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Electrophysiological characteristics of lumbar spinal cord neurons backfired from lateral reticular nucleus in the rat

Journal of Neurophysiology 52(4): 595-611

Electrophysiological characteristics of lumbar spinal cord neurons backfired from lateral reticular nucleus in the rat

Spinal neurons antidromically activated from either the lateral reticular nucleus (LRN) or immediately adjacent areas were identified in the rat lumbar spinal cord. These neurons were widely distributed in both the dorsal and ventral horns of the spinal cord and could be subdivided into 3 main groups according to their location: deep ventromedial (DVM) cells, which project more substantially to the LRN than to other supraspinal targets; cells of the median portion of the neck of the dorsal horn (mNDH), which project exclusively to the LRN; cells lying in other parts of the dorsal horn (superficial layers, nucleus proprius, reticular extension of the neck), by their location they are indistinguishable from cells projecting to other supraspinal targets. The DVM and mNDH cells probably contribute exclusively, or at least preferentially, to the lateral component of the spinoreticular tract (lSRT), defined as the direct spinal pathway to the LRN. The majority of DVM neurons were in lamina VII, with some in laminae VI, VIII, and X. With the exception of a few lamina X cells, the DVM neurons had high conduction velocities. These neurons were divided into 4 subpopulations: innocuous proprioceptive cells responded to small changes in joint position, some showing convergence of nonnoxious cutaneous inputs; high-threshold cells (.apprx. 50% of DVM cells), of which 75% were excited from bilateral receptive fields (mostly symmetric) with noxious cutaneous pinching that extended to subcutaneous tissues, evoked responses that had long-lasting postdischarges continuing up to several minutes; inhibited cells had no demonstrable excitatory receptive fields and a high ongoing activity that was tonically depressed by pressure or pinch, poststimulus effects being long duration; and cells that had no resting discharge and demonstrable excitatory peripheral receptive fields. mNDH cells had recording sites at the medial border of the internal portion of the reticular area of the neck of the dorsal horn. These neurons were divided into 2 subpopulations: cells that responded to both innocuous and noxious mechanical cutaneous stimulation (class 2 cells); and inhibited cells whose sustained ongoing activity (either spontaneous or evoked by intense manipulation of deep tissues) was strongly depressed by repeated innocuous cutaneous stimulation. The dorsal horn cells lying in superficial layers, nucleus proprius, or the reticular extension of the neck of the dorsal horn had properties closely similar to cells of the medial spinoreticular and spinothalamic tracts in the same species. They were essentially excited by cutaneous stimulation and most could be classifed as class 2. From the large variety of cell types observed, the lSRT probably function in several capacities, most notably in kinesthesia and motor reactions of adaptation to the environment. Another role for the lSRT may be the maintenance of descending inhibition on nociceptive transmission at spinal levels.

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Accession: 005349485

PMID: 6491707

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