Biomedical subjects

C Straznicky

Publications and source records attributed to C Straznicky.

At least 55 records · Page 3Linked to original sources

PubMed1989

Neuropeptide Y-like immunoreactivity in neurons of the human retina.

The distribution of neuropeptide Y-like immunoreactivity (NPY-LI) was investigated in wholemounts and in transverse sections of the human retina. NPY-LI was localized to the soma and axonal processes of large ganglion cells (GCs) and to the soma and dendritic arborization of amacrine cells (ACs). NPY-LI GCs were unevenly distributed across the retina, the highest density of 875 cells/mm2 was found in the fovea centralis and the lowest density of 15 cells/mm2 in the peripheral retina. The total number of NPY-LI GCs in the retina was estimated to be about 85,000. The soma sizes of NPY-LI GCs increased from 116 microns 2 +/- 23 (s.d.) in the retinal centre to 251 microns 2 +/- 57 in the retinal periphery. The soma size of NPY-LI ACs was in the range of 40 and 50 microns 2. In transverse sections NPY-LI was seen to be localized to the optic fibre layer, to the somata of GCs, to the scleral sublamina of the inner plexiform layer (AC dendrites) and to the innermost part of the inner nuclear layer (somata of ACs). The gradients of soma sizes and retinal distribution of NPY-LI GCs were taken as an indication that they correspond to the class of large to very large GCs, previously identified in the human retina by Golgi impregnation.

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PubMed1989

Morphological characterization of substance P-like immunoreactive amacrine cells in the anuran retina.

Using substance P immunohistochemistry it was possible to demonstrate a class of morphologically homogeneous group of neurons in the inner nuclear layer (INL) of the retina of two anuran species: Xenopus laevis and Bufo marinus. The number of cells with substance P-like immunoreactivity (SP-LI) was about 250 and 800 in juvenile and 600 and 2500 in adult Xenopus and Bufo, respectively, SP-LI cells had a small soma with one primary dendrite having up to four slender branches, located in the vitreal sublamina of the inner plexiform layer (IPL). Mean dendritic field sizes were 0.12 and 0.30 mm2 in juvenile and 0.29 and 0.65 mm2 in adult Xenopus and Bufo, respectively. The density of SP-LI cells was 40/mm2 in juvenile and 24/mm2 in adult Xenopus compared with 20/mm2 in juvenile and 13/mm2 in adult Bufo. Nearest neighbour distance measurements indicated that SP-LI cells were randomly distributed across the entire retina in both species. The location and the morphology of SP-LI cells indicated that they correspond to a subclass of wide-field amacrine cells, similar to types 20 and 21 described by Golgi techniques in the cat.

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PubMed1989

Retinal ganglion cell death induced by unilateral tectal ablation in Xenopus.

The survival of retinal ganglion cells (GCs) in the left eye was studied on retinal wholemounts from 2-33 weeks after the surgical removal of the right tectum in juvenile Xenopus. Two to five weeks after tectal removal, about 76% of neurons of the retinal ganglion cell (GC) layer showed signs of retrograde degeneration: swelling of their somata and chromatolysis. Neurons that were not affected by the operation were taken to be either displaced amacrine cells (DAs) or GCs not projecting to the tectum. A portion of GCs showing retrograde degeneration became pyknotic and died within the period of 2-16 weeks after operation. Counts of surviving GCs 20-33 weeks after tectal removal amounted to about 55% of the corresponding neuron number in the right intact retina of the same animal. No discernible GC loss was observed in animals where only the optic fibers were cut at their entry point to the tectum indicating that axotomy alone, followed by rapid regrowth to the target, does not adversely influence the survival of GCs. In long-surviving animals, the left optic nerve was exposed to cobaltic-lysine complex and the position of filled optic axons within the brain determined. Optic axons whose tectal target had been removed were seen to cross over to the left intact tectum via the posterior and pretectal commissures. Aberrant projections were detected to the ipsilateral tectum and the diencephalic periventricular grey in addition to an increased projection to the accessory optic nucleus. It is concluded that the removal of the tectum, the main target of optic fiber projection, induces a very substantial GC death. Since only a portion of optic fibers were able to grow to alternative targets, the surviving GCs may have also included those with main projection areas to the diencephalic visual centers.

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PubMed1989

The morphological characterization and distribution of displaced ganglion cells in the anuran retina.

