A spectral model for signal elements isolated from zebrafish photopic electroretinogram.
The zebrafish photopic electroretinogram (ERG) sums isolatable elements. In each element, red-, blue-, green-, and UV- (r, g, b, and u) cone signals combine in a way that reflects retinal organization. ERG responses to monochromatic stimuli of different wavelengths and irradiances were recorded on a white rod suppressing background using superfused eyecups. Onset elements were isolated with glutamatergic blockers and response subtractions. CNQX-blocked ionotropic (AMPA/kainate) glutamate receptors; l-AP4 or CPPG-blocked metabotropic (mGluR6) glutamate receptors; TBOA-blocked glutamate transporters; and l-aspartate inactivated all glutamatergic mechanisms. Seven elements emerged: photopic PIII, the l-aspartate-isolated cone response; b1, a CNQX-sensitive early b-wave element of inner retinal origin; PII, a photopic, CNQX-insensitive composite b-wave element from ON bipolar cells; PIIm, an l-AP4/CPPG-sensitive, CNQX-insensitive, metabotropic subelement of PII; PIInm, an l-AP4/CPPG/CNQX-insensitive nonmetabotropic subelement of PII; a1nm, a TBOA-sensitive, CNQX/l-AP4/CPPG-insensitive, nonmetabotropic, postphotoreceptor a-wave element; and a2, a CNQX-sensitive a-wave element linked to OFF bipolar cells. The first five elements were fit with a spectral model that demonstrates independence of cone-color pathways. From this, Vmax and half-saturation values (k) for the contributing r-, g-, b-, and u-cone signals were calculated. Two signal patterns emerged. For PIII or PIInm, the Vmax order was Vr > Vg >> Vb approximately Vu. For b1, PII, and PIIm, the Vmax order was Vr approximately Vb > Vg > Vu. In either pattern, u-cone amplitude (Vu) was smallest, but u-cone sensitivity (ku362) was greatest, some 10-30 times greater than r cone (kr570). The spectra of b1/PII/PIIm elements peaked near b- and u-cone absorbance maxima regardless of criteria, but the spectra of PIII/PIInm elements shifted from b- toward r-cone absorbance maxima as criterion levels increased. The greatest gains in Vmax relative to PIII occurred for the b- and u-cone signals in the b1/PII/PIIm b-wave elements. This suggests a high-gain prolific metabotropic circuitry for b- and u-cone bipolar cells.
Nelson
Ralph F
RF
Basic Neurosciences Program, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Rockville, Maryland 20892, USA. nelsonr@ninds.nih.gov
Singla
Nirmish
N
D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D001703:Biophysics; D003116:Color; D004305:Dose-Response Relationship, Drug; D004596:Electroretinography / Q000379:methods; D005074:Evoked Potentials, Visual / Q000187:drug effects / Q000502:physiology*; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D010775:Photic Stimulation / Q000379:methods; D025341:Principal Component Analysis; D012160:Retina / Q000166:cytology*; D051245:Retinal Bipolar Cells / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D017949:Retinal Cone Photoreceptor Cells / Q000145:classification / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D013057:Spectrum Analysis; D014795:Visual Pathways / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D015027:Zebrafish
D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; C120673:benzyloxyaspartate; D001224:Aspartic Acid