Behavioural Neuroscience Poster Session
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Introduction
Male and female rats show a number of similarities in the temporal regulation of their copulatory behavior: both sexes experience a refractory period after ejaculation, and both regulate the intervals between non-ejaculatory intromissions. In copulations where the male is given free access to the female, his temporal regulation of intromissions is faster than in copulations where the female is able to escape from the male after an intromission is received (Erskine, 1985). Additionally, following an ejaculation, a female's refractory period is typically shorter than the male's. The testing paradigm that allows the famale to escape from the male is referred to as a "pacing" test. This pacing test has been used to discern if the sexually dimporphic behaviors in the temporal regulation of copulation are the result of differential exposure to androges during early development.
While prenatal androgen treatment disrupts development of female sexual behavior, it is unclear what role prenatal androgen exposure has on the development of paced sexual behavior in the female. This study examines the effects of prenatal alteration of androgens on a female's perinatal genital morphology and adult sexual behavior.
Materials and Methods
To alter androgen levels in utero, two different methods were used. "Exeperiment A" describes how developing females were exposed to testosterone proprionate, whereas "Experiment B" describes how developing females were exposed to androsterone.
EXPERIMENT A
Pregnant rats were injected intramuscularly with 0.5mg of testosterone proprionate from day 10 to parturition.
EXPERIMENT B
Pregnant females were intramuscularly injected with androsterone benzoate or testosterone benzoate from day 10 to parturition.
Results
Effects of Prenatal Testosterone Treatment on Female's Pacing of Copulatory Behavior
Testosterone exposure during early prenatal development led to alteration of the female's pacing behavior. Testosterone-exposed females showed an increase in their intromission rate when compared to controls (Figure 1) (t-test, p<0.05). This increased rate of intromissions did not significantly decrease ejaculation latency. Prenatal treatment with testosterone also abolished the post-ejaculatory refractory period (PERP) in a majority of females. PERP is the interval following an ejaculation where a female occupies the non-copulatory chamber. Because many females did not show a PERP, a significant difference is seen between control and treatment groups (Figure 2) (Chi-Square, p<0.05) when the presence or absence of PERP is examined.
Effects of Prenatal Androsterone Treatment on the Genital Morphology of Females and on the Female's Pacing of Copulatory Behavior in Adulthood
Significant virilization was seen in both the androsterone benzoate and testosterone benzoate treatment groups in terms of anogenital morphology at birth (Figure 3) (t-test, p,0.05).
Androsterone benzoate exposure during prenatal development led to alterations of the female's pacing of sex behavior. The intromission rate of animals exposed to androsterone benzoate was increased when compared with controls (Figure 4) (t-test, p<0.05). Prenatal treatment with either androsterone benzoate or testosterone benzoate abolished the PERP in a significant majority of exposed females (Figure 5) (Chi-Square, p,0.05).
Discussion and Conclusion
The most consistent findings in these studies were the increase in intromission rates and the loss of the female's PERP. While normal females typically leave the male's chamber after ejaculation, most females prenatally exposed to testosterone or androsterone stayed in the chamber with the male.
Disruption of the post-ejaculatory refractory period with early prenatal androgen exposure suggests that the mechanisms underlying the control of male and female refractory periods are sexually dimorphic. However, it is unclear whether these affected mechanisms are peripheral, central, or a combination.
References
Erskine, M.S. (1985) Behavioral Neuroscience. 99:151-161
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