Bursts of spikes in leech T cells produce an AHP, which results from activation of a Na+/K+ pump and a Ca2+-dependent K+ current. Activity-dependent increases in the AHP are believed to induce conduction block of spikes in several regions of the neuron, which in turn, may decrease presynaptic invasion of spikes and thereby decrease transmitter release. To explore this possibility, we used the neurosimulator SNNAP to develop a multi-compartmental model of the T cell. Each compartment was modeled as an equivalent electrical circuit, in which some currents were regulated by intracellular Ca2+ and Na+. The membrane model consisted of a membrane capacitance (Cm), for which we used the value 1 uF/cm2, in parallel with two inward currents (Na+ and Ca2+), two K+ currents, a leak current and pump current. The model incorporated empirical data that describe the geometry of the cell and activity-dependent changes of the AHP (see paper for details). Simulations indicated that at some branching points, activity-dependent increases of the AHP reduced the number of spikes transmitted from the minor receptive field to the soma and beyond. These results suggest that the AHP can regulate spike conduction within the presynaptic arborizations of the cell and could in principle contribute to the synaptic depression that is correlated with increases in the AHP.
Model Type: Neuron or other electrically excitable cell; Electrogenic pump
Cell Type(s): Leech T segmental sensory neuron
Currents: I L high threshold; I K,Ca; I Sodium; I Potassium; Na/K pump
Model Concept(s): Activity Patterns; Axonal Action Potentials; Action Potentials; Invertebrate; Conduction failure; Sodium pump; Touch
Simulation Environment: SNNAP
Implementer(s): Cataldo, Enrico
References:
Cataldo E et al. (2005). Computational model of touch sensory cells (T Cells) of the leech: role of the afterhyperpolarization (AHP) in activity-dependent conduction failure. Journal of computational neuroscience. 18 [PubMed]
Scuri R, Lombardo P, Cataldo E, Ristori C, Brunelli M. (2007). Inhibition of Na+/K+ ATPase potentiates synaptic transmission in tactile sensory neurons of the leech. The European journal of neuroscience. 25 [PubMed]