A previous abrasion in the contralateral eye influences the cell kinetics during healing of a central corneal abrasion.

PURPOSE: To study the influence of a previous erosion in the fellow eye on the proliferative response during healing of a central corneal erosion. METHODS: A corneal abrasion was made on the right eye of 20 rats. After 1 week a corneal erosion was made in the left eye of the pre-treated animals and in 20 previously untreated animals. Cell kinetic methods were used to estimate the labelling index (LI) and the mitotic rate (MR) after 1, 2, 4, 6 and 12 days. RESULTS: After 24 hours the corneal erosions were covered by epithelial cells in 3 of 4 animals in both groups. The LI and the MR were significantly higher in the pre-treated group on the 2nd day after erosion. CONCLUSIONS: The proliferation measured by LI and MR was increased when an abrasion was made in the contralateral eye 1 week earlier. This might explain the faster healing rate of the second eye reported by other authors (Rask et al. 1996). The healing process in the cornea is modulated by systemic influence.

Dynamic MR-imaging in the diagnosis of pigmented villonodular synovitis of the knee.

The aim of this report was to study the rate of contrast enhancement at MRI in pigmented villonodular synovitis (PVNS). Dynamic MRI was performed in a patient with PVNS just before and 1 week and 3 years following synovectomy of the knee. As opposed to patients with rheumatic disease the patient with PVNS showed a slower enhancement rate before synovectomy than 1 week after. At 3 years follow-up the patient with PVNS showed an enhancement rate just above that of the normal controls. The results indicate that PVNS has features more common to hyperplastic or neoplastic lesions than to inflammatory ones. The results at 3 years follow-up also suggest that dynamic MRI may indicate the efficacy of arthroscopic synovectomy.

Early cell kinetic effects of some drugs on the rat corneal and conjunctival epithelia.

The early cell kinetic response in the rat corneal and conjunctival epithelia was studied after a single topical application of dipivefrine, adrenaline and timolol with and without benzalkonium chloride. Benzalkonium chloride alone in different concentrations, 0.004%, 0.01%, 0.02% and 0.04%, respectively, was also evaluated. The stathmokinetic method and the tritiated thymidine technique were used to estimate the mitotic rate and the labelling index. Dipivefrine (Propine) gave a significant depression of the mitotic rate almost to the same extent as adrenaline in the corneal epithelium, whereas no changes were found in the limbal area and in the conjunctiva. Timolol (Oftan) with or without benzalkonium chloride, and benzalkonium chloride in different concentrations gave no obvious changes of the mitotic rate. No distinct drug effects on the labelling index were observed.

Histopathologic changes of the temporomandibular joint disk in patients with chronic arthritic disease. A comparison with internal derangement.

Histopathologic examination was performed of the disk and the posterior attachment extirpated from 17 temporomandibular joints from 15 patients with chronic arthritic disease. Seven patients had rheumatoid arthritis (including two with juvenile type), five had ankylosing spondylitis, and three had psoriatic arthropathy, which affected more joints than the temporomandibular joint. Specimens removed from 16 temporomandibular joints from 15 patients with internal derangement were used for histopathologic comparison. In both groups of patients, inflammatory changes were observed, but no specific histopathologic signs could distinguish the groups. Patients with chronic arthritic disease seemed to have more pronounced changes of vascular proliferation, perivascular cellular infiltrate, inflammatory cells, and fibrosis throughout the soft tissues. Destruction of the disk was another finding evident in patients with chronic arthritic temporomandibular joint disease; there was no visible disk structure in 8 of these 17 joints, compared with 1 of the 16 joints in the internal derangement group.

Time dependency in the regenerative response to injury of the rat corneal epithelium.

In the present study a central corneal epithelial defect (diameter 3.5 mm) was made in both eyes at 12:00 h in one group of rats and at 24:00 h in another group to see if the regenerative proliferation is influenced by circadian rhythms. The labeling index and the mitotic rate were registered at 4-h intervals in the perilimbal conjunctiva, the limbal area, and different parts of the cornea from the following morning until noon the day after that. The most pronounced regenerative proliferation was seen in the midperipheral and peripheral cornea. The regenerative response occurred in both groups 24-28 h after the injury, but was highly influenced by the normal circadian rhythms, especially with regard to the mitotic rate. The results support the theory that even regeneration is influenced by a circadian proliferative factor.

Cell kinetics of conjunctival and corneal epithelium during regeneration of different-sized corneal epithelial defects.

Rats with small (diam. 1.7 mm), medium sized (diam. 3.5 mm) or large (diam. 5.5 mm) corneal epithelial erosions in one eye were killed 1, 2 or 4 days after the injury. The proliferative response was evaluated by measuring the labelling index and the mitotic rate in the corneal epithelium and in the adjacent conjunctiva. The small erosions triggered a proliferative response in the cornea only with the maximum response occurring midperipherally. The medium sized erosions induced a higher and more extensive response in the cornea and also a slight increase of the labelling index in the limbal area. The large erosions induced an even more pronounced response in the peripheral cornea and an increase both of the labelling index and the mitotic rate well beyond the limbal part of the conjunctiva. It is concluded that the magnitude and the extent both of the conjunctival and the corneal regenerative response to a corneal abrasion is correlated to the size of the corneal defect. Temporary reduction in the conjunctival epithelial cell number shows that both cells in the limbal and the extralimbal conjunctiva migrate centripetally during healing of large corneal wounds. It is suggested that the stem cell theory should be modified. The limbal area is probably an area in which conjunctival epithelial cells or conjunctiva-derivated cells transform or differentiate to corneal epithelial cells.

