Hedwig B
Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, United Kingdom.
J Neurophysiol. 2000 Feb;83(2):712-22. doi: 10.1152/jn.2000.83.2.712.
Crickets use different song patterns for acoustic communication. The stridulatory pattern-generating networks are housed within the thoracic ganglia but are controlled by the brain. This descending control of stridulation was identified by intracellular recordings and stainings of brain neurons. Its impact on the generation of calling song was analyzed both in resting and stridulating crickets and during cercal wind stimulation, which impaired the stridulatory movements and caused transient silencing reactions. A descending interneuron in the brain serves as a command neuron for calling-song stridulation. The neuron has a dorsal soma position, anterior dendritic processes, and an axon that descends in the contralateral connective. The neuron is present in each side of the CNS. It is not activated in resting crickets. Intracellular depolarization of the interneuron so that its spike frequency is increased to 60-80 spikes/s reliably elicits calling-song stridulation. The spike frequency is modulated slightly in the chirp cycle with the maximum activity in phase with each chirp. There is a high positive correlation between the chirp repetition rate and the interneuron's spike frequency. Only a very weak correlation, however, exists between the syllable repetition rate and the interneuron activity. The effectiveness of the command neuron depends on the activity state of the cricket. In resting crickets, experimentally evoked short bursts of action potentials elicit only incomplete calling-song chirps. In crickets that previously had stridulated during the experiment, short elicitation of interneuron activity can trigger sustained calling songs during which the interneuron exhibits a spike frequency of approximately 30 spikes/s. During sustained calling songs, the command neuron activity is necessary to maintain the stridulatory behavior. Inhibition of the interneuron stops stridulation. A transient increase in the spike frequency of the interneuron speeds up the chirp rate and thereby resets the timing of the chirp pattern generator. The interneuron also is excited by cercal wind stimulation. Cercal wind stimulation can impair the pattern of chirp and syllable generation, but these changes are not reflected in the discharge pattern of the command neuron. During wind-evoked silencing reactions, the activity of the calling-song command neuron remains unchanged, but under these conditions, its activity is no longer sufficient to maintain stridulation. Therefore stridulation can be suppressed by cercal inputs from the terminal ganglia without directly inhibiting the descending command activity.
蟋蟀使用不同的鸣声模式进行声学通讯。鸣声模式产生网络位于胸神经节内，但受大脑控制。通过对脑神经元的细胞内记录和染色确定了这种对鸣叫的下行控制。在静止和鸣叫的蟋蟀中以及在尾须风刺激期间分析了其对求偶鸣声产生的影响，尾须风刺激会损害鸣叫运动并引起短暂的静音反应。脑中的一个下行中间神经元作为求偶鸣声鸣叫的指令神经元。该神经元的胞体位于背侧，树突向前延伸，轴突在对侧神经索中下行。该神经元存在于中枢神经系统的每一侧。在静止的蟋蟀中它不被激活。对中间神经元进行细胞内去极化，使其放电频率增加到60 - 80次/秒，可可靠地引发求偶鸣声鸣叫。在啁啾周期中，放电频率会有轻微调制，在每个啁啾的相位具有最大活动。啁啾重复率与中间神经元的放电频率之间存在高度正相关。然而，音节重复率与中间神经元活动之间仅存在非常弱的相关性。指令神经元的有效性取决于蟋蟀的活动状态。在静止的蟋蟀中，实验诱发的短串动作电位仅引发不完整的求偶鸣声啁啾。在实验过程中先前已经鸣叫过的蟋蟀中，中间神经元活动的短暂激发可触发持续的求偶鸣声，在此期间中间神经元表现出约30次/秒的放电频率。在持续的求偶鸣声期间，指令神经元活动对于维持鸣叫行为是必要的。抑制中间神经元会停止鸣叫。中间神经元放电频率的短暂增加会加快啁啾速率，从而重置啁啾模式发生器的时间。中间神经元也会被尾须风刺激所兴奋。尾须风刺激会损害啁啾和音节产生的模式，但这些变化并未反映在指令神经元的放电模式中。在风诱发的静音反应期间，求偶鸣声指令神经元的活动保持不变，但在这些条件下，其活动不再足以维持鸣叫。因此，来自终神经节的尾须输入可以抑制鸣叫，而无需直接抑制下行指令活动。
