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Bull Vet Inst Pulawy 56, 411-414, 2012
MORPHOMETRIC COMPARATIVE STUDY
OF THE STRIATUM AND GLOBUS PALLIDUS
OF THE COMMON SHREW, BANK VOLE, RABBIT, AND FOX
BARBARA WASILEWSKA, JANUSZ NAJDZION, MACIEJ RÓWNIAK,
KRYSTYNA BOGUS-NOWAKOWSKA, JACEK J. NOWAKOWSKI,1 AND ANNA ROBAK
Department of Comparative Anatomy, 1Department of Ecology and Environmental Protection,
University of Warmia and Mazury, 10-727 Olsztyn, Poland
[email protected]
Received: December 5, 2011
Accepted: August 30, 2012
Abstract
The morphology of the striatum (St, caudoputamen complex) and globus pallidus (GP) was studied by stereological
methods in representatives of four mammalian orders (Insectivora, Rodentia, Lagomorpha, Carnivora). The aim of our study was to
give the first detailed morphometric characteristics of the St and GP in the animals. The paraffin-embedded brain tissue blocks were
cut in the coronal plane into 50 µm sections, which were stained for Nissl substance. The morphometric analysis of the St and GP has
included such parameters as the volume, numerical density, and total number of neurons. The increase in the volume of the St and
GP was accompanied by an increase in the total number of neurons and a decrease in their numerical density. The percentage
contribution of the GP volume in the corpus striatum shows progressive traits in the common shrew and fox.
Key words: mammals, striatum, globus pallidus, morphometric analysis
The striatum (St, or caudoputamen complex, or
dorsal striatum) and globus pallidus (GP or GPe in
primates) belong to the mammalian basal ganglia. The
St and GP are defined as the corpus striatum. A
morphometric study of the mammalian St and GP has a
long tradition and is related with different quantitative
aspects. Data on the volumes of the brain and various
brain parts in insectivores and primates has been
published by Stephan et al. (16). Age changes in the
neuron density, the area occupied by neurons, and the
absolute number of cells were investigated by Schröder
et al. (14) and Eggers et al. (1) for the whole neuron
population. The most extensive volumetric studies on
the St and/or GP were mainly carried out in the human
(7, 14, 17). The volumetric studies of the St and GP
were carried out in schizophrenia (4) and in the attention
deficit hyperactivity disorder (18). In the available
literature, to our knowledge, there are few comparative
studies analysing the morphometric structure of the
nuclei of the corpus striatum belonging to different
orders of mammals (15, 16).
In this study, the St and GP in representatives
of
four
different
mammalian
orders
were
morphometrically compared. Knowledge about the
number of cells and exact sizes of St and GP could be
supported by selective labelling methods such as
immunocyto- and immunohistochemistry. It would be
also useful to have a validated morphometric model of
the St and also GP, which would help in understanding
parallels and differences among species.
Material and Methods
The studies were carried out on the
telencephalons of four species of mammals: the common
shrew (Sorex araneus – Insectivora, b.w. 11-12 g), bank
vole (Clethrionomys glareolus – Rodentia, b.w. 19-24
g), rabbit (Oryctolagus cunniculus – Lagomorpha, b.w.
3.5-4.5 kg), and fox (Vulpes vulpes – Carnivora, b.w. 810 kg). All experimental procedures were approved by
the Local Ethics Commission. All animals were given
intraperitoneally a lethal dose of 80 mg/kg of Nembutal
(Lundbeck, Denmark) and then they were decapitated.
Paraffin blocks of the brains were cut into 50 µ m
sections in the coronal plane. The sections were stained
for Nissl substance.
Computer reconstructions of the St and GP.
All sections were analysed with a calibrated image
analysis system that consisted of a computer equipped
with morphometric software (Multi-Scan 8.2, Computer
Scanning Systems, Poland) and a light microscope
coupled with a digital camera (CM40P, VideoTronic,
Germany). Partial microscopic images (512 -512 pixel
size) of single brain sections were digitally recorded and
then all these images were joined into one large digital
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section that represented the whole corpus striatum and
the adjoining structures. All sections were taken into
account in the common shrew, every second section in
the bank vole, every fourth section in the rabbit, and
eighth section in the fox.
