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C H Narayanan

Publications and source records attributed to C H Narayanan.

5 recordsLinked to original sources
PubMed1978

Determination of the embryonic origin of the mesencephalic nucleus of the trigeminal nerve in birds.

The precise site of origin and the cells of origin of the mesencephalic nucleus of the trigeminal nerve in birds have been studied by the method of growing embryonic fore-, mid- and hind brain grafts inside a millipore filter chamber filled with amniotic fluid, upon a host chorioallantoic membrane, and by the method of transplantation of cranial neural crest of the mesencephalon between embryo-donors and duck embryo-hosts. The growth and differentiation of grafts grown in the chambers resemble very closely those of normal embryos at corresponding stages of development. Data obtained from a total of 42 grafts representative of the three species of birds used in this study, show that the cells of the mesencephalic nucleus are present only in grafts of embryonic midbrain and totally absent in forebrain and hindbrain grafts. The presence of cells of the mesencephalic nucleus in midbrain grafts suggests that these neurons arise chiefly from the developing mesencephalon. Histological examination of such grafts has shown that these neurons are observed in the leptomeningeal tissue overlying the midbrain region and extend into the various laminae of the optic tecta. A progressive increase in the size of the cells from an immature state confined to the mesodermal tissue to fully mature neurons in the stratum griseum periventriculare of the optic tectum is observed. This is also indicative of a downward migration of these cells. In a few embryonic midbrain grafts mature cells clearly identifiable as belonging to the mesencephalic nucleus are observed in the leptomeningeal tissue and outside the external limiting membrane of the neural tube. These appear to be neurons which had failed to migrate. The resemblance of these latter neurons to those in the stratum griseum periventriculare of the optic tectum lend further support to the hypothesis that the neurons of the mesencephalic nucleus are derived from neural crest of the developing mesencephalon in birds. In interspecific transplantation experiments of cranial neural crest of the mesencephalon, the quail cells occur in the form of clusters and appear to migrate towards the ventricular surface independent of the migration of the cells of the tectum which takes place simultaneously. Three stages in the development of the grafted neural crest material of the quail are observed based on the perikaryal diameter of the cells, and the accumulation of Nissl material in the cytoplasm. The smallest cells are located more superficially near the pial surface, and the larger mature neurons are observed in the stratum griseum periventriculare of the optic tectum. All the layers of the optic tectum including the neuroepithelium on the experimental side are comprised entirely of duck cells...

Animals↗
PubMed1978

Neuronal adjustments in developing nuclear centers of the chick embryo following transplantation of an additional optic primordium.

Following transplantation of an additional optic primordium into the orbital mesenchyme of chick embryos of approximately 2 days of incubation age, the changes in cell number in the ciliary ganglion, accessory oculomotor and trochlear nuclei were studied at various stages of development. Cell counts were made at 1-day intervals from days 9 through 15 for ciliary ganglion, and from days 13 through 15 for the accessory oculomotor and trochlear nuclei. Cell counts for the ciliary ganglion on days 9 and 11 were similar on the operated and control sides which suggests that grafting of an additional optic primordium, and thus enlarging the periphery, is not involved in the control of proliferation. Comparison of the number of cells for the ciliary ganglia and the accessory oculomotor nuclei at days 13 and 15 showed an increase on the affected side ranging from 8 to 27%, and 9 to 33% respectively. We interpret this increase on the experimental side as a reduction in the number of degenerating cells that occur in normal development, as a result of an enlargement of the peripheral field of innervation. Three cases showed an increase in the number of cells in the trochlear nucleus ranging from 9 to 29%. This increase was attributed to an increase in the size of the superior oblique muscle of the operated side as determined by volumetric measurements. On the basis of the evidence we conclude that an enlarged periphery acts by regulating the level of naturally occurring cell death by reducing the amount of cell loss, leading to a corresponding increase in final cell number.

Animals↗
PubMed1978

On the origin of the ciliary ganglion in birds studied by the method of interspecific transplantation of embryonic brain regions between quail and chick.

The development of the ciliary ganglion with reference to the site and cells of origin have been investigated by the method of quail-to-chick transplantation of embryonic fore-, mid-and hindbrain regions, and by the method of transplantation of cranial neural crest from specific brain levels. In chimaerical embryos, quail cells originating from the graft end up in the ciliary ganglion, only when the graft is from the midbrain level of quail embryo donors. In fore- and midbrain grafts the ciliary ganglia of chimaerical embryos are composed of chick cells only. The results indicate that the mesencephalon is the principal site for the precursor cells of the ciliary ganglia and clearly rules out any contribution to the ganglia from either the forebrain or hindbrain levels. In interspecific transplantation of cranial neural crest, quail cells originating from the graft are observed consistently in the ciliary ganglion of the operated side when the grafted neural crest material is derived from the mesencephalon of quail embryo donors. On the basis of the evidence provided, it is concluded that mesencephalon is the principal site and the cranial neural crest of this level the source from which the precursor neurons of the ciliary ganglia are derived.

Animals↗