Jf. Ghersiegea et al., RAPID DISTRIBUTION OF INTRAVENTRICULARLY ADMINISTERED SUCROSE INTO CEREBROSPINAL-FLUID CISTERNS VIA SUBARACHNOID VELAE IN RAT, Neuroscience, 75(4), 1996, pp. 1271-1288
The intracranial distribution of [C-14]sucrose, an extracellular marke
r infused for 30 s into one lateral ventricle, was determined by autor
adiography of frozen-dried brain sections. Within 3.5 min [C-14]sucros
e appeared in: (i) the third ventricle, including optic, infundibular
and mammillary recesses; (ii) the aqueduct of Sylvius; (iii) the velum
interpositum, a part of the subarachnoid space that runs along the ro
of of the third ventricle and contains many blood vessels; (iv) the me
sencephalic and fourth ventricles; and (v) the superior medullary velu
m, a highly vascular extension of the subarachnoid space that terminat
es at the walls of the mesencephalic and fourth ventricles. Within 5 m
in, radioactivity was present in the interpeduncular, ambient and quad
rigeminal cisterns, which encircle the midbrain. By 10 min, approximat
ely 11% of the radioactivity had passed into the subarachnoid space vi
a a previously undescribed flow pathway that included the velum interp
ositum and superior medullary velum. At many places along the ventricu
lar system, [C-14]sucrose appeared to move from cerebrospinal fluid in
to the adjacent tissue by simple diffusion, as reported previously (Bl
asberg R. G. et al. (1974) J. Pharmac. exp. Ther. 195, 73-83; Levin V.
A. et al. (1970) Am. J. Physiol. 219, 1528-1533; Patlak C. and Fenste
rmacher J. D. (1975) Am. J. Physiol. 229, 877-884; Rosenberg G. A. and
Kyner W. T. (1980) Brain Res. 193, 56-66; Rosenberg G. A. et al. (198
6) Am. J. Physiol. 251, F485-F489). Little sucrose was, however, taken
up by: (i) circumventricular organs such as the subfornical organ; (i
i) medullary and cerebellar tissue next to the lateral recesses; and (
iii) the superior and inferior colliculi and cerebral peduncles. For t
he latter two groups of structures, entry from cerebrospinal fluid was
apparently blocked by a thick, multilayered glia limitans. Although [
C-14]sucrose was virtually absent from the rest of the subarachnoid sy
stem after 1 h, it remained in the perivascular spaces and/or walls of
pial arteries and arterioles for more than 3 h. Certain transport pro
teins, protease inhibitors, growth factors and other neurobiologically
active materials are present in cerebrospinal fluid, and their distri
bution to the brain and its blood vessels may be important. The presen
t work shows, in the rat, that the flow of cerebrospinal fluid and the
disposition of its constituents is fairly complex and differs among r
egions. Flow was rapid throughout the ventricular system and into vari
ous subarachnoid velae and cisterns, but was surprisingly slow and sli
ght over the cerebral and cerebellar cortices. The cerebrospinal fluid
-to-tissue flux of material was relatively free at many interfaces, bu
t was greatly restricted at others, the latter indicating that the old
concept of a ''cerebrospinal fluid-brain barrier'' may hold at such p
laces. Finally, radiolabeled sucrose was retained longer within the wa
lls and perivascular spaces of pial arteries and arterioles than in ot
her subarachnoid tissues; one function of the cerebrospinal fluid syst
em or ''third circulation'' may thus be delivering factors and agents
to these pial blood vessels. Copyright (C) 1996 IBRO. Published by Els
evier Science Ltd.