Biology Reference
In-Depth Information
synaptic contacts with both ganglion-cell dendrites and amacrine
processes, and that the amacrine processes made synaptic contacts
back on to the bipolar terminal. The amacrine cell was found to
make such reciprocal contacts with bipolar cells over wide areas
in primates. Also, the amacrine cells were found to extend their
processes throughout the inner plexiform layer and to make synaptic
contacts with each other.
The reciprocal synaptic organization found would obviously be
suitable for a feedback system as required by Rushton's AGC model.
Accordingly, Dowling ( 1967 ) suggested that activation of the amacrine
process by the bipolar terminal might result in an inhibitory synaptic
feedback on to the bipolar terminal, reducing the sensitivity of the
bipolar cell in proportion to its excitation.
Dowling ( 1967 ) also found electrophysiological evidence in
favour of a post-receptor adaptation site. Thus, he pointed to the
study of Lipetz ( 1961 , p. 639) who had found that illumination of one
area in a receptive field of frog ganglion cells may raise the threshold
in other areas of the receptive field - a result previously obtained in
the classical study of the cat retina by Kuffler ( 1953 ). Furthermore,
he found the b-wave of the electroretinogram, assumed to rise from
bipolar cells, to be the first response in the visual system to show
typical adaptation properties.
Search WWH ::




Custom Search