Estrogens and phytoestrogens: brain plasticity of sexually dimorphic brain volumes.

Sexually dimorphic brain volumes (sexually dimorphic nucleus of the preoptic area (SDN-POA) and anteroventral periventricular (AVPV) nucleus) are influenced by estrogens. Phytoestrogens, derived from plants (especially soy products), are molecules structurally and functionally similar to estradiol. The purpose of this study was to examine: the consumption of phytoestrogen (using a phytoestrogen-rich (Phyto-600) versus a phytoestrogen-free (Phyto-free)) diets from conception to adulthood (or changing the diets during adulthood) and characterizing (a) circulating plasma phytoestrogen levels, (b) testosterone levels in males, (c) sexually dimorphic brain volumes (i.e. the SDN-POA and AVPV) and (d) the presence of apoptotic cells in these brain structures in Long-Evans rats. Phyto-600 fed animals displayed total serum phytoestrogens levels 37-fold higher compared to Phyto-free values. Circulating testosterone levels were not significantly altered by the diets. Female SDN-POA volumes were not altered by the diets. Whereas, males fed a Phyto-free diet displayed decreased SDN-POA volumes compared to male Phyto-600 values. Females fed the Phyto-600 diet displayed larger AVPV volumes compared to males on the same diet or females on the Phyto-free diet. Males fed the Phyto-free diet had the largest AVPV values compared to Phyto-600 fed males. When the SDN-POA region was examined in lifelong Phyto-free fed males, apoptotic cells were present versus males fed the Phyto-600 diet and in the AVPV region the opposite results were obtained. In summary, consumption of dietary phytoestrogens (estrogen mimics) can alter hormone-sensitive hypothalamic brain volumes in rodents during adulthood.

Altered sexually dimorphic nucleus of the preoptic area (SDN-POA) volume in adult Long-Evans rats by dietary soy phytoestrogens.

Naturally occurring estrogen-like molecules in plants (phytoestrogens), present via soy, in animal diets can alter morphology and physiology in rodents. Phytoestrogens have the ability to bind estrogen receptors and exert many of the biological responses evoked by physiological estrogens. This study characterized the effects of dietary phytoestrogens on the expression of body and prostate weight, circulating testosterone and estradiol levels, puberty onset, vaginal cyclicity, and volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) in Long-Evans rats. Using different experimental protocols, animals were fed either a phytoestrogen-rich (Phyto-600) or a phytoestrogen-free (Phyto-free) diet. Animals fed the Phyto-600 diet displayed significantly decreased body weights (in males and females), prostate weights and delayed puberty in females compared to that of animals fed the Phyto-free diet. Circulating testosterone or estradiol levels in males or estrous cyclicity were not altered by the diets. The volume of the SDN-POA was significantly altered by a change in diet at 80 days of age where one-half of the males or females fed the Phyto-600 diet (from birth) were switched to the Phyto-free diet until 120 days of age. Males initially fed a Phyto-600 diet but changed to a Phyto-free diet had significantly smaller SDN-POA volumes compared to males fed the Phyto-600 diet (long-term). These data suggest that consumption of phytoestrogens via a soy diet, significantly: (1) decreases body and prostate weight, (2) delays puberty onset, and (3) alters SDN-POA volumes during adulthood.

Steroid hormone influence on brain calbindin-D(28K) in male prepubertal and ovariectomized rats.

Calbindin-D(28K) (CALB), a calcium-binding protein, is thought to buffer intracellular calcium levels in neurons playing several important roles during central nervous system development such as, protecting against apoptosis (programmed cell death), neurodegenerative diseases and influencing sexually dimorphic brain structures. While preliminary research indicates that calbindin levels are modulated by steroids, there has not yet been a comprehensive study to determine the role androgens, androgen metabolites and corticosterone have on CALB expression in males and throughout the estrous cycle in rats. The present study had two main components utilizing Western analysis: (1) examination of the influence of steroid hormones (testosterone, dihydrotestosterone, corticosterone, and estradiol) and aromatase and 5alpha-reductase blockers on rat brain CALB expression in frontal cortex, MBH-POA, and cerebellum of male rats in experiment 1; (2) characterization of CALB abundance in frontal cortex, MBH-POA, and cerebellum throughout the hormonally induced estrous cycle of rats in experiment 2. There were no significant alterations in CALB levels by any of the treatments in experiment 1 or experiment 2 when frontal cortical tissue was examined. In male MBH-POA samples, estradiol treatment significantly increased CALB levels compared to oil-injection and aromatase or 5alpha-reductase blockers. Additionally, DHT treatment significantly increased CALB levels vs. 5alpha-reductase blocker values. In female samples, MBH-POA CALB levels increased from diestrus through proestrus and estrus to metestrus, where metestrus values were significantly higher compared to diestrus levels. In the cerebellum, the only significant alteration in CALB levels, in males, was observed in corticosterone-treated animals where a significant decrease was seen compared to oil injection. In females, cerebellum CALB levels increased from diestrus through proestus, with a slight decrease at estrus. Thereafter, CALB levels increased during metestrus where cerebellar CALB values were significantly higher than diestrus levels. These findings suggest that steroid hormones play an important regulatory role in CALB expression in the brain (except for the frontal cortex) where it potentially influences the development/function and neuroprotective changes of neuroanatomical structures.

