A model of graded synaptic transmission for use in dynamic network simulations

1. The heartbeat central pattern-generating network of the me-dicinal leech contains elemental neural oscillators, comprising re-ciprocally inhibitory pairs of segmental heart interneurons, that use graded as well as spike-mediated synaptic transmission. We are in the process of developing a general computer model of this pattern generator. Our modeling goal is to explore the interaction of membrane currents and synaptic transmission that promote oscillation in heart interneurons. As a first step toward this goal, we have developed a computer model of graded synaptic transmis-sion between reciprocally inhibitory heart interneurons. Previ-ously gathered voltage-clamp data of presynaptic Ca2+ currents and simultaneous postsynaptic currents and potentials (5 mM external [ Ca”‘] ) were used as the bases of the model.. 2. We assumed that presynaptic Ca2+ current was composed of distinct fast (I & and slow (I & components because there ar