單次操弄壓力源對場地制約偏好行為學習的影響效果

The Effects of Acute Stress on Conditioned Place Preference

壓力會影響個體的生理及行為功能，過去有關壓力與生理的研究有較多且一致的證據，至於壓力與行為間則尚未有一致的證據定論。這可能是肇因於壓力源與行為反應之間有較多的影響因子參與其中。本研究以單次施予高台壓力源或禁錮壓力源的不等持續時間為不同壓力強度之操弄，以及壓力源與不同的配對制約作業出現的次序性，來檢驗壓力源本身效果對於實驗動物學習場地制約偏好行為的影響。實驗一在實驗動物進入制約箱前分別給予單次10、30、60分鐘不等時間長度的高台或禁錮壓力源，結果發現僅有施予30分鐘的高台壓力源或禁錮壓力源可有效建立場地制約偏好行為。實驗二檢驗單次30分鐘的高台或禁錮壓力源施予在其與單側制約箱配對制約之前、同時、或之後的時間點，結果發現當高台壓力源是在實驗動物進入制約箱之前施予可有效引發場地制約偏好行為；禁錮壓力源是在配對制約之前或同時施予均可有效建立該行為。綜合上述結果可知，特定持續時間的壓力源所造成的刺激強度，以及操控壓力源在特定的配對制約時間點之變項，都會促進受試習得場地制約偏好行為。這結果顯示在古典制約作業中，單次壓力源的類型與強度，及其在制約作業的時間次序之關係，都會影響其擔任非制約刺激的角色，並進而決定是否具有引發制約行為的能力。

Physiological and behavioral functions could be affected when the individual is under stress. Previous studies accumulate a more consistent evidence for the relationship between stress and physiological function. In contrast, the relationship between stress and behavioral function remains debatable due to inconsistent findings reported in the past. Presumably, multiple factors are involved in mediating behavioral functions altered by the stress. By the use of two types of stressors (elevated stand and restraint), the present study manipulated the intensities of stressor and the temporal sequences to pair the stressor with contextual environment on the acquisition of conditioned place preference. Experiment 1 manipulated different durations (10, 30, or 60 min) of stressor conducted before the beginning of conditioning session. The results showed that the conditioned place preference was significantly formed by only the subjects received 30 min stressor treatment, and such effect was true for either elevated stand or restraint stressor. Experiment 2 evaluated the effects of 30 min stressor presented immediately before, during, or right after the conditioning session of the present task. As the results showed, the conditioned place preference was formed by the stressor (elevated stand or restraint) presented immediately before placing the subject into the association context, rather than conducted afterward. Such effect was also true for the restrain stressor presented during the conditioning session. Together, it was found that conditioned place preference could be acquired by the optimal intensity of the stressor and at certain temporal sequences of stressor presented to the subject for pairing with the environmental context. These data indicate that the type and intensity of acute stressor as well as its temporal sequence of conditioning can be critically important for the stressor to be an unconditioned stimulus (UCS) in the classical conditioning.