The Journal of neuroscience : the official journal of the Society for Neuroscience
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We investigated the ability of human nociceptive primary afferent neurons to encode mechanical pain and to produce vasodilatation. Pain was induced by shooting a light metal cylinder (0.3 g) at different velocities (6-18 m/sec) perpendicularly against the hairy skin of the hand. When single impact stimuli were applied, monotonically increasing stimulus-response functions were obtained in 10 psychophysical experiments using magnitude estimation techniques. ⋯ This suggests that temporal summation of the nociceptive discharge at central neurons becomes increasingly more important for the sensory discriminative experience of pain evoked by repetitive stimulation. We conclude that human nociceptive C-fibers signal brief noxious mechanical stimuli by the total number of action potentials evoked during a short period of time. However, with repetitive stimulation the total number of action potentials evoked from nociceptors is less important for evoking pain and temporal summation of the nociceptive primary afferent discharge becomes the crucial factor for signaling the magnitude of sensation.
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The use of human Schwann cells (SCs) in transplantation to promote regeneration in central and peripheral neural tissues must be preceded by efforts to define the factors that regulate their functional expression. Adult-derived human SCs can be isolated and purified in culture, but the culture conditions that allow their full differentiation have not yet been defined. We tested the functional capacity of these cells to enhance axonal regeneration and myelinate regenerating axons in vivo by transplanting them into the damaged PNS of an immune-deficient rat. ⋯ The number of myelinated axons and the cross-sectional area of the cable were significantly greater in channels seeded with human SCs when compared to channels containing the diluted Matrigel solution alone. We conclude that purified cultured human SCs can survive and substantially enhance axonal regeneration when transplanted into the injured PNS of an immune-deficient rat. Some of the transplanted human SCs are capable of myelinating regenerating rat axons but are less successful than the host SCs.
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The mammalian acoustic startle response (ASR) is a relatively simple motor response that can be elicited by sudden and loud acoustic stimuli. The ASR shows several forms of plasticity, such as habituation, sensitization, and prepulse inhibition, thereby making it an interesting model for studying the underlying neuronal mechanisms. Among the neurons that compose the elementary startle circuit are giant neurons in the caudal pontine reticular nucleus (PnC), which may be good candidates for analyzing the neuronal basis of mammalian behavior. ⋯ Axon collaterals and terminal arbors were found in the reticular formation as well as in cranial and spinal motoneuron pools. The results of this study indicate that giant PnC neurons form a sensorimotor interface between the cochlear nuclear complex and cranial and spinal motoneurons. This neuronal pathway implies that the elementary acoustic startle circuit is composed of only three central relay stations and thus appears to be organized more simply than assumed in the past.