Endocrine basis for two types of individual differences in lordosis reflex intensity

Developmental treatment with ethinyl estradiol, but not bisphenol A, causes alterations in sexually dimorphic behaviors in male and female Sprague Dawley rats

The developing central nervous system may be particularly sensitive to bisphenol A (BPA)-induced alterations. Here, pregnant Sprague Dawley rats (n = 11-12/group) were gavaged daily with vehicle, 2.5 or 25.0 μg/kg BPA, or 5.0 or 10.0 μg/kg ethinyl estradiol (EE2) on gestational days 6-21. The BPA doses were selected to be below the no-observed-adverse-effect level (NOAEL) of 5 mg/kg/day. On postnatal days 1-21, all offspring/litter were orally treated with the same dose. A naïve control group was not gavaged. Body weight, pubertal age, estrous cyclicity, and adult serum hormone levels were measured. Adolescent play, running wheel activity, flavored solution intake, female sex behavior, and manually elicited lordosis were assessed. No significant differences existed between the vehicle and naïve control groups. Vehicle controls exhibited significant sexual dimorphism for most behaviors, indicating these evaluations were sensitive to sex differences. However, only EE2 treatment caused significant effects. Relative to female controls, EE2-treated females were heavier, exhibited delayed vaginal opening, aberrant estrous cyclicity, increased play behavior, decreased running wheel activity, and increased aggression toward the stimulus male during sexual behavior assessments. Relative to male controls, EE2-treated males were older at testes descent and preputial separation and had lower testosterone levels. These results suggest EE2-induced masculinization/defeminization of females and are consistent with increased volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) at weaning in female siblings of these subjects (He, Z., Paule, M. G. and Ferguson, S. A. (2012) Low oral doses of bisphenol A increase volume of the sexually dimorphic nucleus of the preoptic area in male, but not female, rats at postnatal day 21. Neurotoxicol. Teratol. 34, 331-337). Although EE2 treatment caused pubertal delays and decreased testosterone levels in males, their behaviors were within the range of control males. Conversely, BPA treatment did not alter any measured endpoint. Similar to our previous reports (Ferguson, S. A., Law, C. D. Jr and Abshire, J. S. (2011) Developmental treatment with bisphenol A or ethinyl estradiol causes few alterations on early preweaning measures. Toxicol. Sci. 124, 149-160; Ferguson, S. A., Law, C. D. and Abshire, J. S. (2012) Developmental treatment with bisphenol A causes few alterations on measures of postweaning activity and learning. Neurotoxicol. Teratol. 34, 598-606), the BPA doses and design used here produced few alterations.

I. Levels of 5α-reduced progesterone metabolite in the midbrain account for variability in reproductive behavior of middle-aged female rats

At middle-age, the reproductive capacity of female rats begins to decline. Whether there are consequences for social and reproductive behaviors related to changes in estradiol (E(2)), progesterone (P(4)) and its 5α-reduced metabolites, dihydroprogesterone (DHP) and 5α-pregnan-3α-ol-20-one (3α,5α-THP), is of interest. In Experiment 1, 1-year-old female breeder rats that had "maintained their reproductive status" (having 4-5 days estrous cycles, > 60% successful pregnancies after mating, > 10 pups/litter) or their age-matched counterparts with "declining reproductive status" were assessed in social interaction, standard mating, and paced mating when in proestrus. Rats that maintained reproductive status tended to have higher levels of proceptivity, and significantly reduced aggression, towards males, compared to rats with declining reproductive status. Basal midbrain E(2) and DHP levels accounted for a significant proportion of variance in lordosis. In Experiment 2, 1-year-old, age-matched, female breeders that had maintained reproductive status or were in reproductive decline were compared to three-month old, nulliparous females that had regular (4-5 days) or irregular estrous cycles. Age did not influence paced mating but younger rats had greater diencephalon E(2) than did middle-aged rats. After mating, rats with declining/irregular reproductive status had higher P(4) and DHP levels in midbrain than did rats with maintaining/regular reproductive status, albeit differences in midbrain 3α,5α-THP were not seen. Middle-aged rats that maintained reproductive function had greater 3α,5α-THP formation in diencephalon compared to other groups. Thus, age-related changes in central progestogen formation in midbrain or diencephalon may contribute to some variability in expression of reproductive behaviors.