Effects of maternal separation during early postnatal development on male sexual behavior and female reproductive function.

The endocrine response to stress is an important homoeostatic mechanism, and the secretion of glucocorticoids from the adrenal cortex is a central feature of this response. During early postnatal development, the neonatal rat displays a reduced hypothalamic-pituitary-adrenal (HPA) response to stress. This early period has been termed the 'stress hyporesponsive period' (SHRP). Maternal separation (Sep) of neonates from their mothers during early postnatal development alters the HPA response to stress. In this study, we report the effects of Sep during the SHRP. Female rats were time mated and randomly divided into control or Sep groups before birth. The Sep litters were removed from the mothers during the dark cycle for 6 h per day from postnatal day (PND) 2 to 10. On PND 28, the pups from both groups were weighed, the anogenital distance (AGD) was measured and the animals weaned. At 40 days of age, male and female animals from both groups were tested for open-field activity. As the animals matured, vaginal opening and estrous cycles were measured in females, and males were tested for male sexual behavior at adulthood. Basal, stress, and stress recovery serum corticosterone levels were measured from control and Sep male and female animals. Open-field activity was not significantly different between control or Sep male or female animals. Sep did not affect either vaginal opening or estrous cycles in female animals. Corticosterone secretion in response to stress was similar in control and Sep males and females; however, the recovery levels were significantly higher in Sep females than in Sep males or female control values. In male sexual behavior tests, Sep males had significantly longer mount latencies (time to the first mount), longer intromission latencies (time to the first intromission) and a significant reduction in the percent of animals ejaculating versus control values (controls 84 and Sep 50%). Therefore, Sep males as adults displayed altered reproductive behavior, whereas their stress recovery levels of corticosterone returned to near basal levels in a similar fashion to that observed for control non-handled males. In contrast, females displayed normal reproductive physiology, while their recovery levels of corticosterone remained high, unlike that observed with control females. Thus, significant gender differences in response to Sep (during the dark phase of the circadian cycle) were observed in the paradigm used in the present study.

Neuroendocrine regulation of sexually dimorphic brain structure and associated sexual behavior in male rats is genetically controlled.

Steroid hormones, particularly 17beta-estradiol (E2), regulate the development and expression of neural structures and sexual behavior. Recently, we demonstrated that E2-regulated responses are controlled by quantitative trait loci. In this study, we quantified 1) volume of the sexually dimorphic nucleus (SDN) of the preoptic area (POA); 2) medial basal hypothalamic (MBH)-POA aromatase and 5alpha-reductase enzyme activities during prenatal development and in adults; 3) serum LH, testosterone, FSH, E2, prolactin (PRL), and corticosterone levels; 4) reproductive organ (i.e., testis and ventral prostate) weights; and 5) male mating behavior in Noble (NB/Cr) and Wistar-Furth (WF/NCr) rat strains to determine the genetic influence on the measured parameters. Maximal phenotypic divergence in male SDN-POA volumes was seen between NB/Cr versus WF/NCr and BDIX/Cr rats (among nine rat strains initially examined), with the average SDN-POA volume of NB/Cr male rats being significantly greater ( approximately 30%) than that of either WF/NCr or BDIX/Cr males. Subsequent experiments investigated WF/NCr versus NB/Cr male rats in further detail. Significantly higher MBH-POA aromatase activity was seen in adult WF/NCr versus NB/Cr males, while MBH-POA 5alpha-reductase rates were not significantly different (within or between sex) for the two rat strains assayed. Serum LH levels were significantly higher (by greater than sixfold) in WF/NCr versus NB/Cr males, whereas testis organ:body weight and ventral prostate:body weight ratios in WF/NCr versus NB/Cr males were significantly smaller (by approximately 6-fold for testis and approximately 1.5-fold for prostate values). Serum FSH levels were significantly higher (by twofold) in WF/NCr versus NB/Cr males. However, serum testosterone levels were not significantly different, whereas E2 levels were approximately twofold higher (but not significantly different) in WF/NCr versus NB/Cr animals. No significant differences were found in basal (i.e., nonstress) serum PRL or corticosterone levels between the WF/NCr and NB/Cr males. In male copulatory tests, NB/Cr males exhibited significantly more aggressive sexual behavior (e.g., in mounting, intromission, and ejaculation parameters) compared with WF/NCr males. Taken together, these findings indicate that WF/NCr males are, in general, low responders, whereas NB/Cr males are high responders to hormonal signals. The obtained data suggest that the correlative, phenotypic variation in SDN-POA volume (i.e., structure) and reproductive hormone patterns and mating behavior (i.e., function) of WF/NCr versus NB/Cr males is regulated by potentially E2-mediated mechanisms that are genetically controlled.

