Effects of inhibition of gonadotropin releasing hormone secretion on the response to novel objects in young male and female sheep.
This study investigated the actions of blocking the GnRH receptor using a specific agonist on the response of male and female sheep to a novel object placed in their pen. The study is part of a series performed on 46 same sex twin animals. One of the pair received a subcutaneous implant of the GnRH agonist Goserelin acetate every four weeks while the other remained untreated. Implantation began immediately prior to puberty; at 8 weeks in the males and 28 weeks in the females (as timing of puberty is sex specific). To determine the effects of agonist treatment on the reproductive axis blood samples were collected for measurement of testosterone in the males and progesterone in the females. In addition the volume of the scrotum was determined. The present study aimed to determine whether there are sexually differentiated behavioural responses to a novel object at different stages of brain development (8, 28 and 48 weeks of age) and whether these responses are altered by GnRHa treatment. Approach behaviour towards and interactions with the novel object were monitored as was the number of vocalisations per unit time during the test period. GnRHa treatment suppressed testosterone concentrations and testicular growth in the males and progesterone release in the females. Sheep vocalised significantly more prior to weaning (8 weeks of age) than post weaning (28 and 48 weeks of age) suggesting stress on separation from their dams. Our current study shows that males are more likely to leave their conspecifics to approach a novel object than females. As this behaviour was not altered by suppression of the reproductive axis we suggest that, although sex differences are more obviously expressed in the phenotype after puberty, these may be developed during adolescence but not primarily altered during puberty by sex hormones.
Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, G61 1QH, Scotland, UK. Electronic address: jane.robinson@glasgow.ac.uk.
Jane E
JE
Robinson
Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, G61 1QH, Scotland, UK.
Neil P
NP
Evans
Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, G61 1QH, Scotland, UK.
Rebecca
R
Dumbell
Department of Psychosomatic Medicine, Division of Surgery and Clinical Neuroscience, Oslo University Hospital - Rikshospitalet, Oslo, Norway.
Anne-Kristin
AK
Solbakk
Norwegian School of Veterinary Science, P.O. Box 8146 Dep., 0033 Oslo, Norway.
Erik
E
Ropstad
Department of Psychosomatic Medicine, Division of Surgery and Clinical Neuroscience, Oslo University Hospital - Rikshospitalet, Oslo, Norway.
Ira Ronit Hebold
IR
Haraldsen
D000367:Age Factors; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology*; D005106:Exploratory Behavior / Q000187:drug effects / Q000502:physiology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000037:antagonists & inhibitors* / Q000378:metabolism; D017273:Goserelin / Q000494:pharmacology; D006854:Hydrocortisone / Q000097:blood; D008297:Male; D011374:Progesterone / Q000097:blood; D012727:Sex Characteristics; D012756:Sheep / Q000097:blood / Q000254:growth & development / Q000523:psychology*; D013315:Stress, Psychological / Q000097:blood
D017273:Goserelin; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D006854:Hydrocortisone
GnRH; GnRH agonist; Novel object; Oestrogen; Puberty; Sheep; Testosterone