2. ELECTROPHYSIOLOGY O F THE RETINA
47
in darkness and recovering by light toward the “resting state” in a graded
manner. On this basis, the unusual polarity of the distal PI11 as the receptor potential can be accounted for in the following way. The electric
field around the receptors in darkness is such as to make their distal tips
negative owing to a sink existing at or near their distal tips just as in
“excited” receptors. With light the sink disappears or becomes weaker,
and this brings the distal tips to a relative positivity.
The problem remains to be solved of whether or not the electrical
response mediates the flow of information from the distal segment, where
light is absorbed, to the proximal terminal, where synaptic transmission
to secondary neurons takes place. If it does, the amplitude of intracellularly recorded response per photon absorbed should be large enough to
meet the extremely high sensitivity of the visual system (some further
discussion is given by Tomita, 1968).
V. RESPONSES IN THE INNER NUCLEAR LAYER
A. S Potential
Svaetichin ( 1953) observed in the fish that intraretinal micropipettes
record a resting potential of some 40 mV at a certain depth, and, upon
illumination with white light, a 20-30 mV hyperpolarization which is sustained and graded. In the belief that the potential was obtained intracellularly from single cones, he termed it the “cone action potential.”
However, the response was later relocalized in structures proximal to the
receptors (Tomita, 1957; Tomita et al., 1958, 1959; MacNichol and
Svaetichin, 1958; Mitarai, 1958; Oikawa et al., 1959). The response had
to be retenned accordingly, but different viewpoints regarding the origin
and nature of the response brought about different terminologies. For
example, the term “glial membrane potential” (GMP) is one of those,
reflecting the viewpoint of Svaetichin and his co-workers ( Svaetichin
et al., 1961; Laufer et al., 1961; Mitarai et al., 1961; Fatehchand et al.,
1966) that the response is a manifestation of interaction between neurons
and glia cells. They include the horizontal cells, Muller cells, and
amacrine cells as glia cells. Morphological and physiological studies, however, do not always support their view. Structures typical of synapses
have been found between the receptors, horizontal cells, and bipolar cells
in the outer plexiform layer (Stell, 1965; Dowling and Boycott, 1966),
and between the bipolar, amacrine, and ganglion cells in the inner plexiform layer (Dowling and Boycott, 1966). Dowling and Boycott did not
47
in darkness and recovering by light toward the “resting state” in a graded
manner. On this basis, the unusual polarity of the distal PI11 as the receptor potential can be accounted for in the following way. The electric
field around the receptors in darkness is such as to make their distal tips
negative owing to a sink existing at or near their distal tips just as in
“excited” receptors. With light the sink disappears or becomes weaker,
and this brings the distal tips to a relative positivity.
The problem remains to be solved of whether or not the electrical
response mediates the flow of information from the distal segment, where
light is absorbed, to the proximal terminal, where synaptic transmission
to secondary neurons takes place. If it does, the amplitude of intracellularly recorded response per photon absorbed should be large enough to
meet the extremely high sensitivity of the visual system (some further
discussion is given by Tomita, 1968).
V. RESPONSES IN THE INNER NUCLEAR LAYER
A. S Potential
Svaetichin ( 1953) observed in the fish that intraretinal micropipettes
record a resting potential of some 40 mV at a certain depth, and, upon
illumination with white light, a 20-30 mV hyperpolarization which is sustained and graded. In the belief that the potential was obtained intracellularly from single cones, he termed it the “cone action potential.”
However, the response was later relocalized in structures proximal to the
receptors (Tomita, 1957; Tomita et al., 1958, 1959; MacNichol and
Svaetichin, 1958; Mitarai, 1958; Oikawa et al., 1959). The response had
to be retenned accordingly, but different viewpoints regarding the origin
and nature of the response brought about different terminologies. For
example, the term “glial membrane potential” (GMP) is one of those,
reflecting the viewpoint of Svaetichin and his co-workers ( Svaetichin
et al., 1961; Laufer et al., 1961; Mitarai et al., 1961; Fatehchand et al.,
1966) that the response is a manifestation of interaction between neurons
and glia cells. They include the horizontal cells, Muller cells, and
amacrine cells as glia cells. Morphological and physiological studies, however, do not always support their view. Structures typical of synapses
have been found between the receptors, horizontal cells, and bipolar cells
in the outer plexiform layer (Stell, 1965; Dowling and Boycott, 1966),
and between the bipolar, amacrine, and ganglion cells in the inner plexiform layer (Dowling and Boycott, 1966). Dowling and Boycott did not