Infusions of 3alpha,5alpha-THP to the VTA enhance exploratory, anti-anxiety, social, and sexual behavior and increase levels of 3alpha,5alpha-THP in midbrain, hippocampus, diencephalon, and cortex of female rats

17beta-Estradiol (E2) and progesterone (P4) influence the onset and duration of sexual behavior and are also associated with changes in behaviors that may contribute to mating, such as exploration, anxiety, and social behaviors (socio-sexual behaviors). In the midbrain ventral tegmental area (VTA), the P4 metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), modulates lordosis of E2-primed rodents; 3alpha,5alpha-THP can also influence anxiety and social behaviors. To examine if 3alpha,5alpha-THP in the VTA mediates socio-sexual behaviors, we infused 3alpha,5alpha-THP to the VTA of diestrous and proestrous rats. As expected, proestrous, compared to diestrous, rats showed more exploratory (open field), anxiolytic (elevated plus maze), pro-social (partner preference, social interaction), and sexual (paced mating) behavior and had increased E2, P4, dihydroprogesterone (DHP), and 3alpha,5alpha-THP in serum, midbrain, hippocampus, diencephalon, and cortex. Infusions of 3alpha,5alpha-THP to the VTA, but not control sites, such as the substantia nigra (SN) or central grey (CG), of diestrous rats produced behavioral and endocrine effects akin to that of proestrous rats and increased DHP and 3alpha,5alpha-THP levels in midbrain, hippocampus, and diencephalon. Levels of DHP and 3alpha,5alpha-THP, but neither E2 nor P4 concentrations, in midbrain, hippocampus, diencephalon, and/or cortex were positively correlated with socio-sexual behaviors. Thus, 3alpha,5alpha-THP infusions to the VTA, but not SN or CG, can enhance socio-sexual behaviors and increase levels in midbrain, hippocampus, and diencephalon.

Progestin concentrations are increased following paced mating in midbrain, hippocampus, diencephalon, and cortex of rats in behavioral estrus, but only in midbrain of diestrous rats

BACKGROUND

The progesterone (P(4)) metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), acts in the midbrain ventral tegmental area (VTA) to modulate the intensity and duration of lordosis. 3alpha,5alpha-THP can also have anti-anxiety and anti-stress effects in part through actions in the hippocampus. Separate reports indicate that manipulating 3alpha,5alpha-THP levels in the VTA or hippocampus respectively can influence lordosis and affective behavior. 3alpha,5alpha-THP levels can also be altered by behavioral experiences, such as mating or swim stress. Whether endogenous levels of 3alpha,5alpha-THP modulate and/or are increased in response to affective and/or reproductively-relevant behaviors was investigated.

METHODS

In Experiment 1, rats in behavioral estrus or diestrus were individually tested sequentially in the open field, elevated plus maze, partner preference, social interaction, and paced mating tasks and levels of 17beta-estradiol (E(2)), P(4), dihydroprogesterone (DHP), and 3alpha,5alpha-THP in serum, midbrain, hippocampus, diencephalon, and cortex were examined. In Experiments 2 and 3, rats in behavioral estrus or diestrus, were individually tested in the battery indicated above, with, or without, paced mating and tissues were collected immediately after testing for later assessment of endocrine measures.

RESULTS

In Experiment 1, behavioral estrous, compared to diestrous, rats demonstrated more exploratory, anti-anxiety, social, and reproductive behaviors, and had higher levels of E(2) and progestins in serum, midbrain, hippocampus, diencephalon, and cortex. In Experiment 2, in midbrain and hippocampus, levels of 3alpha,5alpha-THP and its precursor DHP were increased among rats in behavioral estrus that were mated. In diencephalon, and cortex, DHP levels were increased by mating. In Experiment 3, in midbrain, levels of 3alpha,5alpha-THP and its precursor DHP were increased among diestrous rats that were tested in the behavioral battery with mating as compared to those tested in the behavioral battery without mating.

