Polyamines as olfactory stimuli in the goldfish Carassius auratus

Electrophysiological responses of goldfish olfactory receptor neurons (ORNs) and goldfish behavioral responses to polyamines were investigated in vivo. Electro-olfactogram (EOG) recordings indicated that polyamines (putrescine, cadaverine and spermine) are potent olfactory stimuli for goldfish with estimated electrophysiological thresholds of 10^-8-10^-7 mol l^-1, similar to that for L-arginine, the most stimulatory amino acid. Although thresholds were similar, the magnitude of the EOG responses to intermediate (10^-5-10^-4 mol l^-1) and high (10^-3 mol l^-1) concentrations of polyamines dwarfed the responses to amino acids and related single amine containing compounds (amylamine and butylamine). The EOG responses to 0.1 mmol l^-1 putrescine, cadaverine and spermine were, respectively, 4.2x, 4.3x and 10.3x the response of the standard, 0.1 mmol l^-1 L-arginine. Electrophysiological cross-adaptation experiments indicated that polyamine receptor sites are independent from those to L-amino acids (alanine, arginine, glutamate, lysine, methionine and ornithine), bile salts (sodium taurocholate and taurolithocholate), the single amine containing compounds (amylamine and butylamine) and ATP. Further, the cross-adaptation experiments revealed the existence of independent receptor sites for the different polyamines tested. Pharmacological experiments suggested that polyamine odorant transduction does not primarily involve the cyclic AMP and IP₃ second messenger pathways. Behavioral assays indicated that polyamines are attractants that elicit feeding behavior similar to that elicited by L-amino acids.