Department of Biology, University of Oklahoma, Norman, OK, United States.
Cellular and Behavioral Neurobiology Graduate Program, University of Oklahoma, Norman, OK, United States.
Front Neural Circuits. 2017 Oct 31;11:83. doi: 10.3389/fncir.2017.00083. eCollection 2017.
Windup is a form of multisecond temporal summation in which identical stimuli, delivered seconds apart, trigger increasingly strong neuronal responses. L-type Ca channels have been shown to play an important role in the production of windup of spinal cord neuronal responses, initially in studies of turtle spinal cord and later in studies of mammalian spinal cord. L-type Ca channels have also been shown to contribute to windup of limb withdrawal reflex (flexion reflex) in rats, but flexion reflex windup has not previously been described in turtles and its cellular mechanisms have not been studied. We studied windup of flexion reflex motor patterns, evoked with weak mechanical and electrical stimulation of the dorsal hindlimb foot skin and assessed via a hip flexor (HF) nerve recording, in spinal cord-transected and immobilized turtles . We found that an L-type Ca channel antagonist, nifedipine, applied at concentrations of 50 μM or 100 μM to the hindlimb enlargement spinal cord, significantly reduced windup of flexion reflex motor patterns, while lower concentrations of nifedipine had no such effect. Nifedipine similarly reduced the amplitude of an individual flexion reflex motor pattern evoked by a stronger mechanical stimulus, in a dose-dependent manner, suggesting that L-type Ca channels contribute to each flexion reflex as well as to multisecond summation of flexion reflex responses in turtles. We also found that we could elicit flexion reflex windup consistently using a 4-g von Frey filament, which is not usually considered a nociceptive stimulus. Thus, it may be that windup can be evoked by a wide range of tactile stimuli and that L-type calcium channels contribute to multisecond temporal summation of diverse tactile stimuli across vertebrates.
牵张是一种多毫秒时间总和的形式，其中相同的刺激，相隔数秒传递，会引发越来越强烈的神经元反应。L 型钙通道已被证明在脊髓神经元反应的牵张产生中起着重要作用，最初在海龟脊髓的研究中，后来在哺乳动物脊髓的研究中也是如此。L 型钙通道也被证明有助于大鼠肢体退缩反射（屈肌反射）的牵张，但以前在海龟中没有描述过屈肌反射的牵张，其细胞机制也没有得到研究。我们研究了通过弱机械和电刺激后肢足部皮肤诱发的屈肌反射运动模式的牵张，通过记录 hip flexor（HF）神经来评估，在脊髓横切和固定的海龟中。我们发现，L 型钙通道拮抗剂硝苯地平，在浓度为 50 μM 或 100 μM 时应用于后肢扩大脊髓，可以显著减少屈肌反射运动模式的牵张，而较低浓度的硝苯地平则没有这种作用。硝苯地平也以剂量依赖性方式类似地减少了由更强的机械刺激诱发的单个屈肌反射运动模式的幅度，表明 L 型钙通道有助于每个屈肌反射以及海龟中屈肌反射反应的多毫秒总和。我们还发现，我们可以使用 4-g von Frey 细丝一致地引发屈肌反射牵张，而通常不认为这是一种伤害性刺激。因此，可能是由广泛的触觉刺激引发牵张，并且 L 型钙通道有助于各种脊椎动物的多毫秒时间总和的触觉刺激。
