Cell loss in the trochlear nucleus of the chick during normal development and after radical extirpation of the optic vesicle

Abstract

Counts have been made of the number of cells in the trochlear nucleus in a series of 22 normal chicks between the ninth day of incubation and the seventy-fifth day after hatching, and in seven animals in which the optic vesicle and adjoining mesoderm were removed during the second day of incubation. Between the ninth and seventeenth days of incubation the number of cells in the normal trochlear nucleus declines from just under 1400 to a little under 700, indicating a cell loss of approximately 50% over this eight day interval. From the seventeenth day onwards there is a further slight fall to between 500 and 600 cells and this number is maintained into the third month after hatching. Following excision of the optic vesicle there is an earlier, and more severe, loss of neuxons in the trochlear center, the number of cells being reduced to just under 1000 at the eleventh day of incubation and falling to just over 300 by the sixth day after hatching. Despite this marked cell loss, at no stage is there any gross evidence of neuronal disintegration or phagocytosis. The possible factors responsible for the normally occurring cell loss and for the hypoplasia in the trochlear nucleus after removal of the optic vesicle are discussed.In the 60 years since Collin ('06) first reported the presence of degenerating cells in the ventral horn of the chick spinal cord between the third and sixth days of incubation, a good deal of evidence has accumulated to show that cellular degeneration may be both of widespread occurrence and of considerable morphogenetic significance in the developing nervous system. Unfortunately, this phenomenon appears to have received rather less attention than it deserves, no doubt because most of the available evidence is in the form of incidental references either to the occurrence of cell loss or to the presence of degenerating neurons in different parts of the central and peripheral nervous systems. However, a few authors have made this the subject of special study (e.g., Ernst, -26; Glucksmann, '30; Hamburger and LeviMontalcini, '49; Hughes, '61 ; Prestige, '65; Bodian, '66) and it has also been considered at some length in three recent reviews (see Glucksmann, '51 ; Hess, '57; and K5l-len, '65). Our attention was drawn to this phenomenon during the course of an experimental study of the development of the avian visual system (Cowan and Wenger, '67) when we observed what ap-J. EXP. ZOOL., 164: 267-280. peared to be a slow, but progressive loss of neurons in the nuclei of origin of the third, fourth and sixth cranial nerves. Preliminary counts of the number of neurons in the trochlear nucleus indicated that there may be a loss of as many as 50% of the cells in this center between the ninth and twentieth days of incubation. In view of the magnitude of this cell loss, and especially since no comparable change was observed in an earlier experimental study of the trochlear nucleus (Dunnebacke, '53), it was considered worthwhile to carry out a more complete study of the number of cells in this n...

Effects of a Snake α-Neurotoxin on the Development of Innervated Skeletal Muscles in Chick Embryo

“…One channel that might transmit this information could be the sensory pathway from the muscle to the motoneuron. The extrinsic ocular muscles offer a situation particularly relevant to this point, since they receive essentially only motor innervation (37). In these muscles as well, the a-toxin causes a marked reduction in size, both of the muscle and of the corresponding motor nerves.…”

Developing dorsal root ganglion neurons require trophic support from their central processes: evidence for a role of retrogradely transported nerve growth factor from the central nervous system to the periphery.

“…Populations of developing neurons come under the influence of their peripheral fields and are able to make compensatory adjustments according to the sizes of the afferent input they receive (10)(11)(12) and the efferent output they project (13)(14)(15)(16). The adjustments are made by way of corresponding alterations in cell number and size within the developing neuronal population.…”

“…Subcutaneous injections of either 20 ,ug of NGF or an equal volume of vehicle (P,/NaCl) were given to the neonates 2 hr before the operation and continued daily through PND-5. NGF and cytochrome c were labeled with 1 mCi of Na125I (specific activity, [13][14][15][16][17] mCi/pg, Amersham; 1 Ci = 37 GBq) by the lactoperoxidase method of Marchalonis (20) with minor modifications. After iodination, the 125I-NGF was dialyzed in 3 liters of Pi/NaCl (pH 7.4) to remove any free Na125I.…”

Neurotrophic factor regulation of developing avian oculomotor neurons: Differential effects of BDNF and GDNF

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