Retinal bipolar cells receive negative feedback input from GABAergic amacrine cells

Area of Science:

• Neuroscience
• Retinal Physiology
• Cellular Biology

Background:

• Bipolar cells and amacrine cells form reciprocal synapses in the inner plexiform layer.
• Both feedforward and feedback connections exist, but feedback synapse properties are poorly understood.
• Amacrine cells are often GABAergic, suggesting potential feedback to bipolar cells.

Purpose of the Study:

• Investigate feedback input from gamma-aminobutyric acid (GABA)ergic amacrine cells onto bipolar cells.
• Characterize the physiological properties and location of GABAergic feedback synapses.
• Determine the specific types of bipolar cells that receive this feedback.

Main Methods:

• Enzymatic dissociation of solitary bipolar cells from goldfish retina.
• Whole-cell patch-clamp recording for voltage-clamping and GABA sensitivity examination.
• Application of varying GABA concentrations to different cell parts (axon terminal, dendrite, soma).

Main Results:

• GABA evoked responses in rod-dominant ON-type bipolar cells and some small-axon terminal bipolar cells.
• Highest GABA sensitivity was localized to the axon terminal.
• GABA increased chloride conductance, causing hyperpolarization via GABAA and benzodiazepine receptors.
• Responses were insensitive to Co ions and showed incomplete desensitization, suggesting tonic signaling.

Conclusions:

• Rod-dominant ON-type bipolar cells and some bipolar cells with small axon terminals receive negative feedback from GABAergic amacrine cells.
• The GABAergic feedback synapse is primarily located at the axon terminal.
• The GABAergic pathway may support tonic signal transmission in the retina.