Showing papers in "Journal of Anatomy in 1962"

Electron microscopy of experimental degeneration in the avian optic tectum.

Abstract: One of the major problems of electron microscopy of the central nervous system is to locate with precision the region involved in the degenerative process in grey or white matter. For this reason, the avian optic tectum was chosen to studythe effects of degeneration of axons and their terminals. Axon section is accomplished simply by unilateral removal of the eye so that the optic nerve afferent fibres to the contralateral hemisphere undergo degeneration (Evans & Hamlyn, 1956). Their trunks are easily located by electron microscopy since they enter the tectum as a superficial layer of myelinated fibres and the terminal ramifications and presynaptic processes are also easily located by reference to a discrete double layer of neuronal perikarya marking the deepest limits of their distribution (Evans & Hamlyn, unpublished; Cowan, Adamson & Powell, 1961). This present work follows naturally from the light-microscopic degeneration studies of Evans & Hamlyn (1956) with the Glees (1946) and Nauta-Gygax (1954) methods. The time courses of the two methods are quite distinct, the Glees method showing rings and clubs, absent from normal tectum, at the 7-11-day stage. At 28-30 days the Glees method is negative, but the Nauta-Gygax picture is fully established. Here electron microscopy has been used to follow these changes in the axons and their presynaptic processes in order to relate them to the different mechanisms of the Glees and Nauta techniques. Few attempts have been made so far to study central nervous degeneration with the electron microscope. De Robertis (1956) has described experimental changes in the ventral acoustic nucleus. Bunge, Bunge & Ris (1960, 1961) have reported on experimental demyelination and remyelination in the spinal cord, the axons remaining apparently unaffected. In this account the simplified classification of the tectal layers used by Cragg, Evans & Hamlyn (1954) modified from van Gehuchten (1892) will be used.

The central connexions of dorsal spinal nerve roots and the ascending tracts in the spinal cord of Lacerta viridis.

Abstract: Until recently our knowledge of the detailed structure of the reptilian nervous system has been based almost entirely on observations made on serial sections of normal material prepared by routine neuro-histological methods. Most of these observations were reported in the older literature and were ably summarised by Kappers, Huber & Crosby, in 1936. In spite of the well-known limitations of the methods a considerable body of knowledge has been built up. Its interpretation, however, in terms of connexions between different parts of the nervous system, has depended in many cases on a presumed homology with tracts or collections of nerve cells similarly situated in the mammalian nervous system, where they have been subjected to more rigorous investigation by experimental methods. Recently, several papers have appeared in which the results of the differential staining of degenerating fibres or cells have been described in the reptilian brain. The degeneration has been caused by lesions so placed that it should demonstrate the connexions of particular nerves or parts of the brain, e.g. Armstrong (1950) for optic connexions, Gamble (1952) for olfactory connexions, and Powell & Kruger (1960) for striato-thalamic connexions. So far this work has been limited to the foreand mid-brain, where it has demonstrated many fundamental differences between reptilian and mammalian anatomy which could not have been demonstrated conclusively in preparations of normal material. The present investigation extends observations of this kind to lower levels of the nervous system and its main purpose is to determine the central connexions of the dorsal roots of spinal nerves and the course and destination of long ascending tracts in the spinal cord.