Maintenance of contractile force of the hind limb muscles by the somato-lumbar sympathetic reflexes

Figures

• 

  Fig. 1. Schematic representation of electrode placement when transecting (a), recording (b), or stimulating (c) lumbar sympathetic nerve fibers while stimulating the tibial nerve. LST, lumbar sympathetic trunk

• 

  Fig. 2. Effect of lumbar sympathetic trunk transection on the tetanic force of the triceps surae muscles. a, b Typical responses of the tetanic force of the triceps surae muscles (lower traces) and mean arterial pressure (upper traces) induced by tetanic stimulation of the intact tibial nerve before (a) and 20 min after (b) lumbar sympathetic trunk (LST) transection. Each upper horizontal bar indicates the tetanic stimulation (0.2 ms, 2T, 10 pulses at 100 Hz) repeated 10 times at 1 Hz. c Averaged waveform of the 30 tetanic contractions before (dotted line) and after (solid line) LST transection. d Summary (n = 6 from six rats) of the changes in the amplitude of the tetanic force, expressed as a percentage of the mean of two controls obtained before LST transection. Each column, vertical bar, or circle indicates the median, interquartile range, and individual data. **p < 0.01 (Mann–Whitney U test)

• 

  Fig. 3. Effect of spinal cord transection on the tetanic force of the triceps surae muscles. a, b Typical responses of the tetanic force of the triceps surae muscles and mean arterial pressure induced by tetanic stimulation of the intact tibial nerve before (a) and 20 min after (b) spinal cord transection. c Averaged waveform of the 30 tetanic contractions before (dotted line) and after (solid line) spinal cord transection. d Summary (n = 5 from five rats) of the changes in the amplitude of the tetanic force, expressed as a percentage of the mean of two controls obtained before spinal cord transection. Each column, vertical bar, or circle indicates the median, interquartile range, and individual data. *p < 0.05 (Mann–Whitney U test)

• 

  Fig. 4. Effect of dorsal root transection on the tetanic force of the triceps surae muscles. a, b Typical responses of the tetanic force of the triceps surae muscles and mean arterial pressure induced by tetanic stimulation of the intact tibial nerve before (a) and 20 min after (b) dorsal root transection in a rat with an intact CNS. c Averaged waveform of the 30 tetanic contractions before (dotted line) and after (solid line) dorsal root transection in the same rat. d Summary (n = 8 from eight rats) of the changes in the amplitude of the tetanic force, expressed as a percentage of the mean of two controls obtained before dorsal root transection. Each column, vertical bar, or circle shows the median, interquartile range, and individual data. Open circles: data from rats with an intact CNS; closed circles: data from rats with spinal cord transection. *p < 0.05 (Mann–Whitney U test)

• 

  Fig. 5. Reflex potentials in postganglionic sympathetic nerves evoked by tetanic stimulation of the tibial nerve. The reflex responses in sympathetic nerves averaged for 60 trials were summarized in the intact CNS (a) and spinalized (b) conditions (n = 4 from four rats). The lower horizontal bars indicate the tetanic stimulation (0.2 ms, 2T, 10 pulses at 100 Hz). The arrows indicate excitatory potentials. Vertical bars indicate percent changes relative to the prestimulus values

• 

  Fig. 6. Effect of lumbar sympathetic trunk stimulation on the tetanic force of the triceps surae muscles. a, b Typical responses of the tetanic force of the triceps surae muscles and mean arterial pressure induced by tetanic stimulation of the intact tibial nerve before (a) and during (b) stimulation (10 Hz) of the cut peripheral end of the LST. c Averaged waveform of the 30 tetanic contractions without (dotted line) and with (solid line) LST stimulation. d Summary (n = 7–9 from eight rats) of the changes in the amplitude of the tetanic force, expressed as a percentage of the prestimulus control level. Each column or vertical bar indicates the median and interquartile range. Each circle indicates individual data for stimulation. Data of sham stimulation are shown as x. Horizontal axis: frequency of LST stimulation. Vertical axis: changes in the peak amplitude of the tetanic force, expressed as a percentage of the control just before LST stimulation. #p < 0.05, ##p < 0.01 (Wilcoxon signed-rank test; compared with the peristimulus control using absolute values of tetanic force)

• 

  Fig. 7. Schematic diagram showing the sympathetic excitation and increase in muscle force afforded by muscle contraction. When the alpha motor neurons innervating the triceps surae muscles where cell bodies are localized in the L4–5 spinal cord and their axons included in the tibial nerve are excited and the triceps surae muscles contract (route 1), the group III and IV afferents of the muscles are excited (route 2). The afferent information is transmitted to the central nervous system via the L3–6 dorsal roots, and then reflexively excites the sympathetic preganglionic neurons in the spinal cord (T11–L2), which are connected through LST to the postganglionic neurons in the L2–4 sympathetic ganglia. Subsequently, the sympathetic postganglionic efferent nerve activity reaches the triceps surae muscles (route 3) and increases their contractile force