APB (DL-2-amino-4-phosphonobutyric acid) has been found to
affect the retinal processing of many vertebrate species as
evidenced by the suppression of the b-wave component
of the electroretinogram (ERG). The present study examined the
effects of APB on the cone contributions to the ERG response
of adult zebrafish (Danio rerio). ERG responses were
obtained from light-adapted adult zebrafish following intravitreal
injection of either saline alone or saline with various
concentrations of APB ranging from 10 μm to 500 μM.
Visual stimuli were 200-ms flashes of various wavelengths and
irradiances. Spectral sensitivity functions were calculated
from the irradiance versus response amplitude functions of the
a-, b-, and d-wave components of
the ERG response. Saline had no effects on the ERG response.
However, APB had differential effects on the sensitivity of
the b- and d-wave components. The effects
of APB on the b-wave component were most apparent in
the ultraviolet and short-wavelength portions (320–440
nm) of the spectral sensitivity function, although the
b-wave was not completely eliminated at these wavelengths.
APB-treated subjects were found to possess the same cone mechanisms
(L-M and M-S) in the middle- and long-wavelength areas of the
spectrum as saline injected subjects, although absolute sensitivity
was lower for the APB-injected subjects. Spectral sensitivity
based on the d-wave response was affected by APB but
only in the short-wavelength region. All results appear to be
independent of the APB dose. These results support the notion
that glutamate receptors play a specific role in zebrafish visual
processing. In addition, the effects of APB support recent
anatomical evidence that the zebrafish retina may possess different
types of glutamate receptors.
Spectral Sensitivity Measured with Electroretinogram Using a Constant Response Method