Relationship between sexual behavior and sexually dimorphic structures in the anterior hypothalamus in control and prenatally stressed male rats.

The present study was designed to examine the effects of prenatal stress on the morphological development of sexually dimorphic structures in the anterior hypothalamus in male rats and to determine if there is a relationship between morphologic development of the brain and copulatory behavior in individual animals. Dams in the stress group were subjected to treatments of heat-light restraint during the third trimester of gestation (day 14 to parturition) three times daily for 45-min periods. At 90 days of age, prenatally stressed and control male offspring were tested during the dark cycle for spontaneous male sexual behavior. Volumes of the sexually dimorphic nucleus of the preoptic area (SDN-POA) and the anteroventral periventricular nucleus (AVPV) were measured. Comparisons were made between copulatory behavior and hypothalamic nuclear volumes. SDN-POA volumes were significantly reduced (feminized; males have a larger SDN-POA than females) in prenatally stressed males that did not copulate, whereas, SDN-POA volumes in prenatally stressed males that copulated were not altered. The few control males that did not copulate (sexually non-active) also had significantly reduced SDN-POA volumes compared to the control males that did copulate (sexually active). The volume of the AVPV was significantly increased (feminized; males have a smaller AVPV than females) in prenatally stressed males that were sexually non-active compared to AVPV volumes in sexually active males. The results obtained in this study provide a strong positive relationship between sexual behavior and the morphology of the two sexually dimorphic structures measured.

Brain aromatase in control versus castrated Norway Brown, Sprague-Dawley and Wistar adult rats.

Brain aromatase cytochrome P450 converts androgens to estrogens that play a critical role in the development of sexually dimorphic neural structures, the modulation of neuroendocrine function(s), and the regulation of sexual behavior. We characterized the influence of surgical castration on brain aromatase in Norway Brown and Wistar adult rats and compared their responses to Sprague-Dawley rats that were surgically or biochemically castrated (with flutamide, a known androgen receptor blocker). Aromata enzyme activity was measured by the tritiated water release assay in the medial basal hypothalmus/preoptic area (MBH/POA) and amygdala brain regions. The present results demonstrate that independent of the rat strain examined, MBH/POA aromatase is regulated by androgens (in Sprague-Dawley, Norway Brown and Wistar males). However, intact Wistar animals displayed significantly higher MBH/POA aromatase levels compared to Sprague-Dawley control values. Conversely, in the amygdala region, there was an apparent lack of androgen hormone action upon aromatase enzyme activity in some of the rat strains tested. The importance of brain aromatase regulating estrogen biosynthesis and influencing brain development and function is covered.

Effects of sexual behavioral manipulation on brain plasticity in adult rats.

The purpose of the present study was to determine the effects of sexual behaviorial manipulation on brain plasticity in adult male rats. Adult male Sprague-Dawley rats that copulated during male sexual behavior testing were divided into four groups: control male; gonadectomized (Gdx) male; sexually active male; and sexually nonactive male. Female animals were used as an additional control group. At the end of a 12-week experimental period, the animals were again tested for male sexual behavior and tested for sexual motivation. Sexual behavior manipulations over the 12-week period resulted in significant differences in mount latency, mount frequency, intromission latency, intromission frequency, ejaculation latency, and the postejaculation interval. In the motivation test, significant differences in the number of approaches, contacts, and crossings of an electrified grid separating the test animal from a receptive female were also observed. Sexually dimorphic nucleus of the preoptic area (SDN-POA) volumes in sexually nonactive males were significantly smaller than in control males or sexually active males. Anteroventral periventricular nucleus (AVPV) volumes in the male groups were not significantly altered by sexual behavioral manipulations, however, the nonactive AVPV vol. was the only vol. not significantly different from the control female vol. These data demonstrate that in the adult rat, sexual behavioral manipulations resulted in significant alterations in behavior and in the vol. of the SDN-POA and that the effect of sexual behavior on the AVPV needs to be further investigated.

