Peptide-mediated glial responses to leydig neuron activity in the leech central nervous system.
Neuronal activity may lead to a variety of responses in neighbouring glial cells; in general, an ensemble of neurons needs to be active to evoke a K+- and/or neurotransmitter-induced glial membrane potential change. We have now detected a signal transfer from a single neuromodulatory Leydig neuron to the giant neuropil glial cells in the central nervous system of the leech Hirudo medicinalis. Activation of a Leydig neuron, two of which are located in each segmental ganglion, elicits a hyperpolarization in the giant neuropil glial cells. This hyperpolarization could be mimicked by bath application of the peptide myomodulin A (1 nM-1.0 microM). Myomodulin-like immunoreactivity has recently been found to be present in a set of leech neurons, including Leydig neurons (Keating & Sahley 1996, J. Neurobiol., 30, 374-384). The glial responses to Leydig neuron stimulation persisted in a high-divalent cation saline, when polysynaptic pathways are suppressed, indicating that the effects on the glial cell were direct. The glial responses to myomodulin A application persisted in high-Mg2+/low-Ca2+ saline, when chemical synaptic transmission is suppressed, indicating a direct effect of myomodulin A on the glial membrane. The glial hyperpolarization evoked by myomodulin A was dose dependent (EC50 = 50 nM) and accompanied by a membrane conductance increase of approximately 25%. Ion substitution experiments indicated that myomodulin A triggered a Ca2+-independent K+ conductance. Thus, our results suggest, for the first time, direct signal transmission from an identified modulatory neuron to an identified glial cell using a myomodulin-like peptide.
Schmidt
J
J
Abteilung für Aligemeine Zoologie, FB Biologie, Universität Kaiserslautern, Germany. Joachim.Schmidt@uni-koeln.de
Deitmer
J W
JW
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002490:Central Nervous System / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D004594:Electrophysiology; D017952:Ganglia, Invertebrate / Q000166:cytology / Q000187:drug effects; D066298:In Vitro Techniques; D007395:Interneurons / Q000502:physiology; D007865:Leeches / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D009431:Neural Conduction / Q000502:physiology; D009457:Neuroglia / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D009479:Neuropeptides / Q000378:metabolism / Q000502:physiology*; D019581:Neuropil / Q000166:cytology / Q000502:physiology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D013126:Spinal Nerve Roots / Q000502:physiology
D009479:Neuropeptides; D015221:Potassium Channels; C053302:myomodulin; D002118:Calcium