Fausto-Sterling - Sexing the Body

The Rodent’s Tale 231
tional to the length of time the ovary had been implanted. 169 Furthermore,
secretions during postnatal development can change the response of adult female
rats to estrogen. 170
Although many mammals have an initial discrete testosterone-sensitive period,
some do not. Pigs, for example, respond to testosterone from birth until
puberty, and the effects of injected hormones on behavior progress with time.
Since juvenile pigs frequently engage in sexual play in both male-male and
male-female combinations, it seems especially possible that experience and
hormone co-produce adult behaviors. 171 In rats, both masculine copulatory
responses and an increased orientation toward other females can result either
from specific sexual experience during adulthood or from hormonal treatments
during puberty or early adolescence. 172 In short, the fact that varying
levels of specific hormones circulate during the course of an individual’s life
span affecting nervous system anatomy and function warrants a life-span approach
to understanding the role of hormones in the development of sex
differences in neural structure. A life cycle, systems account of animal development
does not ignore the weeks between birth and puberty, and a more
complete theory opens new experimental vistas, ones less visible under the
O/A regime. 173
In an article on the sexual differentiation of the nervous system, the neuroanatomist
C. Dominique Toran-Allerand writes: ‘‘It is generally believed that
testicular androgens exert an inductive, or organizational influence in the
developing CNS [central nervous system] during restricted (critical), late fetal
or early postnatal periods of neural differentiation, at which time the tissue
is sufficiently plastic to respond permanently and irreversibly to these hormones’’
174 In their 1959 paper, Young and colleagues concluded their experiments
after testing treated guinea pigs twice, once at six to nine months and
again at one year of age. Guinea pigs, however, can live as long as eight years.
Yet there are no lifelong longitudinal studies of guinea pig mating behaviors
under different hormonal and experiential situations. This is true as well for
virtually all the other rodents studied in similar fashion, although the claim
of permanence may be more accurate for animals such as mice, which normally
live for only one to two years. 175
Behaviors that show up in the months immediately following puberty may
change with subsequent life experience. For instance, perinatally androgenized
female rats, under certain circumstances, will show a lowered frequency
or intensity of lordosis. Extensive testing, however, can overcome
such changes. 176 Similarly, testosterone can typically activate mounting in developmentally
normal female rats. 177 As one reviewer states, ‘‘the essential