Developmental expression of calretinin in the medial basal hypothalamus and amygdala from male and female rats.

Developmental expression of calretinin in the medial basal hypothalamic (MBH) and amygdala region was examined by Western analysis. Males displayed significantly higher calretinin levels compared to females in the MBH (but not the amygdala) on gestational day 19 and 20. These data imply that hormonal factors may regulate developmental MBH calretinin expression. In turn, sexually dimorphic brain structures might be influenced by calretinin levels that can alter sexually dimorphic patterns of steroidogenesis, cellular migration or programmed cell loss mechanism(s) during neuronal development by modulating intracellular calcium concentrations.

Calbindin-D28k is regulated by adrenal steroids in hypothalamic tissue during prenatal development.

Regulation of calbindin-D28k (CALB) in the medial basal hypothalamus (MBH) from male and female fetuses was examined by Western analysis. Control fetal males displayed significantly higher MBH CALB levels compared to females at gestational day 20. Whereas, in general, the lowest CALB levels were recorded in male and female fetuses from long-term prenatally stressed or fetuses from adrenalectomized pregnant rats. These data indicate that corticosterone regulates MBH CALB expression during prenatal development and CALB may be implicated in modulating the sexual differentiation of neural structures within the MBH during perinatal development.

Effects of prenatal testosterone on sexual behavior, reproductive morphology and LH secretion in the female rat.

Sexual differentiation of many brain structures and functions is dependent on levels of testosterone (T) or its metabolites during certain 'sensitive' developmental periods. If T is present during these perinatal periods, masculinization and defeminization of sexual behavior occur; also, reproductive physiology, and central nervous system morphology and function are altered. The purpose of the present study was to characterize the influence of T at specific prenatal developmental intervals on offspring reproductive morphology, physiology, locomotor activity and sexual behavior during postnatal development. To avoid complications induced by endogenous testicular activity, only females were examined. Free T was used because of its relative short half-life, so that the effects induced by its administration on a specific gestational day (GD) could be evaluated. Pregnant rats received a single subcutaneous injection of either sesame oil (controls) or 5 mg of T on GD 16, 17, 18, 19, 20, 21, or 22. Female offspring of pregnant rats exposed to T displayed significant alterations in morphology and behavior. The anogenital distance, measured at 25 days postbirth, was significantly increased if T was administered on GD 16, 17 or 18. T treatment on GD 16 or each day thereafter through GD 20 significantly delayed the normal occurrence of vaginal opening (controls at 37.5 days vs. T treatment which ranged from 38.5 to 41.4 days). Abnormal vaginal morphology (enlarged clitoris) was also observed when T was injected during a similar prenatal interval (i.e. GD 16 to GD 22). Furthermore, prenatal T treatment on GD 18 (and each day thereafter), until GD 22 significantly decreased lordotic behavior compared to control values. However, exposure to T, on any prenatal GD did not alter the animals' ability to exhibit an induced luteinizing hormone (LH) surge. These results suggest that the onset for altered reproductive morphology occurs at least as early as GD 16, whereas the onset of sexual behavior sensitivity occurs precisely at GD 18, and that the normal pattern of adult LH release in females is not altered by prenatal androgen treatment using this specific paradigm.

Inhibition of brain 5 alpha-reductase in pregnant rats: effects on enzymatic and behavioral activity.

Medial basal hypothalamic (MBH) 5 alpha-reductase activity was significantly blocked with a known inhibitor, Proscar (Finasteride), in pregnant rats while their open-field behavior was quantified during the last week of pregnancy. In control animals, open-field behavior significantly decreased (in a stair-step fashion) as a function of increasing gestational age. Conversely, in Proscar-treated animals open-field values significantly increased on day 15 and 17 of gestation compared to control values. These data indicate that inhibition of MBH 5 alpha-reductase during pregnancy significantly increased open-field activity levels during late gestation in rats and provides evidence for a link between the production of 5 alpha-reduced metabolites of progesterone in brain and behavioral activity during pregnancy.

