S. Yazulla et al., DOPAMINERGIC CONTROL OF LIGHT-ADAPTIVE SYNAPTIC PLASTICITY AND ROLE IN GOLDFISH VISUAL BEHAVIOR, Vision research, 36(24), 1996, pp. 4045-4057
Dopamine has been implicated in processes of retinal light and dark ad
aptation, In goldfish retina, horizontal cell dendrites elaborate neur
ite processes (spinules) into cone terminals, in a light- and dopamine
-dependent manner. However, the functions of retinal dopamine and the
horizontal cell spinules in visual behavior are unknown. These issues
were addressed in behavioral, electroretinographic, and anatomical stu
dies of normal fish and those with unilateral depletion of retinal dop
amine induced by intraocular (i.o.) injections with 6-hydroxydopamine
(6-OHDA). Dopamine interplexiform cells (DA-IPC) disappear within 2 we
eks after 6-OHDA injection; cell bodies appear at the marginal zone wi
thin 6 weeks at which time neurites slowly reinnervate the retina with
a sparse plexus over the next 12 months. We found that dopamine deple
tion increased light sensitivity at photopic but not scotopic backgrou
nds by 2.5 log units, an effect mimicked by i.o. injections of dopamin
e D1 and D2 antagonists, The ERG b-wave increment thresholds were the
same for control and dopamine depleted eyes, indicating a normal trans
ition from rod to cone systems in the ON pathway, Light-dependent spin
ule formation was reduced by about 60% in dopamine-depleted retinas, b
ut returned to normal by 3 months and 9 months after injection in the
entire retina, even areas not directly innervated with DA-IPC processe
s. Spinule formation in vivo was inhibited 50% with i.o. injection of
SCH 23390 in control retinas as well as throughout 3 month 6-OHDA inje
cted retinas, including DA-IPC free areas, This latter result indicate
s a volume effect of dopamine, diffusing laterally through the retina
over several millimeters, in regulating spinules. We conclude that DA-
IPCs regulate sensitivity to background at photopic levels not via the
ON pathway, but perhaps the OFF pathway, Goldfish display both increa
sed sensitivity to light and a normal Purkinje shift in the ERG b-wave
whether or not horizontal cell spinules are present, indicating that
dopamine control of photopic vision in fish is not mediated through li
ght-induced spinule formation of horizontal cell dendrites. Copyright
(C) 1996 Elsevier Scence Ltd.