INRA, UMR85 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France.
Psychoneuroendocrinology. 2013 Aug;38(8):1426-34. doi: 10.1016/j.psyneuen.2012.12.011. Epub 2013 Jan 20.
Sheep are gregarious mammals with complex social interactions. As such, they are very sensitive to social isolation and constitute a relevant animal model to study specifically the biological consequences of social stress. We examined previously the behavioral and endocrine responses in ewes isolated socially in the familiar conspecific withdrawal model (FCW) and showed that stressful responses increased and maintenance behaviors decreased, confirming that social isolation is a strong stressor in sheep. Melatonin synchronizes seasonal and circadian rhythms; and several studies reported its implication in cognitive processes as emotion. Here we investigated its role in the modulation of social stressful responses. Firstly, we studied ewes in the FCW model during the day (characterized by low melatonin levels) and the night (characterized by high melatonin levels). We found lower stressful responses (significant lower levels of cortisol plasma, number of foot pawings, of circling attempts) during the night as compared to the day. To investigate whether these effects were due to melatonin or to darkness, we submitted ewes to FCW during the night with lights on, a condition that suppresses melatonin secretion. Ewes infused with melatonin under these conditions showed decreased stressful responses (significant lower levels cortisol plasma, number of vocalizations, time spent with the head out of the cage) as compared to ewes infused with saline. These findings demonstrate that melatonin diminishes the endocrine and behavioral impact of social isolation in ewes and support the idea that melatonin has a calming effect in socially stressful situations.
绵羊是具有复杂社会互动的群居哺乳动物。因此，它们对社会隔离非常敏感，是研究社会应激生物学后果的相关动物模型。我们之前研究了绵羊在熟悉同种撤退模型（FCW）中社会隔离时的行为和内分泌反应，结果表明应激反应增加，维持行为减少，证实了社会隔离对绵羊是一种强烈的应激源。褪黑素使季节性和昼夜节律同步；有几项研究报道了它在认知过程中的情绪作用。在这里，我们研究了褪黑素在调节社会应激反应中的作用。首先，我们在 FCW 模型中研究了白天（褪黑素水平低）和夜间（褪黑素水平高）的母羊。与白天相比，夜间的应激反应较低（血浆皮质醇水平、脚踢次数、转圈尝试次数显著降低）。为了研究这些影响是由于褪黑素还是由于黑暗，我们在夜间开灯的情况下让母羊接受 FCW，这种情况会抑制褪黑素的分泌。在这些条件下，接受褪黑素输注的母羊的应激反应降低（血浆皮质醇水平、发声次数、头部伸出笼子的时间显著降低），而接受生理盐水输注的母羊则没有。这些发现表明，褪黑素可减轻绵羊社会隔离的内分泌和行为影响，并支持褪黑素在社会应激情况下具有镇静作用的观点。
