STUDIES ON SENSORY NEURONS OF THE MOUSE WITH INTRACELLULAR-RECORDING AND HORSERADISH PEROXIDASE INJECTION TECHNIQUES

Dorsal root ganglion (DRG) cells were dissected from the adult mouse with their peripheral nerves, and electrophysiological and morphological studies were performed. The peripheral nerves were stimulated and conducted spikes were intracellularly recorded from cell bodies. Horseradish peroxidase (HRP) was injected into the cell body, and the size of stained cell body and axon, together with the state of myelination, were examined. F-neurons, whose somatic spike is a tetrodotoxin (TTX)-sensitive Na spike, had a large or medium sized cell body with a myelinated axon, and showed a fast conduction velocity (A fibers). A-neurons, whose somatic spike is a TTX-resistant Na spike, had a small cell body with an unmyelinated axon, and showed a slow conduction velocity (C fibers). Most H-neurons, whose somatic spike is a TTX-resistant combined Na-Ca spike, proved to have conduction velocity and morphological features similar to A-neurons, whereas the rest of them had features similar to F-neurons. A roughly linear correlation was exhibited between each pair of cell body size, axon diameter, and conduction velocity. Spike conduction along axons to cell bodies were blocked in all neurons either by an elimination of Na ions from the medium or by an application of TTX. The possibility of transmission of different information by different DRG cells and the developmental differentiation of sensory neurons are discussed.