Nusbaum M P, Kristan W B
J Exp Biol. 1986 May;122:277-302. doi: 10.1242/jeb.122.1.277.
Two pairs of serotonin-containing neurones, designated cells 21 and 61, were characterized physiologically and anatomically in the hirudinid leeches Macrobdella decora and Hirudo medicinalis. Both of these cells are bilaterally paired interneurones and each cell is weakly electrically coupled to the other serotonin-containing cells both intra- and interganglionically. Cells 21 and 61 are excited polysynaptically by individual identified mechano-sensory neurones. Segmental nerve shock sufficient to elicit an episode of swimming strongly excites cells 21 and 61, which then tend to generate bursts of impulses that are phase-locked to the swim motor pattern. Intracellular stimulation of either cell 21 or cell 61 often causes the initiation of swimming, acting in parallel with the nonserotonergic swim-initiator cell 204. Cells 61 and 204 are also weakly electrically coupled. The latency to swim onset by stimulating cell 21 or 61 is similar to that of cell 204 and different from that of the serotonergic Retzius cell. This result, with those in the accompanying paper (Nusbaum, 1986), suggests that unlike the Retzius cell and similar to cell 204, cells 21 and 61 synaptically contact cells of the swim central pattern generator (CPG).
在美洲水蛭（Macrobdella decora）和医用水蛭（Hirudo medicinalis）中，对两对含5-羟色胺的神经元（即21号细胞和61号细胞）进行了生理和解剖学特征分析。这两种细胞都是双侧配对的中间神经元，并且每个细胞在神经节内和神经节间都与其他含5-羟色胺的细胞存在弱电耦合。21号细胞和61号细胞受到单个已识别的机械感觉神经元的多突触兴奋。足以引发游泳发作的节段性神经休克会强烈兴奋21号细胞和61号细胞，然后它们倾向于产生与游泳运动模式锁相的冲动爆发。对21号细胞或61号细胞进行细胞内刺激通常会引发游泳，其作用与非5-羟色胺能的游泳启动细胞204并行。61号细胞和204号细胞也存在弱电耦合。通过刺激21号细胞或61号细胞引发游泳开始的潜伏期与204号细胞相似，与含5-羟色胺的瑞氏细胞不同。这一结果与随附论文（努斯鲍姆，1986年）中的结果表明，与瑞氏细胞不同，与204号细胞相似，21号细胞和61号细胞与游泳中央模式发生器（CPG）的细胞形成突触联系。
