Dynamic response properties of broad spectrum olfactory interneurons in the crayfish midbrain

Intracellular electrodes were used to record electrical activity from interneurons within the olfactory midbrain of the freshwater crayfish, Procambarus clarkii, in isolated, perfused head preparations. Three classes of interneuron were identified on the basis of physiological responses to odors applied to the antennules and on cellular morphology. All of the cell types responded to a broad spectrum of odors, including individual amino acids, sugars, and complex mixtures of compounds. Type I cells responded to odors in monotonic, dose dependent manner with excitatory postsynaptic responses and impulse trains. Type II cell responded to the same group of stimuli with predominant inhibitory postsynaptic potentials. Type III cells responded non-monotonically to increasing odor concentrations, generating optimal impulse numbers and frequencies following relatively brief, low intensity exposures. It is suggested that these large multiglomerular interneurons participate in arousal behaviors rather than contributing to the neuronal circuitry used to identify specific odors or odor mixtures.