48
JERALD J. BERNSTEIN
major class of neurons within the layers of the tectum (layer D; Jacobson
and Gaze, 1965) can possibly be deafferented following optic nerve
regeneration.
These studies demonstrate that there is selective regeneration of nerve
fibers derived from the retina to the original cells of termination within
the optic tectum of fish. The special sensory nerve fibers from the retina
entering the tectum appear to grow directly to the area of previous
innervation and selectively reinnervate the neurons of original termination. The retinotectal map appears to be reestablished except for the
loss of some fibers in a specific area of the optic tectum.
H. Regeneration of the Optic Tectum
The regenerative capacity of the optic tectum in fish has been studied
extensively (Kirsche, 1960, 196513, 1967; Kirsche and Kirsche,
1961; Richter, 1966, 1968). The cells which completely regenerate a
totally ablated optic tectum were derived from matrix zones located in
the ependymal cell zone (lining the third ventricle) of the optic tectum.
There were three matrix zones: a dorsal matrix zone next to the torus
longitudinalis, a caudal matrix zone at the caudal pole of the optic
tectum consisting of groups of undifferentiated and pluripotential cells,
and a basic matrix zone at the base of the tectum. These matrix zones
also act in the development of the optic tectum. During embryological
development, cells which were differentiated from the matrix zone
migrated to the center of the tectum. Thus, the amount of matrix material
(germinative zone) which was available to the animal decreased throughout the animal's life. According to Kirsche (1967) these matrix zones
continually produced cells within the optic tectum. However, the ability
to produce parenchyma was age dependent since as the animal got
older, the matrix zones became thinner until the animal reached an age
when the matrix no longer produced cells for cell renewal. The cells
which were derived were specific for the three matrix zones which have
been mentioned earlier. Extensive unilateral lesions within the optic
tectum of the crucian carp, Carassius carassius, resulted in the complete
restitution of the transected fiber tracts and the neuronal and glial components of the optic tectum. However, if the matrix zones were damaged
by this operation, the optic tectum, even after 300 days of postoperative
recovery, did not show normal cytoarchitectonics. Regeneration did not
occur if the rostra1 portion of the dorsal matrix zone and the caudal
matrix zone were removed. Thus, regeneration only occurred in those
areas where the matrix zone was left intact. After extensive unilateral
JERALD J. BERNSTEIN
major class of neurons within the layers of the tectum (layer D; Jacobson
and Gaze, 1965) can possibly be deafferented following optic nerve
regeneration.
These studies demonstrate that there is selective regeneration of nerve
fibers derived from the retina to the original cells of termination within
the optic tectum of fish. The special sensory nerve fibers from the retina
entering the tectum appear to grow directly to the area of previous
innervation and selectively reinnervate the neurons of original termination. The retinotectal map appears to be reestablished except for the
loss of some fibers in a specific area of the optic tectum.
H. Regeneration of the Optic Tectum
The regenerative capacity of the optic tectum in fish has been studied
extensively (Kirsche, 1960, 196513, 1967; Kirsche and Kirsche,
1961; Richter, 1966, 1968). The cells which completely regenerate a
totally ablated optic tectum were derived from matrix zones located in
the ependymal cell zone (lining the third ventricle) of the optic tectum.
There were three matrix zones: a dorsal matrix zone next to the torus
longitudinalis, a caudal matrix zone at the caudal pole of the optic
tectum consisting of groups of undifferentiated and pluripotential cells,
and a basic matrix zone at the base of the tectum. These matrix zones
also act in the development of the optic tectum. During embryological
development, cells which were differentiated from the matrix zone
migrated to the center of the tectum. Thus, the amount of matrix material
(germinative zone) which was available to the animal decreased throughout the animal's life. According to Kirsche (1967) these matrix zones
continually produced cells within the optic tectum. However, the ability
to produce parenchyma was age dependent since as the animal got
older, the matrix zones became thinner until the animal reached an age
when the matrix no longer produced cells for cell renewal. The cells
which were derived were specific for the three matrix zones which have
been mentioned earlier. Extensive unilateral lesions within the optic
tectum of the crucian carp, Carassius carassius, resulted in the complete
restitution of the transected fiber tracts and the neuronal and glial components of the optic tectum. However, if the matrix zones were damaged
by this operation, the optic tectum, even after 300 days of postoperative
recovery, did not show normal cytoarchitectonics. Regeneration did not
occur if the rostra1 portion of the dorsal matrix zone and the caudal
matrix zone were removed. Thus, regeneration only occurred in those
areas where the matrix zone was left intact. After extensive unilateral