors in the brain and pituitary gland of ovariectomized guinea pigs. Progestin receptors with a dissociation constant of 0.1--0.3 nM were measured by gel filtration in all brain regions studied, pituitary gland and the uterus. The receptor is progestin-specific; biologically potent progestins compete well against [3H]R 5020 for binding, but androgens, glucocorticoids and estrogens do not. The concentration of the cytoplasmic progestin receptor in hypothalamus-preoptic area-septum and midbrain is decreased in vivo by behaviorally effective doses of progesterone. In the pituitary gland, hypothalamus, preoptic area-septum and midbrain, but not other brain regions, the concentration of progestin receptors increases after estradiol benzoate-priming. The increase in the concentration of cytoplasmic progestin receptors in hypothalamus-preoptic area-septum is dependent on the dose of estradiol benzoate injected. After a single injection of a dose of estradiol benzoate routinely used to facilitate the display of sexual receptivity (1.6 microgram estradiol benzoate/animal), the latency to an increase and subsequent decrease in cytoplasmic progestin receptors in the hypothalamus-preoptic area-septum correlates well with the previously reported time course for progesterones facilitation of sexual receptivity after estradiol benzoate injection. The experiments are consistent with the notion that brain progestin receptors mediate at least some of the behavioral effects of progesterone.

Estrous Cyclicity in Mammals

In the previous chapter, several experimental manipulations designed to demonstrate that the secretions of the hypothalamus, the anterior pituitary, and the ovary can have stimulatory and inhibitory effects on one another were discussed. These experimental approaches were basically analytic. They served to dissect the effects of a particular hormone on one tissue from its effects on another tissue. From this analytic approach, an appreciation was gained of the range of potential reactions to hormonal stimuli of individual components of the hypothalamo-hypophyseal-ovarian axis. However, the analytic approach does not indicate which of the potential reactions are actually utilized during the course of normal reproductive cycles. Nor does the analytic method deal with the question of how the various stimulatory and inhibitory actions of hormones become linked together to form a repeatable endocrine pattern with a consistent periodicity. To resolve these problems, one must adopt a more synthetic outlook.

Increased GABAergic transmission in medial hypothalamus facilitates lordosis but has the opposite effect in preoptic area

The role of gamma-aminobutyric acid (GABA) in mediation of lordosis in the rat has been unclear. We report here that GABA plays a dual role in the mediation of lordosis and has differential effects in the medial hypothalamus (MH) and preoptic area/anterior hypothalamus continuum (POA-AH). Bilateral infusion of the GABAA antagonist bicuculline into the MH of cannulated females primed with estradiol benzoate and progesterone (EB + P) resulted in a marked and transient inhibition of ongoing lordosis. A similar pattern of inhibition was seen in females treated with EB only. In contrast, infusion of the same dose of bicuculline into the POA-AH of sexually receptive females had no effect on lordosis whereas infusion of the GABAA agonist muscimol into this site resulted in a short-term inhibition of lordosis. Furthermore, when females were treated with subthreshold doses of EB + P to induce a low level of lordosis responding, infusion of muscimol into the MH resulted in a significant enhancement of lordosis; infusion of bicuculline into the POA-AH also enhanced lordosis responding as compared to saline-infused controls. These data indicate that increased GABAergic neurotransmission in the MH facilitates lordosis whereas increased GABAergic activity in the POA-AH inhibits this behavior.

Hypothalamic progesterone implants and facilitation of lordosis behavior in estrogen-primed ovariectomized guinea pigs

Abstract Adult ovariectomized Hartley guinea pigs were bilaterally implanted in the basal hypothalamus or anterior hypothalamic-preoptic area with stainless steel cannulae with removable inserts. In experiment 1, animals received inserts containing crystalline progesterone, 17α-hydroxyprogesterone or cholesterol 36 h after subcutaneous injection of 3.3 μg estradiol benzoate. Regardless of cannula content, about 43% of animals with implants aimed at the basal hypothalamus displayed heat. Lesions or irritation associated with implants in this region may have increased behavioral responsiveness to estrogen. However, control implanted animals (17α-hydroxyprogesterone and cholesterol) tended to have shorter heat durations and more scattered facilitatory implant sites than progesterone implanted animals, suggesting that progesterone might be acting in basal hypothalamus to facilitate lordosis. Progesterone placed in basal anterior hypothalamic-preoptic area did not facilitate lordosis. Progesterone in basal hypothalamus or basal anterior hypothalamic-preoptic area did not produce inhibitory effects on behavior. In experiment 2, a revised procedure was used to control for sexual behavior resulting from estrogen treatment alone. The control procedures revealed that most of the animals with cannulae in the ventromedial-arcuate area displayed lordosis after estradiol benzoate alone. When animals not displaying estrus in response to estradiol benzoate alone were utilized for further implantation, it was clear that progesterone placed in the ventromedial-arcuate-premammillary area facilitated the expression of short latency, long duration heat. However, animals with cannulae in the basal hypothalamus, regardless of cannula content, had short maximum lordoses. No inhibitory effects of progesterone implants (in ventromedial-arcuate-premammillary area) on lordosis were observed. These results suggest that brain sites selectively responsive to the facilitatory actions of progesterone exist in the ventromedial-arcuate-premammillary region and that the whole basal hypothalamus participates in the normal, full expression of guinea pig behavioral estrus.

