File Name: SLS1_18.DOC

EXPERIMENT SLS1 BSP18

MORPHOLOGY OF NEURONS OF THE CEREBRAL CORTEX

[PIs]{.underline}

[Russia:]{.underline}

T. A. Leontovich, Brain Research Institute, Russian Academy of Medical
Sciences, Moscow

[USA:]{.underline}

O. Lowry, Medical School, Washington University, Saint-Louis, Missouri

[Co-Investigators:]{.underline}

M. A. Makhanov, Brain Research Institute, Russian Academy of Medical
Sciences, Moscow

A. A. Fedorov, Brain Research Institute, Russian Academy of Medical
Sciences, Moscow

Moscow, 1993

[Introduction]{.underline}

Morphological evaluation of neurons of the visual cortex of the brain of
animals exposed to space flight may help gain an insight into mechanisms
underlying adaptive responses of the visual organ to microgravity. It is
known that pyramidal neurons of the III layer of the visual cortex are
actively involved in the development of associative connections between
various cortical compartments. Assuming a greater role of the visual
organ in space due to a reduced efficiency of other sensory systems,
particularly, the somatosensory system, we expected to detect adaptive
developments in the visual cortex, primarily, in the pyramidal neurons
of the III layer. Previous studies demonstrated changes in the geometry
and orientation of dendrites of pyramidal neurons of the visual cortex
of rats flown for 14 days on Cosmos-1887 \[4\]. However, the Cosmos-1887
rats were decapitated 48 hours after recovery. Therefore, potential
effects of the Earth\'s gravity on dendrite tree changes could not be
excluded. In this context, it was important to perform a similar study
of animals sacrificed as soon as possible after recovery. The present
study yielded morphometric data of the geometry and orientation of
dendrites of pyramidal neurons of the III layer of the visual cortex of
rats flown for 9 days on U.S. SLS-1 and sacrificed 2-3 hours or 9 days
after flight.

[Materials and Methods]{.underline}

Samples of the visual cortex of male rats (Sprague-Dowley) from the
basal control group (BC, 5 rats), vivarium control group (V+0, 5 rats),
flight group dissected 2 - 3 hours after recovery (R+0, 5 rats), flight
group dissected 9 days after recovery (R+9, 5 rats), and corresponding
vivarium control group (V+9, 5 rats) were examined.

Rats were decapitated, brain fragments isolated and fixed by U.S.
investigators

at the Columbia recovery site. Further brain fragment fixation,
osmification, silver impregnation (according to the method of Golgi as
modified by the Brain Research Institute) and embedding in celloidin
were performed by a Russian investigator at NASA Ames Research Center.

Within 3 minutes after decapitation a frontal block of the left visual
cortex was dissected. Each isolated fragment was placed into a dark
glass stoppered vial containing 50 ml of 3% K2Cr2O7 in 1% aqueous
solution of Na2SO4 . 10 H20 and allowed to stand in the darkness for 72
hours at +20 oC. Then each fragment was transferred into a dark glass
vial containing 50 ml of 0.2% osmium tetroxide in 3% aqueous solution of
potassium bichromate and allowed to stand in a temperature controlled
container for 48

hours at +37 oC. After that each brain fragment was placed into a Petri
dish containing 50 ml of 1% aqueous solution of silver nitrate, washed
quickly and placed into a dark glass vial containing 50 ml of 1% aqueous
solution of silver nitrate and allowed to stand in the darkness for 7
days at +20 oC.

After silver impregnation brain samples were dehydrated in ethanols of
ascending concentration (70o, 80o, 90o for 15 minutes at each; 96o, 100o
for 1 hour; 100o ethanol - diethyl ether mixture (1: 1) for 30 minutes
at +20 oC), placed into celloidin solutions of ascending concentration
(2.5% for 1 hour; 5% for 12-16 hours), and embedded in 10% celloidin
solution. 72 hours later blocks were placed into a desiccator containing
40-60 ml chloroform to allow the celloidin to become thickened. The
thickened celloidin blocks were shipped to the Institute of Brain
Research, Moscow, for section preparation and morphometric analysis.
Each celloidin block was put onto a separate wooden block of 1 cm x 1 cm
x 1 cm and covered with 2-3 ml 10% celloidin, and the wooden blocks
coupled with celloidin blocks were placed into a desiccator containing
10 ml chloroform for 1-2 hours. Then the block was fixed in a sledge
microtome, and 150 μm sections were made with a knife (employed for
celloidin cutting) and placed into a Petri dish containing 98o ethanol.
After that the sections were transferred from 98o ethanol to a cover
glass, embedded in Canadian fir balsam and allowed to stand for 1 - 2
months to allow the balsam to solidify.

