Finding balance amidst variability: synaptic strength in the leech heartbeat CPG

Abstract

Event Abstract Back to Event Finding balance amidst variability: synaptic strength in the leech heartbeat CPG R. C. Roffman1* and A. L. Waever2 1 Emory University, Department of Biology, Ukraine 2 St. Michael’s College, Department of Biology, Ukraine The middle premotor interneurons of the leech heartbeat CPG provide synaptic input to mid-body heart motor neurons (Norris et al, 2006). The phase of these interneurons relative to the oscillator interneurons shifts with a switch from synchronous to peristaltic coordination mode. This shift in phase of the middle premotor interneurons is critical in setting up the coordination modes in the rear of the animal. These cells receive inputs from multiple different presynaptic partners in the timing circuit of the CPG: electrical excitation from the ipsilateral oscillator interneurons and chemical inhibition from both the ipsilateral and contralateral switch interneuron. The balance between these two opposing inputs is critically important in generating the appropriate phasing of each coordination mode. Previous modeling studies (Weaver et al, 2003, 2005) showed that a specific balance must exist between electrical excitation and chemical inhibition onto the middle premotor interneurons for the network to produce its stereotypical phasing. In constructing the model, two simplifying assumptions were made that are confirmed here experimentally: 1) Electrical coupling from a given ipsilateral oscillator interneuron onto a given middle premotor interneuron is the same on each side i.e. there is neither a systematic left-right asymmetry in the nerve cord nor any mechanism to alter coupling with changes in coordination mode. 2) Electrical coupling from each ipsilateral oscillator interneuron is the same onto both pairs of middle premotor interneurons. A CPG model with these assumptions importantly predicts that each of the four synapses from the switch interneuron onto the middle premotor heart interneurons will have different relative strengths. In order to mimic the proper output of the network, the synapses onto the ipsilateral middle premotor interneuron had to be stronger than the synapses onto the contralateral middle premotor interneuron. The model also predicts that synapses onto the interneurons in ganglion 7 be stronger than the corresponding synapses onto the interneurons in ganglion 6. Here we confirm these predictions experimentally in the living system. The large two-to-four fold animal-to-animal variability in synaptic strength previously reported in this system (Norris et al, 2007, Seaman and Calabrese, 2008) is observed here as well. We will also show this large variability present on the inputs to the important switch interneurons that control the switching behavior. Despite this large variability, the correct relative strengths of all of these synapses are maintained within an animal, producing the proper balance between inhibition and excitation that is necessary to produce the observed phasing in network output despite wide ranging variability in synaptic strength between animals. Supported by NS024072 to RLC and NS064682 to RCR. Conference: 2010 South East Nerve Net (SENN) and Georgia/South Carolina Neuroscience Consortium (GASCNC) conferences, Atlanta , United States, 5 Mar - 7 Mar, 2010. Presentation Type: Poster Presentation Topic: Posters Citation: Roffman RC and Waever AL (1900). Finding balance amidst variability: synaptic strength in the leech heartbeat CPG. Front. Neurosci. Conference Abstract: 2010 South East Nerve Net (SENN) and Georgia/South Carolina Neuroscience Consortium (GASCNC) conferences. doi: 10.3389/conf.fnins.2010.04.00092 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 01 Jan 1900; Published Online: 01 Jan 1900. * Correspondence: R. C Roffman, Emory University, Department of Biology, Colchester, Ukraine, nemoABS01@frontiersin.org Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers R. C Roffman A. L Waever Google R. C Roffman A. L Waever Google Scholar R. C Roffman A. L Waever PubMed R. C Roffman A. L Waever Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.