Date of Award

1988

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

John Caprio

Abstract

Amino acid (AA) responses of olfactory bulb (OB) mitral cells (MC) in the catfish, Ictalurus punctatus, were studied electrophysiologically. A total of 63 cells were recorded in 28 fish in two separate experiments. For the first study, 27 cells in 22 fish were studied with olfactory tract (OT) intact during stimulation with 10$\sp{-6}$ M to 10$\sp{-2}$ M concentrations of 11 AA. MC responses were quantified by interspike interval (ISI) variables sensitive to inhibition (maximum ISI) and excitation (number of action potentials (AP), minimum ISI). APs were also counted in subdivisions to produce a measure sensitive to MC response temporal patterning. These measures were applied during the rise and fall of olfactory receptor input, indicated by the summed receptor output, the electro-olfactogram (EOG). ISI variables, stable during background activity and well water applications, changed significantly upon AA stimulation. Stimulus concentrations regressed against ISI variables showed increases and decreases during stimulation with increasing concentrations. Regressions fitted to these dose-response curves were nonlinear. Responses to some AA were more reproducible than responses to others. This phenomenon may be part of stimulus intensity representation in catfish OB. In study two, MCs were recorded with OT intact and transected, to isolate the OB from the central nervous system. Bulb isolation was conducted on 6 fish and 36 cells (18 different cells each from intact and isolated bulbs). All cells were stimulated with 5 AA at concentrations from 10$\sp{-5}$ M to 10$\sp{-3}$ M. Response changes following OT transection were increased ISIs and decreased maximum ISI. Three response classes (cluster analysis) of ISI variables from the first 1.5 seconds of the response were: inhibition, excitation and inhibition and excitation in one response. Inhibitory responses were rare after tract transection. Correlations of action potential counts evoked by different AA showed that the bulb cell population discriminated stimuli, but individual cells could not. AA discrimination was reduced after OB isolation, because responses became more alike. These data suggest that stimulus quality and intensity representation in the catfish olfactory system involves a central comparison of MC responses.

Pages

124

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