Brain research
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Capsaicin injected intradermally into the human forearm lowered the pain threshold for heat at the injection site. Both the magnitude and duration of hyperalgesia were dose dependent over the range of 0.1-100 micrograms, given in a constant volume of 10 microliter. Thus, capsaicin may be a useful tool in studies of the neural mechanisms of hyperalgesia.
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The postnatal maturation of spinal pathways may account for the gradual time course of postnatal development of behavior and also account for the greater anatomical reorganization which often follows damage to the developing CNS compared to the mature CNS. The purpose of the current study was to examine (1) the prenatal and postnatal development of the descending serotonergic (5-HT) projection to the spinal cord and (2) the effects of a neonatal spinal cord lesion on this development. In addition, we wished to determine (3) whether transplants of fetal spinal cord tissue placed into the neonatal lesion site alter the plasticity of the 5-HT projection to the cord. ⋯ When this same lesion was made in the newborn animal, the innervation was 43% of that on the intact side. When a transplant of fetal spinal cord tissue was inserted into the lesion site in the newborn animals, there was even greater 5-HT innervation caudal to the lesion, 83% of that on the intact side. These results indicate that there is considerable postnatal development and plasticity of the descending serotonergic projection to the spinal cord, and this plasticity is enhanced by the presence of a spinal cord transplant at the site of the lesion.