| Popis: |
Comprehensive reviews dealing with the embryology, morphology, vascularization, innervation, and cytology of avian pineal glands are available. Among species of birds, the morphology and cytology of the pineal gland are remarkably varied. According to Collin, the unique cell type in the avian pineal, the secretory pinealocyte, is evolutionarily derived from a cone-like receptor cell found among some reptiles and anamniotes. The rhythmic variation in melatonin content of the pineal gland of chickens persists as a free-running, circadian rhythm for at least 2 weeks in continuous darkness, but it disappears within 2 weeks in constant light. The autotransplanted pineal gland of chickens apparently released greater amounts of melatonin into the blood at night than during the day, since by bioassay melatonin could be detected there only when sampled at night. The injury occasioned by the surgical removal of the pineal gland can affect the measured response in various ways, including increasing the opacity of the skull and underlying tissues. |
