Introduction

Abstract

The present study was performed to elucidate the mechanism of a rapid nerve cell loss in the nuclei pontis described after mesencephalic lesions in young cats by Torvik (1956). He observed that hemisection of the mesencephalon caused an extensive disintegration of nerve cells in the homolateral nuclei pontis within four days after the operation. After lesions of the caudal part of the mesencephalon a severe neuronal loss was noted also in the inferior olive. Most of the degenerating neurons appeared to pass through a stage of pyknosis and karyorhexis before disintegration, but other types of neuronal change were also described. The changes were considered caused by deafferentation of the pontine nuclei and were regarded as a kind of transneuronal degeneration. During this degeneration an unusual type of glial proliferation was also observed. The nature of the glial proliferation will be dealt with in Part II of this study while the neuronal changes will be studied here.