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.
References:
1. Cataldo E, Brunelli M, Byrne JH, Av-Ron E, Cai Y, Baxter DA (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 18:5-24 [PubMed]
2. 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. Eur J Neurosci 25:159-67 [PubMed] |
