Ma Hanqing, Jia Bing, Li Yuye, Gu Huaguang
School of Aerospace Engineering and Applied Mechanics, Tongji University, Shanghai 200092, China.
College of Mathematics and Computer Science, Chifeng University, Chifeng 024000, China.
Neural Plast. 2021 Jan 18;2021:6692411. doi: 10.1155/2021/6692411. eCollection 2021.
Postinhibitory facilitation (PIF) of neural firing presents a paradoxical phenomenon that the inhibitory effect induces enhancement instead of reduction of the firing activity, which plays important roles in sound location of the auditory nervous system, awaited theoretical explanations. In the present paper, excitability and threshold mechanism for the PIF phenomenon is presented in the Morris-Lecar model with type I, II, and III excitabilities. Firstly, compared with the purely excitatory stimulations applied to the steady state, the inhibitory preceding excitatory stimulation to form pairs induces the firing rate increased for type II and III excitabilities instead of type I excitability, when the interval between the inhibitory and excitatory stimulation within each pair is suitable. Secondly, the threshold mechanism for the PIF phenomenon is acquired. For type II and III excitabilities, the inhibitory stimulation induces subthreshold oscillations around the steady state. During the middle and ending phase of the ascending part and the beginning phase of the descending part within a period of the subthreshold oscillations, the threshold to evoke an action potential by an excitatory stimulation becomes weaker, which is the cause for the PIF phenomenon. Last, a theoretical estimation for the range of the interval between the inhibitory and excitatory stimulation for the PIF phenomenon is acquired, which approximates half of the intrinsic period of the subthreshold oscillations for the relatively strong stimulations and becomes narrower for the relatively weak stimulations. The interval for the PIF phenomenon is much shorter for type III excitability, which is closer to the experiment observation, due to the shorter period of the subthreshold oscillations. The results present the excitability and threshold mechanism for the PIF phenomenon, which provide comprehensive and deep explanations to the PIF phenomenon.
神经放电的抑制后易化（PIF）呈现出一种矛盾的现象，即抑制作用会导致放电活动增强而非减弱，这在听觉神经系统的声音定位中起着重要作用，尚待理论解释。在本文中，通过具有I型、II型和III型兴奋性的Morris-Lecar模型，给出了PIF现象的兴奋性和阈值机制。首先，与施加于稳态的纯兴奋性刺激相比，当每对抑制性刺激和兴奋性刺激之间的间隔适当时，先施加抑制性刺激再施加兴奋性刺激形成刺激对，会使II型和III型兴奋性而非I型兴奋性的放电率增加。其次，获得了PIF现象的阈值机制。对于II型和III型兴奋性，抑制性刺激会在稳态附近诱发阈下振荡。在阈下振荡周期的上升部分的中期和末期以及下降部分的开始阶段，兴奋性刺激诱发动作电位的阈值会变弱，这就是PIF现象产生的原因。最后，获得了PIF现象中抑制性刺激和兴奋性刺激之间间隔范围的理论估计，对于相对较强的刺激，该间隔近似于阈下振荡固有周期的一半，而对于相对较弱的刺激则变窄。对于III型兴奋性，PIF现象的间隔要短得多，由于阈下振荡的周期较短，这更接近实验观察结果。这些结果给出了PIF现象的兴奋性和阈值机制，为PIF现象提供了全面而深入的解释。
