Biomedical subjects

T G Gorgels

Publications and source records attributed to T G Gorgels.

15 recordsLinked to original sources

PubMed1999

Filling-in after focal loss of photoreceptors in rat retina.

We investigated the fate of isolated photoreceptor lesions in rat retina over a time span of 6 months. With a carefully selected dose of UV-A (380 nm) a complete loss of photoreceptors was caused in sharply demarcated areas of 200, 400 or 800 microm wide, without visible damage to other retinal layers. One day after irradiation, all rods were pyknotic. Three weeks later practically all damaged photoreceptors were removed. The size of the lesion had decreased as the surrounding photoreceptors had migrated into the lesion. The outer segment tips had moved inwards up to 200 microm, but the innermost nuclei in the outer nuclear layer had moved inwards substantially less. The distance over which the photoreceptors migrated increased with lesion size, but only 200 microm defects were filled-in completely on the level of the outer segments. Between three weeks and six months after irradiation, no further decrease in lesion size occurred. We conclude that after local loss of photoreceptor cells the bordering photoreceptors rapidly shift into the lesion area, but complete filling-in is limited to very small lesions.

Animals↗

PubMed1999

Temporal sequence of changes in rat retina after UV-A and blue light exposure.

Two spectral types of retinal light damage were induced in pigmented rats by irradiating small retinal patches at either 380 or 470 nm. The temporal sequence of changes in the retina was followed for up to 2 months by funduscopy and histology. For both damage types, fundus changes were best visible after 3 days. Histology showed that 380 nm specifically damaged photoreceptor cells, particularly the rods. All cell compartments of the rods, including the nucleus were affected already after 3 h. In the next days, damaged rods degenerated. At high doses (2.5 x the funduscopic threshold dose) all rods in the irradiated area were lost, resulting in a local photoreceptor lesion, which was still present at 2 months after the irradiation. At 470 nm, damage occurred both in the photoreceptor layer and in the pigment epithelium. Acute changes, at 1 h after irradiation, consisted mainly of damaged mitochondria in these layers. Next, the pigment epithelium showed swelling, an altered melanin distribution and, at high doses (2.5 x threshold), interruptions of the monolayer. Degeneration of photoreceptor cells was initially limited to a few scattered cells, but 3 days after high doses focal areas of massive degeneration were seen. At late stages, the cells of the pigment epithelium recovered and the photoreceptor layer showed a loss of cells. The results show that the spectral damage types are distinct in the early phases, indicating that different mechanisms are involved. Yet, the end effect of both damage types after exposure at doses up to 2.5 x the funduscopic threshold is remarkably similar and consists of local photoreceptor lesions.

Animals↗

PubMed1999

The effects of two stereoisomers of N-acetylcysteine on photochemical damage by UVA and blue light in rat retina.

High doses of light can cause damage to the retina, e.g. during intraocular surgery. Previously, thiols have been demonstrated to protect against retinal damage in various damage models. Such protection is very promising for clinical practice. Retinal light damage can be caused by a relatively short exposure to high irradiance levels. These conditions occur during intraocular surgery. In the current study we therefore investigated whether the thiol N-acetylcysteine protects against retinal light damage under high irradiance conditions in the rat retina. Two stereoisomers of this thiol were tested for protection against two spectrally defined types of retinal light damage. Shortly after administration N-acetyl-L-cysteine in doses of 270-1000 mg/kg intraperitoneally protected against 380 nm (UVA) light but not against 470 nm (blue) light. Two hours after injection the protection had diminished. We observed no protection by the stereoisomer N-acetyl-D-cysteine. From this study we conclude that N-acetyl-L-cysteine protects stereospecifically against retinal damage in the UV but not in the visible part of the spectrum. This limits the possible applications.

Acetylcysteine↗

PubMed1998

Two spectral types of retinal light damage occur in albino as well as in pigmented rat: no essential role for melanin.