Cytoplasmic progestin receptors in female guinea pig brain and their relationship to refractoriness in expression of female sexual behavior.

Summary Cytoplasmic progestin receptors were assayed in the hypothalamus-preoptic area-septum and midbrain of ovariectomized guinea pigs given sequential treatment with estradiol benzoate and progesterone. As little as 50 μg of progesterone injected 40 h after estradiol benzoate caused a failure to display lordosis in response to a second progesterone injection 24 h after the first. Both 50 μg and 500 μg of progesterone decreased the concentration of cytoplasmic progestin receptors 24 h later in hypothalamus-preoptic area-septum and midbrain in estrogen-primed, ovariectomized guinea pigs. Therefore, progesterone injections that caused behavioral refractoriness to further stimulation by progesterone also decreased the concentration of availabke cytoplasmic progestin receptors. When progesterone was administered concurrently with 1.6 μg of estradiol benzoate, 500 μg, but not 100 μg suppressed behavioral responsiveness to a second progesterone injection 40 h later. The high dose, but not the low dose, also decreased the concentration of available cytoplasmic progestin receptors 40 h later in both the hypothalamus-preoptic area-septum and midbrain. These findings are consistent with the notion that a decrease in brain progestin receptor concentration is one of the subcellular mechanisms involved in failure of a second dose of progesterone to facilitate lordosis behavior in estrogen-primed animals exposed to a first dose of progesterone 24–40 h earlier.

Neurotransmitter modulation of steroid action in target cells that mediate reproduction and reproductive behavior

Two major functional interactions between steroid hormones and neurotransmitters are generally recognized. First, steroids affect neurotransmission, and second, through effects on hypothalamic peptides that regulate anterior pituitary function neurotransmitters affect steroid secretion. In recent years, evidence has accumulated which indicates that neurotransmitters can also affect steroid action within postsynaptic steroid target cells. We review evidence for this relationship in pineal, uterus and hypothalamus and propose that the modulation of target cell responsiveness to steroids is an important mechanism by which neurotransmitters affect steroid-dependent processes. The operation of such a mechanism provides a means for environmental, behavioral and emotional events to rapidly and selectively alter steroid effects on behavior and physiology.

Differential fornix ablations and the circadian rhythmicity of adrenal corticosteroid secretion

Suction ablations of the medial or lateral fornix were performed in order to transect selectively the medial corticohypothalamic tract (mcht) which originates in the anteroventral subiculum and travels in the lateral fornix terminating in the basal hypothalamus. The circadian rhythmicity of plasma adrenal corticosteroid levels was assessed in individual animals 1--2 weeks postoperatively. Ablation of the lateral fornix disrupted the periodicity of corticosteroid secretion which is normally synchronized with the light--dark cycle, whereas medial fornix ablation or neocortical ablation caused no such disruption. Group mean levels of plasma adrenal corticoids were higher in the lateral fornix-ablated animals than in the medial fornix-ablated, neocortically ablated, or intact control animals. These findings suggest that the anteroventral subiculum is important in the regulation of adrenal corticosteroid rhythmicity, and that it exerts an inhibitory influence upon corticosteroid release.

Social interactions and androgen levels in birds. I. Female characteristics associated with increased plasma androgen levels in the male ring dove (Streptopelia risoria).

Abstract Male ring doves exposed to female conspecifics exhibit a variety of courtship behaviors and show large and relatively long-lasting elevations in circulating androgens. This series of experiments examined whether (1) a females gonadal condition and (2) contact or auditory cues from the mating situation influence these changes in male androgen levels and courtship behavior. Pairs of doves were placed in breeding cages, their behavior observed for the first 15 min of exposure, and blood obtained from the males 24 hr after pairing. Androgen levels were determined by an RIA. Males exposed to ovariectomized females had lower androgen levels than males exposed to intact females (2.3 ± 0.3 vs 4.0 ± 0.8 ng/ml, X ± SEM ), indicating that a females gonadal condition influences a males endocrine response to her. Deaf males exposed to intact females had lower androgen levels (1.4 ± 0.6 ng/ml) than normal males exposed to females (4.0 ± 0.8 ng/ml), indicating that auditory cues from the mating situation influence female-induced elevations in male plasma androgens. Males exposed to females through glass partitions had androgen levels (2.7 ± 0.6 ng/ml) similar to males given free access to females and higher androgen levels than males in isolation, indicating that contact cues from the mating situation do not necessarily influence female-induced elevations in male plasma androgens. The results also indicate that (1) contact between a pair of doves during early courtship facilitates male aggressive courtship displays and reduces male nest-oriented behavior, and (2) auditory cues from the mating situation facilitates male courtship behavior.

