흰쥐의 중추성 Serotonin 고갈이 강제수영 중 부동자세 시간，불안 및 수동적 회피 학습에 미치는 효과

Effect of Central Serotonergic Depletion on Immobility Time During Forced Swimming, Anxiety and Passive Avoidance Learning in Rats

Purpose : To test if p-chlorophenylalanine(PCPA) induced decrease of immobility time during forced swimming test in rats is an epiphenomenon related with PCPA-induced changes in anxiety level or learning ability. Method : 22 male rats(Sprague Dawley, weighting 180-280gm ) were randomly assigned to PCPA or control group and treated with 300mg/kg of PCPA or saline i.p. at - 72，- 48，and - 2 4 hrs. Number o f segment(ACTO) entered with 4 limbs on the open field(L100 X W100 X H40cm, 25 segments), time(ANX0，sec) spent on the open arm(Ll 10 X W1 Ocm, 50cm from the ground) in the elevated plus maze, and step-through latency(STL0, cut-off time ： 300sec) in the shuttle box(L76.2 X W34.3 X H50.8cm, 7.5w electric bulb in the light chamber, 0.5mA for 3 sec in the dark chamber) were measured consequently at 24hrs after the last injection of PCPA or saline. After 20min of rest, animals were forced to swim for 15 min(cylinder : 9 I 8 X H40cm ； water ： HI5cm, 25 *C). On the next day, the second trial of open field test(ACTl), elevated plus maze test(ANXl), passive avoidance learning test(STLl), and measurement of total immobility time(IT，sec) during the 5min of forced swim were done in the same manner as the first trial except that electrical shock was not given to the animals in the passive avoidance learning test and duration of forced swimming was shortened from 15min to 5min. To evaluate longterm effect of PCPA on maintenance of memory, measurement of stepthrough latency was repeated 7 days after the first trial(STL7). Result ： 1) ACT1 was significantly decreased in the pooled sample, but the effect of PCPA on the general motor activity was not significant. 2) PCPA significantly prolonged the time spent on the open arms in the elevated plus maze test. 3) Comparing to STLO, STL1 was significantly prolonged in both groups. PCPA did not affect STLO or STL1. STL7 was significantly prolonged in the control group, but not in the PCPA group. 4) PCPA shortened IT significantly. Conclusion ： PCPA-induced decrease of immobility time during the forced swimming test in rats seems to be related with disinhibition o f stress-related behavioral suppression. PCPA does not affect acquisition and short-term maintenance of passive avoidance learning, but necessity of further studies about its effect on long-term maintenance of memory is raised