Bull Vet Inst Pulawy 55, 537-539, 2011
EFFECTS OF XYLAZINE ON GLUTAMATE
AND GABA CONTENTS IN THE HIPPOCAMPUS
AND THALAMENCEPHAL IN THE RAT
BAI-SHUANG YIN1,2, HONG-BING WANG1, DU-QIANG GONG1,
GUO-JIANG LI2, AND LI GAO1
1
College of Veterinary Medicine, Northeast Agricultural University, Harbin 150030, China
Department of Veterinary Medicine,
2
Jilin Agriculture Science and Technology College, Jilin 132101, China
[email protected]
Received: December 11, 2010
Accepted: May 6, 2011
Abstract
The purpose of the study was to define if anaesthetic action of xylazine could conceivably result from the potentiation of
inhibitory neurotransmitters or the inhibition of excitatory neurotransmitter systems in the brain. Rats were injected with xylazine at a
dose of 50 mg/kg b.w., and then the hippocampus and thalamencephal were removed at 0.1, 0.25, 0.5, 1, 1.5, 2, 4, and 6 h after the
injection. Glutamate (Glu) and γ-aminobutyric-acid (GABA) were measured in the brain tissue by reversed-phase high-performance
liquid chromatography. The results revealed that the hippocampus Glu level decreased significantly 0.1 h after the injection of
xylazine, the thalamencephal GABA increased significantly 0.1 h after the injection, while the changes in hippocampus GABA and
thalamencephal Glu were not significant. However, all of these changes returned to the normal level after 2 and 4 h, respectively. The
results indicated the relative effects of xylazine on Glu and GABA levels in the hippocampus and thalamencephal.
Key words: rat, xylazine, glutamate, γ-aminobutyric-acid, brain.
Xylazine exhibits analgesic, muscle relaxant, and
slight sedation properties. Furthermore, xylazine also
can evoke some other effects: restrain of ventricle
conduction, decrease in heart rate and venous pressure
(14), restrain of the respiratory system, decrease in body
temperature (13), decrease in plasma concentration of
T3, and significant increase in plasma concentration of
insulin and glucagon (11). Xylazine has been used as a
component of a variety of anaesthetics in domestic and
wild animals in the developing countries (16, 18). It was
demonstrated that anaesthesia could change the
concentration of amino acid neurotransmitters such as
glutamate (Glu) and γ-aminobutyric-acid (GABA) (4, 10,
15). Changes in the concentration of both compounds
may induce many kinds of nervous system diseases (9)
Despite an extensive use of xylazine in veterinary
practice, there is very little information about the effects
of xylazine on amino acid neurotransmitters. Thus this
investigation focuses on the effects of xylazine on Glu
and GABA concentrations.
Material and Methods
Animals. Male and female Sprague-Dawley rats
weighing 200±20 g were used. The animals were housed
at a controlled temperature (20±2°C) and maintained
under light-dark cycles, each consisting of 12 h of light
and 12 h of darkness (lights on from 06:00 to 18:00 h),
with feed and water available ad libitum. The animals
were divided into two groups: the control group and
xylazine treated group (five rats in each group). The
experimental procedures were performed in accordance
with the Local Ethics Committee for Animal
Experiments.
Experimental procedures. A brain tissue was
removed before the treatment (0 h, control) in control
group. The rats were injected intraperitoneally with 50
mg/kg of xylazine (Bayer Ltd, USA), and decapitated
0.1, 0.25, 0.5, 1, 1.5, 2, 4, and 6 h after the injection. The
hippocampus and thalamencephal of control and
experimental rats were dissected on ice and frozen
immediately. Each sample was homogenised in 1 ml of
ice-cold deionised methanol (V/V=50:50) and
centrifuged at 3,000 rpm for 30 min at 4°C. Forty
538
microlitres of supernatant was removed to another test
tube and with added 40 µl of acetonitrile was
centrifuged at 15,000 rpm for 10 min at 4°C. Then 49 µl
of 0.5 mol/L NaHCO3 and 20 µl of 0.5%
dinitro-fluorobenzene were added to the supernatant,
mixed, and heated for 50 min in 65°C water bath.
