A kinetic model of the transient phase in the response of olfactory receptor neurons

A model is presented that predicts the instantaneous spike rate of an olfac tory receptor neuron (ORN) in response to the quality and concentration of an odor stimulus. The model accounts for the chemical kinetics of ligand-re ceptor binding and activation processes, and implicitly the initiation of s econd messenger cascades that lead to depolarization and/or hyperpolarizati on of the ORN membrane. Both of these polarizinig processes are included in the most general form of the model, as well as a process that restores the voltage to its negative resting state. The spike rate is assumed to be lin early proportional to the level of voltage depolarization above a critical negative voltage level. The model includes the simplifying assumption that activation of bound ligand-receptor complexes by G-proteins and other enabl ing molecules follows a Monod function that has the ratio of enabling molec ules to bound unactivated ligand-receptor complexes as its argument. Parame ters are selected that provide an excellent fit of the model to previously published empirical data on the response of cockroach ORNs to pulsed 1-hexa nol stimuli. The sensitivity of model output to various model parameters is investigated and changes to parameters are discussed that would improve th e ability of ORNs to follow rapidly pulsed stimuli.