Polyamines as olfactory stimuli in the goldfish Carassius auratus

Abstract

SUMMARY 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,4.2×, 4.3× and 10.3× 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.