2. ELECl'ROPHYSIOLOGY OF THE RETINA
49
Y-B responses while the Centropomidae L and R-G responses. It is evident that the types of responses are dependent upon the fish species used.
Tamura and Niwa (1967) extended the exploration to some other species
and divided the L response into three subtypes (L,-L,) according to the
peaking wavelengths, and the C response into four (C1-C4) according
to their spectral response patterns. In spite of the difference in classification, the results are similar to those of MacNichol and Svaetichin.
From a number of studies (Mitarai, 1960; MacNichol and Svaetichin,
1958; Yamada and Ishikawa, 1965; Byzov and Trifonov, 1968) the site of
recording of the S potential was suggested to be the horizontal cell.
Recording is easier from retinas having large horizontal cells. The problem is how and where it originates. The localization of S potential in a
horizontal cell might not necessarily mean that the membrane of that
cell is responsible for the electrogenesis. The recorded potential could
be of a passive nature conducted to the recording site from some other
structures. In the discussion below concerning the electrogenesis of S
potential, let us confine our attention to the L response, just to make the
matter simple.
After the theory of glia-neuron interaction had been argued for many
years without much agreement, Trifonov (1968) presented a new hypothesis that the S cell, which is the horizontal cell in synaptic contact
with photoreceptors, is kept depolarized or facilitated in the dark by
transmitter substance continuously released from the receptor terminals,
and that light acts to suppress the release of transmitter with the result
that the S cell is repolarized or disfacilitated. Related to this hypothesis
are the observations of Trifonov and Byzov (1965) on the turtle and
Byzov and Trifonov ( 1968) on the carp that the S cell which is hyperpolarized or disfacilitated in the presence of adapting light responds to a
transretinally applied sclera-positive electric pulse with a depolarization,
the amplitude of which is graded according to the intensity of the stimulating pulse, and, if the intensity is h e d , to the degree of hyperpolarization by light. From the polarity of current pulses effective for eliciting the
depolarizing response, Trifonov and Byzov consider the receptor endings
as the acting site of the pulses which effect a release of transmitter.
The new hypothesis of Trifonov is attractive, particularly when the
vertebrate photoreceptors are found to function in a similar way: depolarized in darkness and repolarized in light. From this new viewpoint,
some of the properties of the S potential, which appeared not to be the
kind of electrical activity usually ascribed to neurons, are now better
understood. Although not always clearly demonstrated as in the photoreceptors, the amplitude of S potential tends to increase (decrease) by
extrinsically applied hyperpolarizing ( depolarizing ) current ( Mura-
49
Y-B responses while the Centropomidae L and R-G responses. It is evident that the types of responses are dependent upon the fish species used.
Tamura and Niwa (1967) extended the exploration to some other species
and divided the L response into three subtypes (L,-L,) according to the
peaking wavelengths, and the C response into four (C1-C4) according
to their spectral response patterns. In spite of the difference in classification, the results are similar to those of MacNichol and Svaetichin.
From a number of studies (Mitarai, 1960; MacNichol and Svaetichin,
1958; Yamada and Ishikawa, 1965; Byzov and Trifonov, 1968) the site of
recording of the S potential was suggested to be the horizontal cell.
Recording is easier from retinas having large horizontal cells. The problem is how and where it originates. The localization of S potential in a
horizontal cell might not necessarily mean that the membrane of that
cell is responsible for the electrogenesis. The recorded potential could
be of a passive nature conducted to the recording site from some other
structures. In the discussion below concerning the electrogenesis of S
potential, let us confine our attention to the L response, just to make the
matter simple.
After the theory of glia-neuron interaction had been argued for many
years without much agreement, Trifonov (1968) presented a new hypothesis that the S cell, which is the horizontal cell in synaptic contact
with photoreceptors, is kept depolarized or facilitated in the dark by
transmitter substance continuously released from the receptor terminals,
and that light acts to suppress the release of transmitter with the result
that the S cell is repolarized or disfacilitated. Related to this hypothesis
are the observations of Trifonov and Byzov (1965) on the turtle and
Byzov and Trifonov ( 1968) on the carp that the S cell which is hyperpolarized or disfacilitated in the presence of adapting light responds to a
transretinally applied sclera-positive electric pulse with a depolarization,
the amplitude of which is graded according to the intensity of the stimulating pulse, and, if the intensity is h e d , to the degree of hyperpolarization by light. From the polarity of current pulses effective for eliciting the
depolarizing response, Trifonov and Byzov consider the receptor endings
as the acting site of the pulses which effect a release of transmitter.
The new hypothesis of Trifonov is attractive, particularly when the
vertebrate photoreceptors are found to function in a similar way: depolarized in darkness and repolarized in light. From this new viewpoint,
some of the properties of the S potential, which appeared not to be the
kind of electrical activity usually ascribed to neurons, are now better
understood. Although not always clearly demonstrated as in the photoreceptors, the amplitude of S potential tends to increase (decrease) by
extrinsically applied hyperpolarizing ( depolarizing ) current ( Mura-