1. ANATOMY AND PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM
9
1965). The pericapillary space ( 100-200 A ) between the endothelial
cells of the blood vessel and neuroglial cell contains basement menibrane. Neurons are not contiguous to endothelial cells of the capillary.
Neuroglial processes lie between blood vessels and neurons ( Mugnaini
and Walberg, 1965). In the shark the two neuroglial types are observed
(Long et al., 1968). Astrocytes are smaller and contain fewer organelles
than neurons. Glial fibrils are often present in the cytoplasm. Oligodendrocytes are smaller than astrocytes, have denser cytoplasm, and possess intensely staining nuclei (Long et al., 1968). These two neuroglial
cell types are also found in bluegills, sand bass, and goldfish (Kruger
and Maxwell, 1967; Robertson, 1963; Robertson et al., 1963). Capillary
walls in the cyclostome (Mugnaini and Walberg, 1965) appear to be
nearly completely invested with astrocyte processes. In the teleost and
shark this investment may be partially derived from ependymal cells
(Kruger and Maxwell, 1967; Long et al., 1968).
The processes of ependymal cells of fish can extend from the ventricular to the pial surface of the brain and generally maintain an
orientation perpendicular to the pial surface. The smooth endoplasmic
reticulum of ependymal cells of the sand bass, Paralabrax nebulifer, is
organized into discoid clusters of membrane at irregular intervals across
the long axes of the processes (Kruger and Maxwell, 1966). The ependymal cell processes generally contain irregularly scattered small densecore vesicles resembling secretory Sranules. Zona occludens ( tight junctions) are numerous at the subpial ependymal end-foot contacts and
appear to intermix with and contact with glial processes. Ependymal and
glial end-feet comprise the subpial specialization in teleosts (Kruger and
Maxwell, 1967). The extensive distribution of vacuoles in the subpial
processes may reflect transport in the direction of exchange of materials
with the subarachnoid space ( Rahmann, 1968). The extensive distribution of glycogen and the occasional contacts with capillary walls suggests that ependyma may parallel some of the functional properties of
astrocytes which are the principal perivascular and glycogen-laden
elements in mammalian brain (Kruger and Maxwell, 1966). Ependymal
cells possess cilia and microvilli that extend into the ventricles and spinal
canals (Schultz et al., 1956). The most remarkable morphological feature of teleost ependymal cells is the evidence for a specialized metabolic role for ependyma because of the large quantities of glycogen and
mitochondria of unusual size, Ependymal cells of the teleost brain appear
to be pluripotential, retaining the embryonic capacity to dedifferentiate
and redifferentiate into spongio- ( glial precursors ) and neuroblasts
( neuronal precursors) ( Kirsche, 1967; Fridberg et al., 1966).
9
1965). The pericapillary space ( 100-200 A ) between the endothelial
cells of the blood vessel and neuroglial cell contains basement menibrane. Neurons are not contiguous to endothelial cells of the capillary.
Neuroglial processes lie between blood vessels and neurons ( Mugnaini
and Walberg, 1965). In the shark the two neuroglial types are observed
(Long et al., 1968). Astrocytes are smaller and contain fewer organelles
than neurons. Glial fibrils are often present in the cytoplasm. Oligodendrocytes are smaller than astrocytes, have denser cytoplasm, and possess intensely staining nuclei (Long et al., 1968). These two neuroglial
cell types are also found in bluegills, sand bass, and goldfish (Kruger
and Maxwell, 1967; Robertson, 1963; Robertson et al., 1963). Capillary
walls in the cyclostome (Mugnaini and Walberg, 1965) appear to be
nearly completely invested with astrocyte processes. In the teleost and
shark this investment may be partially derived from ependymal cells
(Kruger and Maxwell, 1967; Long et al., 1968).
The processes of ependymal cells of fish can extend from the ventricular to the pial surface of the brain and generally maintain an
orientation perpendicular to the pial surface. The smooth endoplasmic
reticulum of ependymal cells of the sand bass, Paralabrax nebulifer, is
organized into discoid clusters of membrane at irregular intervals across
the long axes of the processes (Kruger and Maxwell, 1966). The ependymal cell processes generally contain irregularly scattered small densecore vesicles resembling secretory Sranules. Zona occludens ( tight junctions) are numerous at the subpial ependymal end-foot contacts and
appear to intermix with and contact with glial processes. Ependymal and
glial end-feet comprise the subpial specialization in teleosts (Kruger and
Maxwell, 1967). The extensive distribution of vacuoles in the subpial
processes may reflect transport in the direction of exchange of materials
with the subarachnoid space ( Rahmann, 1968). The extensive distribution of glycogen and the occasional contacts with capillary walls suggests that ependyma may parallel some of the functional properties of
astrocytes which are the principal perivascular and glycogen-laden
elements in mammalian brain (Kruger and Maxwell, 1966). Ependymal
cells possess cilia and microvilli that extend into the ventricles and spinal
canals (Schultz et al., 1956). The most remarkable morphological feature of teleost ependymal cells is the evidence for a specialized metabolic role for ependyma because of the large quantities of glycogen and
mitochondria of unusual size, Ependymal cells of the teleost brain appear
to be pluripotential, retaining the embryonic capacity to dedifferentiate
and redifferentiate into spongio- ( glial precursors ) and neuroblasts
( neuronal precursors) ( Kirsche, 1967; Fridberg et al., 1966).