Evidence that L-AP5 and D,L-AP4 can preferentially block cone signals in the rat retina.

Several lines of evidence suggest that, as concentrations of two agonists of group III metabotropic glutamate receptors are increased, cone contributions to the b-wave are blocked before rod contributions. Application of L-AP5 (L-2-amino-5-phosphonobutyric acid) at concentrations of 50 microM and D,L-AP4 (D,L-2-amino-4-phosphonobutyric acid) at concentrations 2 microM had a greater effect in reducing the amplitude of the rat ERG b-wave at high light intensities than at low light intensities. The amplitude reduction occurs at flash intensities that saturate rod photoreceptor responses.

Opposite effects of GABA(A) and GABA(C) receptor antagonists on the b-wave of ERG recorded from the isolated rat retina.

The largest component in the fully dark-adapted ERG is a corneal-positive response, known as the b-wave, and believed to originate from depolarizing (ON-type) bipolar cells. The two types of GABA receptors, GABA(A) and GABA(C) have been reported to exist on bipolar cells in rat retina. The goal of these experiments was to find whether these GABA receptors participate in the generation of the b-wave of electroretinogram (ERG).

Effects of sodium pentobarbital on the components of electroretinogram in the isolated rat retina.

Photovoltages, the fast P3(t) component of electroretinogram (ERG), were registered between two microelectrodes across the rod outer segments. The P2(t) component, obtained by subtracting the ERGs measured before the application of 50 microM APB from those measured after the application of 50 microM APB, was used as an indicator of depolarizing bipolar cell activity. Measurements of the scotopic threshold response (STR) and the oscillatory potentials (OPs) were used as indicators of third order neuron activity.

Partial rescue of the ocular retardation phenotype by genetic modifiers.

The or(J) allele of the murine ocular retardation mutation is caused by a premature stop codon in the homeodomain of the Chx10 gene. When expressed on an inbred 129/Sv strain, the or(J) phenotype is characterized by microphthalmia and a thin, poorly differentiated retina in which the peripheral portion is affected to a greater extent than the central portion. Such mutant retinae lack differentiated bipolar cells and the optic nerve typically fails to form, leading to blindness.

A dissection of the electroretinogram from the isolated rat retina with microelectrodes and drugs.

The origins of the a- and b-wave of the ERG were studied using simultaneous recordings made across the receptor layer and the full thickness of a piece of isolated albino rat retina. An inwardly directed current flowing across the rod outer segments was eliminated from the recording when postsynaptic activity was blocked with cobalt or when current source density measurements were made along the length of the outer segments. Rod photovoltages were inferred by removing extraneous field potentials from the recordings made across the photoreceptor layer.