Dolores M. Schroeder

Connections of the Nurse Shark's Telencephalon

The extrinsic connections of the telencephalon of the nurse shark are very largely crossed and in this respect differ from those identified in all other vertebrate species so far examined. Studies with Nauta and Fink-Heimer methods have revealed telencephalic projections to the contralateral thalamus and optic tectum as well as to ipsilateral brainstem and rostral spinal cord.

A comparison of dorsal column nuclei and spinal afferents in the European hedgehog (Erinaceus europeaus)

Abstract Lesions were made in the dorsal column nuclei of 19 hedgehogs, Erinaceus curopaeus . Lateral cervical hemisections (dorsal, lateral, and ventral funiculi on one side) were performed in an additional six. Nauta and Fink-Heimer staining techniques were utilized to follow fiber and terminal bouton degeneration. The dorsal column nuclei were found to have connections with the inferior olive, mesencephalic reticular formation, external nucleus of the inferior colliculus, medial pretectal nucleus, zona incerta, ventral nucleus of the lateral geniculate body, ventroposterior nucleus, and posterior complex of the thalamus. The spinal hemisections resulted in heavy degeneration in brain stem and mesencephalon but little in the thalamus. The impressively heavy termination of dorsal column fibers in PO, when contrasted with the meager projection of the rest of the cord, suggests that the VP-PO complex developed under the influence of the dorsal columns.

Nonolfactory Telencephalic Afferents in the Nurse Shark (Ginglymostoma cirratum); pp. 121–138

The nonolfactory afferents to the telencephalon of the nurse shark were determined by tracking ascending degenerating fibers with silver impregnation techniques. Of the three ascending fiber bundles, the largest tract is entirely crossed and terminates in a central telencephalic nucleus. The smaller ipsilateral tract ascends laterally and terminates predominantly in the same cell group, but a few reach a more lateral region. The third group of ascending fibers is in the ventromedial bundle, and they terminate in basal areas primarily ipsilaterally but have a small contralateral component. At least a portion of the latter originate from levels caudal to the diencephalon. It can be concluded that the telencephalon of sharks is not entirely an olfactory structure but has similarities to mammalian thalamotelencephalic organization.

A General Overview of Major Interspecific Variations in Thalamic Organization; pp. 101–111

Three hypotheses have been elaborated based upon the examination of afferent projections to the diencephalon of six vertebrate classes: the first, that the target diencephalic areas should be consider