title: Rapid effects of melatonin on hormonal and behavioral stressful responses in ewes.
abstract: 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.
authors: INRA, UMR85 Physiologie de la Reproduction et des Comportements, F-37380 Nouzilly, France. vanessaguesdon@yahoo.fr
authors: Vanessa
authors: V
authors: Guesdon
authors: Benoît
authors: B
authors: Malpaux
authors: Philippe
authors: P
authors: Delagrange
authors: Michael
authors: M
authors: Spedding
authors: Fabien
authors: F
authors: Cornilleau
authors: Didier
authors: D
authors: Chesneau
authors: József
authors: J
authors: Haller
authors: Elodie
authors: E
authors: Chaillou
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D002940:Circadian Rhythm / Q000502:physiology; D003624:Darkness; D005260:Female; D006854:Hydrocortisone / Q000097:blood; D008550:Melatonin / Q000494:pharmacology* / Q000502:physiology; D017440:Photoperiod; D034561:Sheep, Domestic / Q000097:blood / Q000502:physiology; D012934:Social Isolation / Q000523:psychology*; D013315:Stress, Psychological / Q000097:blood* / Q000523:psychology*; D014828:Vocalization, Animal / Q000187:drug effects
chemical_list: D008550:Melatonin; D006854:Hydrocortisone