Experimental Brain Research

, Volume 149, Issue 4, pp 487–496 | Cite as

Synaptic inputs from low threshold afferents of trunk muscles to motoneurons innervating the longissimus lumborum muscle in the spinal cat

Research Article
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Abstract.

(1) We studied the reflex actions of group I and II afferents to longissimus lumborum (Long) motoneurons in the L1–L5 spinal segments from the epaxial muscle, m. Long, and the hypaxial muscle, m. obliquus externus abdominus (OEA). (2) Postsynaptic potentials (PSPs) recorded from 140 Long motoneurons in 30 spinal cats were analyzed. Under the present experimental conditions, the stimulation of Long and OEA nerves at an intensity below 1.5 times threshold (T) activated only group I muscle afferents, while stimulations at 2–5T activated group II muscle afferents as well. (3) The incidence of PSPs was related to the proximity of the spinal segments of the nerves stimulated to the spinal segment of the motoneurons; the shorter the distance the larger the PSPs and higher incidence of PSPs. The Long motoneurons received group I afferent input mainly from the same and adjacent segments, and received group II afferent inputs from a wider range of segments. (4) A short (i.e., less than 1.0 ms) latency of excitatory PSPs (EPSPs) evoked by ipsilateral group I afferents of Long at the same or adjacent segment indicated a monosynaptic connection. In general, the central latencies became longer as the distance between spinal segments of stimulated nerves and motoneurons increased. Major PSP components were produced by polysynaptic neuronal pathways. The spatial facilitation between PSPs evoked by afferents of different nerves (i.e., ipsilateral Long (iLong) and contralateral Long (cLong) of the same segment; iLongs of different segments; and iLong and iOEA of the same segment) indicated that they shared common interneurons. (5) Although iLong and iOEA muscle afferents produced predominantly EPSPs, and contralateral muscle afferents elicited predominantly IPSPs in Long motoneurons at each spinal segment, the patterns of convergence from Long and OEA muscle afferents of different spinal segments and of different sides differed considerably among motoneurons. (6) These findings demonstrated various input patterns of individual motoneurons within the same motoneuron pool, which might reflect the complexity of neuronal control of the back muscles for various trunk movements, including lateral and dorsal bending, rotating, and fixation of the trunk.

Keywords

Cats Motoneurons Trunk Spinal cord 
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Notes

Acknowledgements.

We are grateful for criticism by Professor P.H. Ellaway of the Division of Neuroscience & Psychological Medicine, Imperial College School of Medicine, Charing Cross Hospital, London, UK.

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Copyright information

© Springer-Verlag 2003

Authors and Affiliations

  1. 1.Department of Veterinary PhysiologyYamaguchi UniversityYamaguchiJapan
  2. 2.Department of Central Nervous SystemTokyo Metropolitan Institute of GerontologyTokyoJapan

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