Crow Terry, Tian Lian-Ming
Department of Neurobiology and Anatomy, University of Texas Medical School, PO Box 20708, Houston, TX 77030, USA.
J Neurophysiol. 2004 Jun;91(6):2874-83. doi: 10.1152/jn.00028.2004. Epub 2004 Feb 25.
Pavlovian conditioning of Hermissenda produces both light-elicited inhibition of normal positive phototactic behavior and conditioned stimulus (CS)-elicited foot-shortening. Rotation, the unconditioned stimulus (US) elicits foot-shortening and reduced forward ciliary locomotion. The neural circuit supporting ciliary locomotion and its modulation by light is known in some detail. However, the neural circuits responsible for rotation-elicited foot-shortening and reduced forward ciliary locomotion are not known. Here we describe components of the neural circuit in Hermissenda that produce anterior foot contraction and ciliary activation mediated by statocyst hair cells. We have characterized in semi-intact preparations newly identified pedal ventral contraction motor neurons (VCMNs) and interneurons (I(b)). Type I(b) interneurons receive polysynaptic input from statocyst hair cells and project directly to VCMNs and cilia-activating motor neurons. Depolarization of VCMNs with extrinsic current in normal artificial seawater (ASW) and high-divalent cation ASW, and under conditions where central synaptic transmission was suppressed with 5 mM Ni(2+) ASW, elicited a contraction of the ipsilateral anterior foot measured from videotape recordings. Mechanical displacement of the statocyst or depolarization of identified statocyst hair cells with extrinsic current elicited spikes and complex excitatory postsynaptic potentials (EPSPs) in type I(b) interneurons and complex EPSPs and spikes recorded in VCMNs. Type I(b) interneurons are electrically coupled and project to VCMNs and VP1 cilia-activating motor neurons located in the contralateral pedal ganglia. The results indicate that statocyst hair-cell-mediated anterior foot contraction and graviceptive ciliary locomotion involve different interneuronal circuit components from the circuit previously identified as supporting light modulated ciliary locomotion.
一是光引发对正常正向趋光行为的抑制，二是条件刺激（CS）引发足部缩短。旋转作为非条件刺激（US），会引发足部缩短并减少前向纤毛运动。支持纤毛运动及其受光调节的神经回路已得到较为详细的了解。然而，负责旋转引发足部缩短和前向纤毛运动减少的神经回路尚不清楚。在此，我们描述了多纹海兔中由平衡囊毛细胞介导产生前足收缩和纤毛激活的神经回路组成部分。我们在半完整标本中对新发现的踏板腹侧收缩运动神经元（VCMNs）和中间神经元（I(b)）进行了特征描述。I(b)型中间神经元从平衡囊毛细胞接收多突触输入，并直接投射到VCMNs和纤毛激活运动神经元。在正常人工海水（ASW）和高双价阳离子ASW中，以及在5 mM Ni(2+) ASW抑制中枢突触传递的条件下，用外部电流使VCMNs去极化，通过录像记录测量到同侧前足出现收缩。平衡囊的机械位移或用外部电流使已鉴定的平衡囊毛细胞去极化，会在I(b)型中间神经元中引发动作电位和复杂的兴奋性突触后电位（EPSPs），并在VCMNs中记录到复杂的EPSPs和动作电位。I(b)型中间神经元通过电耦合，并投射到位于对侧踏板神经节的VCMNs和VP1纤毛激活运动神经元。结果表明，平衡囊毛细胞介导的前足收缩和重力感受性纤毛运动涉及的中间神经元回路成分，与先前鉴定为支持光调制纤毛运动的回路不同。
