Erling Håskjold

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

Abstract 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 μm basement membrane, was regarded as a separate unit. Since the number of vision fields acros 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.

Migration of cells in the rat corneal epithelium

Abstract The migration of cells in the rat corneal epithelium was studied using continuous labelling with tritiated thymidine [3H]TdR, during a 24 h period. Most mitoses resulted in 2 new basal cells. Cells leaving the basal cell layer moved vertically to the surface in all areas of the corneal epithelium. The first labelled cells reached the surface 3 days after the first injection of [3H]TdR. No stream of cells from the conjunctiva to the cornea in the limbal areas was observed, and no centripetal migration of epithelial cells in the cornea could be observed. After a cell has lost its attachment to the basement membrane, it is committed to be exfoliated in a few days without undergoing mitosis. Thus the slow centripetal migration of epithelial cells and the exchange of centrally located cells, as indicated by clinical findings and experimental studies, can only be explained by migration of basal cells.

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

SummaryA 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.

Cell kinetics during healing of corneal epithelial wounds

Abstract. 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 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.

EARLY CELL KINETIC EFECTS OF A SINGLE DOSE OF NARROW‐BANDED ULTRAVIOLET B IRRADIATION ON THE RAT CORNEAL EPITHELUM

Abstract— The right eyes of 40 rats were exposed to a signal erythemogenic dose fo ultraviolet B irradiation (UVB) at 297nm. The irradiation was directed perpenddicualr to the center of the cornea. The left eyes served as controls. The animals were randomly assigned into 10 groups. The labelling index (LI) after pluse labeling the tritiated thymidine and the mitotic rate (MR) after Colcemid administration were registered in the corneal epithelium at predetermined intervals up to 96 h after the irradiation. A mathematical method was used to corealted corresponding corneal areas from the different animals. In the central the LI was considerably reduced up to 36h after the irradiation. The LI increased toward the peripheral cornea and reached normal values at the limbal area. The MR was also reduced up to 36h. However, this reduction was over the entire epithelium. The block in cell proliferation was followed by increased proliferation.

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

SummaryThe 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.

Ocular polyarteritis nodosa: Report of a case

Abstract A patient with bilateral amaurosis as a complication to polyarteritis nodosa is presented. He developed affection of the central retinal arteries and the arteries supplying the optic discs followed by retinal and optic atrophy. After one month no vessels could be observed neither in the retinae nor at the optic discs. The importance of early diagnosis and aggressive immunosuppressive treatment is stressed.

Isolation and culture of basal cells of the human corneal epithelium

Abstract. The present study introduces a method that permits the isolation of a pure population of viable basal cells of the human corneal epithelium. We demonstrate that this population can be maintained in culture with a maintained epithelial phenotype, DNA‐synthesis, migratory and mitotic activity. The isolation procedure permits evaluation of the adhesion between cells in the epithelium and of the surface morphology and histological organisation of the basal cells. This organization is demonstrated to be far more complex than previously recognized. The culture system permits evaluation of the in vitro behaviour of a basal cell population without contaminating superficial cells or stromal cells.

Endogenous candida endophthalmitis. Report of two cases.

Abstract Two cases of endogenous endoopthalmitis as a complication to spontaneous abortion, truly caused by Candida albicans are presented. One patient received no antimycotic treatment. Endophthalmitis resulted in amaurosis in the affected eye, which had to be enucleated. The second patient was treated with intravenously administered amphotericin B and flucytocine, and was cured. The importance of early diagnosis and treatment is stressed.

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 cornel 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 labellinhg 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.