Gonadal hormones profoundly
influence brain physiology and behavior
in vertebrates. During development, these
hormones determine whether brains will function
in a typically male or female fashion. In
adulthood, environmentally induced, or endogenously
programmed, changes in gonadal hormone levels
alter hormone-sensitive functions or behaviors.
These actions of gonadal hormones provide
valuable tools in relating brain structure
to function. In principle, one can relate
sexual differentiation of hormone-sensitive
functions with sexual differentiation of
structures implicated in these functions.
In addition, one can relate changes in structure
and function that are induced by gonadal
hormones in adult animals. The cellular
and molecular mechanisms underlying these
hormonal actions, however, are poorly understood.
Legend: Vasopressin innervation (yellow
dots) in the lateral septum of a female
(left) and male rat (right).
Our lab addresses this issue by studying
a sexually dimorphic group of forebrain
neurons that produce the neuropeptide vasopressin.
The projections of these neurons are much
denser in males than in females. Gonadal
hormones dramatically influence these neurons
throughout life. For example, a drop in
the level of sex hormones in adulthood is
immediately followed by a reduction in vasopressin
gene expression. It takes months, however,
before vasopressin has disappeared from
the terminals of these neurons. Such gradual
changes may explain the gradual changes
found in male sexual behavior and aggressive
behavior after castration.
Research in the lab is centered around
two main questions, How do males end up
having many more vasopressin neurons than
females, and What are the consequences of
a sex difference in vasopressin innervation
for brain function and behavior. Our research
suggests that instead of influencing processes
such as cell birth or cell death, testosterone
permanently influences the neuropeptide
expression in a fixed set of cells. How
testosterone causes permanent changes in
neuropeptide expression is the focus of
our research. Interestingly, our research
suggests that not only sex differences in
gonadal hormone levels, but also the presence
of a different set of sex chromosomes may
directly contribute to the sexual differentiation
of this system.
Legend: Male (left) and female prairie
vole (right) hovering over a pup (middle)
The answer to the second question is quite
intriguing: sex differences in vasopressin
innervation may cause as well as prevent
sex differences in behavior. The latter
can be illustrated with parental behavior
in prairie voles. Female voles, like female
rats, require the hormonal changes associated
with pregnancy to be fully parental at the
time pups are born. Male voles are equally
parental towards their pups. As they don’t
get pregnant, they must follow a different
strategy. Our research suggests that this
strategy involves the sexually dimorphic
vasopressin innervation of the brain, which
is active in male voles but appears insignificant
in female voles. We study whether other
sex difference may also play such a double
For more information, you could
read for example:
De Vries GJ, Boyle PA. 1998. Double duty
for sex differences in the brain. Behav.
Brain Res. 92: 205-213.
De Vries GJ, Panzica GC. 2006
Sexual differentiation of central vasopressin
and vasotocin systems in vertebrates:
different mechanisms, similar endpoints.
De Vries GJ. 2004. Sex differences in adult
and developing brains; compensation, compensation, compensation. Endocrinology, 145: 1063-1068.