Plasma and pituitary gonadotropin (GtII) levels, and the gonadotropin releasing hormone (GnRII) in differents areas of the brain, were measured using radioimmunoassays during the prespawning and the spawning period in a wild population of roach (Rutilus rutilus). GtII pituitary levels did not Vary. On the contrary GtII plasma levels showed variations during the prespawning period and were minimum on the day of arriva1 on the spawning areas, Do. During spawning they increased in ovulated females but also in unovulated animals and returned to low values, 1 month after. During this period GnRII varied inversely in al1 brain structures and was always negatively correlated with the blood plasma GtII levels. ï h i s suggests that al1 the brain GnRII would be involved in the control of the GtII secretion during spawning. This was not the case during the prespawning period, during which only hypothalamic and pituitary GnRlI levels were correlated with GtlI. ïhere were also marked variations in the telencephalic GnRII extra hypothalamic GnRII. It is hypothetized that it could be a link between environmental factors and the hypothalamo-pituitary cornplex. Keynords : Gonadotropin, GnRlI, spawning, Rutilus rutilus, female. Ecolution de la gonadotropine plasmatique (Gt l l ) et des contenus en GnRII de dijJérentes aires cérébrales autour de la phiode de fiai dans une population de gardons (Rutilus rutilus) du lac Leman. 1 La Jemelle. Les niveaux de gonadotropine (Gtll) hypophysaires et plasmatiques ainsi que les contenus en "gonadotropin releasing hormone" (GnRI1) de l'hypothalamus et différentes aires cérébrales ont été mesurés par dosage radioimmunologique. L'expérience s'est déroulée pendant la période précédant le frai et durant la période de frai d'une population sauvage de gardons (Rutilus rutilus). Les contenus hypophysaires en GtII ne varient pas, contrairement aux niveaux plasmatiques de cette hormone. dont les concentrations sont toujours les plus faibles le jour du rassemblement sur les aires de frai. Ils augmentent chez les femelles ovulées, mais aussi chez les poissons non ovulés. Pendant le frai les contenus en GnRlI varient en sens inverse de la GtH dans toutes les structures cérébrales et sont corrélis négativement aux niveaux plasmatiques de (3111. On retrouve des variations similaires de la GtII et du GnRII hypophysaire et hypothalamique avant le frai. hlais, durant cette période, bien que les contenus en GnRlI télencephalique montrent des variations importantes, ils ne sont pas correlés aux niveaux de Gtli plasmatique. Ces résultats sont discutés et plus spécialement les rôles éventuels du GnRlI extrahypothalamique. II est fait l'hypothèse d'un rôle de médiation des facteurs de l'environnement par le GnRll télencephalique. Illots-clés : Gonadotropine, GnRII, frai, Rutilus rutilus, femelle. Aquor. Living Resuur. 8R'OZ 93 7 1 2.70,'0 II'RCX1CR-Gauthier-\'illaro
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