Brain monoamines in relation to the teleost reproductive cycle

Abstract

The technique of high performance liquid chromatography with electrochemical detection was used to identify, detect and measure monoamines within the central nervous system of the juvenile rainbow trout, Salmo gairdneri, the male landlocked Atlantic salmon, Salmo Salar and male and female winter flounder, Pseudopleuronectes americanus. The catecholamines norepinephrine, dopamine and the indoleamine serotonin were found in the brains of these three teleost species. All three monomines were heavily concentrated in the hypothalamus, with norepinephrine being the most concentrated monomine in this area followed by serotonin and dopamine. Norepinephrine concentrations ranged from a low 0.33 ± 0.07 (± S.E.M.) ng/mg in the rhombencephalon of the juvenile rainbow trout to 2.64 ± 0.24 ng/mg in the hypothalamus of the female winter flounder. Dopamine concentrations ranged from 0.08 ± 0.01 ng/mg in the optic tectum of the juvenile rainbow trout to 2.41 ± 0.14 ng/mg in the hypothalamus of the mature male Atlantic salmon. Serotonin concentrations ranged between 0.24 ± 0.01 ng/mg in extrahypothalamic tissues of the male landlocked Atlantic salmon to 1.13 ± 0.11 ng/mg in the hypothalamus of this same species. -- A breakdown of the data obtained for the mature male landlocked Atlantic salmon and mature male and female winter flounder showed a correspondence of these monoamine concentrations with certain stages of the annual gonadal recrudescence cycle. Norepinephrine and dopamine concentrations declined during spermiation in the male landlocked Atlantic salmon. Norepinephrine concentrations increased in extrahypothalamic tissues of the male winter flounder during advanced spermatogenesis. A separate study was conducted on mature male winter flounder to determine if monoamine concentrations were altered by castration, but there were no significant changes in norepinephrine, dopamine or serotonin concentrations in the central nervous system of castrated males compared with sham-castrated and control males. -- Keywords: monoamines; brain; teleosts; gonadel; recrudescence cycle