Pineal gland of a nocturnal bird, Indian spotted owlet, Athene brama: morphological and endocrine observations.

It has been reported that owls (Strigiformes) do not have a pineal gland. However, our light microscopy study revealed an intermediate form of tubulofollicular and solid-type large pineal gland in a tropical owlet, Athene brama. The epithelial cells forming follicles (6-8) in the distal region and the solid cluster of parenchymal cells of different diameters in the proximal region anteriorly tapered with a long cylindrical stalk and continued into commissural organs and choroid plexus. The intrapineal localization of perivascular nerve fibers and blood vessels clearly explained the sympathetic innervation as well as vascularization of this neuroendocrine gland. Further, electron microscopy revealed a developed intracellular structure of the pinealocytes with a large number of mitochondria, Golgi bodies, and granular as well as clear vesicles in the process terminals. The evidence of intrapinealocyte lipid droplets and dense bodies and a moderate amount of melatonin in plasma (ranging from 100-365 pg/mL) during different reproductive phases finally proved a defined secretory activity of the gland in this tropical, nocturnal bird.