PubMed Health⌕ Search

Biomedical subjects

C Straznicky

Publications and source records attributed to C Straznicky.

81 records · Page 5Linked to original sources
PubMed1980

Regeneration of an abnormal ipsilateral visuotectal projection in Xenopus is delayed by the presence of optic fibres from the other eye.

Optic fibre regeneration was studied by [3H]proline autoradiography and by mapping electrophysiologically the direct visuotectal projections to the contralateral and ipsilateral tecta 12-16 weeks after sectioning the right optic nerve in Xenopus two to four weeks after metamorphosis. The experiments were carried out in three groups: (A) optic nerve section in newly metamorphosed animals with embryonic left-eye enucleation; (B) optic nerve section with simultaneous left-eye enucleation; and (C) optic nerve section with delayed left-eye enucleation 5-31 days prior to sacrifice. In all but three animals regenerated optic fibres were demonstrated morphologically both in the contralateral and ipsilateral tecta. The contralateral visuotectal projection was fully restored within the 12-16 weeks in all animals. In animals with embryonic enucleation or in those where the enucleation was carried out simultaneously with optic nerve section, a direct ipsilateral visuotectal projection was established at the same time as the restoration of the contralateral projection. In contrast, no direct ipsilateral visuotectal projection was detectable in the presence of optic fibres from the other eye in the doubly innervated tecta. However, 14-31 days after the removal of the incumbent optic fibres by left-eye enucleation a direct visuotectal projection from the right eye to the ipsilateral tectum was established, and its polarity corresponded to the normal contralateral retinotectal projection. The apparent disparity between morphological and electrophysiological findings in the doubly innervated tectum suggests that superimposed optic fibres are unable to form normal synaptic relations with tectal neurons during early regeneration, delaying the establishment of the induced direct ipsilateral visuotectal projection.

Action Potentials↗
PubMed1980

The retinotectal projections from surgically rounded-up half-eyes in Xenopus.

In Xenopus embryos of stage 32 half of one eye anlage was removed and the remaining half was surgically rounded-up. The visuotectal projections through such half-eyes, recorded after metamorphosis, showed in most cases a deformation of the map which corresponded to the deformation imposed on the half-eye at operation. Some eyes gave normal maps and some showed mirror-reduplication.

Animals↗
PubMed1979

The time of origin of the mesencephalic trigeminal neurons in Xenopus.

Time of origin of the mesencephalic trigeminal cells (MTC) in Xenopus 'has been studied with 3H-thymidine autoradiography. The first MTC's were formed at stage 20, and they continued to arise up to stage 58. The mitotic rate of MTC's was found to be ten per cent at any time from stages 20--50, with a slow decrease thereafter. MTC's in the tectum were distributed in a spatio-temporal manner. Cells generated earliest were located in the rostral pole of the tectum and were followed in caudomedial sequence by cells formed later. The generation times of MTC and the neurons of the sensory trigeminal ganglion (TGC) were strikingly dissimilar, indicating that they probably do not represent a common cell lineage, that is, the former may not arise from the mesencephalic neural crest. It is proposed that the majority of MTC's generated from stage 30 onward, derive through proliferative activity of precursor cells in the di-mesencephalic junction and in the tectal neuroepithelium.

Age Factors↗
PubMed1979

Anomalous ipsilateral optic fibre projection in Xenopus induced by larval tectal ablation.

Unilateral left tectal ablation was carried out in Xenopus between stage 48 and 1 month after metamorphosis. Six to 12 weeks after metamorphosis the retinal projection from the right eye was examined with the use of [3H]proline autoradiography. The autoradiographs indicated that optic fibres whose tectal target was destroyed recrossed to the ipsilateral tectum and basal optic nucleus via the posterior and pretectal commissures. No anomalous recrossing occurred if the tectal ablation was carried out at stage 58 or later. The aberrant optic fibres were restricted to the rostrolateral and central parts of the ipsilateral tectum and they terminated in a discontinuous manner. It is concluded that available surfaces serving as contact guidance cues are needed to direct aberrant optic fibres to the ipsilateral tectum.

Action Potentials↗
PubMed1979

Selection of appropriate medial branch of the optic tract by fibres of ventral retinal origin during development and in regeneration: an autoradiographic study in Xenopus.