Using a drawing unit attached to an Ortolux microscope (Leitz, FRG),
pyramidal neurons of the III layer of the visual cortex were outlined
from histological preparations at a magnification of x400. Altogether 49
neurons were outlined (20 neurons of the R+0 rats, 12 neurons of the R+9
rats, and 17 neurons of BC, V+0 and V+9 rats).

For the purpose of morphometric analysis, neurons of the BC, V+0 and V+9
rats were pooled into one control group because they did not show any
significant differences. By means of a digitizer a graphic drawing of
the neurons was obtained. Morphometric analysis of the geometry of
dendrites of pyramidal neurons was performed with the aid of an IBM PC
software custom built by A. A. Fedorov. All parameters were entered into
a database software developed by M. A. Makhanov. The results were
statistically treated using the Systat-5 package.

[Results and Discussion]{.underline}

Examination of histological preparations of rat brains impregnated
according to the method of Golgi gave evidence that the biosamples were
dissected thoroughly, all structures of the visual cortex were well
preserved, and that neuronal bodies, dendrites

and dendrite spines of the visual cortex samples were adequately
impregnated in all animal groups.

Qualitative, visual examination of the structure of pyramidal neurons of
the III layer of the visual cortex revealed no differences between the
animal groups under study. Morphometric investigation of neuronal cells,
which addressed twenty five parameters of each pyramidal neuron (length
and branching of the dendrite tree, the territory it covers, as well as
the size of the neuronal body) provided quantitative data concerning
neuronal structure. The mean data and the data derived with the aid of
the Wilcoxon-Mann-Whitney test applied to the above pyramidal neurons,
as summarized in Table 1, show the lack of marked deviations from the
normal structure induced by microgravity or Earth\'s gravity in relation
to the SLS-1 experimental setup. Mention should be made of a significant
increase of the body size of pyramidal neurons of the flight animals.
The conclusion about insignificant changes in the structure of the
neuronal dendrite tree drawn from the results of a unifactorial
nonparametric test was supported by the data of multifactorial
discriminant analysis applied to neurons of three groups (Figure 1). The
neuronal distribution across the discriminant factor space,
nonparametric kernel density estimation and statistical analysis of the
results obtained (Wilks lambda p = 0.24, Hotelling-Lawley test p = 0.27
and other tests with a similar probability) give evidence that normal
variability is prevailing over flight-induced changes.

In addition to the above analytical procedures, another method was used
to evaluate the spaceflight effect on the structure of the dendrite tree
of pyramidal neurons: this is multifactorial analysis (Q-factor
analysis) and discriminant analysis previously described in \[5\]. A new
modification was the use of the K-means splitting method instead of the
previously applied factor rotation technique to discriminate neurons of
similar structure. A detailed discussion of correlations between factor
and cluster analysis can be found in \[1\]. The novel analytical
approach we applied helped reliably distinguish between two
norphological types of cells, which differed, primarily, in terms of the
development of apical and basal dendrite systems. Morphological
differences were not limited to a particular animal group. Figure 2
shows the distribution of all neuronal groups subdivided into two
morphological types across the space of the first two discriminant
factors. It is interesting to mention here that two morphological types
of pyramidal neurons were also detected in the III layer of field 17 of
the visual cortex of the human brain (cell groups *a* and *b*) and that
morphological parameters typical of different clusters were very similar
\[4\]. The data derived from the 9-day SLS-1 flight experiment
demonstrated differences in pyramidal neurons of the flown and control
rats as illustrated in Figure 3. These data are in good agreement with
the neuronal distribution of identical

![](media/image1.pct){width="6.805555555555555in"
height="5.708333333333333in"}

[Figure 1.]{.underline} Neruonal distributin of the III layer of the
visual cortex of the R+0, control and R+9 rats in the discriminant
factor space.

