Another
method
for
detect-
ing
hormone receptors
is
im-
munocytochemistry
(ICC).
In
this
method
(described
in
more detail
in
Box
2.1),
we use
antibodies that rec-
ognize
the
hormone receptor (Figure
D).
This method allows
us to map the
distribution
of
hormone receptors
in
the
brain.
We put the
antibodies
on
slices
of
brain tissue, wait
for
them
to
bind
to the
receptors, wash
off the
unbound antibodies,
and use
chemi-
cal
methods
to
visualize
the
antibod-
ies
by
creating
a
tiny dark spot
in the
nuclei
of
target brain cells.
We can
also
use
in
situ
hybridization
(see
Box
2.1)
to
look
for the
neurons that
make
the
mRNA
for the
steroid recep-
tor.
Because these cells make
the
transcript
for the
receptor, they
are
likely
to
possess
the
receptor protein
itself.
What
Happens
at the
Target
Cells?
Once
we
have used autoradiogra-
phy, immunocytochemistry,
or in
situ
hybridization
(or, better yet,
all
three)
to
identify
brain regions
that
have recep-
tors
for the
hormone, those regions
become candidates
for the
places
at
which
the
hormone works
to
change
behavior.
Now we can
take castrated
(B)
Autoradiogram
(D)
Immunocytochemistry
(C)
Autoradiogram
males
and
implant tiny pellets
of
testosterone into
one of
those brain
regions.
We use
RIA
to
ensure
that
the
pellets
are
small enough
that
they have
no
effect
on
hormone levels
in the
blood. Then
we ask
whether
the
small
implant
in
that brain region restores
the
behavior.
If
not, then
in
other
animals
we can
implant pellets
in a
different
region
or try
placing implants
in
a
combination
of
brain sites.
It
turns
out
that such implants
can
restore
male sexual behavior
in
rats
only
if
they
are
placed
in the
medial
preoptic area
(mPOA)
of the
hypo-
thalamus.
Thus,
we
have
found
so far
that testosterone does something
to
the
mPOA
to
permit individual males
to
display sexual behavior.
Now we
can
examine
the
mPOA
in
detail
to
learn
which changes
in the
anatomy,
physiology,
or
protein production
of
this region
are
caused
by
testoster-
one.
We
have more
or
less caught
up
to
modern-day scientists
who
work
on
this very question. Some
of
the
preliminary answers suggested
by
their research will
be
discussed
in
Chapter
12.
(Figure
C
courtesy
of
Dr.
Bruce McEwen;
D
courtesy
of Dr.
Cynthia
Jordan.)
(B)
An
autoradiogram showing that
spinal
motor neurons (purple cell
profiles)
accumulate radioactive tes-
tosterone
(small
dots).
(C) An
autora-
diogram
showing
the
concentration
of
oxytocin receptors
in the
ventro-
medial
hypothalamus
(oval
outlines).
(D)
Immunocytochemistry
revealing
cells
with nuclei that contain andro-
gen
receptors
(dark
circles),
to
which
testosterone
can
bind.
The
somata
of
these neurons
have
been labeled
with
the
tracers
Fluoro-Gold
(white)
and
Fluoro-Ruby
(red).
knockout
organism
An
individual
in
which
a
particular
gene
has
been
disabled
by an
experimenter.
