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

SYNAPTIC PLASTICITY IN THE VM NUCLEUS
males and females were found. In addition, no differences
between the sexes and no effect of the phase of the estrus
cycle were noticed in the numerical density of axosomatic
synapses (F (2,15) 0.10, P 0.905).
Total number of synapses per neuron
According to our estimates, in a diestrus rat the number
of synapses per each VMNvl neuron is 7,000, of which
56% are located on dendritic trunks, 42% on dendritic
spines, and 2% on the soma. In proestrus rats, the number
of synapses per neuron rises to 10,000, 56% of which are
concentrated on dendritic trunks, 42% on dendritic spines,
and 2% on neuronal cell bodies. In males, the number of
synaptic contacts per neuron is similar to that observed in
diestrus rats (7,500), of which 61% are established on
dendritic trunks, 36% on spines, and 3% on neuronal cell
bodies.
As shown in Figure 5B, the total number of synaptic
contacts per neuron located in the VMNvl was influenced
by the sex of the animals and by the phase of the estrus
cycle. These effects were significant for axospinous
(F (2,15) 10.73, P 0.005), axodendritic (F (2,15) 9.36,
P 0.005), and axosomatic (F (2,15) 8.33, P 0.005)
synapses. Proestrus rats had more axospinous and axodendritic
synapses per neuron than diestrus rats (42%
and 45%, respectively) and males (54% and 24%, respectively).
There were no statistically significant differences
in the total number of these synaptic contacts between
diestrus rats and males.
Similar to axospinous and axodendritic synapses, the
number of synapses received by each neuronal cell body
was 32% higher in proestrus than in diestrus rats (Fig.
5B). In addition, and in contrast with the synapses established
on the dendritic trees, the number of axosomatic
synapses established per neuron was higher (46%) in
males than in diestrus rats and did not differ between
males and proestrus rats (Fig. 5B).
Size of postsynaptic densities
No variation across the estrus cycle and no sex-related
differences were noticed in the area of the postsynaptic
densities of individual axodendritic (F (2,15) 1.35, P
0.288) synapses (Fig. 6A). Conversely, ANOVA showed
that the sex of the animals and the phase of the estrus
cycle significantly influenced the surface area of the individual
postsynaptic densities of axospinous (F (2,15) 9.62,
P 0.005) and axosomatic (F (2,15) 6.11, P 0.011)
synapses. Specifically, the surface area of the postsynaptic
densities of these synapses was 30% smaller in females
than in males, irrespective of the phase of the estrus cycle
(Fig. 6A).
However, as shown in Figure 6B, the surface area of all
postsynaptic densities identifiable on each VMNvl neuron,
which depends on the size of individual postsynaptic densities
and on the total number of synapses established per
neuron, was influenced by the sex of the animals and by
the phase of the estrus cycle in axospinous (F (2,15) 5.51,
P 0.016), axodendritic (F (2,15) 5.10, P 0.020), and
axosomatic synapses (F (2,15) 30.54, P 0.005). The total
surface area of postsynaptic densities was significantly
larger in proestrus than in diestrus rats in all types of
synapses (Fig. 6B). In addition, the total surface area of
the dendritic membrane occupied by postsynaptic densi-
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Fig. 6. Graphic representation of the morphometric data obtained
from axospinous (spinous), axodendritic (dendritic) and axosomatic
(somatic) synapses in the ventrolateral division of the VMN of male
rats, and female rats in diestrus and proestrus. Columns represent
means and vertical bars represent 1 SD. A: Surface area of individual
postsynaptic densities. B: Surface area of the postsynaptic densities
per neuron. Tukey’s post-hoc tests: *P 0.05, **P 0.005, compared
with male rats; P 0.05, compared with diestrus rats.
ties was larger in males than in females, but only when
females were in diestrus. In the case of axosomatic synapses,
sex differences in the size of the postsynaptic densities
were present when females were in diestrus as well
as in proestrus.
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