الفهرس | يوجد فقط 14 صفحة متاحة للعرض العام |
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. |