Conduction velocity of A delta fibers of the human peripheral nerves was measured by using pain-related somatosensory evoked potentials following CO2 laser stimulation. It was found to be approximately 9 m/s in the forearm as well as in the lower leg. Because conventional conduction study using electric stimulation reflects only functions of large myelinated fibers related to deep proprioceptive and tactile sensations, the present noninvasive and simple, novel method is the only laboratory examination currently available to investigate physiological functions of the small diameter fibers mediating pain-temperature sensations.

The evolution of motor nerve degeneration was examined in gracile axonal dystrophy (GAD) mutant mice, which develop initial sensory ataxia and subsequent motor paresis. Using the anterior gracilis (AG) muscle, which is innervated at two discrete and well-separated endplate zones, we demonstrated that axonal degeneration occurred first at motor nerve terminals in the distal endplate zone, and then extended gradually from the distal to the more proximal parts of affected axons in the intra-muscular nerve trunk. In contrast to the degeneration in the distal zone, active degeneration was less marked in the proximal endplate zone and, furthermore, most terminal axons had begun to produce regenerating sprouts. Ventral horn cells were histologically normal, even at advanced stages. These results indicate that, as previously observed in sensory nerves, dying back degeneration progresses later in the lower motor neuron system, even within one muscle. The mechanism(s) influencing the activation of axonal regeneration are discussed. This mutant mouse will be a useful model for the study of regenerating phenomena in dying back degeneration of genetically compromised motor neurons, as well as for the study of the pathogenesis of hereditary sensory and motor neuropathies in man.

Pain-related somatosensory evoked potentials (pain SEPs) following CO2 laser stimulation as well as conventional electrically stimulated SEPs (electric SEPs) were examined in 10 patients with peripheral neuropathies in whom the histopathological examination of the sural nerve was done. Results of pain SEPs showed a positive relationship with clinical impairment of pain sensation and densities of small myelinated fibers of the sural nerve. In contrast, results of electric SEPs showed a positive relationship with clinical impairment of deep and tactile sensations and with densities of large myelinated fibers of the sural nerve. Therefore, pain SEPs are considered to be generated by ascending signals mediated through nociceptive receptors and A delta fibers. The pain SEP is only one noninvasive and objective method currently available to investigate a physiological condition of the sensory pathway responsible for pain sense, and is especially useful when combined with the conventional electric SEPs.

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Pain-related somatosensory evoked potentials following CO2 laser stimulation (pain SEPs) and conventional electrically-stimulated SEPs (electric SEPs) were examined in 8 patients with syringomyelia who showed various forms of dissociated sensory loss. Unlike clinical examination using a pin or needle, pain SEP is considered to be an objective and quantitative test to investigate functions of peripheral and central sensory pathways responsible for pain-temperature sensation (A delta fibres and the spinothalamic tract). Pain SEPs were abnormal in all patients. The results were generally compatible with the degree of a clinical impairment of pain-temperature sensation. Subclinical abnormality was detected in 3 patients. Electric median nerve SEPs using the scalp reference (Fz) were normal in 6 out of 8 patients. However, anterior and posterior cervical responses using a noncephalic reference were absent or small in 7 patients. Electric SEPs following tibial nerve stimulation were normal in 7 patients. These findings suggest that the function of the ascending fibres through the dorsal columns is intact in most patients, whereas the dorsal horn, where a fixed cervical potential is generated, is impaired. Pain SEPs combined with electric SEPs therefore appear to be extremely useful for investigating physiological function in the sensory pathways in patients who show 'dissociated sensory loss' such as in syringomyelia.