Patricia Grimes

Aspects of mitotic activity in relation to cell proliferation in the lens epithelium.

The mitotic index in the lens epithelium of young rats was determined in flat mounts at 6-hr intervals over a 24-hr period. The mitotic counts of rats killed between mid-night and early morning were significantly higher than those of animals killed between noon and 6 am . An average mitotic index of 0.26% in the equatorial zone and 0.16% in the pre-equatorial zone, contrasted with the low value of 0.02% in the central area. Mitotic duration was determined with the colchicine technique at a time of the day during which the mitotic index did not change significantly, and was estimated to be 1 hr 12 min. This value was calculated from the linear increase in both the mitotic index and the metaphase index which occurred from 30 min to 3 hr following injection of the drug. On the basis of these data, the intermitotic, or turnover, time was estimated as 19 days for the equatorial zone, 31 days for the pre-equatorial and 250 days for the central area of the lens epithelium of young rats. The results are compared with those obtained from studies on rabbits in previous work of this laboratory in which another technique was employed.

The role of neural mechanisms in the regulation of intraocular pressure in the cat

Abstract The afferent activity evoked by intraocular pressure changes, the effects of stimulation of retrobulbar nerves on the intraocular pressure, and the evidence of the occurrence of central integration were examined in cats over short periods. Afferent activity was recorded from the long ciliary nerves of isolated preparations as well as preparations in situ . Spontaneous activity which could be related to resting pressure levels was not observed in any preparation. An increase of intraocular pressure elicited a discharge of impulses, the frequency of which was directly related to the pressure level. Preparations in situ were generally more stable and yielded more reproducible results. The temporal pattern of the pressure-evoked activity was different from that of activity elicited by mechanical stimulation of the cornea or the iris. Stretching of the nerve endings located in the outer coats of the eye appears to initiate the impulses evoked by raising the intraocular pressure. Stimulation of the ciliary ganglion or its motor root, of isolated perfused eyes or eyes in situ caused a fall in the intraocular pressure. A small increase in the intraocular pressure was observed in the eye without circulation, due to increased inward tension of the chorioid during ciliary muscle contraction. Stimulation of the long ciliary nerves produced a small fall in pressure due to sympathetic nerve activity. This fall is masked in the intact eye due to stimulation of the extraocular structures. Efferent activity recorded from either the long or short ciliary nerves could not be modulated by pressure changes. Retrobulbar injection of lidocaine did not affect the resting intraocular pressure in the cat nor did it affect the rat at which the pressure returned to normal after imposed changes. These observations are discussed in relation to the postulated neural control of the intraocular pressure.

Interference with cell proliferation and induction of polyploidy in rat lens epithelium during prolonged myleran treatment

Abstract Prolonged administration of myleran to young rats interferes with cell proliferation in the lens epithelium by inhibiting mitotic division in cells which have completed DNA synthesis. Repetition of this process in successive cell cycles leads to severe depletion of the epithelial population and to the appearance of cells of increasingly higher ploidy.