Distinctions among electroconvulsion- and proconvulsant-induced seizure discharges and native motor patterns during flight and grooming: quantitative spike pattern analysis in Drosophila flight muscles

In Drosophila, high-frequency electrical stimulation across the brain triggers a highly stereotypic repertoire of spasms. These electroconvulsive seizures (ECS) manifest as distinctive spiking discharges across the nervous system and can be stably assessed throughout the seizure repertoire in the large indirect flight muscles dorsal longitudinal muscles (DLMs) to characterize modifications in seizure-prone mutants. However, the relationships between ECS-spike patterns and native motor programs, including flight and grooming, are not known and their similarities and distinctions remain to be characterized. We employed quantitative spike pattern analyses for the three motor patterns including: (1) overall firing frequency, (2) spike timing between contralateral fibers, and (3) short-term variability in spike interval regularity (CV2) and instantaneous firing frequency (ISI−1). This base-line information from wild-type (WT) flies facilitated quantitative characterization of mutational effects of major neurotransmitter systems: excitatory cholinergic (Cha), inhibitory GABAergic (Rdl) and electrical (ShakB) synaptic transmission. The results provide an initial glimpse on the vulnerability of individual motor patterns to different perturbations. We found marked alterations of ECS discharge spike patterns in terms of either seizure threshold, spike frequency or spiking regularity. In contrast, no gross alterations during grooming and a small but noticeable reduction of firing frequency during Rdl mutant flight were found, suggesting a role for GABAergic modulation of flight motor programs. Picrotoxin (PTX), a known pro-convulsant that inhibits GABAA receptors, induced DLM spike patterns that displayed some features, e.g. left-right coordination and ISI−1 range, that could be found in flight or grooming, but distinct from ECS discharges. These quantitative techniques may be employed to reveal overlooked relationships among aberrant motor patterns as well as their links to native motor programs.

在果蝇（Drosophila）中，高频电刺激全脑可诱发一系列高度刻板的痉挛发作。此类电惊厥发作（electroconvulsive seizures, ECS）会表现为神经系统内特征性的尖峰放电，且可在大型间接飞行肌中的背纵肌（dorsal longitudinal muscles, DLMs）的惊厥发作全程中稳定评估，以此表征易惊厥突变体的相关变化。然而，目前尚不明确ECS尖峰模式与包括飞行、理毛在内的天然运动程序之间的关联，二者的异同也有待进一步阐释。本研究针对三类运动模式开展了定量尖峰模式分析，具体包括：(1) 总放电频率；(2) 对侧肌纤维间的尖峰时序；(3) 尖峰间隔规律性（变异系数2, CV2）与瞬时放电频率（峰间期倒数, ISI⁻¹）的短期变异性。野生型（wild-type, WT）果蝇的此类基线信息，为定量表征主要神经递质系统——兴奋性胆碱能突触传递（cholinergic, Cha）、抑制性γ-氨基丁酸能突触传递（GABAergic, Rdl）以及电突触传递（ShakB）的突变效应提供了便利。本研究结果首次揭示了不同扰动下各运动模式的易损性。我们观察到，在惊厥阈值、尖峰频率或放电规律性方面，ECS放电尖峰模式均出现了显著改变。与之形成对比的是，理毛行为未出现明显异常，而Rdl突变体飞行时的放电频率出现了小幅但可被观测到的降低，这提示γ-氨基丁酸能系统对飞行运动程序存在调控作用。苦毒毛旋花子苷（picrotoxin, PTX）是一种已知的惊厥原，可抑制GABAA受体，其诱导的DLM尖峰模式展现出部分可在飞行或理毛行为中观测到的特征（如左右协调能力与ISI⁻¹范围），但与ECS放电模式截然不同。此类定量分析技术可用于揭示异常运动模式间被忽视的关联，以及它们与天然运动程序之间的联系。