Morphometric analysis. On each digital
section the boundaries of the individual nuclei were
outlined. With the help of IGL Trace software, the 2-D
outlines were transformed into 3-D slabs. To evaluate
the volume of the St and GP, the volumes of the slabs
were totalled according to the formula proposed by
Cavaliero (3, 9). The total volume of the corpus striatum
presented in this study was the sum of the volumes of
the St and GP. The parts of the internal capsule were
almost completely excluded from this structure in the
rabbit and fox. In the common shrew and bank vole the
largest parts of the internal capsule were only excluded.
To evaluate the numerical density of cells in each of the
analysed nuclei, the optical dissector method was
implemented with the guidelines described by West and
Gundersen (19). The total number of neurons in each of
the nuclei was calculated by multiplying the volume of
the given nucleus by the numerical density of cells in it
(19).
Statistical analysis. The statistical analysis was
performed using CSS: Statistica v. 6.0 (Statsoft, USA).
Significant differences of the morphometric parameters
of the St and GP were tested in the one-factor model of
the analysis of variance (ANOVA) and the Tukey’s tests
(post hoc analysis). The comparison of two averages
was made by using the Student’s t- test. The level of the
statistical significance was set at P=0.05.
Results
Volume. The analysis of the volume of the St
and GP showed relative increases in these structures in
the examined mammals (in the fox St was 62 times and
GP was 78 times larger in comparison to the common
shrew) (Table 1). The St and GP volumes of examined
mammals were significantly (P<0.05) different. The
percentage contributions of the St volume in the whole
volume of the corpus striatum was the largest in the
bank vole, and the smallest in the fox (Table 1). To
assess the percentage contributions of the St and GP
volume, the Tukey’s post hoc analysis was used, which
enabled to distinguish three groups of animals. The first
group was formed by the common shrew, the second by
the bank vole and rabbit, and the third by the fox.
Numerical density. The average number of
neurons in 1 mm3 of St and GP decreased with the
growth of the volume of these structures in the analysed
mammals (Table 1). Tukey’s post hoc analysis revealed
the presence of three various groups in regard to the
numerical density of striatal neurons and also pallidal
neurons. The first group constituted the common shrew,
the second the bank vole, and the third the rabbit and
fox. The presence of the negative correlation between
the average numerical density and the average volume
of the St (r= −0.61, N=22, P<0.05; Fig. 1) and GP (r= −
0.55, N=22, P<0.05) was ascertained.
Fig. 1. The correlation between the average numerical density of the St and the average volume of the St.
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Fig. 2. The correlation between the average total number of neurons of the St and the average volume of the St.
Table 1
The morphometric parameters and the percentages of the volume of the St and GP in the corpus striatum
of the studied species
Volume of St (mm3)
Volume of GP (mm3)
Density of St (N/mm3)
Density of GP (N/mm3)
Number of St cells (N)
Number of GP cells (N)
Percentages of the volume of St
Percentages of the volume of GP
Percentage of neurons of St
Percentage of neurons of GP
Common shrew
1.34 ±0.11
0.15 ±0.02
229,595 ±17,658
52,931 ±6,477
308,035±35,059
8,043 ±1,854
89.88 ±1.34
10.12 ±1.34
97.46 ±0.46
2.54 ±0.46
The total number of neurons. The population
of cells of the St and GP was the smallest in the bank
vole and the largest in the fox (Table 1). On the basis of
Tukey’s post hoc analysis, three different groups were
ascertained regarding the total numbers of St and GP
neurons. The first of them was composed of the foxes,
the second of the rabbits, and the third of the common
shrew and bank vole. In the analysed animals, the
presence of correlation between the average total
number of neurons and the average volume was
ascertained in the St (r=0.99, N=22, P<0.05; Fig. 2) and
GP (r=0.98, N=22, P<0.05). The presence of the
negative correlation between the average number of
striatal neurons and the average numerical density of the
St (r= -0.60, N=22, P<0.05) was found.
