1. ANATOMY AND PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM
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The relationship between the age and the regenerative capacity of
the goldfish spinal cord has been determined. In the goldfish the ability
of the animal to reconstitute the spinal cord following complete transection was in relation to the age of the animal (Bernstein, 1964). Young
animals (less than 1 year) were able to reconstitute almost 90% of the
available axons whereas approximately 60% of the axons were reconstituted in 2- and 3-year-old animals. The ability of the glia to regenerate
and reconstitute the diameter of the spinal cord was also related to the
age of the animal, the younger animals reconstituting the diameter of
the spinal cord almost completely (Bernstein, 1964). In some species of
teleosts (Kirsche, 1965b), transection of the spinal cord resulted in the
formation of new neurons derived from ependymal cells. The axons of
the regenerating neurons grew along glial bridges and aided in the
rcconstitution of the former zone of the lesion ( Kirsche, 1965b).
Not only was the spinal cord reconstituted with the formation of new
neurons and glia but the physiological capacity of the spinal cord also
appeared to be reestablished after regrowth of the neurites (Bernstein,
1%4; Kirsche, 1965b). Therefore, there appears to be respecification of
the regenerating axons in the spinal cord which was similar to the regeneration of the optic nerve ( Attardi and Spcrry, 1963; Sperry, 1963, 1965).
One of the interesting aspects of spinal cord regeneration can be
found in the lack of effect of a glial ependymal scar upon the regeneration of the spinal cord of the fish (Bernstein and Bernstein, 1967).
Although the glial ependymal scar appears to be a barrier in regeneration of the mammalian spinal cord, regenerating intramedullary axons
in fish grew through this alleged mechanical barrier. However, if the
spinal cord was arrested (by Teflon) in its growth for 30 days or more,
the severed axons no longer retained the capacity to regrow into the
area of the lesion (Bernstein and Bernstein, 1967). The mechanism for
the cessation of growth has been found to be a special case of contact
inhibition with the regrowing neurites forming foreign synaptic contacts just proximal to the glial scar (Bernstein and Bemstein, 1968).
Not only did the spinal cord of teleost fish regenerate after being
severed but also one could find the complete reconstitution of areas of
spinal cord following ablation. This typc of growth pattern was found
in the regeneration of the caudal neurosecretory system of Tilapia after
removal of the caudal peduncle, tail fin, and caudal spinal cord segments
(Fridberg et al., 1966; Fridberg and Nishiokn, 1966; Imai, 1965). After
extirpation of the entire caudal neurosecretory system of TiZapia, the
entire system was reconstituted (Fridberg et al., 1966). The first elementary neurosecretory granules were found in the perikaryon by the
eleventh day of regeneration. These neurosecretory neurons were derived
75
The relationship between the age and the regenerative capacity of
the goldfish spinal cord has been determined. In the goldfish the ability
of the animal to reconstitute the spinal cord following complete transection was in relation to the age of the animal (Bernstein, 1964). Young
animals (less than 1 year) were able to reconstitute almost 90% of the
available axons whereas approximately 60% of the axons were reconstituted in 2- and 3-year-old animals. The ability of the glia to regenerate
and reconstitute the diameter of the spinal cord was also related to the
age of the animal, the younger animals reconstituting the diameter of
the spinal cord almost completely (Bernstein, 1964). In some species of
teleosts (Kirsche, 1965b), transection of the spinal cord resulted in the
formation of new neurons derived from ependymal cells. The axons of
the regenerating neurons grew along glial bridges and aided in the
rcconstitution of the former zone of the lesion ( Kirsche, 1965b).
Not only was the spinal cord reconstituted with the formation of new
neurons and glia but the physiological capacity of the spinal cord also
appeared to be reestablished after regrowth of the neurites (Bernstein,
1%4; Kirsche, 1965b). Therefore, there appears to be respecification of
the regenerating axons in the spinal cord which was similar to the regeneration of the optic nerve ( Attardi and Spcrry, 1963; Sperry, 1963, 1965).
One of the interesting aspects of spinal cord regeneration can be
found in the lack of effect of a glial ependymal scar upon the regeneration of the spinal cord of the fish (Bernstein and Bernstein, 1967).
Although the glial ependymal scar appears to be a barrier in regeneration of the mammalian spinal cord, regenerating intramedullary axons
in fish grew through this alleged mechanical barrier. However, if the
spinal cord was arrested (by Teflon) in its growth for 30 days or more,
the severed axons no longer retained the capacity to regrow into the
area of the lesion (Bernstein and Bernstein, 1967). The mechanism for
the cessation of growth has been found to be a special case of contact
inhibition with the regrowing neurites forming foreign synaptic contacts just proximal to the glial scar (Bernstein and Bemstein, 1968).
Not only did the spinal cord of teleost fish regenerate after being
severed but also one could find the complete reconstitution of areas of
spinal cord following ablation. This typc of growth pattern was found
in the regeneration of the caudal neurosecretory system of Tilapia after
removal of the caudal peduncle, tail fin, and caudal spinal cord segments
(Fridberg et al., 1966; Fridberg and Nishiokn, 1966; Imai, 1965). After
extirpation of the entire caudal neurosecretory system of TiZapia, the
entire system was reconstituted (Fridberg et al., 1966). The first elementary neurosecretory granules were found in the perikaryon by the
eleventh day of regeneration. These neurosecretory neurons were derived