CONCLUSIONS

Increased levels of 3alpha,5alpha-THP in behavioral estrus versus diestrous rats are associated with enhanced exploratory, anti-anxiety, social, and reproductive behaviors. Rats in behavioral estrus that are mated have further increases in 3alpha,5alpha-THP and/or DHP levels in midbrain, hippocampus, diencephalon, and cortex than do non-mated rats in behavioral estrus, whereas diestrous rats only show 3alpha,5alpha-THP increases in midbrain in response to behavioral testing that included mating.

Mammary Cancer and Social Interactions: Identifying Multiple Environments That Regulate Gene Expression Throughout the Life Span

Now that the human genome has been sequenced, along with those of major animal models, there is an urgent need to define those environments that interact with genes. The traditional view focuses on ways that gene products interact with the nuclear environment to regulate cell function, causing the physiologic changes, behaviors, and diseases manifest throughout development and aging. Although this view is essential, it is equally essential to understand the converse relationship, namely, to identify those environments at higher levels of organization that regulate the expression of specific genes. Given the vastness of this problem, one effective strategy is to start with a trait for which some of the genes have already been identified, such as malignant disease. In rats, social isolation and hypervigilance increase the incidence of mammary tumors, accelerate aging, and shorten the life span. We propose that similar environmental regulation of gene expression may underlie the disproportionately high mortality from premenopausal breast cancer of Blacks, a minority group that can experience high levels of loneliness and hypervigilance. Our goal is to identify which environments-social, psychological, hormonal, and cellular-regulate genetic mechanisms of mammary cancer risk as well as the specific times in the life span when they do so.

Effectiveness of estrogen replacement in restoration of cognitive function after long-term estrogen withdrawal in aging rats

Recent studies suggest that some aspects of learning and memory may be altered by a midlife loss of estrogen, indicating a potential causal relationship between the deficiency of ovarian hormones and cognitive aging. In this study, the effects of estrogen withdrawal and replacement were tested in middle-aged Fischer-344 rats using different memory tasks. Estrogen withdrawal accelerated the rate of cognitive aging. A deficit first occurred 4 months after ovariectomy in working memory, which was tested in a delayed-nonmatching-to-position task, and progressed from long-delay to short-delay trials. Reference memory, which was tested in a place discrimination task and a split-stem T-maze, was not affected by aging or ovariectomy. The efficacy of estrogen in ameliorating the cognitive deficit in old rats depended on the type of treatment (acute vs chronic) and whether the aging-related decline in a particular cognitive process was aggravated by estrogen withdrawal. Chronic estrogen treatment (implants) was effective in improving working memory only when primed with repeated injections of estrogen, indicating that simulating the estrogen fluctuations of the estrous cycle may be more effective than the widely used mode of chronic pharmacological treatment. A challenge with scopolamine revealed that ovariectomy-induced cognitive deterioration coincided with a compromised cholinergic system. Importantly, the estrogen treatment that had restored effectively the cognitive abilities of old ovariectomized rats did not reduce their sensitivity to scopolamine. Taking into consideration that estrogen was highly effective against the amnestic action of scopolamine when tested in young-adult rats, these data emphasize that mechanisms of the protective effect of estrogen differ in young and old rats.

Variation in reproductive traits is associated with short anogenital distance in female rats

Anogenital distance was used as a biomarker for natural variation in prenatal androgenization of female rats and was associated with individual differences in a suite of reproductive characteristics. Females with short anogenital distances were likely to have first vaginal estrus earlier than females with longer anogenital distances and to have first vaginal estrus on the same day as vaginal opening. In young adulthood, females with short anogenital distances had shorter ovarian cycles and less intense lordosis reflexes in response to manual palpation than those with longer anogenital distances, but only when living individually, not in groups. Taken together, these findings indicate that prenatal androgenization affects reproductive traits throughout the life span.