1 - Factor 1 2 - Factor 2

Ellipses - intervals of confidence of the mean (p=0.95)

Dot pattern - Kernel density estimator of neuronal distribution

\- neuron of the control group

\- neuron of the flight group sacrificed immediately after recovery

\- neuron of the flight group sacrificed 9 days after recovery

![](media/image2.pct){width="6.805555555555555in"
height="5.680555555555555in"}

[Figure 2.]{.underline} Distribution of neurons (with respect to their
morphological types) of the III layer of the visual cortex of the R+0,
control and R+9 rats in the space of the first two discriminant factors.

1 - Factor 1 2 - Factor 2

Ellipses - intervals of confidence of the mean (p=0.95)

Dot pattern - Kernel density estimator of neuronal distribution

\- neuron of the control group

\- neuron of the flight group sacrificed immediately after recovery

\- neuron of the flight group sacrificed 9 days after recovery

Shaded areas show symbols of neurons of one of the two morphological
types (with a better developed apical system).

![](media/image3.pct){width="6.805555555555555in"
height="5.708333333333333in"}

[Figure 3.]{.underline} Distribution of neurons (with respect to their
morphological types) of the III layer of the visual cortex of the R+0
and control rats in the space of the first two discriminant factors.

1 - Factor 1 2 - Factor 2

Ellipses - intervals of confidence of the mean (p=0.95)

Dot pattern - Kernel density estimator of neuronal distribution

\- neuron of the control group

\- neuron of the flight group sacrificed immediately after recovery

Shaded areas show symbols of neurons of one of the two morphological
types (with a better developed apical system).

rat groups flown for 14 days \[3\], regardless of the difference in the
time interval between touch-down and sacrifice (2 hours versus 48
hours). Analysis of the neuronal differences between the flown and
control rats (Table 2) belonging to one of the two morphological types
(similar to the *a* group of field 17 of the visual cortex of the human
brain and characterized by a better developed - as compared to the basal
system - apical dendrite system) shows that the greatest changes
occurred during flight in the apical dendrite system. These changes
included an increase of the length of dendrites (Lda) located primarily
parallel to the cortical surface (XLda), which did not modify the
territory occupied by the apical dendrite system (Sdaa, Xpra). These
changes in the dendrite tree may take place due to the elongation of
oblique dendrites propagating from the distal part of the apical
dendritic stem to the I layer of the cortex. With respect to the
dendrite tree of pyramidal neurons of the R+9 rats, it should be
indicated that its structure distincly approximated that of the dendrite
tree of pyramidal neurons of the control rats.

In summary, our investigation of rats exposed to microgravity for 9 days
has shown an elongation of apical dendrites located in the upper layers
of the visual cortex in one of the groups of pyramidal neurons of the
III layer. This elongation can be caused by the requirement for an
additional afferent input and can enhance integrative and associative
processes in the cerebral cortex in microgravity. An increase in the
profile size of the body of pyramidal neurons of the flown rats can be
viewed as another indication of an active restructuring of the dendrite
system of the pyramidal neurons in space.

[Conclusion]{.underline}

A morphometric examination of the geometry and orientation of dendrites
of pyramidal neurons of the III layer of the visual cortex of rats flown
for 9 days on U.S. SLS-1 has been completed. The resultant data have
been processed using the Q factor analysis, discriminant analysis and
K-means splitting method. The findings have shown an increase in the
length of apical dendrites located in the upper layers of the visual
cortex, the dendrites being part of pyramidal neurons of the III layer,
which have a well developed apical system and participate in the
establishment of associative connections between various cortical
compartments. This process can be induced by the need for an additional
afferent input and can act as a foundation for new connections between
the visual cortex and other cortical compartments in microgravity. An
enlargement of the profile size of the body of pyramidal neurons of the
III layer, also observed after flight, can be viewed as another
indication of the restructuring of the dendrite system of these neurons
in microgravity.

[References]{.underline}

1\. Jambou, M. The Hierarchic Cluster - Analysis and Similarities.
Moscow, Finansy i Statistika, 1988 (Russian Transl.).

