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

SYNAPTIC PLASTICITY IN THE VM NUCLEUS
Fig. 3. Electron micrographs obtained from two consecutive serial
sections of the VMN showing identical areas of the neuropil of its
ventrolateral division. A dendritic shaft (d) bears a spine (thin arrow)
that is particularly evident in B and makes an asymmetrical synaptic
contact with an axon terminal. Two other dendritic spines can be
individual postsynaptic densities was determined by dividing
the SA of all synapses by the number of somatic
synapses per neuron.
Percentage of plasmalemma occupied by postsynaptic
densities. The perimeter of the profiles of the dendritic
spines and the length of the postsynaptic densities
were measured in every available photomicrograph using
an MOP-Videoplan. The percentage of plasmalemma of
dendritic spines occupied by postsynaptic densities was
calculated by dividing the perimeter of the spine by the
length of the postsynaptic densities. The percentage of the
plasmalemma of the neuronal cell bodies occupied by
postsynaptic densities was obtained by dividing the SA of
all somatic synapses received by each neuron by the SA of
the neuronal membrane.
Statistical analyses
Differences among groups were assessed by one-way
analysis of variance (ANOVA). Whenever significant results
were found from the overall ANOVA, pair-wise comparisons
were subsequently made with the post-hoc Tukey
HSD test. Throughout the text, data are presented as
means with their coefficients of variation (CV SD/
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seen. One (thick arrows) protrudes from a dendritic shaft (d) and is
contacted at an asymmetrical synaptic thickening, which can be seen
in A and in B, by an axon terminal. The remaining spine (arrowheads)
receives an asymmetrical synapse that is visible only in A. Scale bar
0.5 m.
mean), and hormonal concentrations are shown as means
and SEM. Differences were considered to be significant if
P 0.05. The coefficient of error of the estimates of numerical
densities was calculated on the basis of the mean
number of synapses counted per counting field, the variance
in the number of synapses among the counting fields,
and the number of counting fields, as described by Geinisman
et al. (1996) and Schmitz (1997).
RESULTS
Hormone levels
In keeping with earlier data (Butcher et al., 1974),
plasma estradiol levels showed the expected high values
by 1600 hours on proestrus and had returned to low levels
by the same time on diestrus day 1. The values were 176
(6) pg/ml and 100 (4) pg/ml, respectively.
Neuronal densities and volumes
According to our estimates, the numerical density of
VMNvl neurons, expressed as n 10 -4 /m 3 (CV), was
3,550 (0.09) for proestrus rats, 4,390 (0.10) for diestrus
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