Influence of isobutylmethylxanthine on the direct current electroretinogram of albino rabbit eyes

Serotonin elevates the c-wave of the electroretinogram of the rabbit eye by increasing the transepithelial potential

The influence of serotonin (5-hydroxytryptamine, 5-HT) and serotonin analogues on the direct current electroretinogram (d.c. ERG) and the standing potential of the albino rabbit eye (SP) was studied. After unilateral vitrectomy, corneal recordings were obtained during simultaneous intravitreal perfusion with a control solution alternating with 5-HT at concentrations of 25, 120 and 200 microM. The c-wave increased at 25 and 120 microM when changing from control solution to test solution (P < 0.05) but did not decrease significantly when changing back to control solution (P > 0.05). The c-wave was reversibly elevated at 200 microM (PHS-5-HT, P < 0.01; 5-HT-PHS, P < 0.05). To analyse further the influence on the c-wave, in vivo intraretinal microelectrode recordings were obtained during intravitreal perfusion with 5-HT. The transepithelial potential (TEP) increased (P < 0.01), while the slow PIII was not significantly affected (P > 0.05). The serotonin receptor agonists 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, 5-methoxytryptamine, alpha-methyl-5-hydroxytryptamine and 2-methyl-5-hydroxytryptamine, caused a significant reversible elevation of the c-wave, whereas 5-carboxyamidotryptamine did not. Tropisetron did not block the serotonin effect and LY53857 had an effect of its own on the c-wave. The results seem to indicate that the influence of serotonin on the c-wave is mainly due to an effect on the retinal pigment epithelium (RPE) and that more than one type of serotonin receptor may be involved.

Effects of PhXA41, a prostaglandin analogue, and PGF2 alpha on the corneal and intraretinal d.c. electroretinogram (ERG) of the albino rabbit eye

PhXA41, a prostaglandin F2 alpha analogue, is a new drug alternative for medical treatment of glaucoma. From earlier studies, it is known that certain prostaglandins (pgs) exert an influence on the d.c. electroretinogram (ERG). In the present study, possible effects of intraocular perfusion with PhXA41 (free acid) or PGF2 alpha on the rabbit retina and retinal pigment epithelium (RPE) were evaluated. Unilateral vitrectomy was performed and a continuous intraocular perfusion was established, in which a reference solution was alternated with the test solution. In part one of the experiments, the corneal d.c. ERG and the standing potential of the eye (SP) were recorded from both eyes. In part two, vitreal and intraretinal d.c. ERG were recorded in the vitrectomized eye. PhXA41 and PGF2 alpha produced similar effects, i.e. a significant and reversible c-wave increase at concentrations of 1-10 micrograms/ml. No influence was found in the concentration interval 10-100 ng/ml. There were no changes in a- and b-wave amplitudes at any of the concentrations tested. At a concentration of 10 micrograms/ml, the SP increased significantly. The intraretinal d.c. ERG showed a large reduction of slow PIII accompanied by a small change in transepithelial potential (TEP). Theoretically, a vitreous concentration of less than 1 ng/ml may be reached after topical application. This concentration level does not influence the d.c. ERG in this animal model. At higher concentrations, a significant and reversible c-wave increase seemed to be generated mainly in the inner retina by a reduction of slow PIII generated in the Müller cells. The effect of PhXA41 appears to be mediated by an FP receptor.

A cyclic adenosine monophosphate agonist elevates the b- and c-waves of the rabbit direct-current electroretinogram

The effects of the stable cyclic adenosine monophosphate analogue adenosine 3',5'-cyclic monophosphorothioate Sp-isomer (Sp-cAMPS) on the direct-current electroretinogram and the standing potential of the eye were studied. Corneal recordings were obtained from unilaterally vitrectomized albino rabbit eyes during alternating intravitreal perfusions with Sp-cAMPS and a control solution (Pharmacia eye irrigating solution). The contralateral eye was used as a control. To evaluate further the effects on the c-wave, in vivo intraretinal microelectrode measurements were made during simultaneous intravitreal perfusion of Sp-cAMPS and irrigating solution, respectively. Sp-cAMPS in concentrations of 1, 10 and 100 microM was tested by corneal direct-current electroretinography. There was no significant effect on the a-wave amplitude. The b-wave amplitude was reversibly elevated at an Sp-cAMPS concentration of 100 microM was tested by corneal direct-current electroretinography. There was no significant effect on the a-wave amplitude. The b-wave amplitude was reversibly elevated at an Sp-cAMPS concentration of 100 microM (p < 0.01, n = 7). The c-wave amplitude was reversibly elevated at an Sp-cAMPS concentration of 100 microM (p < 0.01, n = 7). The c-wave amplitude was reversibly elevated at a concentration of 10 microM (p < 0.001, n = 8), and this effect was more pronounced at 100 microM (p < 0.001, n = 7). The SP increased reversibly at a concentration of 100 microM (p < 0.001, n = 7). Microelectrode recordings were performed with Sp-cAMPS at a concentration of 100 microM. The recordings showed significant increases in both the transepithelial potential (p < 0.01, n = 3) and the slow PIII (p < 0.01, n = 3). The effects of Sp-cAMPS on the b-wave as well as the two components of the c-wave suggest influences on both the inner retina and the retinal pigment epithelium of the rabbit eye.