Eric Vukmanic

Publication Date

12-2005

Advisor(s) - Committee Chair

Joseph Bilotta, Elizabeth Lemerise, Dan Roenker

Comments

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Degree Program

Department of Psychology

Degree Type

Master of Arts

Abstract

In recent years, the zebrafish (Danio rerio) has become an important research model for visual neuroscience. Previous research using the electroretinogram (ERG) has provided insight into visual processing in the vertebrate retina, particularly the interactions between cone mechanisms underlying the capacity for color vision. Electrophysiological experiments utilizing the ERG to derive spectral sensitivity functions have demonstrated that zebrafish possess four cone photoreceptors (ultraviolet-, short-, middle-, and long-wavelength sensitive cone types [UV-, S-, M-, and L-cones, respectively]) and two opponent mechanisms (the middle-wavelength cones minus short-wavelength cones mechanism [M-S] and long-wavelength cones minus middle-wavelength cones mechanism [L-M]). However, little research has targeted the retinal circuitry that is responsible for processing the neural signals arising from the interactions between these cones mechanisms. Although some research has examined the cone mechanisms of the On-pathway in the zebrafish retina, few experiments have investigated the cone mechanisms of the Off-pathway and their contributions to the opponent mechanisms observed in ERG-derived spectral sensitivity. This project employed pharmacological manipulations of the retinal circuit to assess visual processing of Off-pathway retinal neurons. By suppressing the response properties of Off-pathway neurons, their specific contributions to the remaining ERG waveform and b-wave spectral sensitivity could be examined. The first objective of this experiment was to resolve discrepancies in the literature pertaining to the role of N-methyl-D-aspartate (NMDA) receptors in Off-bipolar cell signal transduction. The NMDA receptor antagonist 2-amino-7-phosphonoheptanoic acid (AP-7) was used to block NMDA receptor function in order to determine their contribution to the ERG d-wave response. The second objective was to test if the ‘push-pull’ hypothesis described in the primate literature could be applied to zebrafish. Here, 6-cyano-7-ntroquinoxaline-2,3-dione (CNQX) was used to block amino-3-hydroy-5-methylisoxazole-4-propionic acid (AMPA)/kainite receptors, assessing their contribution to the d-wave. Finally, a combination of both drugs was administered in an attempt to completely block Off-pathway responses, with special attention being paid to the opponent mechanisms. Adult zebrafish were presented 200 ms full-field flashes of light stimuli ranging from 320 to 640 nm in 20-nm intervals. Spectral sensitivity functions were derived for the control group (saline-injected) and the three experimental conditions described previously. Results showed that AP-7 suppressed the d-wave response and converted the L-M opponent mechanism to a nonopponent L+M mechanism. CNQX also reduced the d-wave and increased the amplitude of the b-wave. Additionally, CNQX induced a similar effect on the L-M mechanism as did AP-7. A combination of both drugs completely eliminated the d-wave and both opponent mechanisms. These results suggest that 1) NMDA receptors are involved in Off-bipolar cell signal transduction, 2) the ‘push-pull’ model can be applied to the zebrafish retina and 3) a complete blockade of the Off-pathway disrupts the retinal circuitry’s capacity to compare cone inputs. More broadly, these results confirm that zebrafish serve as an excellent model to investigate the neural mechanism responsible for color vision.

Disciplines

Psychology | Social and Behavioral Sciences

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