Earlier we showed that two spectral types of retinal damage occur in the pigmented rat. In the present study we investigated whether the same is true for albino rats. When investigating this issue we implicitly investigated the role of melanin in both damage types. An albinotic (Wistar) and a pigmented (Long Evans) strain of rats were used. Under anesthesia, a small part of the retina was irradiated at either 380 nm or at 470 nm. Three days later, the retina was analysed by funduscopy and prepared for light microscopy. Funduscopy showed no signs of damage in the albinotic retina. In the pigmented retina a decoloration of the fundus was noticed after irradiations starting from retinal doses of 0.6+/-0.1 J cm-2 at 380 nm, and from 489+/-71 J cm-2 at 470 nm. By light microscopy, retinal damage was found in the albino retina. The histologic manifestations at 380 nm differed from those at 470 nm. Irradiation at 380 nm at a dose of 0. 5-0.9 J cm-2 damaged a few scattered photoreceptor cells. At doses of 1.2-1.6 J cm-2 all rods were damaged, while the other retinal layers showed no changes. These findings were similar to those found at 380 nm in the pigmented rat. At 470 nm, damage was found most prominently in the retinal pigment epithelium. These cells showed swelling and an increased number of dark inclusions. Threshold damage occurred at doses of 250-500 J cm-2. Again, the pathology in the pigmented rat was highly similar to that in the albino rat. The results show that both spectral damage types occur in albino as well as in pigmented retina. Therefore, melanin plays no crucial role in these light damage types.

Albinism, Ocular↗

PubMed1998

Ultraviolet-B induced hyperplasia and squamous cell carcinomas in the cornea of XPA-deficient mice.

In Xeroderma Pigmentosum (XP) patients, due to a defective repair of UV-induced DNA damage, neoplastic changes occur in sunlight-exposed areas of the skin and eyes. There are seven complementation groups in XP (XP-A to XP-G). Recently, we have generated XPA-deficient mice (group-A XP) by gene targeting in embryonic stem cells. In order to evaluate UV-B sensitivity, XPA-deficient mice (n = 20), wild type (n = 7) and heterozygous mice (n = 13) were exposed to low daily doses of UV-B for 14 weeks at a cumulative dose of 22 kj m-2 (250-400 nm). For a period of 32 weeks, the mice were checked twice a week for the development of pathology. The UV-B treatment induced eye abnormalities in the XPA-deficient mice. Initially, photophobia was noticed, followed by a loss of transparency of the cornea, eventually affecting nearly all XPA-deficient mice (19 out of 20). In 12 out of 19 mice, the pathology progressed to give eye protrusion. Histology of these eyes showed hyperplasia and squamous cell carcinomas of the corneal epithelium. No eye-lesions were found in control (wild-type and heterozygous) mice that were exposed to the same UV-B dose. The corneal abnormalities found in the XPA-deficient mice appear to be similar to those found in human XP patients. These results confirm the role of the functional XPA gene in protecting the cornea from pathology by UV-B irradiation. In addition, they suggest that the XPA-deficient mouse is a suitable animal model for the study of XPA ocular disorders.

Animals↗

PubMed1997

Effect of body temperature on retinal damage by 488 nm light in rat.

Retinal light damage is influenced by the body temperature during exposure, but previous studies do not agree on the magnitude of the effect. A study in rats with broadband green light reported a much larger effect than a study with 380 nm light. The present study set out to clarify whether the spectral composition of the damaging light is responsible for this discrepancy by using 488 nm instead of 380 nm light. Wavelengths in the range of 470-550 nm are known to produce a different damage type than 380 nm. Small patches of retina of anesthetized rats were exposed to 488 nm radiation of an argon ion laser. Body temperature was varied between 30 and 40.5 degrees C. Three days after irradiation, the retina was inspected by funduscopy and prepared for light microscopy. The dose of radiation needed for a just visible change in fundo decreased by 6% per degree increase in body temperature. Damage was mainly found in the retinal pigment epithelium. Temperature had no effect on damage morphology. The temperature effect at 488 nm is much smaller than reported for broadband green light. We conclude that the spectral composition of the damaging light is not responsible for the discrepancy on the magnitude of the temperature effect. Other differences between the studies must be responsible, such as difference in retinal irradiance levels.

Animals↗

PubMed1995

Ultraviolet and green light cause different types of damage in rat retina.