Changes in noradrenergic transmission alter the concentration of cytoplasmic progestin receptors in hypothalamus

Summary These experiments were designed to determine whether drug-induced changes in NA transmission affect lordosis behavior of female guinea pigs by altering steroid action within hypothalamic target cells. In the first experiment, we examined the effects of the dopamine-β-hydroxylase inhibitor, U-14,624, on cytoplasmic progestin receptors (measured using a one-point [3H]R5020 binding assay) in hypothalamus (HYPO), preoptic area (POA), cerebral cortex (CORT) and midbrain (MB) of estradiol benzoate (EB)-primed females. At 12 h after U-14,624 administration, specific binding of [3H]R5020 was 36% less in cytosol from HYPO (binding in POA, CORT, and MB was not affected by U-14,624) in drug-treated than in non-drug-treated controls. To determine whether this reduction in [3H]R5020 binding was due to competition of U-14,624 with [3H]R5020 for progestin receptors, we examined the effects of U-14,624 on [3H]R5020 binding in vitro. U-14,624 had no effects on [3H]R5020 binding under these conditions. By using a range of [3H]R5020 concentrations to assay cytoplasmic progestin receptors, we found that the reduction in [3H]R5020 binding on hypothalamic cytosol after U-14,624 treatment was due to a lower concentration of progestin receptors rather than to a lower progestin receptor affinity for [3H]R5020. Several lines of evidence indicate that the lower (compared to non-drug-treated females) concentration of these receptors was attributable to a reduction in NA transmission. First, U-14,624 caused a significant reduction in regional brain NE content. Second, activation of α-adrenergic receptors with clonidine completely reversed the effects of U-14,624 on cytoplasmic progestin receptors, although clonidine had no effect on progestin receptors when administered alone. Third, blockade of α-adrenergic receptors by i.p. injection of phenoxybenzamine (Pb) resulted in a relative reduction of specific [3H]R5020 binding in hypothalamic (but not POA, CORT or MB) cytosol of EB-primed females. There was a 3–4 h delay between the blockade of α-receptors by Pb (determined using a [3H]WB4101 binding assay) and a significant effect on the concentration of progestin receptors in cytoplasm of HYPO. The effects of Pb on hypothalamic progestin receptors did not appear to be due to a peripheral action of the drug. When administered intraventricularly, Pb caused a relative reduction in specific [3H]R5020 binding in hypothalamic (but not POA, CORT or MB) cytosol of EB-primed females. The lower concentration of progestin receptors in HYPO after drug treatment also did not appear to be attributable to the release of adrenal progesterone. The concentrations of progesterone in plasma at 0.5, 2, 4, and 12 h after Pb and at 12 h after U-14,624 administration were not different from control values. Furthermore, the concentration of cytoplasmic progestin receptors was lower only in HYPO after Pb and U-14,624 treatment, whereas injection of 100 μg progesterone caused a reduction in the concentration of these receptors in all brain areas examined. The lower concentration of cytoplasmic progestin receptors in HYPO after drug treatment might be attributable to a drug-induced interference with the EB-induced increase in the concentration of these receptors. This hypothesis is supported by the finding that Pb has no effect on hypothalamic progestin receptors in the absence of EB priming. Thus, changes in NA transmission might alter EB action in HYPO in addition to altering target cell sensitivity (through effects on progestin receptor concentration) to progestins. On the basis of these results we propose that the modulation of target tissue responsiveness to steroids is an important mechanism by which neurotransmitters affect steroid-dependent processes. The operation of such a mechanism would provide a rapid means by which environmental, behavioral and emotional events could modulate steroid-dependent behaviors and anterior pituitary function.

GABAergic Control of Receptivity in the Female Rat

GABAergic neurotransmission has been implicated in the control of the steroid-dependent behavior, lordosis. GABA has dual effects on lordosis: it facilitates lordosis through actions in the medial hypothalamus (mHYP) and it inhibits lordosis through actions in the preoptic area (POA). In the present study, gonadally intact and ovariectomized female rats were behaviorally tested with a sexually active male. Brains were removed from sexually receptive female either 1 or 24 h after behavioral testing. There was a significant difference in endogenous GABA concentration in HYP and POA between receptive, postreceptive and ovariectomized nonreceptive females. Specifically, GABA levels in postreceptive females were higher in the HYP (20%) and lower in the POA (21%) in comparison to receptive females (p less than 0.05). There was also a significant change in binding parameters of 3H-muscimol in the HYP and POA of receptive females as compared to 24 h postreceptive and ovariectomized rats. Attempts to modulate 3H-GABA release from hypothalamic tissue slices by estrogen or progesterone in ovariectomized rats yielded no effect on this parameter.