Nurme Karin, Merivee Enno, Must Anne, Di Giulio Andrea, Muzzi Maurizio, Williams Ingrid, Mänd Marika
Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Kreutzwaldi Street 1, 51014 Tartu, Estonia.
Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Kreutzwaldi Street 1, 51014 Tartu, Estonia.
J Therm Biol. 2018 Feb;72:101-117. doi: 10.1016/j.jtherbio.2018.01.008. Epub 2018 Jan 31.
The main purpose of this study was to explain the internal fine structure of potential antennal thermo- and hygroreceptive sensilla, their innervation specifics, and responses of the sensory neurons to thermal and humidity stimuli in an elaterid beetle using focused ion beam scanning electron microscopy and electrophysiology, respectively. Several essential, high temperature induced turning points in the locomotion were determined using automated video tracking. Our results showed that the sensilla under study, morphologically, are identical to the dome-shaped sensilla (DSS) of carabids. A cold-hot neuron and two bimodal hygro-thermoreceptor neurons, the moist-hot and dry-hot neuron, innervate them. Above 25-30 °C, all the three neurons, at different threshold temperatures, switch from regular spiking to temperature dependent spike bursting. The percentage of bursty DSS neurons on the antenna increases with temperature increase suggesting that this parameter of the neurons may encode noxious heat in a graded manner. Thus, we show that besides carabid beetles, elaterids are another large group of insects with this ability. The threshold temperature of the beetles for onset of elevated locomotor activity (OELA) was lower by 11.9 °C compared to that of critical thermal maximum (39.4 °C). Total paralysis occurred at 41.8 °C. The threshold temperatures for spike bursting of the sensory neurons in DSS and OELA of the beetles coincide suggesting that probably the spike bursts are responsible for encoding noxious heat when confronted. In behavioural thermoregulation, spike bursting DSS neurons serve as a fast and firm three-fold early warning system for the beetles to avoid overheating and death.
本研究的主要目的是分别使用聚焦离子束扫描电子显微镜和电生理学方法，解释叩头虫触角潜在的温度和湿度感受感器的内部精细结构、其神经支配细节以及感觉神经元对温度和湿度刺激的反应。使用自动视频跟踪确定了运动中几个重要的、高温诱导的转折点。我们的结果表明，所研究的感器在形态上与步甲科昆虫的圆顶形感器（DSS）相同。一个冷-热神经元和两个双峰湿-热感受器神经元，即湿-热神经元和干-热神经元，为它们提供神经支配。在25-30°C以上，所有这三个神经元在不同的阈值温度下，从规则发放转变为温度依赖性发放。触角上发放的DSS神经元的百分比随温度升高而增加，这表明神经元的这个参数可能以分级方式编码有害热。因此，我们表明除了步甲科昆虫外，叩头虫也是具有这种能力的另一大类昆虫。与临界热最大值（39.4°C）相比，甲虫开始升高运动活动（OELA）的阈值温度低11.9°C。在41.8°C时发生完全麻痹。甲虫DSS中感觉神经元发放的阈值温度与OELA的阈值温度一致，这表明当面对有害热时，发放可能负责编码有害热。在行为体温调节中，发放的DSS神经元作为甲虫避免过热和死亡的快速而可靠的三重早期预警系统。
