Susana Isabel Ferreira da Silva de Sá ESTROGÉNIOS E ...

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dependent translocation of ribonucleoprotein particles
from the nucleus to the cytoplasm (Watson, 1959). Since
VMNvl neurons seem to be activated in response to estrogen,
we have additionally analyzed the density of nuclear
pores in the same groups of animals.
Animals
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EXPERIMENTAL PROCEDURES
Young-adult male and female Wistar rats were maintained under
standard laboratory conditions (12-h light/dark cycle and ambient
temperature of 22 °C) and had free access to food and water. The
group of males consisted of six animals whereas the group of
females was composed of six rats in proestrus and six rats in
diestrus day 1 (diestrus). The estrus cycle was monitored by daily
inspection of vaginal cytology for at least 3 weeks before killing.
Only regularly cycling rats were used in the present study. Animals
were killed at 3 months of age between 14 and 16 h. All studies
were performed in accordance with the European Communities
Council of 24 November 1986 (86/609/EEC) and Portuguese Act
no. 129/92. All efforts were made to minimize the number of
animals used and their suffering.
Hormonal determinations
Prior to perfusion, 500 l of blood were taken directly from the
heart into Eppendorf tubes. The serum was separated by centrifugation
and stored at 20 °C until the time of assay. The concentrations
of 17 -estradiol were determined by radioimmunoassay
techniques (MP Biomedicals, Irvine, CA, USA).
Tissue preparation
Animals were anesthetized with 3 ml/kg of a solution containing
10 mg/ml of sodium pentobarbital and 40 mg/ml of chloral hydrate
given i.p. and killed by transcardiac perfusion of a fixative solution
containing 1% paraformaldehyde and 1% gluteraldehyde in
0.12 M phosphate buffer, pH 7.2. After removal from the skulls, the
brains were weighed and post-fixed for 1hinfresh fixative. They
were then cut longitudinally in the mid-sagittal plane to separate
the cerebral hemispheres, which were transected in the coronal
plane through the posterior border of the optic chiasm. After
removal of the occipital poles, the cerebral hemispheres were
mounted on a vibratome with the rostral surface up and serially
sectioned in the coronal plane at 40 m. When the VMN was first
identified as being formed by two well-defined clusters of cells, the
dorsomedial division and the VMNvl, separated by a cell-poor
central zone (Bleier et al., 1979; Simerly, 1995; Madeira et al.,
2001), one 500 m-thick coronal section containing the VMN was
collected, followed by a sequence of alternate 40 and 500 mthick
sections. The 40 m-thick sections were mounted and
stained with Thionin for precise identification of the boundaries of
the VMN and of its dorsomedial division and VMNvl and used as
reference for the micro-dissection of the VMNvl in the adjacent
500 m-thick sections.
The four blocks of tissue containing the VMNvl that were
collected per animal were postfixed for 2hina2%solution of
osmium tetroxide in 0.12 M phosphate buffer, dehydrated in
graded ethanols and embedded in Epon according to the isector
method (Nyengaard and Gundersen, 1992) to obtain isotropic,
uniform random sections. From each block, eight serial 2 m-thick
sections of the VMNvl were cut, which provided a total of 32 serial
semithin sections per animal. These semithin sections were
stained with Toluidine Blue and coverslipped with Entellan. Pyramids
were trimmed on each of the blocks and series of 10–12
ultrathin sections were cut, collected on Formvar-coated grids and
double stained with uranyl acetate and lead citrate.
S. I. Sá and M. D. Madeira / Neuroscience 133 (2005) 919–924
Quantifications were made in neurons photographed from
sections obtained from all blocks containing the VMNvl. From
each block, alternated sections were sampled and in each of
these sections only one neuron was photographed, which provided
an average of 20 neurons per animal. The presence of the
nucleus and of a complete nucleolus was considered the only
requisite for sampling neurons. These neurons were photographed
at primary magnification of 5400 and enlarged photographically
to a final magnification of 16,200.
Stereological analyses
In VMNvl neurons, RER is often seen as being formed by short,
independent segments and the ribosomes occur mainly as unbound
rosettes scattered throughout the cytoplasm (Fig. 1). Nissl
bodies are rare and, when present, they are usually small and
located in the periphery of the soma (Millhouse, 1978). Conversely,
the Golgi apparatus (Fig. 1) is seen in almost every region
of the cell body and is arranged in several distinct patches, either
stretched out along the perimeter of the nucleus or modulated in
curvilinear arrays (Millhouse, 1978). The volume of these organelles
was determined on the basis of their volume density (Vv)
and on the volume of the cytoplasm of the neuronal somata. The
Vv was estimated by point counting using an appropriate test point
system (Jensen and Gundersen, 1982). Points that fell on the
channel system and on the surrounding cytosol (Fig. 1) were
counted as points on the RER, and those that fell on the field
Fig. 1. Electron micrograph of a VMNvl neuronal cell body. The
electron-dense cytoplasm contains relatively few short segments of
RER, which are outlined by dotted lines, and numerous groups of
polyribosomes and patches of Golgi complex, which are outlined by
dashed lines. The box delineates the part of the cell nuclear envelope
that is shown at higher magnification in the inset. Inset. Note that the
membrane of the nuclear envelope is perpendicularly sectioned. Four
nuclear pores (arrowheads) can be seen. Scale bars1.0 m; inset0.2
m.