Aivojen sukupuoli murrosiässä

Behavior was assayed in adult male Syrian hamsters
that had experienced adolescent brain development in
either the presence or the absence of gonadal hormones. In
these studies, hamsters were gonadectomized either before
(Adolescence without Hormones) or after puberty (Adolescence
with Hormones). Six weeks later, testosterone was
replaced and the males were tested with receptive females.
Males in the Adolescence without Hormones group consistently
displayed signiWcantly fewer mounts, intromissions,
and ejaculations than males in the Adolescence with Hormones
group, even after up to 17 days of testosterone treatment
and three exposures to a receptive female (Fig. 1).
Thus, the absence of gonadal hormones during adolescent
brain development results in a long-lasting impairment of
testosterone-induced reproductive behavior. Conversely,
the presence of gonadal hormones during adolescent brain
development enhances testosterone-induced male reproductive
behavior in adulthood, or in other words, masculinizes
behavioral responses. We have also found that
pubertal gonadal hormones alter the adult male’s behavioral
responses to ovarian hormones [102]. Adult male Syrian
hamsters normally show lordosis behavior if treated
with estrogen and progesterone and tested with a stud male
[20,65,126]. However, lordosis latency is signiWcantly
shortened in males that experience adolescence without
hormones, and is similar to lordosis latencies of hormoneprimed
female hamsters. Thus, testicular hormones during
puberty appear to both masculinize and defeminize behavioral
responses in adulthood.

In one study,
spatial cognition was compared in males with IHH beginning
before puberty and in males with acquired hypogonadotropic
hypogonadism in adulthood [50]. Spatial
cognition was impaired in males not exposed to pubertal
steroids, both in comparison to healthy control subjects
and males with acquired IHH in adulthood [50]. Women
with CPP also show diVerences from control subjects in
spatial functioning [30], suggesting that early exposure of
the brain to pubertal hormones also aVects this cognitive
system in females. With respect to psychosocial development,
clinical hormone treatment of patients with absent or
delayed puberty that is begun during the normal age range
for puberty results in normal development, but hormonal
treatments started after the age of 20 are ineVective
(reviewed in [73]). Thus, although clinical treatment typically
precludes the study of gonadal steroid and brain interactions
in humans, the information that is available
provides evidence for an organizational eVect of gonadal
hormones during adolescence on spatial cognition and psychological
function.

Agonistic behaviors in female rodents may also be organized
during adolescence. If female mice are ovariectomized
at the onset of puberty (30 days of age), treated with testosterone
for 3 weeks during adolescent development, and
then tested 6 weeks after discontinuation of testosterone
treatment, levels of aggressive behavior toward another
female in a neutral arena are much higher than in females
treated with vehicle [29]. Thus, adolescent exposure to
androgen has long-term eVects on aggression in female
mice. In addition, the development of sex diVerences in the
topography of dodging behavior, a stereotypical movement
shown by rats when protecting food against an intruder,
requires the presence of ovarian hormones both neonatally
and during puberty [34].

Taken together, these data suggest a possible link
between individual diVerences in puberty onset and individual
diVerences in behavior and risk for psychopathology. In
humans, the direct eVects of hormones on the brain, socialization
by other individuals, and internal perceptions of
pubertal body changes cannot be experimentally separated.
However, the number of studies showing a lasting eVect of
early puberty on individual diVerences suggests that
gonadal hormones may organize neural circuits. Future
experiments on pubertal timing in animal models of eating
disorders, depression, or other types of psychopathology
are needed to link the observed correlations in the human
literature to a causal eVect of the timing of the onset of
puberty.

Ihmisen kohdalla artikkeli keskittyi syömishäiriöiden ja masennuksen yhteyteen sukupuoleen ja murrosiän ajoitukseen. Tarinan yksi pääjuoni oli joka tapauksessa se, että aivojen sukupuolittumiselle on murrosiässä herkkyysvaihe, jolloin tapahtuu hormonien ohjaamina paljon muutoksia, jollaisia ei synny sitä ennen eikä myöskään sitä myöhemmin samojen hormonien vaikutuksesta. Ja että murrosiän ajoittumisella voi olla merkitystä siihen, minkälaiseksi kehitys ohjautuu.

Tämä herkkyysvaiheen ajoitus on todella mielenkiintoinen asia. Tuli mieleen, että se voisi liittyä mm. sentapaisiin asioihin kuin sukupuoli-identiteetin ja seksuaalisen suuntautumisen määräytymiseen niissä tapauksissa, joissa selitys ei löydy genetiikasta tai varhaislapsuuden hormonitasoista. Nykytutkimushan ei ole pystynyt osoittamaan mitään trans- tai homogeeniä - eikä pelkkä ankea lapsuuskaan taida mennä selityksestä.