Vehovszky Agnes, Szabó Henriette, Elliott Christopher J H
Balaton Limnological Research Institute, Hungarian Academy of Sciences, PO Box 35, 8237 Tihany, Hungary.
J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2004 Oct;190(10):837-46. doi: 10.1007/s00359-004-0539-y. Epub 2004 Aug 14.
In the pond snail Lymnaea stagnalis octopamine-containing (OC) interneurons trigger and reconfigure the feeding pattern in isolated CNS by excitation of the central pattern generator. In semi-intact (lip-mouth-CNS) preparations, this central pattern generator is activated by chemosensory inputs. We now test if sucrose application to the lips activates the OC neurons independently of the rest of the feeding central pattern generator, or if the OC interneuron is activated by inputs from the feeding network. In 66% of experiments, sucrose stimulated feeding rhythms and OC interneurons received regular synaptic inputs. Only rarely (14%) did the OC interneuron fire action potentials, proving that firing of OC interneurons is not necessary for the sucrose-induced feeding. Prestimulation of OC neurons increased the intensity and duration of the feeding rhythm evoked by subsequent sucrose presentations. One micromolar octopamine in the CNS bath mimicked the effect of OC interneuron stimulation, enhancing the feeding response when sucrose is applied to the lips. We conclude that the modulatory OC neurons are not independently excited by chemosensory inputs to the lips, but rather from the buccal central pattern generator network. However, when OC neurons fire, they release modulatory octopamine, which provides a positive feedback to the network to enhance the sucrose-activated central pattern generator rhythm.
在池塘蜗牛椎实螺中，含章鱼胺（OC）的中间神经元通过激发中枢模式发生器来触发并重新配置孤立中枢神经系统中的摄食模式。在半完整（唇-口-中枢神经系统）标本中，这个中枢模式发生器由化学感应输入激活。我们现在测试将蔗糖施加到唇部是否能独立于摄食中枢模式发生器的其他部分激活OC神经元，或者OC中间神经元是否由来自摄食网络的输入激活。在66%的实验中，蔗糖刺激了摄食节律，并且OC中间神经元接收到规则的突触输入。OC中间神经元仅偶尔（14%）产生动作电位，这证明OC中间神经元的放电对于蔗糖诱导的摄食并非必要。对OC神经元的预刺激增加了随后蔗糖呈现所诱发的摄食节律的强度和持续时间。在中枢神经系统浴液中加入1微摩尔的章鱼胺模拟了OC中间神经元刺激的效果，当蔗糖施加到唇部时增强了摄食反应。我们得出结论，调节性OC神经元并非由唇部的化学感应输入独立激发，而是由颊部中枢模式发生器网络激发。然而，当OC神经元放电时，它们释放调节性章鱼胺，这为网络提供正反馈以增强蔗糖激活的中枢模式发生器节律。