Primary malignant melanoma of the lacrimal sac.

A case report of a primary malignant melanoma of the lacrimal sac is presented. After excision a local recurrence appeared one year later. Wide, but incomplete excision and postoperative irradiation resulted in local tumour control for 4 years. The patient succumbed to a uremic death caused by a rectal cancer removed 3 years before the occurrence of the malignant melanoma.

Cell kinetics of the rat corneal epithelium.

In the rat corneal epithelium the mitotic rate (MR) is almost equal throughout the epithelium in the morning (Haaskjold et al. 1988). The labelling index (LI) shows a marked reduction in the central cornea, which could suggest a lack of uptake of tritiated thymidine via the salvage pathway (Haaskjold et al. 1989). In the present study we have used [3H]deoxycytidine, and [3H]thymidine after prior treatment with a methotrexate regimen to elucidate this discrepancy. Deoxycytidine is incorporated into DNA independent of thymidine kinase, while methotrexate, which depletes the cells of reduced folates, makes the cells completely dependent on the salvage pathway. With both techniques the same pattern of labelling was observed, confirming that in the morning the ratio between the MR and the LI differs throughout the cornea. Based on previous observations, an analysis of the MR/LI ratio during 24 h was performed, showing that these parameters were strongly correlated. This suggests that there may be different circadian variations in the cell proliferation parameters throughout the corneal epithelium. The methotrexate regimen may be a useful tool to investigate the salvage pathway.

Inhalation of organic solvents does not promote synovial tissue inflammation in rats.

Organic solvent exposure is known to give rise to a variety of manifestations in the nervous system both in man and in animals. Cardiac and skeletal muscle can also be affected, and strange collagen-like diseases, arthritis and arthralgia have been reported. In this work PVG rats were exposed to inhalation of toluene, commercial hexane, an industrial steel primer, and a cold vulcanizer for 4 months. No signs of synovitis appeared, either macroscopically or histologically, and there were no systemic signs of inflammation as detected by increased acute phase reactants.

Circadian variation in cell proliferation and maturation. A hypothesis for the growth regulation of the rat corneal epithelium.

The rat corneal epithelium has been chosen as a model for studying growth regulation. In this epithelium a large single cohort of cells enters the S phase during a fairly short time period once a day. The factor responsible for this wave of cell proliferation is unknown, but it may be a chemical signal from the central nervous system (the suprachiasmatic nucleus or the corpus pineale). The mature cell compartment of the corneal epithelium is assumed to produce a negative feedback factor (chalone), counteracting the effect of the circadian proliferative factor on the local cell proliferation. When no circadian factor is being produced, during most of the 24 h, the chalone seems to enhance the maturation process. During diminished chalone production (e.g. after cell injury and subsequent regeneration), we will get a more or less unrestricted cell proliferation in the tissue with a delayed maturation process prolonging the chalone depletion. This interaction between the circadian proliferative factor and the negative feedback factor for regulation of proliferation with its accompanying stimulatory effect on maturation, may represent a general mechanism in the regulation of cell proliferation in any tissue. Since in at least some organs virtually all cells entering the S phase do this as a single wave once a day, this mechanism may be enough to explain the regulation of cell proliferation during both normal and regenerative conditions.

Two cell kinetic methods studied on the rat corneal epithelium.

A stathmokinetic method (using Colcemid) and the [3H]thymidine technique (pulse labelling with tritiated thymidine, [3H]TdR) have been evaluated in the rat corneal epithelium. The dose is not of critical importance for the Colcemid method, thus indicating an all or nothing effect within the dose range studied. A one point estimate is sufficient to calculate the mitotic rate (MR), and in the rat corneal epithelium a 4 h accumulation period is recommended. After administration of [3H]TdR there is an increasing response with increasing dose, followed by a levelling off at higher doses. It seems reasonable to use the lowest maximal effective dose. The labelling index (LI) can be reliably registered 1 h after administration of the drug. For each of the drugs we found corresponding results after topical application and intraperitoneal injection. Hence, topical application of small doses of both Colcemid and [3H]TdR makes interesting in vivo experiments on larger animals and even on human beings possible. Due to the extreme regularity of the corneal epithelium this part of the eye is an interesting organ for cell kinetic studies and provides an excellent tool for evaluating cell kinetic methods.

Circadian variations in the DNA synthesis of the rat corneal epithelium. A study using double labelling with tritiated thymidine.

