Serotonin uptake and release mechanisms in developing cultures of rat embryonic raphe neurons: Age- and region-specific differences

The development ol serotonergic neurons of the rat raphe was followed in pr imary neuronal cell cultures taken at embryonic days embryonic day 13 and e mbryonic day 14 from three different raphe sub-groups, topographically defi ned with respect to their position to the isthmus as rostral (R1), intermed iate (R2) and caudal (R3). In neurons cultivated from embryonic day 13 raph e serotonin, immunoreactivity was detected after only two days in vitro in the rostral R1 and the intermediate R2 sub-groups. Within two weeks of cult ivation the number of serotonergic neurons as well as the dendritic branchi ng continuously increased in all three sub-groups. In cultures obtained fro m embryonic day 13 raphe a specific uptake of [H-3]serotonin could not be d etected during the first days in vitro. Specific uptake as well as regulate d serotonin release, however, was clearly discernible in these cultures aft er nine days in vitro, indicating developmental differentiation of the init ially immature serotonergic neurons in culture. In contrast, serotonergic n eurons obtained from the three raphe: sub-groups at embryonic day 13 took u p and released [H-3]serotonin, as early as after two days in culture. Basal as well as stimulated serotonin release was diminished when preincubating the cells with tetanus toxin, which cleaves synaptobrevin thereby blocking exocytosis, Our data indicate that the differential development of serotonergic neurons in the various raphe sub-groups in vivo is also sustained in culture. The differences observed when comparing neurons from embryonic days 13 and 14 s uggest that a short time-period of about 24 h appears to be crucial for the developmental upregulation of serotonin uptake, storage and release. (C) 2 000 IBRO. Published by Elsevier Science Ltd. All rights reserved.