Studies on transneouronal degeneration in the central nervous system

Abstract

(1) ti study has been :made of transneuronal cell degeneration in the main and accessory olfactory bulbs of the rabbit, after destruction of the olfactory mucosa, and in the auditory relay nuclei of the cat following destruction of the cochlea. To facilitate the interpretation of the cellular changes in the auditory relay nuclei an additional investigation of the projection of the cochlea v=as done by the use of silver methods for demonstrating degenerating nerve fibres and terminals.

(2) Following deaffe entation all layers of the olfactory bulb, except the periventricular layer, show severe shrinkage, and the periglomerular, tufted, mitral and granule cells undergo transneuronal atrophy.

(3) Bodian-stained preparations of the olfactory bulb show that the dendrites of the mitral and tufted cells atrophy, and that there is a loss of the fine colïaterals of the mitral cell axons in the outer part of the molecular layer subjacent to the lateral olfactory tract.

(4) Golgi-Cox preparations of the bulb show that periglomerular tufted and mitral cells which are undergoing transneuronal degeneration are more resistant to impregnation by this method.

(5) The primary auditory nerve fibres of the cat terminate in the anteroventral, postereventrai and dorsal cochlear nuclei. No fibres end in the superior olivary and medial trapezoid nuclei.

(6) In one experiment in which the cochlear nuclei were destroyed it was found that these two nuclei project 'to the two preolivary nuclei and the lateral superior olive of the same side, to the medial trapezoid and laterd lemnisoal nuclei of the opposite side and to the proximal halves of the medial superior olive of both sides.

(7) Following destruction of the cochlea transneuronal cell degeneration is seen in the ventral cochlear, lateral superior olivary and preolivary nuclei of the same side, and in the medial trapezoid and lateral lemniscal nuclei of the opposite side. The cells of the two divisions of the ventral cochlear nucleus and the lateral superior olive show the most obvious atrophy. No ch nge is seen in the spindle -cell layer of the dorsal cochleas nucleus.

(8) In both the time -course and severity of degeneration the cells of the different auditory relay nuclei closely resemble each other and those of the lateral geniculate nucleus of the same species. Little change is found after survival periods of less than 60 clays, and after this period the degenerative process appears to be more or less stationary.

(9) There is no evidence of any cell loss in the auditory relay nuclei up to 359 days after destruction of the cochlea.

(10) The cellular atrophy which occurs in the ventral cochler nucleus is due to the interruption of the direct auditory afferent fibres which terminate in this nucleus. The cellular changes which are found in the other auditory relay nuclei, however, are considered to be secondary to those in the ventral coohlear nucleus.

(11) In one experiment in wàich the vestibular nerve was incidentally involved, transneuronal cell cogeneration was found in the medial and descending vestibular nuclei.