THE ELECTRORETINOGRAM AFTER APPLICATION OF VARIOUS SUBSTANCES TO THE ISOLATED RETINA

Moniliform deformation of retinal ganglion cells by formaldehyde-based fixatives

Protocols for characterizing cellular phenotypes commonly use chemical fixatives to preserve anatomical features, mechanically stabilize tissue, and stop physiological responses. Formaldehyde, diluted in either phosphate-buffered saline or phosphate buffer, has been widely used in studies of neurons, especially in conjunction with dyes and antibodies. However, previous studies have found that these fixatives induce the formation of bead-like varicosities in the dendrites and axons of brain and spinal cord neurons. We report here that these formaldehyde formulations can induce bead formation in the dendrites and axons of adult rat and rabbit retinal ganglion cells, and that retinal ganglion cells differ from hippocampal, cortical, cerebellar, and spinal cord neurons in that bead formation is not blocked by glutamate receptor antagonists, a voltage-gated Na(+) channel toxin, extracellular Ca(2+) ion exclusion, or temperature shifts. Moreover, we describe a modification of formaldehyde-based fixatives that prevents bead formation in retinal ganglion cells visualized by green fluorescent protein expression and by immunohistochemistry.

Dissociation of field potential from neuronal activity in the isolated retina: failure of the b-wave with normal ganglion cell response

The b-wave of the isolated rabbit retina was compared with the ganglion cell response to light before and after modification of the retina's incubating medium. Marked diminution of the b-wave, with no reduction in ganglion cell response, was observed under three experimental conditions: (1) following a short period of anoxia; (2) following a short period in 0.2 mM Ca++; (3) in a small percentage of preparations, simply as a result of prolonged incubation in control medium. In contrast, a short period in 50 mM K+ led to a parallel fall and parallel recovery of both responses. It is apparent that under selected conditions the field potentials which constitute the b-wave are poorly correlated with the retina's neural activity.

Information processing in the retina: importance of chloride ions

Electrophysiological recording methods were applied to the isolated, retina-eyecup preparation of the rabbit. Perfusion with a chloride-free solution has a selective, reversible effect on the retinal network. This study establishes chloride ions as an important requirement for certain "information channels" within the retina.

Effects of cardiac glycosides on electrical activity in the isolated retina of the frog

Ouabain added to physiological salt solutions bathing the isolated frog retina irreversibly abolishes the electrical response to light (the electroretinogram or ERG). The time course of abolition depends on the concentration of ouabain in the medium and the surface of the retina to which it is applied. When the glycoside is placed on the receptor surface, in 7 min the ERG is completely eliminated by 10(-4)M ouabain and more than 90% inhibited by 3 x 10(-5)M ouabain. The effect is slower at lower concentrations and when the solution is applied to the vitreous surface of the retina. The evidence suggests that abolition of the ERG by ouabain is due principally to inhibition of the active transport of sodium: (a) Structurally modified glycosides which are considerably less potent inhibitors of alkali cation-activated ATPase activity in preparations of frog retinal outer segments are also poorer inhibitors of electrical activity in isolated retinas. (b) Replacing much of the sodium in the medium bathing the retina by choline, Tris, or sucrose significantly protects the retina from ouabain. It is suggested that in a standard sodium environment essentially constant activity of the sodium pump is required to prevent rapid and irreversible change. The cellular sites most critically dependent on the sodium pump have not been identified.