PURPOSE: To assess the influence of wavelength on retinal light damage in rat with funduscopy and histology and to determine a detailed action spectrum. METHODS: Adult Long Evans rats were anesthetized, and small patches of retina were exposed to narrow-band irradiations in the range of 320 to 600 nm using a Xenon arc and Maxwellian view conditions. After 3 days, the retina was examined with funduscopy and prepared for light microscopy. RESULTS: The dose that produced a change just visible in fundo was determined for each wavelength. This threshold dose for funduscopic damage increased monotonically from 0.35 J/cm2 at 320 nm to 1600 J/cm2 at 550 nm. At 600 nm, exposure of more than 3000 J/cm2 did not cause funduscopic damage. Morphologic changes in retinas exposed to threshold doses at wavelengths from 320 to 440 nm were similar and consisted of pyknosis of photoreceptors. Retinas exposed to threshold doses of 470 to 550 nm had different morphologic appearances. Retinal pigment epithelial cells were swollen, and their melanin had lost the characteristic apical distribution. Some pyknosis was found in photoreceptors. CONCLUSIONS: Damage sensitivity in rat increases enormously from visible to ultraviolet wavelengths. Compelling evidence is presented that two morphologically distinct types of damage occur in the rat retina, depending on the wavelength. Because two types also have been described in monkey, a remarkable similarity seems to exist across species.

Animals↗

PubMed1992

Spectral transmittance of the rat lens.

The spectral transmittance of the isolated rat lens for radiation of wavelengths from 300 to 700 nm was measured using a spectrophotometer. Transmittance decreased from 93-95% at 700 nm, to 70-80% at 400 nm, 50-60% at 360 nm, 4-18% at 320 nm, and to < 2% at 310-300 nm. These results indicate that the rat lens is remarkably transparent for UVA radiation, which has consequences for rat vision, and for interpretation of earlier studies on retinal light damage.

Animals↗

PubMed1991

Outgrowth of the pyramidal tract in the rat cervical spinal cord: growth cone ultrastructure and guidance.

In order to examine the mode of outgrowth of the pyramidal tract in the rat, the ultrastructure of its pathway in the dorsal funiculus of the spinal cord was analysed. The analysis was performed by means of serial sections of the third cervical segment before and during the arrival of pyramidal tract axons, and focussed on the morphology and microenvironment of the growth cones. Growth cones appear as elongated terminal enlargements without side branches. Two zones could be discerned: the distal, usually lamellipodial fine granular zone, containing no organelles, except for an occasional clear vesicle; and the proximal organelle-rich zone, which contains various organelles, such as agranular reticulum and vesicular structures. In addition, the proximal organelle-rich zone contains round or elliptic structures, limited by two concentric membranes, that enclose reticular and vesicular elements. The electron density of these structures varied from as low as the surrounding growth cone matrix to as dark as lysosomal structures, suggesting their involvement in turnover processes. At embryonic day 20, the most ventral part of the dorsal funiculus, where the first pyramidal tract axons are due to arrive within two days, is populated by axons that are relatively small compared to those in the rest of the dorsal funiculus. At birth, the arrival of the first pyramidal tract axons is marked by the presence of numerous large growth cone profiles in between small axons in the most ventral part of the dorsal funiculus; no circumscript bundle separated from the ascending sensory fiber tracts is present yet. The growth cones descend, club-shaped and 1 to 2 microns in diameter, without lamellipodia or filopodia. Within the same area a second growth cone type is present, which contains dense-core vesicles and has spread-out lamellipodia. Most of these growth cones are ascending and they probably belong to primary afferent or propriospinal fibers. At postnatal day 2, the pyramidal tract can be readily delineated from the adjacent fasciculus cuneatus where myelination has already started, but no glial boundary is present. The abundant growth cones are 1-2 microns wide and extend single unbranched lamellipodia, up to 15 microns long, which often enfold parallel axons or other growth cones. At postnatal day 4, growth cones are scarce in the tract. They measure 1 micron or less in diameter and each extends a single, straight lamellipodium or filopodium over 1 to 7 microns in the caudal direction.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

Junctional specializations between growth cones and glia in the developing rat pyramidal tract: synapse-like contacts and invaginations.

