Meeting Abstract
Organisms’ production of rhythmic behaviors is controlled by central pattern generators (CPGs), whose output can be modulated by neurotransmitters, such as the peptide, SGRNFLRamide (SGRN), as well as by sensory feedback. The cardiac ganglion (CG) of Homarus americanus is a CPG that consists of 4 premotor and 5 motor neurons, which are electrically and chemically coupled and thus produce synchronous driver potentials (DPs) that generate bursts of action potentials to drive cardiac contractions. We examined the role of stretch in altering the CPG by isolating the CG along with muscles surrounding and underlying the premotor cells. We recorded intracellularly from a motor neuron, while stretching the muscle fibers. Tonic stretch decreased DP cycle periods and increased burst durations as a function of force. The effects were larger in motor neurons with longer intrinsic burst durations. When perfused with 10-9M SGRN, the effects on the CG due to stretch were enhanced, while 10-8M SGRN decreased the effects of stretch. Mathematical modeling is one way to tease apart the components of a complex system to test hypotheses. One model that has been used to examine the CG is the Morris-Lecar model, which uses two model ionic currents and can reproduce a variety of oscillatory behavior. Starting with two Morris-Lecar oscillators (representing premotor and motor neurons), coupled by electrical and excitatory synapses, we added an additional current to model stretch feedback and ran the model with multiple reversal potentials. Many simulations mirrored some of our experimental results, including state-dependent relationships, but none reproduced all of the effects we have seen experimentally.