The hormone-sensitive early postnatal periods for sexual differentiation of feminine behavior and luteinizing hormone secretion in male and female rats.

The purpose of this study was to determine the duration of the hormone-sensitive postnatal period during which a single injection of testosterone propionate (TP) influences feminine behavior and luteinizing hormone (LH) secretion in male and female rats. Male pups were castrated on the day of birth (day 1) between 6 and 12 h postpartum. On postnatal day 3, 4, 5, 6, 7, 8, or 9 female pups and castrated males (fales) were injected subcutaneously with testosterone propionate (TP-500 micrograms). The females were laparotomized at 60 days of age, and ovarian tissue was removed for histological analysis. Female behavior was evaluated at 100 days of age. At 150 days of age, the ability of steroids to facilitate LH secretion was determined. Tests for lordosis indicated a diminished lordotic quotient (LQ) with both females and fales treated with TP on postnatal day 3, 4, 5, 6, or 7. On day 8 or 9, however, the lordotic response was at control levels. Females in all TP treated groups had significantly reduced number of corpora lutea. Females and fales treated with TP on postnatal day 3, 4, 5, 6, 7, 8, or 9 failed to exhibit an LH surge as adults. The results indicate that the neural control of feminine behavior (LQ) is hormone-sensitive to a single injection of TP up through the 7th day of postnatal life, whereas the neural substrate regulating LH secretion was sensitive in the present study at least up through day 9 in both fales and females.

Onset of the hormone-sensitive perinatal period for sexual differentiation of the sexually dimorphic nucleus of the preoptic area in female rats.

The volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) of the rat brain is severalfold larger in males than in females. The volume of the SDN-POA can be influenced significantly by the hormonal milieu during the perinatal "critical period" of sexual differentiation of the brain. The purpose of the present study was to determine the onset of this period of sexual differentiation of the SDN-POA. Pregnant rats received no treatment or were injected subcutaneously with oil on day 17, 18, or 20, or testosterone (T;5 mg) on days 16-22 of gestation. On postnatal day 15, unilateral SDN-POA volumes from female offspring prenatally exposed to testosterone on day 16 or 17 were not different from values of control (untreated or oil-injected) offspring. Female offspring from mothers treated with testosterone on day 18, 19, or 20 of gestation showed a significant and similar increase in SDN-POA volume over values from control animals. SDN-POA volumes from female offspring exposed to testosterone on day 21 or 22, although larger than those of controls, were not different statistically. We conclude that with the specific paradigm used in this study SDN-POA development is insensitive prior to day 18 of gestation, the day on which the onset of the hormone-sensitive period occurs.

Termination of the hormone-sensitive period for differentiation of the sexually dimorphic nucleus of the preoptic area in male and female rats.

The volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) in the rat brain is several-fold larger in males than in females. The volume of the SDN-POA can be influenced significantly by the hormone milieu during early postnatal life. The purpose of the present study was to identify when termination of the sensitive period occurs during which exogenous androgen administration influences SDN-POA volume in males gonadectomized on the first day of postnatal life (fales) or intact females. Analysis of the SDN-POA in fales showed that testosterone propionate (TP, 500 micrograms) treatment on days 2, 3, 4, or 5, significantly increased its volume over values from oil-treated fales. In contrast, TP treatment in fales on days 6, 7, or 8, failed to increase SDN-POA volume. A similar pattern was observed in females treated with TP. Females treated with TP (500 micrograms) on days 2, 3, 4, or 5, showed a significant increase in SDN-POA volume compared to the values from oil-injected animals, while the same TP treatment in females on days 6, 7, or 8, resulted in no such enhancement. The absolute and relative change in SDN-POA volume following postnatal androgen treatment is greater in males than in females. We conclude that (1) SDN-POA development is sensitive to hormone action through postnatal day 5 and then abruptly becomes insensitive to this dosage of TP, and (2) although the temporal pattern of the response is similar in males and females, androgen exposure postnatally results in a consistently greater increase in the male SDN-POA volume than in the female's. This greater response may be due to exposure prenatally to endogenous androgen in males.

Fetal male masculinization in control and prenatally stressed rats.