The ultrastructure of contacts between axonal growth cones and glial cells in the developing pyramidal tract was examined by serial sectioning at the third cervical spinal cord segment in 0-, 2-, and 4-day-old rats. Junctional specializations, composed of synapse-like contacts and invaginations, were frequently observed at the contact zone between growth cones and glial elements. The synapse-like contacts consist of clear, round vesicles of 43 +/- 6 nm in the presynaptic growth cone, a pre- and a postsynaptic density, separated by a cleft of 12.1 +/- 0.9 nm. The invaginations consist of small protrusions of the growth cone into the glial element. The invaginated glial membrane is coated. Within the glial element, close to the invagination, frequently organelles were observed that closely resemble endosomes and prelysosomes. Therefore, it is suggested that the invagination represents a stage in endocytosis or possibly phagocytosis of the protruding part of the growth cone by the glial cell. The junctional specializations are formed by growth cones and, less frequently, by axon shafts. The targets of these specialized contacts are, in general, immature glial cells located within the tract area. Occasionally, however, invaginations were also observed into myelinating oligodendrocytes, suggesting that the population of immature target cells includes oligodendrocyte precursors. With regard to the functional significance of these temporary growth cone-glial contacts, several possibilities are discussed, including the suggestion that outgrowing pyramidal tract axons provide immature glial cells with chemical messages, which may influence the timing of glial cell maturation in the tract.

Animals↗

PubMed1990

A quantitative analysis of axon outgrowth, axon loss, and myelination in the rat pyramidal tract.

A quantitative analysis of the development of the pyramidal tract (PT) was carried out at the level of the caudal medulla oblongata and at the sixth cervical spinal segment (C6), in rats ranging in age from embryonic day 20 (E20) to the adult of 90 days postnatally (P90). The axon number in the right medullary PT rises from 27,000 axons at E20 to 391,000 axons at P4. Growth cones are abundant during this period, but can still be observed occasionally at P7. After P4, the axon number is reduced by 62%, to 150,000 in the adult. A rapid axon loss until P14 is followed by a gradual axon loss, continuing beyond the third postnatal week. A similar biphasic axon loss was observed in the cervical PT. At P2 and at P7, concentrations of electron-dense material were observed in 0.5-0.7% of the axon profiles in the medullary PT. Since at P21 this feature was only observed in 0.2% of the axons, it might represent an early sign of axon loss. Myelination starts in the medullary PT at P7. Especially during the third postnatal week, the number of myelinated axons increases rapidly. In the adult rat PT, both at medullary and cervical levels, about one third of the axons are still unmyelinated. The results indicate that the development of the rat PT is characterized by a gradual outgrowth of its fibers and by a protracted, biphasic axon loss. Furthermore, comparing the PT at the medulla, at C3, and at C6, a rostrocaudal decrease in axon number was observed during development as well as at the adult stage. Therefore, no evidence was found for increased axon branching in the tract in the cervical intumescence.

Aging↗

PubMed1990

Immunoelectron microscopic localization of cell adhesion molecule L1 in developing rat pyramidal tract.

The glycoprotein L1 is a cell adhesion molecule that has been proposed to function in the peripheral nervous system in axon fasciculation and onset of myelination. In this report we localize L1 during the development of a major central pathway: the pyramidal tract. The (sub)cellular localization of L1 was determined both by pre-embedding staining on Vibratome sections and by immunogold labelling on ultracryosections in developing rat pyramidal tract at the fifth cervical segment. On arrival at the fifth cervical segment, i.e. at postnatal day 1, growth cones of pioneer fibres did not exhibit L1-immunoreactivity. In the contact zone between pyramidal tract growth cones and glial processes no L1-immunoreactivity was observed. A clear L1-immunoreactivity was noted on small unmyelinated other axons situated in the entrance area of the pyramidal tract growth cones. Also on later arriving, i.e. between postnatal days 2 and 10, small unmyelinated fasciculating pyramidal tract axons L1 were present. It is our impression that L1 is localized in an irregular patchy way on the outer side of the axonal membrane. During the onset of myelination, i.e. between postnatal days 10 and 14, L1 could not be detected on axons ensheathed by oligodendrocytic processes. When myelination is largely completed, i.e. at postnatal day 21, the L1 antigen could be localized within the axoplasma of both unmyelinated and myelinated pyramidal tract axons. Furthermore, L1 could be observed occasionally on small unmyelinated pyramidal tract axons. Whereas compact myelin was always L1-negative, L1 was noted periaxonally between the axolemma and compact myelin and at (para)nodal regions at the contact zone between axolemma and oligodendrocytic processes. From these results it may be deduced that: (1) L1 is involved in fasciculation of outgrowing later arriving pyramidal tract fibres: (2) L1 is not involved in the onset of myelination in this central tract; (3) L1 might play an additional adhesive role in myelinated rat pyramidal tract.

