Neuroscience
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Immunoreactivity to pituitary adenylate cyclase activating polypeptide-38 was detected in numerous nerve fibres in layers I and II of the dorsal horn of the rat and some of these fibres extended into the deeper layers of all segments of the spinal cord. Immunoreactivity was also detected in the lateral funiculus projecting into the intermediolateral cell column of the lower cervical and thoracic segments and in the lateral pathway terminating in the intermediate gray area of the lower lumbar and sacral segments. Neurons in the lateral horn area were not immunoreactive nor were the ventral horn motoneurons. ⋯ A few weakly-labelled cells were occasionally seen in the dorsal motor nucleus of vagus. A population of neurons in the trigeminal, nodose and dorsal root ganglia from all segments of the spinal cord displayed low to intense immunoreactivity. The presence of immunoreactivity in nodose and dorsal root ganglia, dorsal horn, spinal autonomic nuclei, solitary tract and in certain areas of the medulla suggests that this peptide may participate in a variety of sensory and autonomic functions.
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Repetitive firing of nerve fibres results in the slowing of their conduction velocity. The extent of conduction velocity slowing throughout a standard electrical stimulus (20 s, 20 Hz, 2 x electrical threshold) was examined in identified C-fibres dissected from the saphenous nerve of anaesthetized rats. The aim of this study was to establish whether the different functional classes of C-fibre could be identified on the basis of their activity-dependent slowing of conduction velocity. ⋯ Moreover, it is possible to use this axonal property to separate the two classes of non-nociceptive afferent C-fibre (i.e. mechanoreceptors and cold thermoreceptors). In addition, one can also use this parameter to differentiate between the afferent and non-afferent populations of inexcitable C-fibres. The ability to identify a particular fibre type on the basis of an axonal property provides a useful tool for the functional classification of fibres in experiments where axons are separated from their terminals.