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

This study aimed to clarify whether the reflex excitation of muscle sympathetic nerves induced by contractions of the skeletal muscles modulates their contractility. In anesthetized rats, isometric tetanic contractions of the triceps surae muscles were induced by electrical stimulation of the intact tibial nerve before and after transection of the lumbar sympathetic trunk (LST), spinal cord, or dorsal roots. The amplitude of the tetanic force (TF) was reduced by approximately 10% at 20 min after transection of the LST, spinal cord, or dorsal roots. The recorded postganglionic sympathetic nerve activity from the lumbar gray ramus revealed that both spinal and supraspinal reflexes were induced in response to the contractions. Repetitive electrical stimulation of the cut peripheral end of the LST increased the TF amplitude. Our results indicated that the spinal and supraspinal somato-sympathetic nerve reflexes induced by contractions of the skeletal muscles contribute to the maintenance of their own contractile force.