NEURONAL PRIMING IN THE LOCUST OLFACTORY SYSTEM.

A. Bäcker* and G. Laurent. Division of Biology, 139-74, California Institute of Technology, Pasadena, CA 91125, USA.
Odors are represented in the antennal lobe (AL) of the locust by odor-specific, but overlapping, evolving assemblies of projection neurons (PNs). We are interested in studying the dependence of these patterns on odor concentration. We recorded intracellularly from locust PNs in vivo while using a computerized odor delivery system to deliver 1-sec long airborne odor pulses at concentrations between 0.01x and 1x saturated vapor. We found that a PN that responds to an odor at low concentration will in general respond to the same odor at higher concentrations with a similar yet more pronounced response, be it excitatory (greater depolarization, more spikes), inhibitory (deeper slow hyperpolarization, fewer spikes) or both. The converse is not true. A response to an odor at high concentrations does not in general imply that a neuron will respond at lower concentrations. This suggests the existence of a threshold, for each neuron/odor pair, above which the neuron responds in a recognizable way to that odor. Preliminary data suggest that such a threshold can be lowered after temporary exposure to the odor at high concentration (specifically for that odor), in a way that depends on odor concentration, duration of exposure and time since the sensitizing exposure, and can last over 10 mins.

Supported by the Sloan Center for Theoretical Neurobiology at Caltech, NIDCD and the McKnight Foundation.


Keywords: pattern recognition, multiple chemical sensitivity (MCS), coding, dynamic.