SATELLITE CELLS AND NERVE-TERMINALS IN THE CRAYFISH OPENER MUSCLE VISUALIZED WITH FLUORESCENT DYES

Nerve terminals and associated cells on the muscle's surface were visu alized in the crayfish opener muscle with several fluorescent dyes in conjunction with confocal microscopy and conventional fluorescence mic roscopy. The nerve terminals of the excitatory and inhibitory axons we re best seen with 4-diethylaminostyryl-N-methylpyridinium iodide (4-Di -2-Asp). This dye is selectively accumulated in mitochondria, which ar e numerous both in the axons and in synapse-bearing terminal varicosit ies. Muscle nuclei were also clearly visualized, because they excluded 4-Di-2-Asp but were stained by acridine orange (AO). A positive attra ction between muscle nuclei and nerve terminals was evident by visual inspection and was confirmed by spatial statistics. Additional flat ce lls on the muscle's surface appeared as bright rings with elongated pr ocesses that were often close to or overlapped nearby nerve terminals. The structure of these cells was established by electron microscopy a fter labeling them with fluorescent polystyrene beads, which could be found over structures on the muscle surface in sections of embedded sp ecimens. The flat surface cells were distinct from peripheral glial ce lls closely associated with axons and nerve terminals. Nevertheless, s patial statistics showed that the surface cells were grouped near nerv e terminals. They occupied a small fraction of the muscle cell's surfa ce. Their functional role has not been determined in crustacean muscle s. (C) 1995 Wiley-Liss, Inc.