الفهرس 
المقدمةيوجد فقط 14 صفحة متاحة للعرض العام
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المستخلص
Abstract
Six experiments were undertaken to investigate the role of
dopamine in different brain regions (hypothalamus, basal
ganglia, frontal cortex and brain stem) in the acquisition and
retention of avoidance responses. In experiment 1, rats were
trained to avoid electric shock 0.5 rnA on a distributed learning
paradigm (25 trial per day). This experiment revealed that there
are two types of rats according to their learnability, the high
avoidance rats (group 1) that achieved 89.5 % conditioned
avoidance responses (CARs) and the low avoidance rats (group
2) that achieved 6.3 % CARs. In experiment 2, the low
avoidance rats (group 3) received 25 mg /kg L-dopa after three
days of training, this treatment facilitated the development of
CARs from 9.9 % to 52.7 %. In experiment 3 and 4, unknown
rats (group 4) received 25 mg/kg L-dopa and (group 5) received
0.1 mglkg Haloperidol before training. This treatment facilitate
the acquisition in group 4 (40.2 % CARs) due to L-dopa but
inhibit the CARs (0 %) in group 5 due to haloperidol. In
experiment 5 and 6, Retention were tested in high avoidance rats
24 h., 48 h., and 72 h. after acquisition stage with 25 mglkg Ldopa
(group 6), and with 0.1 mglkg Haloperidol (group 7)
before retention tests, this treatment made severe decreasing of
CARs in group 7 from 88.86 % to 1.3 % due to haloperidol. Ingroup
6, L- dopa had no effect on total number of avoidance but
simply increase the speed of escape responses. Dopamine levels
in different brain ar-eas.were measured to evaluate its role in
these behavioral differences. Our results suggested that the
activity of dopaminergic receptors in basal ganglia not
dopamine concentration only has an important role in avoidance
learning.