A prominent circadian rhythm was found in the labelling indices (LI) of the peripheral rat corneal epithelium and of the adjacent conjunctival epithelium, while almost no diurnal variation was found in the central area. Application of a double labelling technique indicated that there are rhythmic pulses of high and low influx of cells into the S phase and similar pulses of efflux of cells from the S phase. Results of the study indicate that there are different cohorts of cycling cells all over the rat corneal epithelium. Cells belonging to a rapidly proliferating cohort are observed in the peripheral cornea. There is a gradual reduction in the fraction of labelled DNA-synthesizing cells towards the centre. The considerably lower fraction of cells taking up tritiated thymidine (3H)TdR in the central cornea may be due to a higher fraction of basal cells having reached higher levels of differentiation. This may result in a shift from the salvage to the de novo pathway. The slowly proliferating cohort seems to have a prolonged S phase duration and displays practically no diurnal variation in the LI. The DNA-synthesizing cells belonging to this latter cohort probably use the salvage pathway for DNA synthesis resulting in uptake of (3H)TdR all over the cornea. The LI is thus not a reliable indicator of cell proliferation in the corneal epithelium, due both to the heterogeneity of the cell proliferation, and in particular due to the lack of labelling of the centrally located DNA-synthesizing cells. To what extent these properties may also be present in other proliferating tissues with different levels of differentiations, may be questioned.

Cell kinetics during healing of corneal epithelial wounds.

After removing a circular area of the central corneal epithelium of the rat eye, the labelling indices and the mitotic rates were measured at various times after wounding, both in the cornea and in the adjacent conjunctival epithelium. The proliferative response was most marked in the corneal epithelium adjacent to the wound, but there was also a definite response in the epithelium covering the denuded areas, and in the conjunctival epithelium. The study demonstrated that the conjunctival epithelium. The study demonstrated that the conjunctiva itself plays a role in the healing of a central corneal epithelial wound. The similarities in the cellular response may indicate that both epithelia are under the influence of the same growth-suppressing factors (chalones), and must be looked upon as a unit. However, no support was found for the theory that the limbal area serves as a generative organ for the corneal epithelium.

Circadian variation in the mitotic rate of the rat corneal epithelium. Cell divisions and migration are analyzed by a mathematical model.

A stathmokinetic method was used to study the diurnal variation in the mitotic rate (MR) of the rat corneal epithelium, and in the adjacent conjunctival epithelium. A prominent circadian variation in cell proliferation was observed in both epithelia, both showing almost the same pattern, which may indicate that both tissues are submitted to the same regulatory mechanisms. The average rate of cell renewal during a 24 h period indicated a mean cell renewal time of 12.3 days. This is longer than previously assumed. The MR declined toward the central cornea. Based on the above observations and the known centripetal migration of cells in the corneal epithelium, we have developed a mathematical model showing isomorphism with the renewal of the corneal epithelium.

The labelling index is not always reliable. Discrepancies between the labelling index and the mitotic rate in the rat corneal epithelium after intraperitoneal and topical administration of tritiated thymidine and colcemid.

Many cell kinetic studies are based on the assumption that tritiated thymidine injected into an animal is available for incorporation into DNA for only a short time, and that it labels all cells in the S phase. The present study indicates that this is not the fact for the rat corneal epithelium. The labelling index (LI) declines considerably from the limbal area to the central cornea, while the mitotic rate is almost constant all over the corneal epithelium. The LI should therefore not be used as the only criterion in the assessment of proliferation rate.

Cell renewal of the rat corneal epithelium. A method to compare corresponding corneal areas from individual animals.

A stathmokinetic method to study the mitotic rate in the corneal epithelium of the rat is described and applied. Horizontal and vertical diameter sections were used. In order to analyze the mitotic rate in the various parts of the corneal epithelium, each vision field (objective 100, eye piece 12.5), comprising 182 microns basement membrane, was regarded as a separate unit. Since the number of vision fields across the cornea varies from specimen to specimen, we constructed a mathematical method to correlate corresponding corneal areas from different eyes. Using this method it is shown that the mitotic rate is almost equal all over the cornea, with no definite reduction in the central areas. There is no area of significantly high proliferation rate, either in the limbal area or in the adjacent conjunctiva.

The influence of technical procedures on cell countings in the rat corneal epithelium: a statistical analysis.

We have performed a statistical analysis on cell counts from different areas of the rat corneal epithelium by using the number of cells per high power microscopical vision field (1250 x) as a unit. Each vision field consisted of 182 micron basal membrane. The number of vision fields varied from 29 to 39 in the horizontal and vertical diameter sections used. Only small variations were found in the number of cells from the different vision fields inside one single section. This confirm the extreme regularity of this epithelium. However, when comparing different sections, even from the same eye, the variations were much greater. Further, sections prepared for autoradiography showed a 10% reduction of the number of cells compared with the sections only stained with hematoxylin. A large proportion of the variation in the cell counts must be a result of the technical procedures, and is thus not an intrinsic property of the corneal epithelium. This conclusion may also be valid in cell counts from other epithelial structures.

Retinal vascular tortuosity and recurrent retinal haemorrhages in a patient with non-chromaffin paraganglioma.

The present report describes the history of a 66-year-old man suffering from recurrent retinal haemorrhages combined with retinal vascular tortuosity. He also developed a non-chromaffin paraganglioma in the neck, and the coincidence of these two rare diseases is discussed.