Peroxidase activity at CNS nodes of Ranvier and in initial axon segments of lumbosacral alpha-motoneurons after intramuscular administration of horseradish peroxidase.

The occurrence of peroxidase activity in central (CNS) and peripheral nervous system (PNS) parts of alpha-motor axons was studied by light and electron microscopy in adult cats after injection of horseradish peroxidase (HRP) into the medial gastrocnemius muscle. The intrafunicular parts of the axons were virtually free of HRP-positive bodies except at a few nodes of Ranvier. Most of these nodes were weakly HRP-positive and contained, irrespective of a survival time between 25 and 48 h, only a few HRP-positive bodies randomly scattered in the nodal axoplasm. In contrast to this and as described elsewhere (J. Neurocytol., 15 [1986] 253-260), the nodal regions of alpha-motor axons at the level of the ventral root showed strong and characteristic accumulations of HRP-activity. The initial axon segments and adjoining axonal parts contained many HRP-positive bodies. We conclude that the CNS and the PNS parts of an alpha-motor axon differ with regard to the way nodal regions interact with retrogradely transported HRP. Possible mechanisms behind this difference are discussed.