The fine structural organization of the locus coeruleus in the rat with reference to noradrenaline contents

Combination of glyoxylic acid perfusion and postfixation in permanganate was used in an electron microscopic study of the locus coeruleus (LC) of the rat to give good preservation of fine structure and a reproducible demonstration of noradrenaline (NA) storage granules. Medium-sized LC cells (18 × 30 μm) contained a moderate number of small granular vesicles (SGV) and a few large granular vesicles (LGV), mainly near the Golgi apparatus. Dendritic branches were identified by their SGV content up to the tip. Dendrites were occasionally in close contact with each other or with the soma of LC cells, forming dendro-dendritic or dendro-somatic contacts. Numerous axon terminals containing many SGV and some LGV were observed in the neuropil, and they tended to contact dendrites and somata of LC cells or dendrites of unknown origin. These neuronal contacts were devoid of synaptic specializations except for an array of dense perpendicular lines between the juxtaposed membranes. Small oval cells (10 × 15 μm) devoid of SGV occurred frequently in the peripheral part of the nucleus, and they were occasionally in direct contact with LC cells.