THE DEVELOPMENT OF THE SEROTONERGIC FIBER NETWORK OF THE LATERAL VENTRICLES OF THE RAT-BRAIN - A LIGHT AND ELECTRON-MICROSCOPIC IMMUNOCYTOCHEMICAL ANALYSIS
A. Dinopoulos et I. Dori, THE DEVELOPMENT OF THE SEROTONERGIC FIBER NETWORK OF THE LATERAL VENTRICLES OF THE RAT-BRAIN - A LIGHT AND ELECTRON-MICROSCOPIC IMMUNOCYTOCHEMICAL ANALYSIS, Experimental neurology, 133(1), 1995, pp. 73-84
The development of the serotonergic innervation of the lateral ventric
les of the rat brain during the first five postnatal weeks was studied
with immunocytochemical techniques at the light and electron microsco
pic levels. In the lateral ventricles of newborn rats serotonergic fib
ers are only rarely seen. During the first postnatal week the number o
f serotonergic fibers increases but they are straight and thick, beari
ng only a few varicosities. By the end of the second postnatal week, h
owever, they become finer, exhibit a large number of varicosities, and
form a dense supraependymal network. During the following weeks this
network becomes slightly denser but the morphology of fibers as well a
s their distribution pattern remain unchanged. Examination of sagittal
vibratome sections revealed that a group of serotonergic fibers leave
s the medial forebrain bundle and turning dorsocaudally between the co
rpus callosum and the caudate/putamen enter the lateral ventricle from
its rostral pole. They then spread to form the supraependymal network
of the lateral ventricles and probably of the rest of the ventricular
system. Ultrastructural analysis showed that serotonin varicosities a
re located close to the ventricular surface of the ependymal lining bu
t never make synapses with the ependymal cells. Examination of a large
number of labeled fibers and varicosities showed that they are never
located between the ependymal cells or in the subependymal layer. This
finding was confirmed by examining series of semithin sections. On th
e basis of these and previous findings we suggest that serotonergic fi
bers arising in the midbrain raphe nuclei enter the lateral ventricle
from its rostral pole, form a dense network within the ventricles, and
release their content into the cerebrospinal fluid. This system, as j
udged with morphological criteria, matures by the end of the second po
stnatal week. (C) 1995 Academic Press, Inc.