Postnatal development of female sheep pineal gland under natural inhibitory photoperiods: an immunocytochemical and physiological (melatonin concentration) study

E. Redondo1, S. Regodon2, J. Masot1, A. Gázquez1 and A. Franco2

1Department of Histology and 2Department of Anatomy and Embriology, Faculty of Veterinary Medicine, University of Extremadura, Cáceres, Spain

Offprint requests to: Eloy Redondo, Histología, Facultad de Veterinaria, Universidad de Extremadura, Avenida de la Universidad S/Nº, 10.071 Cáceres. Spain. Fax: 34 927 257110. e-mail: eloy@unex.es

 

Summary. The purpose of this study was to determine structural and immunocytochemical changes taking place during the day and at night in developing sheep pineal gland under natural non-stimulatory photoperiods (summer solstice). Additionally, the diurnal cycle of plasma melatonin levels was charted and differences between diurnal and nocturnal pineal melatonin concentrations were analyzed. 36 ewes of three different ages were examined: infants (1-6 months old), pubertal and early fertile age (9-24 months old) and adults (36-60 months old). Plasma and pineal gland melatonin levels were higher in pubertal sheep than in infants or adults. Pubertal sheep pineal glands were also heavier, contained a larger number of pinealocytes and interstitial cells and displayed more evident innervation and vascularisation than infants or adults. There was no difference in the number of pinealocytes and interstitial cells between animals killed during daylight or at night. Gland weight, pinealocyte nuclear profile areas and plasma melatonin concentrations were all significantly higher at night than during the day. Histol. Histopathol. 18, 7-17 (2003)

Key words: Pineal gland, Sheep, Melatonin, Postnatal development, Long photoperiod

DOI: 10.14670/HH-18.7