Chromatography. Detection by RP-HPLC was
performed using a C18 column (4.6 mm×200 mm, 5 µm)
and chromatographic system (Waters 2695, USA) at
room temperature. The eluent containing 0.05 mol/L
sodium acetate (pH 6.9) and deionised acetonitrile
(V/V=50:50) was pumped through the column at 1
ml/min. The detection was made at 350 nm.
Statistical analysis. The results were analysed by
variance analysis. Experimental data were expressed as
the mean±standard deviation (X±SD). SPSS 13.0 was
used for statistical analysis of the data. The differences
between control values and those obtained after
treatment were considered significant at P<0.05.
Results
Thalamencephal concentrations of Glu and GABA
in control animals and rats injected with xylazine are
shown in Table 1. As can be seen from the Table, Glu
concentrations did not change significantly after drug
injection, compared with control group. GABA
concentrations changed markedly after the injection
compared with controls (P<0.01, P<0.05).The
concentrations achieved the maximum value at 0.25 h
after injection and the minimum value was detected at 4
h after injection.
In the hippocampus, Glu concentrations reached the
minimum value at 0.25 h after injection; while the
maximum value of Glu concentrations was detected in
control rats (Table 2). This difference was significant
(P<0.01 or P<0.05). GABA concentrations were not
significantly changed after drug injection as compared
with control group (P＞0.05).
Table 1
Glu and GABA concentrations in the thalamencephal in control (0) and xylazine injected rats
3
GLU (µg/mL)
GABA (µg/mL)
0
10.38 ± 1.33
3.61±0.56
0.1
10.24 ± 1.19
6.41±0.52▲
0.25
9.57 ± 0.85
12.29±0.73▲▲
0.5
9.06 ± 0.72
9.88±0.45▲▲
1
9.13 ± 0.56
7.10±0.66▲▲
1.5
10.07 ± 0.75
5.31±0.55▲
2
10.08 ± 0.63
4.82±0.43▲
4
10.12 ± 0.88
3.54±0.78
6
10.19 ± 0.92
3.76±0.32
▲
P<0.05; ▲▲ P<0.01 compared with control group.
Table 2
Glu and GABA concentrations in the hippocampus before and after injection of xylazine
Time after injection (h)
0
GABA (µg/mL)
23.91 ± 1.09
13.69±0.46
21.62 ± 1.27
▲
13.94±0.38
13.41 ± 0.83
▲▲
14.02±0.45
13.74 ± 0.67
▲▲
14.13±0.29
15.57 ± 0.55
▲▲
14.17±0.27
1.5
18.55 ± 1.23
▲
14.33±0.37
2
22.55 ± 1.08
14.43±0.34
4
23.08 ± 1.31
14.38±0.42
6
23.55 ± 1.08
14.31±0.56
0.1
0.25
0.5
1
▲
GLU (µg/mL)
P<0.05, ▲▲ P<0.01.
539
Discussion
References
The knowledge about the neurotransmitters
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is still incomplete. Within the mammalian central
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excitatory amino acid neurotransmitter. Apart from its
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GABA is one of the major inhibitory neurotransmitter
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Hypoxia may increase GABA levels by inhibiting
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It has been shown that isoflurane inhibits the
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mechanisms.
We found that at the beginning of injection, the
hippocampus Glu level first decreased and then
increased. On the other hand, thalamencephal GABA
level first increased then decreased, as the action of
xylazine had been reduced. These findings are very
important to understand the role of xylazine for
defending nerve injury in the combined anaesthesia.
1.
Acknowledgments: This study was funded by
two grants financed by the Northeast Agricultural
University doctoral research start-up funding and
Heilongjiang province post-doctoral research start-up
funding (LBH–Q07016).
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