Peroxidase activity at nodes of ranvier in lumbosacral ventral spinal roots and in the PNS-CNS transitional region after intramuscular administration of horseradish peroxidase.

The axoplasm of nodes of Ranvier in feline lumbosacral ventral spinal roots was analysed by light and electron microscopy 18-168 h after the injection of horseradish peroxidase (HRP) into the medial gastrocnemius muscle. Three main HRP distribution patterns were distinguished at PNS nodes (bordered by Schwann cells only) of large fibres transporting HRP. The type A pattern, characterized by a distal accumulation of HRP-positive bodies and a proximal system of vesiculotubular membrane profiles. The incidence of this type of node was highest at relatively short survival times. The type B pattern, which appeared somewhat later, resembled the type A node with the addition of a disc-like, proximal accumulation of HRP activity. The type C pattern which contained scattered HRP-positive bodies and delicate strands of membraneous profiles, dominated 72 h after injection. The number of HRP-positive PNS-CNS borderline nodes (bordered by both Schwann cells and glial cells) was less than 5% of the corresponding value in the same fibres of the ventral root proper. A highly segregated state of the axoplasm of PNS-CNS borderline nodes was noted only in two cases. The observations indicate a functional difference between nodal axoplasm at the PNS-CNS borderline and nodal axoplasm in the PNS part of the alpha motor neuron.