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Central delay of the laser-activated rat tail-flick reflex
Peggy J Danneman1, Judith A Kiritsy-Roy, Thomas J Morrow
1Unit for Laboratory Animal Medicine, The University of Michigan, Ann Arbor, MI 48109 USA Department of Neurology, The University of Michigan, Ann Arbor, MI 48109 USA Department of Physiology, The University of Michigan, Ann Arbor, MI 48109 USA Veterans Affairs Medical Center, Ann Arbor, MI 48105 USA.
Pain
|July 1, 1994
Summary
This study quantifies the temporal components of the rat tail-flick reflex, revealing C-fiber mediation and a central delay of 82.3 ms. This delay offers a window for supraspinal pain modulation.
Area of Science:
- Neuroscience
- Physiology
- Pain Research
Background:
- The tail-flick (TF) reflex latency is influenced by nociceptor activation, afferent conduction, central processing, and efferent motor activation.
- Previous research had not precisely determined the contribution of each temporal component to the overall reflex latency.
Purpose of the Study:
- To quantitatively determine the temporal parameters of the heat-activated rat tail-flick reflex.
- To elucidate the role of C-fibers in mediating the TF reflex.
- To calculate the central delay within the TF reflex arc.
Main Methods:
- Utilized a CO2 infrared laser to activate cutaneous nociceptors synchronously in awake rats.
- Measured TF reflex latency (EMG response) and afferent conduction velocity.
- Recorded dorsal horn activity and evoked potentials (EPs) during laser and electrical stimulation in anesthetized rats.
- Calculated central delay by subtracting known temporal components from total TF latency.
Main Results:
- Afferent conduction velocity was estimated at 0.76 +/- 0.11 m/sec, indicating C-fiber mediation.
- Nociceptor activation by laser stimulation required 60.00 +/- 7.33 msec.
- Ventral horn stimulation elicited a TF response in 4 msec.
- Central delay was calculated to be 82.3 +/- 13.08 msec.
Conclusions:
- The study successfully delineated the temporal components of the rat tail-flick reflex.
- The significant central delay suggests a substantial period for supraspinal modulation of pain reflexes.
- Findings provide a basis for understanding how descending pathways influence spinal reflex activity.