• J Sandkühler and A A Eblen-Zajjur.
• II. Physiologisches Institut, Universität Heidelberg, Germany.
• Neuroscience. 1994 Aug 1;61(4):991-1006.

AbstractThe properties of rhythmic low-threshold and multireceptive spinal dorsal horn neurons were determined. Multiple neuron recordings were made via a single electrode in the lumbar spinal cord of pentobarbital-anesthetized or decerebrate, unanesthetized, spinalized rats. The background activity of a total of 223 neurons was analysed: 21.0% of 176 fully characterized neurons were low threshold, 73.3% multireceptive and 5.7% nociceptive-specific neurons. Twenty of 100 neurons tested were driven by antidromic stimulation at the upper cervical cord. To identify and evaluate rhythmic harmonic oscillations in the discharges of spinal dorsal horn neurons during background activity and steady-state noxious heat-evoked responses, interspike interval, autocorrelation and autospectral analysis were performed. The background activity of 99 of the 223 neurons (44.4%) of our sample was rhythmic. The distribution of the fundamental spectral frequencies has a bimodal shape, the first band between 0.5 and 2 Hz and the second between 6 and 13 Hz. Low-threshold and multireceptive neurons had a similar incidence of rhythmicity (54.1 and 43.4%, respectively). Only one of 20 neurons with long ascending projections presented rhythmic background activity. Activation of heat-sensitive nociceptors within the cutaneous receptive fields of the neurons had a strong anti-rhythmic effect in nine of 15 (60%) neurons. No change was observed in the pattern of autospectra of non-rhythmic neurons or low-threshold neurons during noxious stimulation. Twenty-four of 37 (66.6%) rhythmic neurons retained their rhythmic background discharges during reversible cold-block spinalization at the upper thoracic cord. The incidence of neurons with burst-like discharges was highest among multireceptive neurons (98/129, 75.9%) and non-rhythmic neurons (89/124, 71.8%). Thus, rhythmicity exists in sensory neurons of the spinal dorsal horn probably generated within its local neuronal network and partially modulated by supraspinal descending systems. Rhythmicity is depressed by activity in primary afferent nociceptors. The role of rhythmicity for information transfer and neuronal plasticity is discussed.

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