Development and histology of the pineal gland in animals

Abstract

The pineal gland, which develops as a median diverticulum of the caudal part of the roof of the diencephalon, is a neuroendocrine gland that regulates the daily body rhythm. The gland remains attached to the brain by short stalk. The parenchymal cells of the gland are composed primarily of pinealocytes and interstitial cells. Pinealocytes are arranged in clumps and cord within lobules. The endings of the cytoplasmic processes of these cells come in contact with the blood capillaries and other parenchymal cells. Interstitial or glial cells constitute 5% of the gland and are believed to be astroglia-like cells. They are reminiscent of the pituicytes of the posterior lobe of the hypophysis and are abundant in the pineal stalk, which connects with the diencephalon. In addition to the two cell types, the pineal gland also contains calcified concretions called brain sand. These structures are thought to be deriving from precipitation of calcium phosphates and carbonates on carrier proteins. Pineal gland obtains information about light and dark from the retina by retinohypothalamic tract. Pineal activity increases during darkness and decreases in light. Circadian changes of melatonin secretion play an important role in daily rhythms. Melatonin, which is released in the dark, regulates reproduction in mammals. It inhibits the steroidogenic activity of gonads via inhibiting the neurosecratory neurons that produce GnRH in the hypothalamus. Pineal gland is thought to be responsible for the seasonal sexual activity. In addition it is believed that pineal gland can also affect the emotions in winter due to decreased day length. Recent studies showed that melatonin, the major hormone of the pineal gland, inhibits the growth of mammary tumors in animal models of human breast cancer with its direct inhibitory action on the proliferation of estrogen-responsive MCF-7 human breast cancer cells in culture. © 2013 Nova Science Publishers, Inc. All rights reserved.