HISTOLOGY AND HISTOPATHOLOGY

Cellular and Molecular Biology

 

Effects of a non-selective ß-blocker on adult rat anterograde axonal transport and retinal ganglion layer after increased intraocular pressure

F. Díaz1, A. Villena1, M. Moreno2, L. Vidal1, C. Parrado1, J. García-Campos2 and I. Pérez de Vargas1

1Department of Histology and Histopathology, School of Medicine, University of Malaga, Malaga, Spain and 2Department of Ophthalmology, School of Medicine, University of Malaga, Malaga, Spain

Offprint requests to: Florentina Díaz PhD, Facultad de Medicina, Boulevard Louis Pasteur, 32, 29071 Málaga, Spain. e-mail: fdiaz@uma.es


Summary. The aim of this study was to examine the effects of timolol in an experimental model of elevated intraocular pressure (IOP). Three episcleral veins of rats with normal IOP were cauterized. Three months later we examined the effects on anterograde axonal transport from the retinal ganglion cells (RGCs) to the superior colliculus (SC) as well as on the number of neurons in the retinal ganglion layer (RGL). These parameters were also studied in a group of rats submitted to treatment with timolol after confirming that their IOP was still raised after two weeks. After the surgical procedure, the mean IOP of the experimental eyes increased to 33.5±1.06 mmHg (1.25 fold compared to the control group) and three months later the IOP remained significantly elevated; however, after a long period of treatment with timolol the IOP was 14.05±0.81 mmHg, similar to that of the control group. In the group with normal IOP, labelling with horseradish rabbit peroxidase (HRP) at 120 minutes and 24 hours postinjection showed continuous staining from the retina to the SC. In the experimental group the optic nerve head (ONH) was completely negative, although in the group treated with timolol there was partial block of axonal transport in the ONH, in which the staining was slightly more intense. The number of neurons in the RGL, counted by immunohistochemical labelling with Neu-N, showed that in eyes with normal and elevated IOP there were 423±11 neurons/mm2 and 283±10 neurons/mm2, respectively. After treatment with timolol the number of neurons (331±10 cells/mm2) increased compared with elevated IOP eyes, although the number did not reach that of the control group. These results indicate that treatment with timolol, started two weeks after the surgical procedure, was partially neuroprotective because the loss of neurons in the RGL was lower than in untreated animals, though not sufficient to re-establish normal axonal transport. Histol Histopathol 20, 1077-1085 (2005)

Key words: Glaucoma, Intraocular pressure, Retinal ganglion layer, Anterograde axonal transport

DOI: 10.14670/HH-20.1077