The number, dendritic morphology, and retinal distribution of displaced ganglion cells were studied in two anuran species, Xenopus laevis and Bufo marinus. Horseradish peroxidase or cobaltic lysine complex was applied to the cut end of the optic nerve, and the size, shape, and retinal position of retrogradely filled ganglion cells displaced into the inner nuclear layer were determined in retinal wholemount and sectioned material. Approximately 1% of ganglion cells in Xenopus and 0.1% in Bufo were found to be displaced. In both species, many of the previously described orthotopic ganglion cell types (Straznicky & Straznicky, 1988; Straznicky et al., 1990) were present among displaced ganglion cells. In Xenopus more displaced ganglion cells were found in the retinal periphery than in the retinal center, and they formed 3 or 4 distinct bands around the optic nerve head. In Bufo the incidence of displaced ganglion cells was higher along the visual streak than in the dorsal and ventral peripheral retina. These results indicate that the distribution of displaced ganglion cells approximates the retinal distribution of orthotopic ganglion cells. One of the likely mechanisms to account for this developmental paradox may be that the formation of the inner plexiform layer, adjacent to the ciliary margin, acts as a mechanical barrier by preventing the entry of some of the late developing ganglion cells into the ganglion cell layer.

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PubMed1989

Dendritic morphology of identified retinal ganglion cells in Xenopus laevis: a comparison between the results of horseradish peroxidase and cobaltic-lysine retrograde labelling.

Following the application either of cobaltic-lysine complex or a 30% solution of horseradish peroxidase (HRP) in a sealed tube to the cut end of the optic nerve of young adult Xenopus frogs, the dendritic morphology of large ganglion cells was studied in retinal wholemount preparations, and compared with that in animals of the same size as revealed by the short time administration of HRP crystals. In the former two groups of animals, after 24 h survival, the size of the dendritic arborization of characterized ganglion cell types, Types I and III, were found to be significantly larger (61-79% and 180-187%, respectively) than those which survived 3 days after the administration of HRP crystals. These findings suggest that the very fine dendritic branches of large ganglion cells may remain unlabelled after a short-time exposure to HRP.

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PubMed1988

Lack of axon regeneration of isthmic neurons in juvenile Xenopus.

In young adult Xenopus laevis frogs the axons of isthmic neurons projecting to the contralateral tectum were severed at the postoptic commissure and the survival of such neurons was studied between 2 and 26 weeks after the operation. Pyknotic neurons were first observed in the isthmic nucleus 2 weeks after axotomy. The continued neuron loss resulted in the decrease from 2920 in intact animals to 1520 surviving isthmic neurons in animals 26 weeks after the operation. These findings suggest that (i) severed axons of the isthmic neurons are not able to regenerate to their natural target, and (ii) isthmic neurons require continuous contact with appropriate tectal target for their survival.

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PubMed1988

The ultrastructural organization of the isthmic nucleus in Xenopus.

The isthmic nucleus (IN) of the frog brain forms a linkage, relaying visual information from one tectum to the other. It receives afferent input from the tectum of the same side and projects bilaterally to both tecta. The ultrastructural features of the tecto-isthmic synaptic connections were studied in young postmetamorphic Xenopus frogs. Most synaptic profiles in the isthmic nucleus have spheroidal vesicles and an asymmetric zone of apposition. Frequently, synaptic glomeruli consisting of up to 8 terminal boutons surrounding a shaft dendrite were observed. The synaptic density in the rostral IN was slightly higher than in the middle or caudal portions. Partial deafferentation by transection of the tecto-isthmic pathway or total deafferentation by removal of the tectum was followed by a widespread degeneration of terminals in the ipsilateral IN. In the former case, the density of synapses in the IN decreased initially by about 64%, and then increased by 30 days after operation to about 50% of the normal synaptic density. After tectal removal, all the terminal boutons in the isthmic neuropil degenerated by 3 days after operation. These studies, along with recent findings, indicate that most, if not all, of the afferent fibres to IN are of tectal origin.

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PubMed1988

Morphological classification of retinal ganglion cells in adult Xenopus laevis.

Retrograde transport of horseradish peroxidase (HRP) was used to characterise the soma and dendritic arborization of retinal ganglion cells in adult Xenopus laevis toad. HRP was administered to the cut end of the optic nerve and the morphological characteristics of HRP-filled ganglion cells were analysed in retinal wholemount preparations using computer assisted morphometry. Ganglion cells were classified according to their soma size, dendritic branching pattern, dendritic field and the number of shaft dendrites. Ganglion cells were divided into 3 major classes on the basis of soma sizes and extent of dendritic field: large (soma size, mean 258.04 micron 2 +/- 52.03 SD; dendritic field size 0.104 mm2 +/- 0.23), medium size (126.7 micron 2 +/- 37.01; 0.041 mm2 +/- 0.013) and small (87.3 micron 2 +/- 22.69; 0.0061 mm2 +/- 0.0035). A more detailed analysis allowed 12 morphologically distinct subgroups to be identified (Types I-XII). Quantitative studies showed that large cells comprise about 1%, medium size about 8-9% and the small cells over 90% of total ganglion cell population. The number of large and medium size ganglion cells corresponded well with the number of myelinated optic fibres and the number of small neurons with the number of unmyelinated optic fibres in the optic nerve. Large ganglion cells were correlated with Class 4 and 5, medium size ganglion cells with Class 3 and small ganglion cells with Class 1 and 2 functionally characterized ganglion cells in the frog retina (Maturana et al. 1960). The retinal distribution of large ganglion cells appear to suggest certain similarities to mammalian alpha type ganglion cells.

