| Summary: | The effects of polyamines as odorants to goldfish olfactory receptors were investigated by in vivo electrophysiological recordings. Electro-olfactogram (EOG) recordings indicated that polyamines (putrescine, cadaverine and spermine) are potent olfactory stimuli for goldfish with estimated electrophysiological thresholds of 10-100nM, similar to that for L-arginine, the most stimulatory amino acid. Although thresholds were similar, the magnitude of the EOG responses to intermediate and high concentrations of polyamines dwarfed those to amino acids and single amine containing compounds (amylamine and butylamine). The EOG responses to 0.1mM putrescine, cadaverine and spermine were, respectively, 4.2x, 4.3x and 10.3x that of the standard, 0.1mM L-arginine. Electrophysiological cross-adaptation experiments indicated the independence of polyamine receptor sites from those to L-amino acids (arginine, methionine, alanine, glutamate, lysine and ornithine), bile salts (Na+ taurocholate and taurolithocholate), single amine containing compounds, and ATP. Further, cross-adaptation experiments indicated that independent receptors exist for the different polyamines tested. During continuous application of forskolin (5-20micromolar), an adenylate cyclase activator, EOG responses to bile salts were eliminated, while responses to L-amino acids, polyamines and ATP were only partially attenuated. These results suggest that polyamine odorants, in contrast to bile salt, L-amino acid and nucleotide odorants are transduced by a non-cAMP second messenger pathway. Although polyamines result in large EOG responses, olfactory receptor neurons responding excitedly to polyamines are likely few in number, because polyamine application to the olfactory mucosa failed to increase integrated multi-unit activity recorded from the sensory surfaces of olfactory lamellae. Preliminary data suggest that olfactory bulb neurons that respond excitedly to L-amino acids are inhibited by polyamines. The present results indicate polyamines are potent odorants to goldfish, distinct from L-amino acids, bile salts and nucleotides.
|
|---|