The formation of the branches of the optic tract has been studied with the use of [3H]proline autoradiography, during development and during regeneration of the optic nerve in Xenopus with one compound ventral (VV) eye made by the embryonic fusion of two ventral eye fragments. The formation of the optic pathway was abnormal in that the lateral branch failed to develop, suggesting that fibres from a VV retina selectively entered the tectum via the medial branch during development. Three months after section of the optic nerve of a VV eye, regenerated fibres were present both in the contralateral and ipsilateral tecta. On the ipsilateral side regenerated fibres entered the tectum via the medial branch only. Retinal fibres entered the contralateral tectum through both branches in some animals and through the medial branch only in others. It is concluded that mechanical factors alone are insufficient to explain the phenomenon of selection of the appropriate medial branch by fibres of ventral retinal origin either during development or in regeneration. Some form of fibre-substrate interaction seems to be necessary; and this ability of fibres from a VV eye to take the path appropriate for ventral retina argues strongly that the VV eye is not a regulated system in terms of cell specificities.

Animals↗
PubMedDate not supplied

Synaptic circuitry of serotonin-synthesizing and serotonin-accumulating amacrine cells in the retina of the cane toad, Bufo marinus.

The synaptic connections of amacrine cells synthesizing or accumulating serotonin in the retina of the cane toad, Bufo marinus, were studied by using preembedding double-labeling electron-microscopic immunocytochemistry. The binding sites of an anti-serotonin antibody were revealed by the diaminobenzidine reaction, whilst a colloidal gold-conjugated secondary antibody was used to detect an antibody to phenylalanine hydroxylase. Since the latter antibody recognizes tryptophan 5-hydroxylase, one of the synthesizing enzymes for serotonin, as well as tyrosine hydroxylase, the rate-limiting enzyme for catecholamine synthesis, the double labeling of the present study enabled us to identify three groups of labeled profiles at the ultrastructural level. The profiles of serotonin-synthesizing amacrine cells contained both diaminobenzidine reaction product and colloidal gold particles, whilst those of serotonin-accumulating and dopaminergic amacrine cells contained only diaminobenzidine reaction product or colloidal gold particles, respectively. The synapses of serotonin-synthesizing or serotonin-accumulating amacrine cells were distributed all through the inner plexiform layer of the retina. The profiles of serotonin-synthesizing amacrine cells predominantly received synapses from, and made synapses onto, unlabeled amacrine cell dendrites. They also received synapses from, and made synapses onto, bipolar cell terminals. They also made synapses onto presumed ganglion cell dendrites. However, the profiles of serotonin-accumulating cells made synapses only with unlabeled amacrine cell processes. There were close contacts between the profiles of serotonin-synthesizing and serotonin-accumulating amacrine cells. No synaptic relationships were observed between dopaminergic and serotonin-synthesizing or serotonin-accumulating amacrine cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Serotonin synthesis and accumulation by neurons of the anuran retina.

Serotonin-synthesizing and serotonin-accumulating neurons were studied in the retinas of Xenopus laevis and Bufo marinus. All previously identified cell types exhibiting serotonin-like immunoreactivity (SLI) were labeled by intravitreal injection of 5,7-dihydroxytryptamine (5,7-DHT). They included two amacrine cell types (large and small) in both species, and one bipolar cell type in Xenopus. Incubation of retinas in culture medium in the ambient light reduced SLI in amacrine cells and enhanced the labeling in bipolar cells. After incubation, some photoreceptor cell bodies and large numbers of outer segments also displayed SLI in both species. Incubation with the serotonin-uptake inhibitor, fluoxetine, reduced immunolabeling in bipolar cells and outer segments to the level in the untreated retinas. Both large SLI and 5,7-DHT-accumulating amacrine cells in Xenopus and Bufo were labeled with an antibody raised against phenylalanine hydroxylase (PH), which binds to tryptophan 5-hydroxylase, one of the synthesizing enzymes for serotonin. Small SLI and 5,7-DHT-accumulating amacrine cells in both species represented two populations, one with and the other without PH-like immunoreactivity (PH-LI). The anti-PH antibody failed to label any SLI or 5,7-DHT-accumulating bipolar cells in Xenopus. These observations indicate that all large and some small SLI amacrine cells in the retinas of Xenopus and Bufo synthesize serotonin, while other small SLI amacrine, bipolar and photoreceptor cell bodies, and outer segments only accumulate serotonin.

5,7-Dihydroxytryptamine↗