Mv. Ugrumov et al., DEVELOPMENT OF THE SUPRACHIASMATIC NUCLEUS IN RATS DURING ONTOGENY - SEROTONIN-IMMUNOPOSITIVE FIBERS, Neuroscience, 58(1), 1994, pp. 161-165
The innervation of the suprachiasmatic nucleus by serotoninergic fiber
s has been studied in rats from the 22nd embryonic until the 21st post
natal day. The serotoninergic fibers were detected with the pre-embedd
ing immunocytochemical technique at the electron-microscopic level usi
ng antibodies to serotonin. Serotonin-immunopositive fibers were alway
s identified as axons as they contained numerous synaptic vesicles bot
h in fetuses and postnatal rats. Moreover, immunopositive dense core v
esicles appeared in the axons after birth. From the end of fetal life
onwards, the serotonin-immunopositive axons made specialized contacts
with the immunonegative neurons, mainly with their dendrites and to a
lesser extent with cell bodies and axons. In fetuses, only immature sy
napses (presynapses) were observed. After birth, presynapses were repl
aced by typical synapses with the thickened pre- and postsynaptic memb
ranes, accumulations of dense materials at the pre- and postsynaptic m
embranes as well as with an accumulation of synaptic vesicles at the p
resynaptic membrane. The functional significance of the serotoninergic
input to the suprachiasmatic nucleus in ontogenesis is discussed.