Neuroscience 2003 Abstract
| Presentation Number: | 605.10 |
|---|---|
| Abstract Title: | Effects of chemical and electrical synapses on phase relationships in a complete model of the heartbeat CPG in the medicinal leech. |
| Authors: |
Weaver, A. L.*1
; Calabrese, R. L.1
1Dept. Biol., Emory Univ., Atlanta, GA |
| Primary Theme and Topics |
Motor Systems - Pattern Generation and Locomotion |
| Secondary Theme and Topics | Motor Systems<br />- Invertebrate Motor Systems |
| Session: |
605. Pattern Generation Models Poster |
| Presentation Time: | Tuesday, November 11, 2003 9:00 AM-10:00 AM |
| Location: | Morial Convention Center - Hall F-I, Board # H85 |
| Keywords: | Hirudo medicinalis, network model, oscillatory networks, synchronization |
The leech heartbeat central pattern generator (CPG) consists of seven bilateral pairs of heart interneurons that coordinate the activity of heart motor neurons. In the CPG, front and rear premotor interneurons are coordinated differently on the two sides by intervening switch interneurons. We have extended a previous network model that included the front premotor interneurons to construct a model of the entire heartbeat CPG.
In our CPG model, we implemented known synaptic and neuronal properties. In contrast to the front premotor interneurons, the switch interneurons fire in accelerating spike frequency bursts and only on the synchronous side. The switch interneurons were modeled using a three conductance neuron model that was tuned to fit experimental data. The rear premotor interneurons show similar activity to and were modeled in the same manner as the front premotor interneurons (Hill et al. 2001).
To reproduce experimentally observed CPG phasing data (Morris & Calabrese, SFN Abstr 2001), we varied synaptic strength onto the rear premotor interneurons. We found that 1) increased chemical inhibition from the switch interneurons shortens the burst duration of the rear premotor interneurons without changing the phase of the beginning of the burst, and 2) strengthened electrical coupling from the front premotor interneurons brings the peristaltic-side rear premotor interneurons into phase with those in the front, despite simultaneous inhibition from the switch interneuron. A combined parameter sweep of inhibitory and electrical strengths found a set of parameters that reproduced the experimentally recorded CPG phases. Our model thus provides insight into the roles of chemical and electrical synapses producing the asymmetric pattern of interneuron activity that characterizes the heartbeat CPG.
In our CPG model, we implemented known synaptic and neuronal properties. In contrast to the front premotor interneurons, the switch interneurons fire in accelerating spike frequency bursts and only on the synchronous side. The switch interneurons were modeled using a three conductance neuron model that was tuned to fit experimental data. The rear premotor interneurons show similar activity to and were modeled in the same manner as the front premotor interneurons (Hill et al. 2001).
To reproduce experimentally observed CPG phasing data (Morris & Calabrese, SFN Abstr 2001), we varied synaptic strength onto the rear premotor interneurons. We found that 1) increased chemical inhibition from the switch interneurons shortens the burst duration of the rear premotor interneurons without changing the phase of the beginning of the burst, and 2) strengthened electrical coupling from the front premotor interneurons brings the peristaltic-side rear premotor interneurons into phase with those in the front, despite simultaneous inhibition from the switch interneuron. A combined parameter sweep of inhibitory and electrical strengths found a set of parameters that reproduced the experimentally recorded CPG phases. Our model thus provides insight into the roles of chemical and electrical synapses producing the asymmetric pattern of interneuron activity that characterizes the heartbeat CPG.
Supported by NIH 1K12GM00680 (ALW, Fellowships in Research & Science Teaching) & NIH NS24702 (ALW & RLC).
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2003 Neuroscience Meeting Planner. New Orleans, LA: Society for Neuroscience, 2003. Online.
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