Mangan P S, Curran G A, Hurney C A, Friesen W O
Department of Biology, University of Virginia, Charlottesville 22901.
J Comp Physiol A. 1994 Dec;175(6):709-22. doi: 10.1007/BF00191843.
Expression of swimming in the medicinal leech (Hirudo medicinalis) is modulated by serotonin, a naturally occurring neurohormone. Exogenous application of serotonin engenders 'spontaneous' swimming activity in nerve-cord preparations. We examined whether this activity is due to enhanced participation of swim motor neurons (MNs) in generating the swimming rhythm. We found that depolarizing current injections into MNs during fictive swimming are more effective in shifting cycle phase in nerve cords following serotonin exposure. In such preparations, the dynamics of membrane potential excursions following current injection into neuronal somata are substantially altered. We observed: 1) a delayed outward rectification ('relaxation') during depolarizing current injection, most marked in inhibitory MNs; and 2) in excitor MNs, an enhancement of postinhibitory rebound (PIR) and afterhyperpolarizing potentials (AHPs) following hyperpolarizing and depolarizing current pulses, respectively. In contrast, we found little alteration in MN properties in leech nerve cords depleted of amines. We propose that enhanced expression of swimming activity in leeches exposed to elevated serotonin is due, partly, to enhancement of relaxation, PIR and AHP in MNs. We believe that as a consequence of alterations in cellular properties and synaptic interactions (subsequent paper) by serotonin, MNs are reconfigured to more effectively participate in generating and expressing the leech swimming rhythm.
医用蚂蟥（医蛭）的游泳行为表现受血清素调节，血清素是一种天然存在的神经激素。外源施加血清素会在神经索制剂中引发“自发”游泳活动。我们研究了这种活动是否是由于游泳运动神经元（MNs）在产生游泳节律时的参与度提高所致。我们发现，在虚拟游泳期间向MNs注入去极化电流，在血清素暴露后的神经索中更有效地改变周期相位。在这类制剂中，向神经元胞体注入电流后膜电位偏移的动态变化显著改变。我们观察到：1）去极化电流注入期间出现延迟外向整流（“松弛”），在抑制性MNs中最为明显；2）在兴奋性MNs中，分别在超极化和去极化电流脉冲后，抑制后反弹（PIR）和超极化后电位（AHPs）增强化。相比之下，我们发现在胺类耗尽的蚂蟥神经索中，MNs的特性几乎没有变化。我们提出，暴露于血清素水平升高的蚂蟥中游泳活动表达增强，部分原因是MNs中松弛、PIR和AHP增强。我们认为，由于血清素改变了细胞特性和突触相互作用（后续论文），MNs被重新配置，以更有效地参与产生和表达蚂蟥游泳节律。
