Donovan E. Fleming

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 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.

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 malnutrition, maternal stress, or ACTH injections during pregnancy on sexual behavior of male offspring

Abstract Pregnant rats were subjected to nutritional stress, environmental stress (immobilization-illumination-heat), or injections of adrenocorticotropic hormone (ACTH) during the third trimester of gestation. Masculine and feminine behavior potentials of the male offspring were determined in adulthood. Compared to control males, male copulatory behavior was severely impaired in all three experimental groups. The prenatally stressed animals showed a significant reduction in the cumulative percent ejaculating and an increase in the number of intromissions prior to the first ejaculation compared to control animals. When tested for female behavior, all three treatment groups displayed a significantly greater lordosis quotient than the control males. Gestation length was increased in the mothers exposed to environmental stress and ACTH injections but not in the nutritional stress animals. At birth, offspring from all experimental groups showed a significant reduction in body weight when compared with control offspring. These results confirm and extend earlier data which indicate that exposure of the mother to stress during the period of fetal sexual differentiation may impair masculine and feminine sexual behavior of the male offspring.

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.

Pre- or postnatal testosterone and flutamide effects on sexually dimorphic nuclei of the rat hypothalamus.

Utilizing the sexually dimorphic nature of hypothalamic nuclei, a determination of the effects of pre- or postnatal flutamide and testosterone treatments were examined in male and female rats. Statistical analysis compared treatments, sex, and time of injection in terms of the sexually dimorphic nucleus of the preoptic area (SDN-POA) and the anteroventral periventricular nucleus (AVPV) volumes and lengths. The present findings establish that pre- or postnatal hormonal environments are crucial in influencing sexual morphology on the developing brain.

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.

Effect of pharmacologically-induced arousal on the evoked potential in the unanesthetized rat.

Abstract Three positive-negative wave complexes of the visually evoked response (VER) in the unanesthetized rat were examined following iterative photic stimulation. EEG activation was induced by physostigmine, amphetamine, or pilocarpine in order to compare the peak latency and amplitude values of the VER components during arousal. It was served that the peak latency of only one component, a late negative wave occurring at approximately 160 msec was affected by the drug treatments. Except for one negative-positive amplitude measure occurring between 70 and 90 msec, the effect of drug-induced activation was to suppress the amplitude excursion of the remaining wave components. These observations agree with other VER studies in which arousal level was modified by type of behavioral task. It is suggested that the late negative wave peaking at 160 msec comprised the first wave of a photically evoked after-discharge burst.

The Photically Evoked Afterdischarge: A Model for the Study of Drugs Useful in the Treatment of Petit Mai Epilepsy

Lightly restrained albino rats were administered dipropylacetic acid, trimethadione, diphenylhydantoin, saline, and a pentylenetetrazol challenge. The results were attributed to the locus of action of the anticonvulsants and strongly support the usefulness of the photically evoked afterdischarge as a model for the evaluation of thalamically active drugs, with particular reference to those useful in the control of petit mal epilepsy.

Sexual dimorphism and aromatase in the rat retina

The present study: (a) determined the effects of both pre- and early postnatal androgen hormonal manipulation on retinal thickness, (b) examined the presence of the aromatase enzyme by immunocytochemistry in retinal tissue and (c) quantified aromatase activity in the rat retina. The results suggest that retinal thickness is influenced by perinatal hormone manipulation via aromatizable androgens that have implications for the sex differences seen in visual information processing and performance.