Avian nucleus isthmi ventralis projects to the contralateral optic tectum.

Injections of HRP throughout the upper tectal strata led in 4 cases to the appearance of retrogradely labeled neurons within n.isthmi ventralis, contralateral to the experimental side. An additional case proved that this projection courses through the ventral supraoptic commissure.

The locus of optic nerve head representation in the retinotopic projection over nucleus geniculatus lateralis ventralis and nucleus griseum tectalis in the chick also lacks a retinal projection.

Recently we have demonstrated the presence of a gap in the avian retinotectal projection, that corresponds with the locus of retinotopic representation of the elongated optic nerve head. The present report describes an equivalent gap in the optic neuropiles of the avian ventral geniculate nucleus and griseum tectalis formation, detected after filling optic terminals anterogradely from the contralateral eye with peroxidase. A projection-less strip appears at the expected retinotopic position in both grisea intersecting radially all the strata of the corresponding neuropiles.

Segment-related, mosaic neurogenetic pattern in the forebrain and mesencephalon of early chick embryos: I. Topography of AChE-positive neuroblasts up to stage HH18.

Histochemical mapping of AChE-positive neuroblasts in sectioned and whole-mounted preparations of the chick embryo mesencephalon and prosencephalon allows a correlation of early neural tube morphogenesis (segmentation, longitudinal compartmentation) with the heterochronic pattern of neurogenesis. One significant finding is that the initial appearance of neuroblasts in the forebrain does not follow neuromeric segmentation, but evolves in parallel with it. Early neuroblasts appear as separate, distinct groups within specific matrix territories at the center of the transverse neuromeric segments.

Location of the rostral end of the longitudinal brain axis: review of an old topic in the light of marking experiments on the closing rostral neuropore.

The rostral end of the forebrain was classically defined on the basis of descriptive data. Different assumptions on the mode of closure of the rostral neuropore caused three different theories of the rostral end of the forebrain to be formulated (His 1893a; von Kupffer, '06; Johnston, '09). Some recent descriptive and experimental data have put these theories into question.

The locus of optic nerve head representation in the chick retinotectal map lacks a retinal projection.

Retinotopic representation of the optic nerve head of the contralateral eye lies at the rostrodorsal face of the avian tectum. Since the homologous mammalian retino-collicular map shows an optic disc gap, the present anterograde HRP transport experiments were designed to detect an equivalent gap in the avian tectal retinorecipient strata. Sections tangential to the tectum at the locus of pecten representation displayed a thin, elongated, projection-less strip, crossing radially all retinorecipient laminae.

Solitary magnocellular neurons in the avian optic tectum: cytoarchitectonic, histochemical and [3H]thymidine autoradiographic characterization.

Solitary magnocellular neurons are described in the adult chick optic tectum on the basis of their large size, polygonal shape, intensely basophilic perikarya, characteristic position at the border between the stratum griseum centrale and the stratum album centrale, decreasing density along a rostrocaudal gradient, and intense activity of NADH-diaphorase. These characteristics distinguish this population from the adjacent ganglion cells of the stratum griseum centrale, which are more numerous, smaller, paler staining and have background levels of NADH-diaphorase. Moreover, the solitary magnocellular neurons appear unlabeled after tritiated-thymidine administration after stage 17+, and are thus born before the stratum griseum centrale neurons, which are generated after stage 19.

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

The 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.

Autoradiographic and Golgi study on the early development of n. isthmi principalis and adjacent grisea in the chick embryo: a tridimensional viewpoint.

Neurogenesis, cell migration and early histogenesis of the isthmic nuclear complex in chick embryos were investigated in autoradiographic and Golgi material. The aim of the experimental observations was to detect whether the apparent origin of different grisea of this complex at separate matrix territories (neuromeres) was accompanied by peculiar generation patterns, consistent with predictions of neuromeric theory. Differential birthday patterns were indeed obtained for a) n.

Hyperthermia and the neurotoxicity of exogenous glutamate in infant rats.

A substantial elevation of the excitatory neurotransmitter glutamate can be produced in the brain of 3-day old rats, either after subcutaneous injection of monosodium glutamate (4 mg/g), or by hyperthermic treatment (40 degrees C, 3 h). In the glutamate-treated animals a large increase in the GABA levels has also been observed while the elevation of this amino acid in the hyperthermic animals is insignificant. Although the magnitude of the increase of glutamate in both cases is rather similar, in the hyperthermic animals no cerebral lesions such as those produced in the glutamate-treated animals could be observed.

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

An 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 5 1/2 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.

A Golgi-study of oculomotor neuroblasts migrating across the midline in chick embryos.

The Golgi-Stensaas impregnation technique was employed at appropriate stages of development to study the morphology of the oculomotor neuroblasts as these migrate across the midline. Data reported in previous publications were confirmed, such as the timing of the migration (occurring between the 4th and the 9th days of inoculation), the fact that the migrating cells carry their axons across the midline as trailing processes, and the absence of pre-existing fibrillar structures able to provide contact guidance for this migration. The most striking new fact discovered is that the leading processes of the oculomotor neuroblasts are often branched, and that all these branches are uniformly oriented towards the midline.

Do oculomotor neuroblasts migrate across the midline in the retal rat brain?

Toluidine blue-stained semithin sections and Cajal-Castro preparations are used to study in rat fetuses whether oculomotor neuroblasts migrate across the midline at a certain period of development. In confirmation of previous studies, a group of oculomotor neuroblasts was detected which first grow cytoplasmic processes into the mesencephalic midline, and afterwards translocate their somata towards the midline, between the 12th and the 15th days of gestation. At this moment a midline mass of neuroblasts characterizes the meeting at this landmark of both left and right migrating neuroblastic groups.