Modulatory Mechanisms at a Primitive Neuromuscular Synapse: Membrane Currents, Transmitter Release and Modulation by Transmitters in a Cnidarian Motor Neuron
Open Access
- 1 December 1995
- journal article
- Published by Oxford University Press (OUP) in American Zoologist
- Vol. 35 (6) , 520-528
- https://doi.org/10.1093/icb/35.6.520
Abstract
The phylum Cnidaria arose early in metazoan evolution and, assuming monophyly, is regarded as being close to the ancestral metazoan. The simplicity of structure in the cnidariannervous system is not reflected in the physiology of neurons. The motor neurons that control swimming in the jellyfish Polyorchis penicillatus epitomise this operational complexity. Synchrony in the contraction of the swimming muscle sheets is achieved by compensatingfor the conduction time of motor APs propagating to distant parts of the motor network. This depends on motor APs continuously decreasing in duration as they propagate through the network which in turn leads to a decrease in the delay of muscle action potential initiation. Two membrane currents are critical for this mechanism, a fast, transient K+ current (IK-fast). and a transient Ca++ current. A PCR-based screen of genomicDNA produced clones having considerable sequence identity with the Shaker, Shal, Shab and Shaw subfamilies. One full-length clone, jShakl when expressed in Xenopus oocytes reveals an A-like Shaker current which activates at very positive voltages. Motor neuron activity can be modulated by two endogenous transmitters, dopamine and FMRFamide-related peptides which are found endogenously. Dopamine causes a long lasting hyperpolarization by activating a potassium current that is regulated by D2 receptors. In addition dopamine reduces action potential duration. Pol-RFamides, on the other hand have an excitatory effect by blocking the slowly inactivating current, IK-slowKeywords
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