David Eliason and Dr. Reuben W. Rhees, Anthropology

It has been shown that several structures in the mammalian brain exhibit differences between males and females. These variations are referred to as sexually dimorphic areas. In recent years, study of the brain has demonstrated the complex interconnections between the sexual behavior of individuals and the neurological functions of the brain. It is now considered appropriate to refer to the brain as a part of the reproductive system in reference to the determining factor it plays in development of the sexual organs and in regulating the behavior of the organism. The mammalian fetus originally possesses the potential to become either male or female in terms of the internal sexual organs. Specialization occurs through the activity of hormones such as testosterone, which causes the male (or Wolffian) reproductive system to grow in the place of the female (or Müllerian) system. The gender orientation of the brain parallels this process, to the extent that the presence or absence of specific hormones during a critical period of time the determines the sexual condition of the brain, and ultimately, the sexual behavior of the organism.

Quantitative analysis of specific hormonal and enzymatic activity within the brain of the rat has placed the genesis of neuro-sexually dimorphic areas in the final days of perinatal development and the first few days of postnatal life. The metabolic conversion of testosterone to estradiol through the activity of the enzyme, aromatase, occurs during this critical period. It has been observed that the activity of testosterone, and more specifically, the aromatization of testosterone to estradiol during this period, is directly related to the degree of masculinization in the rat brain. The absence of androgens (such as testosterone) will retard the masculinization and favor feminization of the brain and subsequent behavior of the rat, regardless of the genetic sex or development of the sexual organs.

While it is understood that hormones play a vital role in the sexual differentiation of the rat brain, very little is known about the sources of these hormones. Some possible hormonal origins include the fetal testes and adrenal glands, the placenta, and the maternal adrenal glands. The purpose of this experiment was to determine the role, if any, of the maternal adrenal glands in the masculinization of the fetal rat brain and if feminization of the male rat brain is achieved in the absence of these particular developmental factors. The adrenal glands consist of two halves, the medulla and the cortex. The glucocorticoids released by the cortex are in response to stressors on the maternal body, and rise notably during pregnancy. In an effort to eliminate the activity of the adrenal cortex during pregnancy the mothers were adrenalectomized before impregnation. The degree to which the fetal brain might be affected by the absence of the maternal adrenal glands can be observed through the general sexual behavior of the male offspring once they are of an age conducive to normal sexual activity. It was hypothesized that some degree of demasculinization would be discovered due to the decrease in androgens available to the fetal brain during the critical stage of sexual development. Due to the fact that pregnancy has been established as a significant source of stress, and the mother normally utilizes her adrenal hormones in compensating for the stress. It was hypothesized that the health of the pups born to a mother without adrenal glands would be compromised. In addition to testing the sexuality of male rat offspring, the quality of the litters born to adrenalectomized mothers would be rated through investigation of such parameters as litter size, average fetal body weight, and gestation length.

A group of female Nulliparus female rats were adrenalectomized and allowed to recover for fourteen days before being impregnated. A second group of female rats were impregnated at the same time to act as a control group. After the offspring were delivered, the mothers and pups were housed under controlled conditions. The male rat pups were tested for sexual behavior at the age of 90 days.

Immediate data concerning the quality of the litters appears to support the hypothesis concerning the possible contributions of the maternal adrenal glands to the health of the developing fetus. Gestational duration, litter size, and fetal body weight on day 20 after fertilization were recorded for the control and experimental groups.

Gestational Period:
Control                                                                       21.5 ± 0.7 days
Adrenalectomized                                                 22.5 ± 0.5 days

Litter Size:
Control                                                                      13 ± 4 pups
Adrenalectomized                                                14 ± 3 pups

Fetal Body Weight (day 20):
Control                                                                     Female (n=31) 4.lg±0.2g; Male(n=23) 4.3g±0.3g
Adrenalectonmized                                            Female (n=13) 3.lg±0.lg; Male(n=12) 2.8g±0.2g

The difference of one day in the gestational period was not considered significant, and the discrepancy in litter size (as the adrenalectomized mothers actually had larger litters on the average) was also inconclusive. The difference in body weight at day 20 (normally one day before the pups are born) was significant. The females averaged 1 gram less in body weight and the males 1.5 grams.

The second portion of the experiment investigated the sexual behavior of the male offspring in an effort to represent any possible alterations in the hormonal activity in the fetal rat promoting formation of the male brain. The males were maintained until they reached the age of 90 days, at which time male rats are normally sexually active. Females were rendered receptive through a process of ovariectomy followed by the administration of hormones (0. 1 mg estradiol benzoate followed 42 hours later by 1 mg of progesterone). Six hours after administration of the progesterone, the females were introduced into a plexiglass mating arena (45 x 27 x 40 cm). The mating performance was observed and several measurements were taken: time to first mount or intromission (mount latency and intromission latency); the number of mounts or intromissions to ejaculation (mount frequency and intromission frequency); time to ejaculation (ejaculation latency); and the time from ejaculation to the next intromission (post-ejaculatory interval).

In comparison between the males born to adrenalectomized mothers and those in the control group, the only significant differences noted were in the mount latency and ejaculation latency (or time to each of these events).
First Mount Latency:
Control                                                4.95 ± 1.2 minutes
Adrenalectomized                         24.50 ± 4.76 minutes

Ejaculation Latency:
Control                                               20.90 ± 3.79 minutes
Adrenalectomized                        29.00 ± 5.41 minutes

Ultimately, the males in both groups exhibited the same degree of sexual activity. However, the time before the first mount was almost 15 minutes longer among the males born to adrenalectomized mothers. The average time before ejaculation was 9 minutes longer among the same group.

In conclusion, the effects of the adrenal gland during pregnancy on the developing rat pups is noted. Most significant among the parameters of the litter quality is the decrease in the average fetal weight at day 20 in offspring to adrenalectomized females. Although all of the experimental males achieved ejaculation, the sexual behavior of male offspring appears to be retarded by the absence of the maternal adrenal gland. Further study would be required to determine the actual mechanisms of adrenal hormone activity during pregnancy and the effects on various aspects of the developing fetus.