Adrenergic effects on the corneal and intraretinal direct-current electroretinogram and on the standing potential of albino rabbit eyes

Abstract

This study was undertaken to investigate further the responsiveness of the albino rabbit retinal pigment epithelium and the inner retina to adrenergic agents as reflected in changes of the direct-current electroretinogram and of the standing potential of the eye. After unilateral vitrectomy on albino rabbits, a continuous intraocular perfusion with a reference solution was established. The reference solution was then alternated with the test solution. The direct-current electroretinogram and the standing potential were recorded from both eyes with a scleral contact lens and a reference electrode connected to matched calomel half-cells. An in vivo experimental technique that allows intraocular perfusion of a test substance and simultaneous intraretinal microelectrode measurements was also used. The alpha-adrenergic agonist phenylephrine (0.04 microM, n = 8) produced a reversible increase in c-wave amplitude (48%, p < 0.001) and also a small increase in b-wave amplitude (12%, p < 0.002). There was no significant influence on the a-wave amplitude. The standing potential was elevated at 1694 +/- 362 microV (mean +/- SEM) (p < 0.002). The alpha 2-adrenergic agonist clonidine caused similar effects on the electroretinogram, although at a higher concentration (40 microM, n = 5), with an elevation of the c-wave (25%, p < 0.001) and a small b-wave increase (12% p < 0.002). No significant influence on the a-wave or on the standing potential was found. Intraretinal direct-current electroretinogram-recordings during intraocular perfusion with phenylephrine showed an increase in transepithelial potential (p < 0.004; n = 6), accompanied by a reduction of the slow PIII (p < 0.0035; n = 6). The c-wave increase resulting from alpha-adrenergic stimulation seems to be generated partly across the retinal pigment epithelium, with an increase in transepithelial potential, combined with a reduction of the slow PIII. The elevation of the b-wave amplitude, together with the influence on the slow PIII, suggests alpha-adrenergic effects also on the inner retina. The experimental technique used in this study with intraocular perfusion after vitrectomy and simultaneous intraretinal direct-current recordings seems to be a practicable method for studies of the influence of pharmacologic agents on the retina and the retinal pigment epithelium.

Effects of Pituitary Adenylate-Cyclase-Activating Polypeptide on the Direct-Current Electroretinogram of the Rabbit Eye

“…However, the ERG amplitude levels are influenced by the surgical preparation and/or the irrigation. During control conditions, the b-and c-wave amplitude levels were significantly reduced compared to the contralateral eye, results which are in accordance with previous reports from our laboratory [5,10,11]. The a-wave amplitude was not affected, as in some of the earlier studies using similar techniques [5,8].…”

“…The experimental procedure for the perfusion system was first described by Textorius et al [7] and further developed by Jarkman and Nilsson [8]. The head of the animal was fixated with a specially designed headholder.…”

“…The method of intraretinal microelectrode recordings during perfusion of the vitreous cavity in vivo has been described earlier [10]. Anesthesia and pupil dilatation were performed according to the description above.…”

Corneal Toxicity of Xylazine and Clonidine, in Combination with Ketamine, in the Rat

“…(D) Finally, we speculate that a major role in the mechanism of action of XYL and CLO could be played by the interaction with corneal · 2 -or, possibly · 1 -adrenergic receptors [41], whose function is still not clear but probably essential for corneal homeostasis. In fact, it is known that the transport of chloride ions from the aqueous to the tear side, which is very important for the continuous corneal dehydration and maintenance of transparency, is under adrenergic control [15,17,18,42].…”