Guesdon Vanessa, Meurisse Maryse, Chesneau Didier, Picard Sophie, Lévy Frédéric, Chaillou Elodie
ISA Lille, 48 bd Vauban, F-59046 Lille cedex, France.
INRA, UMR85 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France; CNRS, UMR 6175, F-37380 Nouzilly, France; Université de Tours, F-37041 Tours, France; IFCE, F-37380 Nouzilly, France.
Physiol Behav. 2015 Aug 1;147:63-70. doi: 10.1016/j.physbeh.2015.04.013. Epub 2015 Apr 9.
Regulation of neuroendocrine responses is often studied in animals housed indoors in individual contiguous pens. In sheep, these housing conditions are used to control the environment, facilitate biological sampling and limit social stress. However, this type of housing also prevents exploratory behaviors and could induce stereotypies, non-compliant with welfare and possibly associated with a state of stress. In this context, we investigated the impact of housing in a single-pen, with other familiar conspecifics, on emotional state by evaluating behavioral, hormonal and neuronal measures in adult ewes. We hypothesized that emotional state would be more negative in animals housed in a single-pen for one week (Pen) than in freely moving animals (Free) but less negative than in socially isolated subjects (Isol). We tested our hypothesis in ovariectomized ewes to avoid the interaction with sexual steroid variations. Our behavioral, endocrine and neuronal (Fos activation of the corticotropin-releasing hormone neurons in the paraventricular nucleus of the hypothalamus) measures confirmed that withdrawing familiar conspecifics was sufficient to induce strong stress responses in Isol ewes, but there was no indication that Pen ewes were stressed. However, the latter showed less mastication activity than Free ewes, probably due to limited accessibility to straw. The highest plasma prolactin levels were observed in Isol and Free animals, which might result from stress and physical activity, respectively. In Free ewes, plasma dopamine was low, consistent with its inhibitory control of prolactin. However, Isol animals had both high levels of prolactin and dopamine, suggesting a dysregulated balance in socially stressed ewes. As in other species, we suggest that the regulation of prolactin by dopamine varies with stress and/or social context. Overall, this study shows that the impact of housing conditions on different neuroendocrine systems should be considered more in the future.
神经内分泌反应的调节通常在室内单独相邻围栏中饲养的动物身上进行研究。在绵羊中，这些饲养条件用于控制环境、便于进行生物样本采集并限制社会压力。然而，这种饲养方式也会阻碍探索行为，并可能诱发刻板行为，不符合动物福利，还可能与应激状态有关。在此背景下，我们通过评估成年母羊的行为、激素和神经元指标，研究了与其他熟悉的同种动物一起单栏饲养对其情绪状态的影响。我们假设，单栏饲养一周的动物（围栏组）的情绪状态会比自由活动的动物（自由组）更消极，但比社会隔离的动物（隔离组）消极程度要低。我们在去势母羊中验证这一假设，以避免性类固醇变化的干扰。我们的行为、内分泌和神经元（下丘脑室旁核促肾上腺皮质激素释放激素神经元的Fos激活）指标证实，将熟悉的同种动物分开足以在隔离组母羊中诱发强烈的应激反应，但没有迹象表明围栏组母羊处于应激状态。然而，后者的咀嚼活动比自由组母羊少，可能是因为获取稻草的机会有限。在隔离组和自由组动物中观察到最高的血浆催乳素水平，这可能分别是由应激和体力活动导致的。在自由组母羊中，血浆多巴胺水平较低，这与其对催乳素的抑制性控制一致。然而，隔离组动物的催乳素和多巴胺水平都很高，这表明在社会应激母羊中平衡失调。与其他物种一样，我们认为多巴胺对催乳素的调节会随应激和/或社会环境而变化。总体而言，本研究表明，未来应更多地考虑饲养条件对不同神经内分泌系统的影响。
