Ultrastructural and histochemical studies of neurosecretory cells and sinus gland in optic lobe of the giant freshwater prawn Macrobrachium rosenbergii de Man

Abstract

Cells in the optic lobes of the giant freshwater prawn, Macrograchium rosenbergii de Man, were classified under light and transmission electron microscopy (TEM). In light microscopic (LM) study , sections were stained with chrome-hematoxylin phloxine (CHP) and aldehyde fuchsin (AF). Four major cell types; A, B, C and D, could be distinguished by LM observation,based on morphology and stainability of the cells. Umder TEM, three additional sugtypes are revealed; D1, D2 and D3, based on different ultrastructure features. Type C, D1, D2 and D3 cells are likely neurosecretory cells since they stained positively with CHP and AF, and contain secretory granules adn abundant organelles necessary for synthesizing secretory products. All of the type D cells are of large size (10-35 ?m) and featured by abundant rough endoplasmic reticula, well developed Golgi complex, tubular mitochondria and secretory granules of different size. The optic lobe, optic peduncle brain and thoracic ganglion of the giant freshwater prawn, Macrobrachinm rosenbergii de Man, were examined for the presence of specific acetylcholinesterase (AChE) by histochdemical technique. Neurons and axons containing AChE were detected in all the tissues studied. AChE-postitive neurons were found in the medulla externa and medulla interna of the optic lobe; they were small monopolar neurons whose axons running proximally toward the optic peduncle. The optic lobes of adult prawn, Macrograchium rosenbergii de man were examined for the presence of catecholamines and 5-Hydroxytryptamine (5-HT) by using glyoxylic acid fluorescenc histochemical technique. Cells in the compound eye, medulla interna and those connecting medulla interna and medulla terminals contain yellow fluorescence, suggesting the presence of 5-HT. The sinud gland of the giant freshwater prawn, Macrobrachium rosenbergii, was observed by transmission electron microscopy. The gland is composed of neurosecretory axon and glial cells, and surrounded by blood sinus. The glial cells is stellate in shape and sends out cytoplasmic processes which lie among the neurosecretory axons. Its cytoplasm contains numerous glycogen granules, mitochondria, and endoplasmic reticulum. The neurosecretory terminals are packed with vesicles which can be morphologically classified into three thpes, basing on their electrom density and size. Type-1 vesicles contain electron-dense material and are 120-140 nm in diameter; type-2 vesicles also contain electron-dense material and are 100-120 nm in diametrer; type-3 vesicles containelectron-lucent material and are 150-170 nm in diameter. The sinus glands of the giant freshwater prawn,Macrobrachium rosenbergii de Man, were examined under secanning electron microscopy. The glands are composed of several, uniform, axon terminals of 5 ?m in diameter. The terminals are either individually separated or grouped together and covered by the basement membrane. Glial cells are observed both inside and on the surface of the sinus gland.