Burdohan J A, Comer C M
Department of Biological Sciences, University of Illinois at Chicago 60607, USA.
J Neurosci. 1996 Sep 15;16(18):5830-43. doi: 10.1523/JNEUROSCI.16-18-05830.1996.
Escape responses of cockroaches, Periplaneta americana, can be triggered by wind and mediated by a group of "giant interneurons" that ascend from cercal mechanoreceptors to motor centers. Recently it has been observed that escape also can be triggered by tactile stimulation of the antennae, and it is then independent of the giant interneurons. Here we identify a descending antennal mechanosensory pathway that may account for escape. Cobalt backfills demonstrated that a limited number of cells in the head ganglia have axons that project through all three thoracic ganglia. Comparison with known wind-sensory pathways indicated that wind is not a reliable stimulus for activating descending antennal pathways. However, direct touch stimulation of an antenna reliably evoked short-latency responses in cells with axons in the cervical connectives. Intracellular recording and dye injection revealed members of this pathway, referred to as descending mechanosensory interneurons (DMIs). The two axons of largest diameter in the cervical connectives were found to belong to DMIs, and these large-caliber interneurons were studied in detail. One had a soma in the supraesophageal ganglion, and the other in the subesophageal ganglion. Both had extensive neuritic arborizations at the same level as the soma and axonal arbors in all three thoracic ganglia. Each of these DMIs exhibited short-latency responses to small antennal movements, demonstrated a degree of directional sensitivity, and rapidly conducted impulses to thoracic levels. These cells have properties suggesting that they play a role in a short-latency behavior such as touch-evoked escape.
美洲大蠊的逃避反应可由风触发，并由一组从尾须机械感受器上升至运动中枢的“巨型中间神经元”介导。最近观察到，触角的触觉刺激也能触发逃避反应，且此时该反应与巨型中间神经元无关。在此，我们确定了一条下行触角机械感觉通路，它可能是逃避反应的原因。钴逆行填充显示，头部神经节中数量有限的细胞具有穿过所有三个胸神经节的轴突。与已知的风感觉通路比较表明，风不是激活下行触角通路的可靠刺激。然而，直接触摸刺激触角能可靠地在颈神经连索中有轴突的细胞中诱发短潜伏期反应。细胞内记录和染料注射揭示了该通路的成员，即下行机械感觉中间神经元（DMI）。在颈神经连索中发现两条直径最大的轴突属于DMI，对这些大口径中间神经元进行了详细研究。一个神经元的胞体位于食管上神经节，另一个位于食管下神经节。两者在与胞体相同的水平以及所有三个胸神经节中都有广泛的神经分支和轴突分支。每个DMI对触角的微小运动都表现出短潜伏期反应，具有一定程度的方向敏感性，并能迅速将冲动传导至胸段水平。这些细胞的特性表明它们在诸如触觉诱发逃避等短潜伏期行为中发挥作用。
