Three flexor muscles of the posterior tentacles of the snail Helix pomatia have recently been described. Here, we identify their local motor neurons by following the retrograde transport of neurobiotin injected into these muscles. The mostly unipolar motor neurons (15–35 µm) are confined to the tentacle digits and send motor axons to the M2 and M3 muscles. Electron microscopy revealed small dark neurons (5–7 µm diameter) and light neurons with 12–18 (T1 type) and 18–30 µm diameters (T2 type) in the digits. The diameters of the neurobiotin-labeled neurons corresponded to the T1 type light neurons. The neuronal processes of T1 type motor neurons arborize extensively in the neuropil area of the digits and receive synaptic inputs from local neuronal elements involved in peripheral olfactory information processing. These findings support the existence of a peripheral stimulus–response pathway, consisting of olfactory stimulus—local motor neuron—motor response components, to generate local lateral movements of the tentacle tip (“quiver”). In addition, physiological results showed that each flexor muscle receives distinct central motor commands via different peritentacular nerves and common central motor commands via tentacle digits, respectively. The distal axonal segments of the common pathway can receive inputs from local interneurons in the digits modulating the motor axon activity peripherally without soma excitation. These elements constitute a local microcircuit consisting of olfactory stimulus—distal segments of central motor axons—motor response components, to induce patterned contraction movements of the tentacle. The two local microcircuits described above provide a comprehensive neuroanatomical basis of tentacle movements without the involvement of the CNS.

中文翻译：

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蜗牛后触手中负责局部触手运动的新型外周运动神经元。

蜗牛Helix pomatia后触手的三块屈肌最近有描述。在这里，我们通过跟踪注射到这些肌肉中的神经生物素的逆行运输来识别它们的局部运动神经元。大多数单极运动神经元 (15–35 µm) 仅限于触手数字，并将运动轴突发送到 M2 和 M3 肌肉。电子显微镜显示数字中有小的暗神经元（直径为 5–7 µm）和亮神经元，直径为 12–18（T1 型）和 18–30 µm（T2 型）。神经生物素标记神经元的直径对应于 T1 型光神经元。T1 型运动神经元的神经元过程在手指的神经纤维区广泛分布，并从参与外周嗅觉信息处理的局部神经元元件接收突触输入。这些发现支持外周刺激-反应通路的存在，由嗅觉刺激——局部运动神经元——运动反应成分组成，以产生触手尖端的局部横向运动（“箭袋”）。此外，生理学结果表明，每块屈肌分别通过不同的触须周围神经接收不同的中枢运动命令，通过触手数字接收共同的中枢运动命令。公共通路的远端轴突段可以接收来自数字中局部中间神经元的输入，在没有体细胞激发的情况下外围调节运动轴突活动。这些元件构成了由嗅觉刺激——中央运动轴突的远端部分——运动反应成分组成的局部微电路，以诱导触手的模式收缩运动。