The Structure And Electrophysiological Characteristics Of X-organ-sinus Gland Complex Of Chinese Shrimp, Fenneropenaeus Chinensis

The X-organ-sinus gland (XO-SG) system is an important neurosecretory organ in Crustacean, analogous to vertebrate hypothalamo-neurohypophyseal system. XO-SG complex secrets several kinds of neuropeptidergic hormones controlling complex physiological processes, such as molting, hemolymph glucose levels and color change. Chinese shrimp is one of the most important economically valuable crustacean in China. Due to the limited knowledge on this system, eyestalk ablation is still a main method to promoting gonad development and maturation. Many basic problems of this system have not been clarified yet. The author studied the microstructure and ultrastructure of XO-SG complex, and carried out the primary culture of neurosecretory cells; The electrical activity of neuron's membrane is the basis of hormone secretion. Patch clamp recording technique was used to study the properties of the voltage-gated ion channels expressed by the culture neurosecretory cells. This research provided basis for further study of the secretory regulation mechanism and for controlling the reproduction and growth. The following results main obtained in this work are summarized below:1,Histological, cytological and immunohistochemical methods used to study microstructure and ultrastructure of the Chinese shrimp XO-SG complex showed that the Chinese shrimp XO-SG complex structure was lower than that of some other crustaceans. HE dyeing distinguished five neuron types on the basis of the size and form of cells; and identified six types of neurosecretory terminals on the basis of the size, morphology and electron density of the neurosecretory granules. Exocytosis was observed in the SG of Chinese shrimp. Immunohistochemical localization showed that CHH and MIH coexisted and had their own specificity in some neurons. 2,A method for culturing medulla terminalis (MT) neurons in the eyestalk of Chinese shrimp, Fenneropenaeus chinensis was for the first time established. Six types of neurosecretory cells were distinguished on the basis of size and form of soma and outgrowth pattern of cells, such as "Small cells", "Veilers", "Branchers", etc.. The outgrowth of neurons were dependent on themselves, not on the addition ofgrowth factors or serum to the medium. Culturing conditions and medium had some effects on the outgrowth of neurons. Immunocytochemical researches showed "Veilers" and "Branchers" were immunoactive to anti-CHH-A and anti-MIH respectively.3,The whole -cell patch clamp technique was first used to study the properties of the voltage-gated ion channels expressed by the cultured secretory neurons(24~48hrs after plating) of medulla terminalis in the eyestalks of Fenneropenaeus chinensis. Under current clamp, spontaneous and induced excitability and secretion were observed in CHH-secreting neurons, no excitability was observed in MIH-secreting cells. When solutions that suppressed the outward currents were used, tetrodotoxin(TTX)-sensitive Na+ current (INa)and Cd2+-sensitive Ca2+ current (ICa) were resolved in two cell types. When holding potential(Vh) was -50mV, ICa was activated at potential -40~-30mV, was maximal at -10~0mV. In the presence of 1μmol/L TTX and 0.5mmol/L Cd2+, two cell types expressed a slowly-rising, TEA-sensitive K+ current and a transient K+ current . Two kinds of outward currents were activated at the same potential of –40mV.