2\. Makhanov, M.A., Fedorov, A.A. Application of Methods of
Multifactorial Analysis to the Study of Spaceflight Effects on the
Neuronal Structure of the Rat Brain. Bull. Experim. Biol. Med., 1992,
vol. CXIV, No. 7, pp. 91-92 (in Russian).

3\. Belichenko, P.V., Makhanov, M.A., Fedorov, A.A., Krasnov, I.B.,
Leontovich, T.A. Effects of Space Flight on Dendrites of Neurons of the
Rat Brain. The Physiologist, 1990, vol. 33, No. 1, Suppl., S12-S15.

4\. Makhanov, M.A. Application of Multivariate Analysis to Studies of
Neuronal Structure of the Neocortex. Swedish-Soviet Symposium \"New
Research in Neurobiology\", 6 - 8 November, 1990, p. 17.

5\. Makhanov, M.A., Fedorov, A.A., Belichenko, P.V. Morphometric Study
of the Microlevel Organization of Pyramidal Neurons of Layer III in the
Human Visual and Parietal Cortex. Proceed. Intern. Symp. \"Neuronet -
1990\", Czechoslovakia, Sept. 10-14, 1990, pp. 230-233.

[Table 1]{.underline}

Morphometric parameters of pyramidal neurons of the III layer of the
visual cortex of the brain of SLS-1 flight and control rats

  ----------- ---------- ---------- ---------- ---------- ---------- ----------
  Parameter   F mean     K mean     A mean     F/K prob   F/A prob   A/K prob

  ----------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  D          6.25       5.71       5.83                             

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ----------- ---------- ----------
  Scl        498.6      367.2      479.5      **0.009**              0.051

  ---------- ---------- ---------- ---------- ----------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- -----------
  Bd         38.1       37.2       42.0                  0.053      **0.048**

  ---------- ---------- ---------- ---------- ---------- ---------- -----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Bda        15.0       14.3       15.1                             

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ----------- ----------
  Bdb        23.1       22.9       26.9                  **0.032**   0.059

  ---------- ---------- ---------- ---------- ---------- ----------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Ld         3557       3457       3650                             

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Lda        1571       1513       1502                             

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Ldb        1986       1944       2148                             

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Sda        100269     93375      94752                            

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Sdaa       50924      45614      44367                            

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Sdab       40290      39868      43419                            

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Rmaxa      333        343        328                              

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Rmaxb      170        168        165                              

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ----------- ---------- ----------
  Xpr        298        275        282        **0.043**              

  ---------- ---------- ---------- ---------- ----------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Ypr        466        484        471                              

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ----------- ----------
  Xpra       248        221        201                   **0.043**   

  ---------- ---------- ---------- ---------- ---------- ----------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Ypra       311        329        327                              

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Xprb       265        256        268                              

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Yprb       225        218        240                              

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  XLd        2023       1927       2011                             

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  YLd        2390       2349       2497                             

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  XLda       842        757        710                              

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  YLda       1109       1100       1131                             

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  XLdb       1181       1171       1300                             

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  YLdb       1280       1248       1367                             

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

Xmean - mean value of the parameter in the group

X/Yprob - probability (p \< 0.1, p \< 0.05 - in bold) of the differences
of the means (Mann-Whitney U test)

F group = flight animals sacrificed at the day of recovery

K = control rats

A group = flight animals sacrificed 9 days after recovery

Designations:

Scl - area of the maximum profile field of the cellular body

D - number of dendrites

Bd - number of free terminals

Ld - total length of dendrites

Sda - area of the dendrite territory

Rmax - maximal radius

XLd, YLd - Ld projection onto the axis which is parallel or
perpendicular to the cortical surfaces

Xpr, Ypr - distance between the extreme points of the Sda projection
onto the axis which is parallel or perpendicular to the cortical
surfaces

Letter a or b at the end of the code means that the parameter has been
calculated for the apical or basal dendrite tree, respectively.

