Calabrese Lab Projects Electrophysiology of HN cells Network model of the leech heartbeat timing network Neuronal networks that produce rhythmic motor patterns that underlie behaviors such as swimming in the lamprey or the beating of crayfish swimmerets can be described as chains of coupled segmental oscillators. In these systems, progressive phase differences between segments are essential for the generation of appropriate motor output. The neuronal network that paces the heartbeat of the leech can also be viewed as a chain of coupled oscillators, albeit with a length of only two segments. In the leech there are two centers of oscillation in the 3rd and 4th ganglion. These centers are coupled by coordinating fibers which are the neuritic processes of heart interneurons of the 1st and 2nd ganglia. Together these neurons form the timing network that paces the heartbeat of the leech. We are studying the intersegmental coordination of segmental oscillators in the leech using a realistic neuronal network model. Individual neurons are modeled as single compartments with Hodgkin and Huxley type conductances. We are testing the idea that the observed 15% phase lag between the segmental oscillators (the 4th ganglion leads the 3rd) may be the result of inherent differences in the periods of the segmental oscillators. We are also exploring the possibility that asymmetries in the synaptic coupling between the oscillators may affect their phase relationship. Calcium imaging and fluorescent study of HN cells How does intracellular Ca concentration correlate to spiking activity of HN cell? What is its contribution into synaptic transmission? Does intracellular Ca regulate Ca channels and other ion channels in HN cells? Which mechanisms regulate Ca homeostasis/turnover in HN cells? What is the spatial distribution of Ca channels and stores in the HN neuron? Where in the neuron are Ca input and release initiated? Is there any relation and coordination between extracellular Ca input and release of Ca from intracellular stores? What is the spatial distribution of the inhibitory synaptic connection between HN neurons? Is the inhibitory synaptic connection monosynaptic or multisynaptic? Is there a critical quantity of synapses which should be switched on to maintain the reciprocal interaction of HN cells? To answer these questions, we are observing HN cells filled with calcium-sensitive dyes, and are studying effects of destroying small parts of HN cells with focused light. Anatomically realistic Modeling How does the shape of an HN neuron contribute to its behavior? How do different spatial distributions of ion channels affect the cell's computation? Are these anatomical contributions important to the HN network as a whole? To address these questions, we are building anatomically realistic, multi-compartmental models of HN cells. Half-Center Oscillator model database (HCO-db) Last updated June 7, 2012. Please send comments to adolocm@emory.edu.