Functional organisation of a corollary discharge mechanism

感觉神经科学中的一个基本问题是处理自我产生的感觉信息和来自环境的信息，这些信息发生在同一通路中。例如，像蟋蟀这样的动物，在种内交流时会反复发出非常响亮的声音信号，它们如何防止听觉通路脱敏，或者如何区分自己的声音信号和歌唱对手的声音？作为这个问题的解决方案，神经科学家提出了一种必然的放电机制，该机制由动物自身的运动活动激活，并介导到感觉区域，以干扰自我产生的信号的处理。推论放电的证据是令人信服的，但这一神经处理原理的细胞基础仅在弱电鱼类、蝌蚪游泳、小龙虾逃跑行为和蟋蟀鸣叫中得到证实。在蟋蟀中，我们最近发现了一种必然的放电中间神经元（CDI），它在声音产生阶段被激活，并抑制听觉传入和中间神经元，每当动物在唱歌过程中产生声音脉冲时。因此，它们对自身产生的声音脉冲的反应明显降低，而听觉通路的灵敏度得以维持。为了补充这一必然的放电机制，我们现在希望在三个领域取得进展。1. CDI是如何激活的？证据指向产生歌唱活动的运动网络。然而，这个网络还没有被详细研究。因此，我们将通过细胞内记录、染料注射和电流注射实验来识别这个运动网络的中间神经元，这些实验证明了神经元在模式识别中的功能重要性。然后，我们将使用运动网络中间神经元和CDI的同步记录来分析它们之间的任何突触连接。这些实验将首先说明必然放电是如何产生的。我们预计，中间神经元的运动网络，这是积极的阶段与声音的生产，驱动CDI与兴奋性突触后电位。这将导致一个全面的细胞理解的必然放电机制。2.此外，我们想分析CDI是否影响听觉通路以外的感觉通路。这对我们理解必然放电通路的组织结构很重要。CDI在听觉神经元中有丰富的轴突输出分支，但其他轴突分支投射到所有神经节的机械感觉神经末梢中。因此，CDI的树枝状模式也适用于调节其他感觉通路，那么它是局部还是整体的必然放电通路？我们将分析风敏感和振动敏感通路中的神经处理。这些通路在唱歌时被自我产生的刺激激活，但同时也必须介导逃避反应。一种感觉处理问题，与听觉信号的处理最为相似。我们将用吹气或振动刺激来刺激这些通路，我们将记录初级传入神经和中间神经元的活动，以揭示唱歌过程中的任何抑制迹象。如果实验表明，感觉处理是由一个必然的放电调制，我们将再次使用双细胞内记录来分析CDI和传入和这些途径的中间神经元之间的突触相互作用。我们的实验将揭示，如果CDI全局调节感觉过程中唱歌，因为它是由其结构所示。3.最后，我们将分析CDI的树枝状模式的细节与组织切片。这将显示其轴突分支与机械感觉神经柱的重叠。我们还将使用免疫组织化学来证明GABA是否是介导抑制性突触后电位的中间神经元的递质。

A fundamental problem in sensory neuroscience is the processing of self-generated sensory information and information from the environment that occurs in the same pathway. For example how can animals like crickets, which repetitively generate very loud acoustic signals for intraspecific communication, prevent their auditory pathways from desensitisation or distinguish their own sound signals from the sound of singing rivals? As a solution to this problem neuroscientists proposed a corollary discharge mechanism that is activated by the animals own motor activity and that is mediated to sensory areas to interfere with the processing of self-generated signals. The evidence for corollary discharges is compelling but the cellular basis of this principle of neural processing has been demonstrated only in weakly electric fish, tadpole swimming, crayfish escape behaviour and in singing crickets. In crickets we recently identified a corollary discharge interneurone (CDI), that is activated in the phase of sound production and that inhibits auditory afferents and interneurons, whenever the animals produce a sound pulse during singing. As a consequence their responses to self-generated sound pulses are distinctly reduced and the sensitivity of the auditory pathway is maintained. To complement this picture of the corollary discharge mechanism we now want to progress in three areas. 1. How is CDI activated? Evidence points towards the motor network that generates the singing activity. This network however, has not yet been studied in any detail. We will therefore identify the interneurons of this motor network by intracellular recordings, dye injection and current injection experiments, which demonstrate the functional importance of neurons for pattern recognition. Then we will use simultaneous recordings of the motor network interneurons and of CDI to analyse any synaptic connections between them. These experiments will tell how the corollary discharge is generated in the first place. We expect that interneurons of the motor network, which are active in phase with sound production, drive CDI with excitatory postsynaptic potentials. This would lead to a comprehensive cellular understanding of the corollary discharge mechanisms. 2. Furthermore we want to analyse if CDI affects sensory pathways other than the auditory pathway. This is important for our understanding of the organisation of corollary discharge pathways. CDI has profuse axonal output arborisation in the auditory neuropil but other axonal collaterals project into the mechanosensory neuropils of all ganglia. The arborisation pattern of CDI is therefore suited to modulate other sensory pathways as well - so is it a local or a global corollary discharge pathway? We will analyse neural processing in a wind-sensitive and vibration-sensitive pathway. These pathways are activated by self-generated stimuli during singing but at the same time also have to mediate escape responses. A problem of sensory processing that is most similar to the processing of auditory signals. We will stimulate these pathways with wind puffs or vibration stimuli and we will record the activity of the primary afferents and interneurons to reveal any signs of inhibition during singing. If the experiments demonstrate that sensory processing is modulated by a corollary discharge we will again use double intracellular recordings to analyse the synaptic interaction between CDI and afferents and interneurons of these pathways. Our experiments will reveal, if CDI globally modulates sensory processing during singing, as it is indicated by its structure. 3. Finally, we will analyse the details of CDI's arborisation pattern with histological sections. This will show the overlap of its axonal arborisations with mechanosensory neuropils. We also will use immunohistochemistry to demonstrate if GABA is the transmitter of the interneurone that mediates the inhibitory postsynaptic synaptic potentials.