Neuroscience Institute, Georgia State University, Atlanta, GA 30302-5030, USA.
Department of Biology, Georgia State University, Atlanta, GA 30302-5030, USA.
Int J Mol Sci. 2023 Sep 27;24(19):14638. doi: 10.3390/ijms241914638.
Temperature sensation involves thermosensitive TRP (thermoTRP) and non-TRP channels. larval Class III (CIII) neurons serve as the primary cold nociceptors and express a suite of thermoTRP channels implicated in noxious cold sensation. How CIII neurons code temperature remains unclear. We combined computational and electrophysiological methods to address this question. In electrophysiological experiments, we identified two basic cold-evoked patterns of CIII neurons: bursting and spiking. In response to a fast temperature drop to noxious cold, CIII neurons distinctly mark different phases of the stimulus. Bursts frequently occurred along with the fast temperature drop, forming a peak in the spiking rate and likely coding the high rate of the temperature change. Single spikes dominated at a steady temperature and exhibited frequency adaptation following the peak. When temperature decreased slowly to the same value, mainly spiking activity was observed, with bursts occurring sporadically throughout the stimulation. The spike and the burst frequencies positively correlated with the rate of the temperature drop. Using a computational model, we explain the distinction in the occurrence of the two CIII cold-evoked patterns bursting and spiking using the dynamics of a thermoTRP current. A two-parameter activity map (Temperature, constant TRP current conductance) marks parameters that support silent, spiking, and bursting regimes. Projecting on the map the instantaneous TRP conductance, governed by activation and inactivation processes, reflects temperature coding responses as a path across silent, spiking, or bursting domains on the map. The map sheds light on how various parameter sets for TRP kinetics represent various types of cold-evoked responses. Together, our results indicate that bursting detects the high rate of temperature change, whereas tonic spiking could reflect both the rate of change and magnitude of steady cold temperature.
温度感觉涉及热敏瞬时受体电位（thermoTRP）和非-TRP 通道。幼虫三级（CIII）神经元作为主要的冷伤害感受器，表达了一系列与有害冷觉有关的 thermoTRP 通道。CIII 神经元如何编码温度尚不清楚。我们结合计算和电生理方法来解决这个问题。在电生理实验中，我们确定了 CIII 神经元的两种基本冷诱发模式：爆发和放电。在对有害冷的快速温度下降的反应中，CIII 神经元明显标记了刺激的不同阶段。爆发通常与快速温度下降同时发生，在放电率中形成一个峰值，可能编码温度变化的高率。单个尖峰在稳定温度下占主导地位，在峰值后表现出频率适应。当温度缓慢下降到相同值时，主要观察到放电活动，爆发在整个刺激过程中零星发生。尖峰和爆发频率与温度下降率呈正相关。使用计算模型，我们使用 thermoTRP 电流的动力学来解释 CIII 两种冷诱发模式爆发和放电的发生区别。双参数活动图（温度，恒定 TRP 电流电导）标记支持沉默、放电和爆发状态的参数。瞬时 TRP 电导由激活和失活过程控制，将其投影到图上，反映了温度编码响应作为在图上跨越沉默、放电或爆发域的路径。该图阐明了各种 TRP 动力学参数集如何代表各种类型的冷诱发反应。总之，我们的结果表明，爆发检测到温度变化的高率，而紧张性放电可能反映了稳定冷温度的变化率和幅度。
