DEVELOPMENTAL-CHANGES IN THE CONTENT OF DOPAMINE IN THE OLFACTORY-BULB OF THE EUROPEAN EEL (ANGUILLA-ANGUILLA)

The concentrations of dopamine (DA) and of its major metabolite, dihyd roxyphenylacetic acid (DOPAC), were measured in discrete areas of the eel brain. To investigate the developmental changes in the content of DA and DOPAC, the assays were performed in yellow eels (i.e. at the fe eding stage) and silver eels (i.e. at the migratory stage). DA and DOP AC were unevenly distributed in the eel brain. In yellow eels, the con centration of DA was highest (16-19 pmol/mg protein) in the olfactory bulb (OB), mesencephalic tectum-diencephalon (MT-D) and medulla oblong ata (MO) and lowest in the cerebellum (CB, 1 pmol/mg protein), whereas intermediate values were measured in the telencephalon (TE; 10 pmol/m g protein). The metabolic rate of DA, as reflected by the DOPAC/DA rat io, was highest in the OB and CB, with progressively smaller values be ing observed in the TE, MT-D, and MO. A significant increase in the co ncentrations of DA (+80%) and DOPAC (+122%) was observed in the OB of silver eels compared with yellow eels, whereas no significant differen ces were detected in the concentrations of DA and DOPAC in the other b rain areas as a function of the developmental stage. The results are d iscussed in terms of the possible involvement of environmental, behavi oral and developmental factors.