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PubMed1987

The formation of the area centralis of the retinal ganglion cell layer in the chick.

In adult domestic chickens, the neurones in the retinal ganglion cell layer are very unevenly disposed such that there is a sixfold increase in neurone density from the retinal edge to the retinal centre. The formation of the high ganglion-cell-density area centralis was studied on chick retinal wholemounts from the 8th day of incubation (E8) to 4 weeks after hatching (4WAH). The density of viable neurones and the number and the distribution of pyknotic neurones in the ganglion cell layer were estimated across the whole retina. Between E8 and E10, the distribution of neurones in the ganglion cell layer was anisodensitic with 53,000 mm-2 in the centre compared to 34,000 mm-2 in the periphery of the retina. Thereafter, a progressively steeper gradient of neurone density developed, which decreased from 24,000 mm-2 in the retinal centre to 6000 mm-2 at the retinal periphery by 4WAH. Neuronal pyknosis in the ganglion cell layer was observed between E9 and E17. From E11 onwards, consistently more pyknotic neurones were found in the peripheral than in the central retina. It was estimated that over the period of cell death approximately twice as many neurones died per unit area in the retinal periphery than in the centre. Retinal area measurements and estimation of neurone densities in the ganglion cell layer after the period of neurone generation and neurone death indicated differential retinal expansion, with more expansion in the peripheral than in the central retina. These observations allow us to conclude that the formation of the area centralis of the chick retina involves (1) slightly higher cell generation in the retinal centre, (2) higher rate of cell loss in the retinal periphery and (3) differential retinal expansion.

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PubMed1987

The effects of tectal lesion on the survival of isthmic neurones in Xenopus.

The isthmic nucleus (IN) is a visual relay centre of the frog brain. It receives afferent projection from the optic tectum of the same side and projects bilaterally to both tecta. In young postmetamorphic Xenopus frogs, the survival of neurones in the IN on both sides was studied following the complete removal of the right tectum. In 6- to 8-week-old frogs, the right tectum was surgically removed and the operated animals allowed to survive for 1 to 13 weeks after operation. In selected animals, 3 days before the intended sacrifice, the postoptic commissure was transected and the cut isthmotectal fibres filled with horseradish peroxidase (HRP). In serial paraffin sections of the midbrain, the numbers of surviving and dying (pyknotic) neurones in the left and right IN were counted. The soma size of viable isthmic neurones and the volume of both IN were measured. Pyknotic neurones were seen between 1 and 6 weeks after operation in both the left and right IN, although the rate of cell loss was much greater in the latter. Virtually all the neurones of the right IN degenerated by 6 weeks after tectal ablation. In contrast, approximately 60% of neurones of the left IN survived. HRP histochemistry showed labelled isthmic neurones both in the left and right IN up to 3 weeks after operation. Thereafter, HRP-labelled neurones appeared only in the left IN. These observations indicate that the removal of the natural target of isthmic neurones brings about severe neurone death.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1986

Naturally occurring and induced ganglion cell death. A retinal whole-mount autoradiographic study in Xenopus.

The retina in frogs grows continuously throughout the whole life of the animal by the addition of rings of cells at the ciliary margin. Naturally occurring neuron death cannot, consequently, be established by counting surviving neurons. A new approach, retinal whole-mount auto-radiography was introduced in this study to estimate cell loss occurring in the ganglion cell layer over a long period of time. 3H-thymidine injection at stage 53 (midlarval stage) labels a ring of cells, thereby marking the extent of retina formed up to the time of isotope administration. In the present study the number of neurons in the ganglion cell layer within the autoradiographically identified central retinal sector was estimated from midlarval stage to 6 months after metamorphosis in Xenopus laevis. The mean neuron number in the central retinal sector formed up to stage 53 was 17,420 and this was reduced by 20% to 13,515 by 6 months after metamorphosis. Optic nerve section at the time of isotope injection and subsequent regeneration brought about a reduction of the number of surviving neurons in the part of the retina formed up to stage 53 to 7,720, or to about 57% of the normal neuron number in an equivalent retinal area of an intact eye of the same age. A further reduction to 20% of normal neuron population was observed in retinae where the optic nerve failed to regenerate. The surviving neurons are assumed to be amacrine cells. The bulk of natural neuron loss in the retinal centre occurs during premetamorphic stages while little further loss takes place in the next 6 months suggesting that the underlying mechanism is a fine tuning of the developing retinal projections.

