Smooth endoplasmic reticulum in fish mauthner cells at different functional states

The ultrastructure of Mauthner cells of goldfish fry and adult xenotoca in intact slate and after prolonged natural stimulation has been studied quali tatively and quantitatively. Additionally, Mauthner cells of intact adult g oldfish and adult rotan Percottus glehni were investigated. In all adult fi sh the dendroplasm of the two major dendrites was shown to contain a regula r network of smooth endoplasmic reticulum, with cisterns and tubules arrang ed transversally to the dendrite stem. In the Mauthner cells of intact gold fish fry, the reticulum was not clearly expressed, the transversal cisterns occurred occasionally. After stimulation, however, it became more develope d probably due to proliferation of additional transversal cisterns. The per iodicity of transversally oriented cisterns in the dendrites of Mauthner ce lls in each fish species studied was nearly the same. However, the number o f transversal cisterns per unit of dendrite length, and the total length of cisterns and tubules per unit of cross-section area varied both within and among the species. These parameters increased after stimulation. It is suggested that the proliferation of the transversal cisterns in the e ndoplasmic reticulum and the extent of their development depend on the func tional state of the afferent synapses and the plasticity of the smooth reti culum reflects the involvement of postsynaptic mechanisms in regulation of Mauthner cell stability presumably via the regulation of calcium homeostasi s under varying conditions of functioning. (C) 1998 IBRO. Published by Else vier Science Led.