Journal of Neuroscience, Vol 5, 117-127, Copyright © 1985 by Society for Neuroscience
Embryonic development of glial cells and their junctions in the locust central nervous system
LS Swales and NJ Lane
The embryonic development of the specialized glial cells that form the
perineurial blood-brain barrier in the locust CNS has been studied by
freeze-fracture and tracer uptake. These cells migrate to form bracelet
cell arrangements around the nervous tissues between day 4 to day 10 of
embryonic differentiation which lasts 14 days in toto. A number of
different kinds of intercellular junction form between the bracelet cells
from day 8 to day 13 of development. These include gap junctions with
features characteristic of arthropods, which seem to assemble by lateral
migration of 13-nm E face intramembranous particles (IMPs), which
ultimately cluster to form a large number of mature plaques of varying
diameters. Less numerous are tight junctions which serve to restrict entry
of exogenous molecules, including lanthanum and cationic ferritin, thereby
forming the blood-brain barrier; these appear to assemble by migration of
individual 8- to 10-nm P face IMPs into ridges which are found between the
overlapping fingers of the perineurial bracelet cell processes. Septate
junctions also mature at this stage in embryonic development by apparent
assembly of IMPs into characteristic aligned rows; these may serve to slow
down the entry of positively charged molecules as well as being adhesive,
although anionic ferritin may leak into the CNS even after septate and
tight junction formation. The observed changes in cellular associations and
the formation of the blood-brain barrier coincide with the onset of mature
neuronal electrical properties and spontaneous synaptic input.