Merivee Enno, Must Anne, Nurme Karin, Di Giulio Andrea, Muzzi Maurizio, Williams Ingrid, Mänd Marika
Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Tartu, Estonia.
Department of Science, University of Roma Tre, Rome, Italy.
Front Behav Neurosci. 2020 Feb 6;14:1. doi: 10.3389/fnbeh.2020.00001. eCollection 2020.
Environmental thermal conditions play a major role at all levels of biological organization; however, there is little information on noxious high temperature sensation crucial in behavioral thermoregulation and survival of small ectothermic animals such as insects. So far, a capability to unambiguously encode heat has been demonstrated only for the sensory triad of the spike bursting thermo- and two bimodal hygro-thermoreceptor neurons located in the antennal dome-shaped sensilla (DSS) in a carabid beetle. We used extracellular single sensillum recording in the range of 20-45°C to demonstrate that a similar sensory triad in the elaterid also produces high temperature-induced bursty spike trains. Several parameters of the bursts are temperature dependent, allowing the neurons in a certain order to encode different, but partly overlapping ranges of heat up to lethal levels in a graded manner. ISI in a burst is the most useful parameter out of six. Our findings consider spike bursting as a general, fundamental quality of the classical sensory triad of antennal thermo- and hygro-thermoreceptor neurons widespread in many insect groups, being a flexible and reliable mode of coding unfavorably high temperatures. The possible involvement of spike bursting in behavioral thermoregulation of the beetles is discussed. By contrast, the mean firing rate of the neurons in regular and bursty spike trains combined does not carry useful thermal information at the high end of noxious heat.
环境热条件在生物组织的各个层面都起着重要作用；然而，对于小型变温动物（如昆虫）行为体温调节和生存至关重要的有害高温感觉，相关信息却很少。到目前为止，仅在一种步甲的触角圆顶形感器（DSS）中的尖峰爆发热感受器和两个双峰湿温感受器神经元的感觉三联体中，证明了明确编码热的能力。我们在20-45°C范围内使用细胞外单感器记录，以证明叩头虫中类似的感觉三联体也会产生高温诱导的爆发性尖峰序列。爆发的几个参数取决于温度，使神经元能够以一定顺序分级编码不同但部分重叠的热范围，直至致死水平。爆发中的ISI是六个参数中最有用的。我们的研究结果认为，尖峰爆发是许多昆虫群体中广泛存在的触角热感受器和湿温感受器神经元经典感觉三联体的一种普遍、基本特性，是编码不利高温的一种灵活可靠方式。本文讨论了尖峰爆发可能参与甲虫行为体温调节的情况。相比之下，规则和爆发性尖峰序列组合中神经元的平均放电率在有害热的高端不携带有用的热信息。