The present experiments were designed to test the hypothesis that males in utero masculinize the development of other males. This effect was examined during fetal development in males from control and prenatally stressed rats. A code identified the number of cervical-flanking males between the target male and the cervical end of the uterus. The male parameters morphology (anogenital distance) and body, adrenal, and testis weights were recorded on the eighteenth and twentieth gestational days and categorized by the cervical-flanking male classification. At Day 18, control fetuses with two cervical-flanking males in utero displayed significantly greater anogenital distance values than did males with no cervical-flanking male. At Day 20, control fetuses with two cervical-flanking males had testicular weights significantly greater than those of fetuses with one or zero cervical positioned male. Prenatal stress markedly impaired male fetal development at gestational Days 18 and 20 while suppressing the cervical-flanking male effect. These results confirm and extend previous data that indicate: (a) prenatal stress disrupts normal fetal development, resulting in long-term changes; and (b) androgens via a cervical-flanking blood-flow mechanism influence littermate morphology and sexual development during the prenatal period. Our findings also demonstrate that a general masculinizing effect could not be made across the measured male parameters since the effect of males positioned at the cervical-flanking region in utero appears to be dependent upon maternal sources of variance. Finally, androgens prenatally have an apparent positive interaction with somatic growth.

Relationships between sexual activity, plasma testosterone, and the volume of the sexually dimorphic nucleus of the preoptic area in prenatally stressed and non-stressed rats.

The sexually dimorphic nucleus of the preoptic area (SDN-POA) has recently been shown to be reduced in cross-sectional area in prenatally stressed male rats. As masculine copulatory behavior is also reduced in prenatally stressed animals, the present study was designed to test a possible relationship between the entire volume of the SDN-POA and masculine sexual activity in both prenatally stressed and control adult male rats. We report here that prenatally stressed adult males have significantly reduced SDN-POA volumes, reduced levels of sexual activity and lower plasma testosterone levels as compared to control animals. Additionally, however, a strong positive relationship was demonstrated between SDN-POA volume and sexual activity in both stressed and control animals. SDN-POA volumes of sexually active animals from stressed and control groups are approximately equal. SDN-POA volumes of sexually non-active animals are also equal and are about two times smaller than those of sexually active animals, either stressed or control. Similar correlations are reported between SDN-POA volume and testosterone level, and between testosterone level and sexual activity. It is concluded that (1) SDN-POA volume is predictive of sexual activity in both stressed and control male rats, (2) there is a relationship between SDN-POA volume and plasma testosterone level, and (3) the SDN-POA likely has multiple roles in the circuitry underlying masculine reproductive processes and hormone regulation.

Effects of prenatal stress on sexually dimorphic asymmetries in the cerebral cortex of the male rat.

Diamond and collaborators have reported sexual dimorphic right greater than left thickness asymmetries in the cerebral cortices of male Long-Evans rats. In the present work we report that normal Sprague-Dawley males show a similar cortical asymmetry. On the other hand, Sprague-Dawley males whose mothers were subjected to treatments of prenatal stress three times daily during the third trimester of gestation showed a nonsignificant left greater than right pattern in the same cortical areas--a pattern characteristic of the female cortex. These results are consistent with other findings from our laboratory wherein we have recently shown that prenatal stress during the third trimester of gestation demasculinizes sexually dimorphic regions of the preoptic hypothalamus in male rats. It is concluded that stress mediated changes in the prenatal environment can have a profound effect on the developmental processes which shape the morphology of sexually dimorphic regions of the brain in male offspring. Normal male anatomy is biased in the direction of a feminine structure. Such an anatomical picture is consistent with demasculinized and feminized behavior patterns exhibited by male offspring of prenatally stressed dams.

Effects of prenatal stress on differentiation of the sexually dimorphic nucleus of the preoptic area (SDN-POA) of the rat brain.

The present study was designed to determine the effects of prenatal malnutrition or environmental stress on the development of the sexually dimorphic nucleus of the preoptic area (SDN-POA). Pregnant rats were divided into a control group and two treatment groups (immobilization-illumination-heat or environmental stress, and nutritional stress). The two forms of stress were administered during the third trimester of gestation (days 14-20). Male and female offspring were sacrificed at birth, 20, and 60 days postnatally. The cross-sectional area of the SDN-POA was identified under light microscopy and was measured. The data confirm previous studies by showing a significant sex difference in the SDN-POA between control male and female rats. Prenatally stressed males sacrificed 20 and 60 days after birth showed SDN-POA areas 50% smaller than the nuclear areas of control males. The size of the SDN-POA of female offspring, however, was not significantly altered by prenatal treatments.