In this study we took into consideration the
value of the total number of neurons of the whole corpus
striatum. We used this value in order to estimate the
percentage contributions of the total neuronal population
of the St and GP (Table 1). Tukey’s post hoc analysis
revealed the presence of two groups of animals for the
Bank vole
3.01 ±0.27
0.22 ±0.02
72,641 ±6,078
15,642 ±2,462
218,926±26,929
3,369 ±586
93.32 ±0.30
6.68 ±0.30
98.48 ±0.22
1.52 ±0.22
Rabbit
26.10 ±0.62
2.20 ±0.11
40,462 ±4,731
6,947 ±1,082
1,051,746±150,173
14,993 ±2,599
92.23 ±0.39
7.77 ±0.39
98.57 ±0.31
1.43 ±0.31
Fox
83.21 ±0.22
11.72 ±0.55
26,390 ±1,133
4,123 ±339
2,203,879±99,634
48,746 ±6,079
87.66 ±0.50
12.34 ±0.50
97.84 ±0.24
2.16 ±0.24
percentage contribution of cellular population of the St
and GP. The first group was formed by the common
shrew and fox and the second by the bank vole and
rabbit.
Discussion
The presented results indicate that the volumes
of the St and GP showed a relative increase in the
examined mammals, meaning that the smallest volume
was found in the common shrew and the largest volume
in the fox. However, the comparison of the present
volumetric data with the data of other authors is often
difficult, because most of those observations were
carried out using the miscellaneous methods of measure
(2, 16). Stephan et al. (16) included the nucleus
accumbens in the St. The most information concerns the
volume of St and GP in the man (47, 6, 7, 1414, 17176).
The volumetric percentages of the GP in the corpus
striatum are the largest in the common shrew and the fox
(presented results), which suggests that GP plays a more
414
important role in both these species. This increase
probably is a consequence of the tremendous relative
enlargement of other brain parts, for instance, of the St
in both animals (our study) and of the isocortex in the
fox (11). According to Stephan (15), the percentage of
the St volume in relation to the telencephalic volume or
to the whole brain volume shows a clear decrease in this
parameter in insectivores and primates. The percentage
of the St volume showed the lowest value in the man
(15).
In the present study, we observed that with the
increment of the volume of the St and GP, the numerical
density of the cell population of these structures
decreases. The presence of the negative correlation
between the volume of given structure and the average
numerical density of the cell population in it has
previously been described by Kowiański et al. (55),
Równiak et al. (1313) in the amygdala, and Najdzion et
al. (8) in the medial geniculate body. In the mouse, St
neuron-packing density ranges from approximately
50,000 to 100,000 neurons/mm3 (1210). In the bank
vole, the representative of the rodents, the numerical
density is comparable with this value (72,641.60). In the
rat, the value of the numerical density is two times larger
than in the bank vole (141,500 neurons/mm3) (1010).
However, the numerical density of the GP cells of the rat
does not show considerable differences (17,300
neurons/mm3) (1010). In the man, the numerical density
of striatal and pallidal neurons has been examined by
some authors (77, 1717). The value of this parameter in
the man is clearly smaller in comparison with the
numerical density of cell population of the analysed
structure in the common shrew, bank vole, rabbit, and
fox (77, 17).
The presented results indicate that the total
number of neurons generally showed a relative increase
in the examined mammals. An increase in the total
number of neurons with an increase in the volume has
been shown by Kowiański et al. (55) in the claustrum
and Równiak et al. (1313) in the amygdala of mammals.
According to Fentress et al. (2) the St of an adult mouse
contains approximately 690,000 neurons on each side
but in the bank vole it has three times less neurons. The
differences in the total number of neurons are probably
the result of the differences in size and weight of the
body mass in both analysed animals. In the man, the
total number of neurons in the St is 68.1 million (66),
while in the GP/GPe ranges from 540,000 to 465,000
(1717).
The current study provides quantitative data on
the volume, numerical density, and total number of
neurons of the St and GP in representatives of four
mammalian orders. We hope that these results have
cognitive, as well as practical value and they may help
in understanding the pathophysiology and proper
functioning of the nervous system.
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