Chem. Senses 28: 207-218,
2003
© Oxford University Press 2003
Olfactory Sensitivity to Catecholamines and their Metabolites in the Goldfish
1 Centro de Ciências do Mar, Universidade do Algarve, Campus de Gambelas, 8000-810 Faro 2 Departamento de Biologia, Universidade de Évora, Apartado 94, 7001 Évora Codex, Portugal
Correspondence to be sent to: Peter Hubbbard, Centro de Ciências do Mar, Universidade do Algarve, Campus de Gambelas, 8000-810 Faro, Portugal. e-mail: phubbard{at}ualg.pt
The current study assessed the olfactory sensitivity of the goldfish
(Carassius auratus L.) to the catecholamines, their immediate
precursors and metabolites by use of the electro-olfactogram (EOG). The
olfactory system of the goldfish was found to be sensitive to both adrenaline
and dopamine with thresholds of detection of 10-7.8 and
10-7.9 M respectively, but less so to noradrenaline (threshold of
detection 10-6.3 M). The 3-O-methoxy metabolites
(metadrenaline, normetadrenaline and 3-O-methoxytyramine) evoked
larger amplitude EOGs than the non-metabolized form with lower thresholds of
detection. However, the olfactory system was less sensitive to the amino acid
precursors L-tyrosine and L-DOPA, and markedly less so
to the 
-deaminated metabolites (3,4-dihydroxyphenyl glycol,
3,4-dihydroxy mandelic acid and dihydroxyphenyacetic acid). Sensitivity to
metabolites, both -deaminated and 3-O-methoxylated, was
similar to the -deaminated forms. Cross-adaptation studies suggested
that, while there is some degree of commonality of the receptor mechanisms
with L-tyrosine and L-serine, a proportion of the
response to the catecholamines is due to distinct receptor subtypes.
Similarly, the 3-O-methoxy metabolites also had (a) separate receptor
mechanism(s), although, again, there was overlap with the adrenaline/dopamine
receptor site(s). Presence of the -adrenoreceptor antagonist prazosin
or the peripheral DA2 dopamine receptor antagonist domperidone
caused partial attenuation of the EOG responses to adrenaline and dopamine,
but had much less effect on the responses to their 3-O-methoxy
metabolites. The ß-adrenoreceptor antagonist sotalol had no such effect.
This suggests that the olfactory catecholamine receptors are structurally and
functionally distinct from systemic adreno- and dopamine receptors. The
current study raises the possibility that release of catecholamines or their
3-O-methoxy metabolites to the water may play a role in chemical
communication.
Key words: adrenaline, dopamine, electro-olfactogram (EOG), metabolites, teleost
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