Possible removal route of osmiophilic material (lipofuscin) from spinal ganglia of Torpedo marmorata.

The spinal ganglia of Torpedo marmorata have been studied in semithin and ultrathin sections with the view to study the formation and possible mode of removal of lipofuscin. This study suggests that osmiophilic bodies among them lipofuscin originate from degenerating mitochondria. These osmiophilic products concentrate at the neuronal cell border with the satellite cells. The satellite cells have long dense membranous processes which interdigitate, forming a compact myelin sheath but also loosely arranged membranes surrounded by vacuolated plasma. The perinuclear cytoplasmic portion of the satellite cell however contains a rich assemblage of cell organelles well provided for an active metabolism. In this active area which invaginates the neuronal cytoplasm, osmiophilic granules but smaller can be seen, similar to those in the neighbouring neuron. Similar granules are found in cells within the connective tissue space and in the capillary wall. Satellite cells appear not only to be ensheathing cells, providing a perineuronal myelin cover but also capable of removing intra-neuronal debris. It appears that these osmiophilic bodies are taken to the capillary wall by detached satellites or 'handed on' to phagocytes having penetrated between the ensheathing satellites. These cells could take the osmiophilic material to capillaries.