Electrophysiologic evidence for an intersegmental reflex pathway between lumbar paraspinal tissues

Area of Science:

• Neuroscience
• Spinal Cord Research
• Biomechanics

Background:

• Spinal stability is crucial for preventing low back dysfunction.
• Reflex interactions between vertebral segments likely contribute to sensorimotor integration of lumbar paraspinal tissues.
• Altered or abnormal reflexes may be linked to low back pain and paraspinal muscle spasms.

Purpose of the Study:

• To find electrophysiologic evidence of intersegmental reflexes between adjacent lumbar vertebral segments.
• To confirm a previous method for evoking paraspinal reflexes.

Main Methods:

• Electrophysiologic recordings from lumbar paraspinal nerves/muscles in anesthetized cats.
• Electrical stimulation of paraspinal nerves or facet capsules in adjacent segments.
• Control experiments including nerve cutting, intrathecal lidocaine, and local anesthesia to verify reflex activity.

Main Results:

• Electrical stimulation of the medial branch of the dorsal ramus evoked reflex compound action potentials in adjacent segments (1-2 segments away) with conduction velocities of 3.5-6.1 m/sec.
• Electrical stimulation of facet capsules evoked multifidus muscle activity, but this was attributed to volume conduction, not reflex action, as it was unaffected by central or peripheral nerve blocks.
• Local anesthesia at the facet or muscle insertion site reduced multifidus activity, suggesting a local, non-reflexive response to facet capsule stimulation.

Conclusions:

• Afferent impulses via the medial branch of the dorsal ramus can reflexly alter efferent activity to adjacent lumbar segments, indicating an intersegmental paraspinal reflex.
• This reflex may span at least one or two vertebral segments.
• Facet capsule stimulation likely caused multifidus activity via volume conduction, not reflex action, highlighting the need for rigorous controls in such studies.