Arborization of initial axon collaterals of spinocervical tract cells stained intracellularly with horseradish peroxidase.

The initial axon collateral arborizations of two feline spinocervical tract cells have been analysed after intracellular staining with horseradish peroxidase. The images of the cells were reconstructed in the light microscope from transverse serial sections. The cell bodies were situated in laminae IV or III of the lumbar dorsal horn. Each cell exhibited one initial collateral. These emerged from the parent axons at distances of about 310 and 580 micron, respectively, from the cell body. The collaterals branched, mainly symmetrically, in laminae III-VI and IV-VI, respectively. The total collateral lengths were about 12,000 and 10,900 micron; altogether 329 and 274 stained terminals were found per collateral in laminae III-VI and IV-VI, respectively. The great majority of boutons were found in laminae IV and V. The terminals were distributed mainly in spherically arranged groups of 3-12 boutons, usually connected to each other by thin terminal axons. The light microscopically investigated sections were 're-embedded' and processed for electron microscopy. The ultrastructural investigation showed boutons with axo-dendritic, axo-somatic or axo-axonal synapses.