1. ANATOMY AND PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM
25
tract appears to regenerate completely in the carp, Cyprinus carpio
( Westerman, 1965; Westerman and von Baumgarten, 1964). Sectioning
of the olfactory tract resulted in regeneration of the axons from the
olfactory bulb. Thc regenerated axons appeared to selectively reinnervate lower centers in the telencephalon. After regeneration of the olfactory crura, a previously acquired conditioned response to olfactory
stimuli was reestablished and operated animals responded appropriately
upon subsequent testing with no retraining.
In Lebistes reticulatus, the guppy, a complete telencephalon was
regenerated within 60-120 days following complete extirpation ( March,
1963). There appeared to be no difference in the size or shape of the
telencephalon in regenerates and normal animals. Segaar found that,
excluding lesions of the rostra1 telencephalon which did not regenerate,
selected portions of the telencephalon of the stickleback were reconstituted following ablation ( Segaar, 1965; Scgaar and Nieuwenhuys, 1963).
Regeneration appeared to start from the ependymal layer of the telencephalon. This ependymal layer has been demonstrated to be a matrix
zone for the regeneration of the optic tectum and telencephalon (Kirsche,
1965a,b, 1967). New neurons and nerve fibers were developed within the
reconstituted telencephalic hemisphere ( Segaar, 1965). The reconstituted neural units are arranged in the same cytoarchitecture as found in
normal animals. This return of normal cytoarchitectonics was concomitant with the return of normal courtship patterns (Segaar, 1965).
In contrast, the telencephalon of goldfish does not reconstitute
ablated areas although tracts do regenerate ( Bernstein, 1967). In a series
of operations such as either bilateral or unilateral ablation, removal of
only the lateral portion of the hemisphere, or stab wounds in the hemisphere, it was found that the parenchyma of the goldfish telencephalon
did not reconstitute the ablated mass. Following stab wounds, necrotic
areas were replaced by neuroglial and ependymal cells. Although the mass
of the telencephalon of goldfish was not reconstituted, new neurons were
derived from the ependymal cells lining the common ventricle (Bernstein and Sadlack, 1969). Goldfish were injected with tritiated thymidine
following unilateral telencephalic lesions. Neurons were found with
reduced silver grains (by autoradiography ) on the &16 postopcrative
day. However, there werc few new neurons formed and the
numbers of total cells (glial, ependymal, and neurons) dividing was
low and divisions ceased by the sixteenth postoperative day. The number
of total new cells formed were not adequate to reconstitute the ablated
telencephalic parenchyma ( Bernstein and Sadlack, 1969). Regeneration
of the telencephalon is species and age specific in the fish. The nervous
system of different species of fish appears to mature at differing rates.
25
tract appears to regenerate completely in the carp, Cyprinus carpio
( Westerman, 1965; Westerman and von Baumgarten, 1964). Sectioning
of the olfactory tract resulted in regeneration of the axons from the
olfactory bulb. Thc regenerated axons appeared to selectively reinnervate lower centers in the telencephalon. After regeneration of the olfactory crura, a previously acquired conditioned response to olfactory
stimuli was reestablished and operated animals responded appropriately
upon subsequent testing with no retraining.
In Lebistes reticulatus, the guppy, a complete telencephalon was
regenerated within 60-120 days following complete extirpation ( March,
1963). There appeared to be no difference in the size or shape of the
telencephalon in regenerates and normal animals. Segaar found that,
excluding lesions of the rostra1 telencephalon which did not regenerate,
selected portions of the telencephalon of the stickleback were reconstituted following ablation ( Segaar, 1965; Scgaar and Nieuwenhuys, 1963).
Regeneration appeared to start from the ependymal layer of the telencephalon. This ependymal layer has been demonstrated to be a matrix
zone for the regeneration of the optic tectum and telencephalon (Kirsche,
1965a,b, 1967). New neurons and nerve fibers were developed within the
reconstituted telencephalic hemisphere ( Segaar, 1965). The reconstituted neural units are arranged in the same cytoarchitecture as found in
normal animals. This return of normal cytoarchitectonics was concomitant with the return of normal courtship patterns (Segaar, 1965).
In contrast, the telencephalon of goldfish does not reconstitute
ablated areas although tracts do regenerate ( Bernstein, 1967). In a series
of operations such as either bilateral or unilateral ablation, removal of
only the lateral portion of the hemisphere, or stab wounds in the hemisphere, it was found that the parenchyma of the goldfish telencephalon
did not reconstitute the ablated mass. Following stab wounds, necrotic
areas were replaced by neuroglial and ependymal cells. Although the mass
of the telencephalon of goldfish was not reconstituted, new neurons were
derived from the ependymal cells lining the common ventricle (Bernstein and Sadlack, 1969). Goldfish were injected with tritiated thymidine
following unilateral telencephalic lesions. Neurons were found with
reduced silver grains (by autoradiography ) on the &16 postopcrative
day. However, there werc few new neurons formed and the
numbers of total cells (glial, ependymal, and neurons) dividing was
low and divisions ceased by the sixteenth postoperative day. The number
of total new cells formed were not adequate to reconstitute the ablated
telencephalic parenchyma ( Bernstein and Sadlack, 1969). Regeneration
of the telencephalon is species and age specific in the fish. The nervous
system of different species of fish appears to mature at differing rates.