Ciliary body degeneration in the Royal College of Surgeons dystrophic rat

The architecture of the mouse ciliary processes and their changes during retinal degeneration

In contrast to most mammalian species, the ciliary processes in the mouse eye form an irregular pattern. Different strains were studied using scanning electron microscopy. The ciliary processes of C57BL/6J animals showed quadrant-specific characteristics: in the superior quadrant, large and radial oriented processes were present. In the inferior quadrant, the processes were small but still mainly radial oriented. In the temporal quadrant, the processes showed a radial, longitudinal course, some being L-shaped. In the nasal quadrant, few processes were oriented longitudinal. In DBA/2 animals, the processes were shorter and the radial orientation less developed. NMRI animals showed the shortest processes with no increase towards the superior quadrant. Additionally we investigated age-related changes in the ciliary processes of Pde6b(rd1) mice, which develop retinal degeneration. In C57BL/6J mice, the ciliary body shape, size and architecture was comparable between 3 and 10 months of age, but showed a mild shortening of the pars plicata in the temporal, inferior and nasal quadrants in animals older than 20 months of age. The parameters of the ciliary body in 3 months old Pde6b(rd1) mice were comparable to those of age-matched C57BL/6J mice. Pde6b(rd1) mice 10 months old revealed significant shortening of the total width of the ciliary body and of the length of ciliary processes in all quadrants. The shape and architecture of the ciliary processes remained preserved.

Morphological changes in the anterior segment of the Abyssinian cat eye with hereditary rod-cone degeneration

PURPOSE

The purpose of this study was to investigate morphological changes of the anterior segment of the eye in Abyssinian cats with progressive rod-cone degeneration and to correlate them with blood flow data obtained in the same animals.

METHODS

Sections of the left eyes of six normal cats and of eight cats with different stages of hereditary retinal degeneration were prepared for transmission and scanning electron microscopy. Tangential and sagittal sections were also stained with antibodies against substance P, tyrosine hydroxylase, panneuronal marker PGP9.5, nitric oxide synthase, synaptophysin, and smooth muscle alpha-actin.

RESULTS

In Abyssinian cats with hereditary rod-cone degeneration, significant changes were observed in the iris consisting of irregularities in the vascular wall of smaller arteries without changes in their innervation pattern. The ciliary processes were shorter than in normal cats, and their structure appeared more compact and retracted. Slight changes were also observed in the anterior part of the ciliary epithelium. The anterior chamber angle region did not appear to be affected.

CONCLUSIONS

Clear morphological correlations to the physiological blood flow data were observed in the anterior eye segment, pointing not only to functional but also morphological vascular abnormalities in this animal model for retinitis pigmentosa.

Membrane voltage and whole-cell currents in cultured pericytes of control rats and rats with retinal dystrophy

PURPOSE

Retinal vascular changes are associated with retinitis pigmentosa in man and the retinal dystrophy of the Royal College of Surgeons (RCS) rat. Recently we demonstrated that retinal capillary pericytes possess electrical membrane characteristics typical for smooth muscle cells and may thus regulate retinal blood flow in vivo.

METHODS

In the present study we compared cultured pericytes of 5-7 day old RCS and control rats by measurement of membrane voltage (Vmem) with microelectrodes and currents with the whole-cell configuration of the patch-clamp technique.

RESULTS

Resting membrane voltage (-37.6 mV +/- 1.0 mV, n = 106 and -36.6 mV +/- 0.7 mV, n = 102, respectively) and whole-cell currents, which are mainly determined by a potassium conductance, were comparable in pericytes of control and RCS rats. The electrogenic component of the Na(+)-K(+)-ATPase in RCS rat pericytes was reduced, because depolarization of their membrane voltage by Na(+)-K(+)-ATPase inhibitor ouabain (10(-4) mol.1-1 or K+ free solution was significantly decreased compared to control pericytes. Norepinephrine (10(-5) mol.1-1) depolarized Vmem of control rat pericytes by delta 7.0 mV +/- 1.3 mV (n = 7), whereas it hyperpolarized Vmem of RCS rat pericytes by delta 2.0 mV +/- 0.8 mV (n = 11). The depolarization of Vmem by histamine (10(-5) mol.1-1) was significantly reduced in pericytes of RCS rats (delta 2.6 mV +/- 0.4 mV, n = 7) compared to control pericytes (delta 4.3 mV +/- 0.5 mV, n = 6). In pericytes of RCS rats ATP-induced activation of inward and outward currents and depolarization of membrane voltage were also significantly reduced.

CONCLUSIONS

The data indicate that there are differences in the electrophysiological properties of retinal capillary pericytes of 5-7 days old RCS and control rats. Whereas resting membrane voltage and K+ conductance are comparable in both groups, there are significant differences in the electrical activity of Na(+)-K(+)-ATPase and in the effects of vasoactive substances on the membrane voltage and currents. These differences might contribute to the vascular changes observed in RP, and possibly accelerate the progress of retinal dystrophy.

Carbonic anhydrase activity is increased in retinal pigmented epithelium and choriocapillaris of RCS rats

BACKGROUND

In Royal College of Surgeons (RCS) rats the retinal pigmented epithelium (RPE) exhibits defective phagocytosis of rod outer segments, causing degeneration of the photoreceptor layer. It is not known whether another function of the RPE, ion and fluid transport, is also affected by the disease. One enzyme involved in modulation of RPE transport activities is carbonic anhydrase (CA). To clarify whether changes in CA activity are correlated with the process of retinal degeneration, the localization of CA activity in RCS rat eyes was investigated.

METHODS

Eyes of 12 RCS rats and 12 age-matched congenic controls of different ages were studied, using a modified histochemical method of Hansson for light and electron microscopy.

RESULTS

Control eyes showed CA staining in corneal endothelium, both layers of ciliary epithelium, Müller cells, inner segments of photoreceptors, and RPE cells. In RPE the apical membranes were most intensely stained. In RCS rats, changes in CA staining were seen only in the posterior segment of rats 6 and 7 months of age. Most of the RPE cells were more intensely stained than those of age-matched controls, especially due to increased CA activity in the basolateral membrane infoldings. Adjacent endothelial cells of the choriocapillaris and of retinal capillaries developed staining for CA activity.

CONCLUSION

Changes in CA activity in the RPE and adjacent capillary endothelium, together with previously described changes in RPE morphology in RCS rats, indicate changes in ion and fluid transport across the RPE. Since the retina was already impaired when the increase in CA activity occurred, we hypothesize that the causative factor is not the genetic defect per se, but the destruction of the retina.