Correlation between spontaneous bursts of activity recorded from the dorsal roots in an isolated hamster spinal cord preparation

At a temperature of 25-27 degrees C spontaneous antidromic activity has been demonstrated in lumbar and thoracic dorsal roots of an isolated spinal cord preparation taken from the golden hamster. A characteristic pattern of bursts of action potentials has been identified, which develops within 1-2 h following dissection and persists for more than 8 h. Simultaneous recordings made from pairs of dorsal roots have revealed correlations between the patterns of spontaneous activity in dorsal roots separated by up to sixteen segments longitudinally and across the cord. The strongest correlations were found between pairs of adjacent roots on the same side of the cord which produced a cross-correlation histogram having a single peak with a mode close to 0 ms. As the separation between the roots was increased the cross-correlation histogram became bimodal, with peaks equidistant on either side of 0 ms. Activity recorded in ipsilateral and contralateral pairs of roots supplying the same spinal segment also produced bimodal cross-correlation histograms. Transverse sectioning of the cord did not abolish spontaneous activity in any of the spinal roots examined, although there was a progressive reduction in the frequency of the bursts of spontaneous activity with shorter lengths of cord. These results suggest that each spinal segment is capable of generating spontaneous activity, and that there is a system by which adjacent segments are linked, allowing the activity to spread up and down the cord from the point of origin. The networks associated with the spread of dorsal root activity and primary afferent depolarization (PAD) in the spinal cord are discussed.