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The "ON"-bipolar agonist, L-2-amino-4-phosphonobutyrate, blocks light-evoked cone contraction in xenopus eye cups
1Department of Anatomy and Cell Biology, University of Kansas School of Medicine, Kansas City 66103.
Abstract:
Rhythmic photoreceptor metabolism in relationship to light-dark cycles is now thought to be regulated through a retinal feed-back mechanism with dopamine serving as a principal signal initiating light-evoked events. In order to test the hypothesis that depolarizing "ON"-bipolar neurons participate in the retinal signalling pathway, we determined the effects of L-2-amino-4-phosphonobutyrate (L-APB) on light-evoked cone contraction in eye cups from Xenopus laevis. L-APB blocked the response stereospecifically when applied over a broad concentration range. The high specificity of L-APB in retina suggests that sign-inverting bipolar neurons which depolarize in light are in the signalling pathway. One possibility is that this pathway conveys signals that regulate dopamine release.
Insights
Depolarizing "ON"-bipolar neurons are involved in retinal signaling. L-2-amino-4-phosphonobutyrate (L-APB) confirmed their role in light-evoked cone contraction, suggesting a pathway regulating dopamine release.
Area of Science:
- Neuroscience
- Retinal Physiology
- Phototransduction
Background:
- Rhythmic photoreceptor metabolism is regulated by retinal feedback mechanisms.
- Dopamine is a key signal initiating light-evoked events in the retina.
Purpose of the Study:
- To investigate the role of depolarizing "ON"-bipolar neurons in the retinal signaling pathway.
- To test the hypothesis that these neurons participate in light-evoked cone contraction.
Main Methods:
- Experiments were conducted using eye cups from Xenopus laevis.
- The effects of L-2-amino-4-phosphonobutyrate (L-APB) on light-evoked cone contraction were determined.
- L-APB was applied over a broad concentration range.
Main Results:
- L-APB stereospecifically blocked the light-evoked cone contraction response.
- The drug demonstrated high specificity in the retina.
- This suggests the involvement of sign-inverting bipolar neurons.
Conclusions:
- Depolarizing "ON"-bipolar neurons are part of the retinal signaling pathway.
- This pathway likely conveys signals regulating dopamine release.
- L-APB serves as a valuable tool for studying retinal circuitry.