Norris Brian J, Weaver Adam L, Wenning Angela, García Paul S, Calabrese Ronald L
Department of Biology, Emory University, Atlanta, GA 30322, USA.
J Neurophysiol. 2007 Nov;98(5):2992-3005. doi: 10.1152/jn.00877.2007. Epub 2007 Sep 5.
The central pattern generator (CPG) for heartbeat in medicinal leeches consists of seven identified pairs of segmental heart interneurons and one unidentified pair. Four of the identified pairs and the unidentified pair of interneurons make inhibitory synaptic connections with segmental heart motor neurons. The CPG produces a side-to-side asymmetric pattern of intersegmental coordination among ipsilateral premotor interneurons corresponding to a similarly asymmetric fictive motor pattern in heart motor neurons, and asymmetric constriction pattern of the two tubular hearts, synchronous and peristaltic. Using extracellular recordings from premotor interneurons and voltage-clamp recordings of ipsilateral segmental motor neurons in 69 isolated nerve cords, we assessed the strength and dynamics of premotor inhibitory synaptic output onto the entire ensemble of heart motor neurons and the associated conduction delays in both coordination modes. We conclude that premotor interneurons establish a stereotypical pattern of intersegmental synaptic connectivity, strengths, and dynamics that is invariant across coordination modes, despite wide variations among preparations. These data coupled with a previous description of the temporal pattern of premotor interneuron activity and relative phasing of motor neuron activity in the two coordination modes enable a direct assessment of how premotor interneurons through their temporal pattern of activity and their spatial pattern of synaptic connectivity, strengths, and dynamics coordinate segmental motor neurons into a functional pattern of activity.
药用蚂蟥心跳的中枢模式发生器（CPG）由七对已确定的节段性心脏中间神经元和一对未确定的中间神经元组成。已确定的七对中间神经元中的四对以及那对未确定的中间神经元与节段性心脏运动神经元形成抑制性突触连接。CPG在同侧运动前中间神经元之间产生节段间协调的左右不对称模式，这与心脏运动神经元中类似的不对称虚拟运动模式相对应，并且与两个管状心脏的不对称收缩模式同步且呈蠕动状。我们使用来自69条离体神经索中运动前中间神经元的细胞外记录以及同侧节段性运动神经元的电压钳记录，评估了在两种协调模式下运动前抑制性突触输出到整个心脏运动神经元集合的强度和动态，以及相关的传导延迟。我们得出结论，尽管不同标本之间存在很大差异，但运动前中间神经元建立了一种刻板的节段间突触连接性、强度和动态模式，该模式在不同协调模式下是不变的。这些数据与先前对两种协调模式下运动前中间神经元活动的时间模式以及运动神经元活动的相对相位的描述相结合，能够直接评估运动前中间神经元如何通过其活动的时间模式以及突触连接性、强度和动态的空间模式，将节段性运动神经元协调成一种功能性活动模式。
