T4 depresses olfactory responses to l-alanine, plasma t3, and t4
outer-ring deiodination in smoltifying atlantic salmon.
Morin, P. P., T. J. Hara, and J. G. Eales.
Department of Zoology, University of Manitoba, Winnipeg, Manitoba,
Canada, R3T 2N, Department of Fisheries and Oceans, Freshwater
Institute, Winnipeg, Manitoba, R3T 2N6
APStracts 2:0222R, 1995.
During natural or induced smoltification Atlantic salmon exhibit
spring elevations in olfactory activity and plasma L-thyroxine (T4).
To determine if T4 influences olfactory activity, we administered T4
to late parr in early April and measured olfactory bulb electro
-encephalogram (EEG) and olfactory epithelium electro-olfactorogram
(EOG) responses to L-alanine nasal stimulation, plasma T4 and 3,5,3'
-triiodo-L-thyronine (T3) levels, and hepatic and brain
monodeiodination. T4 treatment raised plasma T4 to 15 ng/ml,
simulating the smolt T4 surge, and depressed plasma T3 and EEG
responses, without modifying EOG responses. Decreased plasma T3 may
be explained by inhibition of hepatic T4 outer-ring deiodination
generating T3, and stimulation of inner-ring deiodination degrading
T4 and T3. Brain T4 outer-ring deiodination was also strongly
inhibited. In conclusion, creation of a high plasma T4 concentration
simulating the natural smolt peak depressed olfactory bulb responses
to L-alanine, due to either the high T4 concentration or the
depressed T3 availability in brain induced by T4. T4 may terminate
the period of heightened olfactory responsiveness during
smoltification.
Received 16 June 1994; accepted in final form 6 July 1995.
APS Manuscript Number R332-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 August 1995.