Changes in concentrations of cortisol and melatonin in plasma, expression of synaptophysin, and ultrastructural properties of pinealocytes in goat kids in situations of stress due to early weaning: the effect of melatonin.
OBJECTIVE
To analyse the changes in some histo-physiological parameters of the pineal gland of goat kids in situations of stress due to early weaning, and the effect of exogenous treatment with melatonin.


METHODS
Twenty-four 6-day-old Verata goat kids were used; 12 suckled their dams throughout the study (non-weaned groups), and the other 12 were removed from their dams and fed a milk replacer (weaned groups). Six goat kids in each group were treated with melatonin, and the other six with double-distilled pyrogen-free water (Day 0). On Days 28-29, blood samples were collected at 0600, 1000, 1400, 1800, 2200, 0200 and 0600 hours, to determine concentrations of cortisol and melatonin in plasma. On Days 29 and 30, six animals per group (three at 1400 and three at 0200 hours, respectively) were subject to euthanasia and the weight of their pineal glands determined. The structural immunocytochemistry, morphometric analysis, ultrastructural analysis and immunotransmission electron microscopy of the pineal glands were established.


RESULTS
Concentrations of cortisol in plasma were significantly higher in weaned than in non-weaned goat kids (p<0.05), and treatment with melatonin reduced the concentrations in weaned kids (p<0.05). Concentrations of melatonin in plasma showed a similar pattern in the four groups, with peak values at 0200 and troughs at 1400 hours. Mean concentrations of melatonin in plasma in weaned goat kids were significantly lower than those in the other groups (p<0.05). In weaned goat kids not treated with melatonin, the weight and volume of the pineal gland, and number of pinealocytes, were significantly lower when compared with those from non-weaned kids (p<0.05). Quantitative ultrastructural analysis of pinealocytes showed the relative volume of mitochondria, rough endoplasmic reticulum and Golgi complex was significantly lower in weaned than non-weaned goat kids (p<0.05); treatment with melatonin significantly increased these parameters in weaned kids.


CONCLUSIONS
Taken together, these results indicate that treatment with melatonin in goat kids in situations of stress due to premature weaning could play an important role in the improvement of histo-physiological function of the pineal gland.
Histology and Pathology, Department of Animal Medicine, Faculty of Veterinary Medicine, University of Extremadura, 10003 Cáceres, Spain. eloyredo@gmail.com
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D000818:Animals; D005260:Female; D006041:Goats / Q000502:physiology*; D006854:Hydrocortisone / Q000097:blood*; D008297:Male; D008550:Melatonin / Q000097:blood* / Q000494:pharmacology*; D041941:Milk Substitutes; D010870:Pineal Gland / Q000648:ultrastructure*; D013312:Stress, Physiological; D016708:Synaptophysin / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014886:Weaning
D016708:Synaptophysin; D008550:Melatonin; D006854:Hydrocortisone