Aging↗

PubMed1989

A quantitative analysis of the development of the pyramidal tract in the cervical spinal cord in the rat.

A quantitative electron microscopic analysis was undertaken of the development of the pyramidal tract, at the level of the third cervical spinal segment, in rats ranging in age from the day of birth to three months old. The axon number was calculated as the product of axon density, determined in a systematic random sample of electron micrographs, and tract area. During the first postnatal week the tract contains thin unmyelinated axons and growth cones. Growth cones are abundant in neonatal rats, but can still be observed occasionally at the end of the first postnatal week, indicating a continuous addition of pyramidal tract axons during the first postnatal week. Myelination starts around P10. By the end of the first postnatal month approximately 50% of the axons have already been myelinated. Myelination proceeds during further maturation, but in the three month old rat 28% of the axons are still unmyelinated. The total number of axons increases rapidly after birth up to 153,000 at the fourth postnatal day. Subsequently, the number of axons is reduced by nearly 50% to 79,000 in the adult rat. The axon loss is most prominent during the second postnatal week, when 32,000 axons are eliminated, but continues for several weeks at a slower rate.

Animals↗

PubMed1989

B-50/GAP43 is localized at the cytoplasmic side of the plasma membrane in developing and adult rat pyramidal tract.

The neuron-specific phosphoprotein B-50/GAP43 has been implicated in axonal outgrowth, since high levels of B-50/GAP43 are found in growth cones and during development of the nervous system. In adult brain, the B-50 levels are decreased. B-50 is primarily found in axons and presynaptic terminals. It is phosphorylated by protein kinase C, and this process has been implicated in the modulation of membrane signal transduction. During the outgrowth of the pyramidal tract, high levels of B-50 have been reported, whereas a low amount of B-50 persists into the adult stage. By immunoelectron microscopy, using immunogold labeling on cryosections and pre-embedding peroxidase labeling, we examined the distribution of B-50 in the pyramidal tract at the third cervical segment in developing 2-d-old and adult 90-d-old rats. B-50 immunoreactivity was found in axons and growth cones of the outgrowing tract. In the adult pyramidal tract, both unmyelinated and myelinated axons contained B-50 immunoreactivity. The immunogold label was predominantly located at the plasma membrane. Since the peroxidase reaction product was observed exclusively intracellularly, we conclude that the B-50 immunoreactivity is predominantly located at the cytoplasmic side of the plasma membrane of axons and growth cones. The high immunoreactivity in growth cones and axons of the outgrowing pyramidal tract further supports the hypothesis that B-50 plays a role in neurite outgrowth. The presence of B-50 in the adult pyramidal tract cannot merely be attributed to transport to the synapse. Therefore, it is suggested that B-50 plays, in addition, a local, growth-associated role in the adult tract.

Aging↗

PubMed1987

Immunocytochemical distribution of the protein kinase C substrate B-50 (GAP43) in developing rat pyramidal tract.

The neuron-specific phosphoprotein B-50 is a major substrate of kinase C in fetal nerve growth cones, neonatal neural and synaptosomal plasma membranes. B-50 is identical to a growth-associated protein GAP43. Similarly, increases in B-50 occur during rat brain development, neuronal differentiation and axon regeneration. To document the relation between the expression of B-50 and the outgrowth of central axons, we studied B-50 in the developing pyramidal tract in rats at postnatal days 2, 7 and 90 (P2, P7 and P90), at the third cervical spinal segment C3, using affinity-purified antibodies to B-50. At P2 and P7, when outgrowth of pyramidal tract fibers is occurring, B-50 immunoreactivity (BIR) is intense in these fibers. BIR is reduced from P2 to P7 in the ascending fiber tracts of the cuneatus and the gracilis, which develop earlier. At P90 when most of the dorsal funiculus fibers have reached their targets and many are myelinated, BIR is dramatically reduced. In agreement, a 10-fold decrease in B-50 content was measured at P90, as compared to P7. Therefore, our results indicate that B-50 is only expressed relatively abundant in axons of the funiculus posterior during outgrowth. By inference, B-50 may be a differentiating marker to detect elongating fibers.

Animals↗