Olfactory transduction is thought to be mediated by a G protein-coupled increase in intracellular adenosine 3',5'-monophosphate (cAMP) that triggers the opening of cAMP-gated cation channels and results in depolarization of the plasma membrane of olfactory neurons. In olfactory neurons isolated from the channel catfish, Ictalurus punctatus, stimulation with olfactory stimuli (amino acids) elicits an influx of calcium that leads to a rapid increase in intracellular calcium. In addition, in a reconstitution assay a plasma membrane calcium channel has been identified that is gated by inositol-1,4,5-trisphosphate (IP3), which could mediate this calcium influx. Together with previous studies indicating that stimulation with olfactory stimuli leads to stimulation of phosphoinositide turnover in olfactory cilia, these data suggest that an influx of calcium triggered by odor stimulation of phosphoinositide turnover may be an alternate or additional mechanism of olfactory transduction.

https://science.sciencemag.org/content/sci/249/4973/1166.full.pdf

Odor stimuli trigger influx of calcium into olfactory neurons of the channel catfish.

Introduction Ollaetion Morphological basis an overview Peripheral olfactory organ Central projections Registration of olfactory activities Electroolfactogram (EOG) ExtraceUular recordings of action potentials Electroencephalogram (EEG) Cross-adaptation Responses to chemical stimuli Amino acids Steroid hormones Bile salts Prostaglandins (PGs) Other compounds Gustation Morphological basis an overview Taste buds Gustatory nerves and central projections Recordings of gustatory responses Responses to chemical stimuli Amino acids Carboxylic acids Nucleotides Bile salts CO2 and pH Toxins and other compounds Future prospects and research needs Summary and conclusions Olfaction Gustation Acknowledgements References

The diversity of chemical stimulation in fish olfaction and gustation

1.

Peripheral olfactory and gustatory responses of the channel catfishIctalurus punctatus to amino acids and derivatives have been studied using extracellular electrophysiological recording techniques.




2.

Amino acids are highly effective stimuli for both chemosensory systems with taste more sensitive than smell. Threshold for L-alanine, the most effective gustatory stimulus tested, averaged 10−11.5±1.7 M, the lowest electrophysiological threshold reported for taste in any vertebrate. Threshold for L-cysteine, the most effective olfactory stimulus tested, averaged 10−8.8±0.8 M. In both systems the L-isomer of anα-amino acid was always more stimulatory than its enantiomer.




3.

Averaged olfactory and gustatory neural activity or underwater electro-olfactogram (EOG) recordings increased exponentially with logarithmic increase of stimulus concentration from threshold to 10−2M (Figs. 1, 2, 5).




4.

The olfactory receptors were highly responsive to amino acids containing 5 to 6 carbon atoms having unbranched (Table 2) and uncharged (Table 3) side chains; a major exception was the large response to the 3 carbon amino acid L-cysteine.




5.

The gustatory receptors were highly responsive to amino acids containing 3 to 4 carbon atoms having unbranched and uncharged side chains; a major exception was the large response to L-arginine, a 6-carbon positively charged amino acid (Table 5).




6.

Esterification of the primary carboxyl group of particular amino acids resulted without loss of stimulatory activity indicating for these cases an ionically charged carboxyl group is unnecessary for receptor response (Tables 4, 5).




7.

The molecular requirements of the amino acid receptor sites for olfaction and taste in the channel catfish appear to be similar in part to those described for other amino acid chemoreceptive system, in bacteria fish and animal.

Olfaction and taste in the channel catfish: An electrophysiological study of the responses to amino acids and derivatives

The characteristics of the electro-olfactogram (EOG): its loss and recovery following olfactory nerve section in rainbow trout (Salmo gairdneri).

Extracellular electrophysiological recordings from single olfactory bulb (OB) neurons in the channel catfish, Ictalurus punctatus, indicated that the OB is divided into different functional zones, ...

Electrophysiological Evidence for a Chemotopy of Biologically Relevant Odors in the Olfactory Bulb of the Channel Catfish

Recording the olfactory receptor activity of marine fishes presents problems due to the shunting of the electrical signals by the highly conductive sea water, which results in significant signal loss. By recording the large signal-to-noise ratio D. C. potentials using the underwater electro-olfactogram (EOG), we were able to study olfactory receptor properties of freshwater and marine fishes in a comparable manner.

W. L. Silver

Papers

The underwater electro-olfactogram: a tool for the study of the sense of smell of marine fishes.