[Table 2]{.underline}

Morphometric parameters of pyramidal neurons of the III layer of the
visual cortex of the brain of SLS-1 flight and control rats
(morphological type with the predominant apical tree)

  ----------- ---------- ---------- ---------- ---------- ---------- ----------
  Parameter   K mean     F mean     A mean     F/K prob   F/A prob   A/K prob

  ----------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  D          5.46       5.92       5.6                              

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ----------- ---------- ----------
  Scl        341        455        436        **0.045**              

  ---------- ---------- ---------- ---------- ----------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Bd         36.7       38.5       40.2                             

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Bda        15.5       17.0       17.0                             

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Bdb        21.6       21.5       23.2                             

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Ld         3423       3769       3934       0.056                 

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ----------- ---------- ----------
  Lda        1632       1830       1939       **0.031**              

  ---------- ---------- ---------- ---------- ----------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Ldb        1791       1938       1995                             

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Sda        94927      107989     106894                           

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Sdaa       50769      60253      61428                            

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Sdab       37511      40055      41846                            

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Rmaxa      362        354        354                              

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Rmaxb      162        172        172                              

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Xpr        280        310        308        0.056                 

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Ypr        491        481        492                              

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Xpra       238        275        253                              

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Ypra       338        335        357        0.065                 

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Xprb       253        264        275                              

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Yprb       210        225        244                              

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ----------- ---------- ----------
  XLd        1933       2129       2181       **0.049**              

  ---------- ---------- ---------- ---------- ----------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  YLd        2301       2553       2693       0.056                 

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ----------- ---------- ----------
  XLda       835        986        959        **0.014**              

  ---------- ---------- ---------- ---------- ----------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  YLda       1165       1289       1426       0.065                 

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  XLdb       1098       1142       1222                             

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  YLdb       1135       1264       1266                             

  ---------- ---------- ---------- ---------- ---------- ---------- ----------

Xmean - mean value of the parameter in the group

X/Yprob - probability (p \< 0.1, p \< 0.05 - in bold) of the differences
of the means (Mann-Whitney U test)

F group = flight animals sacrificed at the day of recovery

K = control rats

A group = flight animals sacrificed 9 days after recovery

Designations:

Scl - area of the maximum profile field of the cellular body

D - number of dendrites

Bd - number of free terminals

Ld - total length of dendrites

Sda - area of the dendrite territory

Rmax - maximal radius

XLd, YLd - Ld projection onto the axis which is parallel or
perpendicular to the cortical surfaces

Xpr, Ypr - distance between the extreme points of the Sda projection
onto the axis which is parallel or perpendicular to the cortical
surfaces

Letter a or b at the end of the code means that the parameter has been
calculated for the apical or basal dendrite tree, respectively.

[Legend to Figures]{.underline}

[Figure 1.]{.underline} Neuronal distribution of the III layer of the
visual cortex of the R+0, control and R+9 rats in the discriminant
factor space

1 - Factor 1 2 - Factor 2

Ellipses - intervals of confidence of the mean (p = 0.95)

Dot pattern - Kernel density estimator of neuronal distribution

\- neuron of the control group

\- neuron of the flight group sacrificed immediately after recovery

\- neuron of the flight group sacrificed 9 days after recovery

[Figure 2.]{.underline} Distribution of neurons (with respect to their
morphological types) of the III layer of the visual cortex of the R+0,
control and R+9 rats in the space of the first two discriminant factors

1 - Factor 1 2 - Factor 2

Ellipses - intervals of confidence of the mean (p = 0.95)

Dot pattern - Kernel density estimator of neuronal distribution

\- neuron of the control group

\- neuron of the flight group sacrificed immediately after recovery

\- neuron of the flight group sacrificed 9 days after recovery

Shaded areas show symbols of neurons of one of the two morphological
types (with a better developed apical system)

[Figure 3.]{.underline} Distribution of neurons (with respect to their
morphological types) of the III layer of the visual cortex of the R+0
and control rats in the space of the first two discriminant factors

1 - Factor 1 2 - Factor 2

Ellipses - intervals of confidence of the mean (p = 0.95)

Dot pattern - Kernel density estimator of neuronal distribution

\- neuron of the control group

\- neuron of the flight group sacrificed immediately after recovery

Shaded areas show symbols of neurons of one of the two morphological
types (with a better developed apical system)