J.M. Génis-Gálvez

A golgi study on the early sequence of differentiation of ganglion cells in the chick embryo retina.

SummaryAn examination of retinal structure in chick embryos, impregnated with the Golgi-Stensaas method between 2 and 6 days of incubation, discloses, on the one hand, a uniform typology of the proliferating ventricular cells, the pre- and postmitotic forms of which were tentatively identified; on the other hand, postmitotic neuroblasts are evidenced in the stages of differentiation previous to the growth of their neurites.In the earliest embryos (up to 51/2 days of incubation), all cells that detach from the ventricular lining to differentiate as neurons do so while the ventricular cell precursor has an interphasic configuration. This means that, although they free themselves from the scleral attachment site, they keep for a while a vitreal attachment. The vitreally-attached endfeet subsequently transform into axonal growth cones, sprouting filopodia and lamellipodia. While the axons grow towards the optic nerve head, cell bodies and remaining scleral processes are progressively retracted inwards, leading to the appearance of typical ganglion cells.After 51/2 days of incubation, a great number of postmitotic neuroblasts detach while still in the G1 phase of the ventricular cell cycle. Those of them that show the longest leading processes become also ganglion cells, after their leading tip has acquired a growth cone configuaration and has bent into the optic fiber layer.These results on early mechanisms of ganglion cell genesis are discussed in relation to data in the literature, and a simple hypothesis is offered which explains the biphasic pattern in which presumptive ganglion cells detach from the ventricular lining of the chick retina.

Two modes of free migration of amacrine cell neuroblasts in the chick retina

SummaryThe migration of amacrine neuroblasts toward the prospective amacrine cell layer in the chick embryo retina has been studied, in Golgi-stained sections, between days 5 and 9 of embryogenesis.Two distinct populations of presumptive amacrine neuroblasts have been identified on the basis of their shape and migratory behavior. One population (smooth amacrine neuroblasts) display smooth, monopolar or bipolar contours, moving freely across the retina without major changes in the original postmitotic shape, and give processes only after reaching the primitive inner plexiform layer. The second population (multipodial amacrine neuroblasts) includes multipolar neuroblasts with abundant filiform and/or lamelliform processes sprouting in various directions; these highly plastic cells begin modifying their shapes at the time of release from the ventricular lining and continue to do so as they move toward their definitive location.Thus, the well-known heterogeneity of adult amacrine cells seems to be preluded by differences in neuroblastic migratory patterns, suggesting the existence of at least two different subsets of amacrine cell precursors.

Developmental study of axon formation in the horizontal neurons of the retina of the chick embryo

SummaryAmong the types of horizontal cells of the avian retina, one has been described that has an axon terminating, in a typical structure. The present study analyses the histogenesis of this axon whose initial outgrowth occurs on day 14 of incubation (HH-40). The axon terminal is first detectable, towards day 15 of incubation (HH-41), in the form of a varicose thickening possessing short filopodia. The formation of the axon and the growth of the axon terminal is coincident with a retraction of the perikaryal process. The axon usually originates from one of the pricipal dendrites and in these stages shows short and fine filopodia throughout its length. From day 16 onwards (synaptic) spines may be distinguished, both in the dendritic field and on the axon terminal. The growth of the axon, in the phase when the axon terminal still has not formed, may exhibit deflections and deviations in its course, the possible cause and mechanism of which are discussed.

Effect of ethanol on the morphohistogenesis and differentiation of cerebellar granule cells in the chick embryo

In this present study we analyse, with the help of the Golgi method, the effect of ethanol on the morphological differentiation of the cerebellar granule cells in the chick embryo. Ethanol seems to affect the process of cell migration from the early stages of differentiation. Some granule cells appear to differentiate in an inverted position. These observations also confirm, on the basis of their axon morphology, the existence of three types of granule cells in the chick cerebellum.

Early Morphological Differentiation of the Bipolar Neurons in the Chick Retina A Golgi Analysis

We report a histogenetic study of the bipolar cells of the chick embryo retina between days 5 and 9, using the Golgi technique. On day 8, at the level of the developing outer plexiform layer, small delicate spines appear on the outer processes of the bipolar cells, which represents the commencement of their dendritic ramification. At a later staige in development che detachment of Landolts club from the outer limiting membrane is observed in some cells The inner ramifications of the bipolar cell, at the inner plexiform layer, appear later than those of the outer process.

The midget bipolar cells in the chick retina

This paper reports the existence of midget bipolar cells on the chick retina, as determined by the staining methods of Golgi-Stensaas and Golgi-Colonnier. We date the appearance of these cell types at days 13 (HH-39) and 14 (HH-40) of incubation and describe them morphologically throughout their development until the time of hatching, at which time the cells show an adult structure. As an adjunct to this work we classify the midget bipolar cells into four groups.

Oil Droplets in the Chameleon (ChamaIeo chamaleo) Retina

The cones of the chameleon retina have, in the scleral portion of their inner segment, an oil drop whose morphology is similar in all the photoreceptors possessing this droplet. The irregularities in the membrane surrounding the lipid matrix show close relationships with the surrounding mitochondria.

IMMUNOHISTOCHEMICAL LOCALIZATION OF GABA IN CHAMELEON RETINA (CHAMALEO CHAMALEO)

We used a policlonal antiserum against GABA and demonstated GABA‐immunoreactivity (GABA‐IR) in several populations of amacrine cells in the inner nuclear layer (INL), and other cells in the inner plexiform layer (IPL) of the central and peripheral retina of the chameleon. Horizontal cells do not contain GABA‐IR and the chameleon retina is therefore an exception among non‐mammals. GABA‐IR was not seen in cell bodies in the position of photoreceptor, bipolar and interplexiform cells suggesting that GABA is not involved in synaptic transmission in the outer plexiform layer of chameleon retina.

Amacrine cells with a rectilinear dichotomy of dendrites in the chick retina

With Golgi impregnation, a simple amacrine cell type is described in the chick retina. The most relevant morphological feature of these retinal neurons is a single straight, radial trunk which dichotomizes tangentially in a rectilinear expansion in the 5th stratum of the inner plexiform layer (IPL).

Short axon ganglion cells in the chick retina

Using Golgis staining technique, we investigated some ganglion cells whose axons do not project out of the retina area. These axons, after following a short trajectory through the optic nerve fiber layer or through the 5th stratum of the inner plexiform layer (IPL), change their direction and end in the inner stratum of the IPL.