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PubMed1986

The development of the trigeminal (V) motor nucleus in normal and tubocurare treated chick embryos.

The generation of cells and the naturally occurring neuronal death was studied in the trigeminal motor neuron pool in normal and tubocurare treated chick embryos between the 5th and 18th days of incubation. 3H-thymidine autoradiography revealed that the generation time extends from the 2nd to the 5th day of incubation, wherein about 50% of trigeminal motoneurons are born on the 3rd day. Maximum neuron number was found on the 7th day of incubation which steadily decreased to about 50% of the originally generated neurons by the 13th day. Nuclear pyknosis occurred from the 6th to the 13th day of incubation with a peak of neuron loss on the 7th day. Tubocurare, administered daily from the 5th day of incubation rescued most of the generated motoneurons which would otherwise have died. Cell nuclear area measurements in the motoneuron pool of the tubocurare treated animals showed a marked hypertrophy accompanying the increased neuronal survival. These observations indicate that tubocurare treatment prevents naturally occurring neuron death and causes significant nuclear hypertrophy within the trigeminal motoneuron pool innervating special, branchial arch derived muscles. Thus these neurons respond to tubocurare treatment in a manner similar to motoneurons of the spinal cord.

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PubMed1986

The development of the neurons of the glossopharyngeal (IX) and vagal (X) sensory ganglia in chick embryos.

The timetable of cell generation, neuronal death and neuron numbers in the fused proximal glossopharyngeal (IX) and vagal (X) ganglion and distal IX and X ganglia were studied in normal and nerve growth factor (NGF) treated chick embryos. 3H-thymidine was injected between the 3rd and 7th days of incubation and embryos sacrificed on the 11th day. Neurons in the distal IX and X ganglia were generated between the 2nd and 5th days of incubation, the peak mitotic activity occurring on the 4th and 3rd days, respectively. Neurons of the proximal IX and X ganglion were generated between the 4th and 7th days, with maximum neuron generation on the 5th day of incubation. Counts of neurons in the 3 ganglia between the 5th and 18th days of incubation showed a maximum of 22,000 on the 8th day in the proximal IX and X ganglion and this decreased to 12,000 by the 13th day. In the distal IX ganglion, the neuron number decreased by 44% from 4,500 on the 6th day to 2,500 by the 11th day. A similar decrease of 43% was found in the distal X ganglion, the neuron number falling from 11,500 on the 7th day to 6,500 by the 11th day of incubation. Neuronal cell death in these ganglia extended from the 5th to the 12th day of incubation, maximum cell death occurring at or after the cessation of mitotic activity. NGF administration from the 5th to the 11th day of incubation did not have a measurable effect on the neurons of proximal IX and X and distal IX ganglia, but increased neuronal survival by 30% in the distal X ganglion.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1986

The thoracic sympathetic neurons of the chick: normal development and the effects of nerve growth factor.

The generation and degeneration of sympathetic neurons in the third thoracic ganglion (segment 19) of the chick were studied between embryonic days (E) 7-18 using 3H-Thymidine autoradiography and routine cell counts. Cumulative radiolabelling experiments indicated that few sympathetic neurons were generated on E6-7. 10% of the sympathetic neurons were generated on E8 and a further 20% on E9. The final 70% of neurons completed the mitotic cycle between E10-12. Cell counts demonstrated that the neuronal population increased from 10,166 +/- 423 (mean +/- SEM) to 22,291 +/- 767 between E8-10 and remained stable up to E14. The population subsequently declined by 37%, to 14,157 +/- 831, by E18. Pyknotic neurons were found at all stages of development, but were most apparent between E7-15. The effects of Nerve Growth Factor (NGF) on the number of both surviving and pyknotic neurons in the ganglion were also examined. E9 embryos treated with NGF from E5-8 showed a 57% increase in the number of sympathetic neurons. This increase therefore occurred prior to the decline in neuronal number and was not accompanied by a decrease in the number of visibly pyknotic neurons. It is therefore possible that early NGF treatment increases the number of sympathetic neurons through a mechanism other than the attenuation of cell death.

