By Daniel P. Dougherty (MBI Postdoc) and his team of students
The process of smelling, called olfaction, requires reliable communication of information about chemical identity and concentration of odors from the environment to the brain. Many animals use olfaction to find food, locate mates, avoid danger and navigate their surroundings. The chemical reactions and neural processes required of olfaction involve several temporal and spatial scales which makes a detailed understanding of its functional basis quite challenging.
During the 2004 MBI Summer Program, a group of undergraduate and graduate students studied the issue. Their project focused on the dynamics of the olfactory receptor neuron (ORN). ORN are situated in the nasal epithelium and interface directly with odor molecules that become dissolved in the nasal mucosa. The response to these odorants requires the cooperation of two distinct processes within the ORN.
The first is an electrochemical signal transduction cascade that occurs in the cilia of ORN upon binding of odor molecules to special receptors. The second is an action potential generation mechanism in the soma of ORN that allows neuroelectrical signals to be communicated to the olfactory bulb and higher processing centers in the brain. The students developed a mathematical model which synthesized a body of experimental data concerning the biochemical signaling and electrical spike generation processes of ORN.
Their model predicted that the total number of spikes per spiking episode is a nonmonotonic function of log odorant concentration, first increasing then decreasing, in agreement with experimental observations. Their model was also able to explain why action potentials predominantly occur only during the activation phase of a response, not during the desensitization phase. In the future, their model of ORN spiking behavior will be used for a indepth study of doseresponse relations and coding capacity of these chemicalsensing cells.
Geraldine Wright and Daniel P. Dougherty are postdoctoral fellows at the Mathematical Biosciences Institue. This material is based upon work supported by the National Science Foundation under Agreement No. 0112050.
Reisert, J., & Matthews, H.R. (1999). Journal of Physiology (London), 519, 801813.
Dougherty, D.P., Badamorj, D., Carlton, M., Musielak, M., Wherity, L., & Yew, A.C. (2004). Mathematical Biosciences Technical Report Series 27.