Author:
BALKEMA GRANT W.,CUSICK KATHLEEN,NGUYEN TRI-HUNG
Abstract
Previous work suggests that photoreceptor synaptic ribbon length
and absolute dark-adapted threshold may vary during a 24-h diurnal
cycle. To test this hypothesis, we examined the length of
photoreceptor synaptic ribbons and the dark-adapted threshold
in black (+/+) and albino (c2J/c2J) C57BL/6J
mice at six times over a 24-h period. Testing began 2 h after
light onset (ZT 2:00) and continued at successive 4-h intervals
(12 h:12 h light:dark). We determined the length of the synaptic
ribbons in frozen sections by labeling them with an antibody
specific for synaptic ribbons. Synaptic ribbons vary in length
at different points in the diurnal cycle in both types of mice,
but the synaptic ribbons in black mice are longer than those
in albino mice by an average of 0.33 μm. The synaptic ribbons
of black mice also have a larger response to changes in the
light cycle. Ribbon length in black mice ranges from 1.66 μm
to 1.4 μm, whereas ribbon length in albino mice ranges from
1.32 μm to 1.25 μm. The shortest ribbons are evident
6 h after light onset in both types of mice, whereas the longest
ribbons appear within 2 h after light onset. These changes in
synaptic ribbon length support the idea that photoreceptor synaptic
ribbons are dynamic structures whose length changes over a 24-h
diurnal cycle. Examining black and albino mice with a water-maze
behavioral assay showed that visual thresholds in black and
albino mice vary over the 24-h diurnal cycle. The visual thresholds
of albino mice are elevated compared with black mice at all
times tested. This is consistent with previous findings of visual
thresholds in hypopigmented mice. The lowest threshold (greatest
sensitivity) is present 2 h after light onset (ZT 2:00) and
corresponds to the time when synaptic ribbons are the longest.
The highest threshold is observed 6 h after light onset, the
time when synaptic ribbons are shortest. These results show
that synaptic ribbon length and visual sensitivity vary together
in relation to the time.
Publisher
Cambridge University Press (CUP)
Subject
Sensory Systems,Physiology
Cited by
38 articles.
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