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PubMed1986

The formation of axonal projections of the mesencephalic trigeminal neurones in chick embryos.

Horseradish peroxidase-wheat germ agglutinin conjugate (HRP) was injected into masticatory and eye muscles of 6- to 15-day-old chick embryos and posthatched chicks to establish the timetable of axonal outgrowth and distribution of central and peripheral terminations of mesencephalic trigeminal neurones (MTN). HRP-labelled MTN first appeared on the 10th day of incubation and by the 14th day most of MTN became labelled, indicating that axonic outgrowth to peripheral targets occurred between the 10th and 14th days of incubation. Peripheral targets included the pterygoideus lateralis and medialis, protractor quadratus, pseudotemporalis superficialis and profundus, and adductor mandibulae of jaw-closing muscles. HRP-filled central axonic processes of MTN were identified first on the 13th day of incubation and they terminated exclusively in the motor nucleus of the trigeminal nerve. Between the 10th and 13th days of incubation, at the peak of naturally occurring cell death in the MTN pool, a consistently lower percentage of neurones could be labelled with HRP than in older embryos and in posthatched chicks. This finding suggests that many MTN die before establishing contact with peripheral targets.

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PubMed1985

The effect of nerve growth factor on developing primary sensory neurons of the trigeminal nerve in chick embryos.

The response to nerve growth factor (NGF) of two sensory neuron populations of the trigeminal nerve was studied in chick embryos. NGF promoted neuronal survival and cellular hypertrophy in the Gasserian ganglia with minimal effect on the neuron population of the mesencephalic trigeminal nucleus. NGF induced prolific neurite outgrowth from cultured Gasserian ganglia, in contrast, cultured mesencephalic trigeminal neurons remained refractory to NGF treatment. The apparent lack of response of mesencephalic trigeminal neurons to NGF may be explained either by their derivation from placodal material rather than from the neural crest, or their lost sensitivity to NGF due to interaction with the local environment in the central nervous system.

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PubMed1985

Nerve growth factor treatment does not prevent dorsal root ganglion cell death induced by target removal in chick embryos.

In chick embryos, on the 3rd day of incubation, the developing right wing bud was removed. One group of the operated embryos was treated with a daily dose of 20 micrograms purified nerve growth factor (NGF) from the 5th day of incubation and sacrificed on the 12th day. The other group was sacrificed on the 12th day of incubation and served as control. NGF was also administered to intact, unoperated embryos for comparison. The size of the dorsal root ganglia in segments 13-16 innervating the wings, were estimated and the number of surviving dorsal root ganglion cells counted both on the right (operated) and left (intact) sides. Although NGF brought about an increase in the size of the ganglia and an increase in the number of dorsal root ganglion cells bilaterally, it was not able to prevent excessive cell death of dorsal root ganglion cells on the operated side. The number of surviving neurons in the dorsal root ganglia on the operated side in embryos with or without NGF administration was only about 30-50% of the number of the intact side. These results show that cell death induced by target removal cannot be offset by NGF administration. It is concluded that NGF may act as a growth promoting agent for developing sensory neurons but other peripheral trophic factor/s are also needed for the maintenance and survival of dorsal root ganglion cells.

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PubMed1984

Post-metamorphic retinal growth in Xenopus.

The postmetamorphic growth of the retina in Xenopus was studied using 3H-thymidine ( 3HT ) autoradiography and quantitative morphometric assays. 3HT was administered to tadpoles at stages 58, 62 and 66 and the animals sacrificed between 3 weeks and 12 months after metamorphosis. Reconstructions were made from serial sections and the position of labelled cell groups in the retina were established. On the reconstructed retina, regions formed up to stage 58, between stages 58 and 66 and after metamorphosis were measured. The area of the dorsal, ventral, temporal and nasal retinal halves was also determined from stage 58 through to adult. The entire retinal area increased 10-fold from stage 58 to 12 months after metamorphosis, the fastest growing region being the retinal periphery due to continuous cell addition at the ciliary margin. Concommitant with the retinal area growth, the number of ganglion cells increased from 20,000 to 85,000 over the time of investigation. Asymmetric cell addition to the ciliary margin from stage 58 onwards resulted in a predominantly crescentic retinal growth along the nasoventral ciliary margin. Consequently, the optic nerve head became displaced away from the geometric centre of the eye into the dorso-temporal retinal quadrant. These results suggest that besides a sustained cell production exclusively at the ciliary margin, a passive area expansion contributes to the overall retinal growth from the metamorphic climax to adulthood. It is also apparent that the steady increase of the number of retinal ganglion cells and optic fibers necessitates a continuous remodelling of the retinotectal connections throughout the lifespan of the animal.

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