MULTIPLE EXCITATORY RECEPTOR TYPES ON INDIVIDUAL OLFACTORY NEURONS - IMPLICATIONS FOR CODING OF MIXTURES IN THE SPINY LOBSTER

The aim of our paper was to investigate whether single olfactory recep tor neurons (ORNs) of the spiny lobster Panulirus argus functionally e xpress more than one type of receptor, examine the consequences of thi s on coding of mixtures, and compare principles of odorant mixture cod ing by spiny lobsters with that by the channel catfish, which has been studied extensively using the same experimental and analytical proced ures (Caprio et al. 1989; Kang and Caprio 1991). We examined responses of individual taurine-sensitive ORNs to binary mixtures of excitatory compounds, either competitive agonists (taurine, beta-alanine, hypota urine> or non-competitive agonists (taurine, L-glutamate, ammonium chl oride, adenosine-5'-monophosphate. Responses to mixtures were compared to two indices: mixture discrimination index (MDI) and independent co mponent index (ICI). Binary mixtures of competitive agonists had MDI v alues close to 1.0, as expected for competitors. Mixtures of non-compe titive agonists had ICI values averaging 0.83, indicating the effects of the components are not independent. We conclude that individual olf actory cells of spiny lobsters can express more than one type of recep tor mediating excitation, one of which typically has a much higher den sity or affinity, and that spiny lobster and catfish olfactory cells e ncode mixtures of two excitatory agonists using similar rules.