Classification and mapping of neurosecretory cells in the optic, supraoesophageal and thoracic ganglia of the female spiny lobster Panulirus homarus (Linnaeus, 1758) and their secretory activity during vitellogenesis

Abstract

The crustacean endocrine system consists of epithelial type of endocrine glands and endocrine structures of neural origin. The neurosecretory cells are of great significance in the crustacean endocrine system with respect to the number of neurohormones regulating reproduction. The study describes the general morphology of the central nervous system as well as the neurosecretory cells in the optic, supraoesophageal and thoracic ganglia of the spiny lobster, Panulirus homarus. The central nervous system of P. homarus follows the general arthropod pattern which consists of a ganglionated nerve cord extending from the cephalic region to the end of the abdomen. The neurosecretory cells are characterized by the presence of large nucleus, abundant cytoplasm, granules, vacuoles etc. in their perikarya showing differences in their size and shape. Based on these characteristics, the neurosecretory cells are classified into different cell types. The optic ganglia have six types of neurosecretory cells, whereas the supraoesophageal ganglion and the thoracic ganglia have eight neurosecretory cell types. Cyclic changes are observed in the perikarya of neurosecretory cells in relation to the synthesis of neurosecretory material. The secretory changes in the different neurosecretory cell types follow a basic pattern with four phases, viz. synthetic phase, vacuolar phase, secretory phase and quiescent phase. The secretory cycle of different neurosecretory cell types in the optic ganglia, supraoesophageal ganglia and thoracic ganglia were correlated with the ovarian developmental stages. The cyclic secretory activity of neurosecretory cells in the optic, supraoesophageal and thoracic ganglia points to secretion of certain hormones, which regulate the process of vitellogenesis