Turtle Flexion Reflex Motor Patterns Show Windup, Mediated Partly by L-type Calcium Channels

Area of Science:

• Neuroscience
• Physiology
• Pain Research

Background:

• Windup is a neuronal response characterized by temporal summation of identical stimuli delivered seconds apart.
• L-type calcium channels are implicated in spinal cord neuronal windup and the flexion reflex in mammals.
• Flexion reflex windup and its cellular mechanisms in turtles remained unstudied.

Purpose of the Study:

• To investigate windup of the flexion reflex motor patterns in turtles.
• To explore the role of L-type calcium channels in turtle flexion reflex windup.

Main Methods:

• Studied windup of flexion reflex motor patterns in *in vivo* spinal cord-transected turtles.
• Stimulated dorsal hindlimb foot skin with weak mechanical and electrical stimuli.
• Recorded hip flexor (HF) nerve activity and applied L-type calcium channel antagonist nifedipine.

Main Results:

• Nifedipine (50-100 μM) significantly reduced flexion reflex windup in turtles.
• L-type calcium channels contribute to individual flexion reflex amplitude and multisecond summation.
• Flexion reflex windup was consistently evoked by a 4-g von Frey filament, suggesting broader stimulus applicability.

Conclusions:

• L-type calcium channels are crucial for flexion reflex windup in turtles.
• These findings suggest L-type calcium channels mediate temporal summation of diverse tactile stimuli across vertebrates.
• Windup may be evoked by a wider range of tactile stimuli than previously thought.