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Retrograde synaptic communication via gap junctions coupling auditory afferents to the Mauthner cell
A E Pereda1, T D Bell, D S Faber
1Department of Anatomy and Neurobiology, Medical College of Pennsylvania, Philadelphia, USA.
Summary
Depolarizing currents in goldfish Mauthner cells can cause presynaptic eighth nerve fibers to backfire, revealing a novel retrograde communication pathway via voltage-dependent gap junctions. This electrical coupling synchronizes and recruits afferent fibers, enhancing responses to weak inputs.
Area of Science:
- Neuroscience
- Cellular Neuroscience
- Synaptic Plasticity
Background:
- The goldfish Mauthner (M-) cell receives input from large myelinated club endings of the eighth nerve via mixed electrotonic and chemical synapses.
- Understanding the interplay between electrical and chemical signaling at these synapses is crucial for deciphering neural circuit function.
Purpose of the Study:
- To investigate the phenomenon of presynaptic backfiring at the Mauthner cell-eighth nerve synapse.
- To elucidate the mechanisms underlying the voltage dependence of electrical coupling.
- To explore the potential for retrograde intercellular communication at this synapse.
Main Methods:
- Paired pre- and postsynaptic recordings from goldfish Mauthner cell and eighth nerve afferents.
- Voltage-clamp and current-clamp techniques to analyze synaptic potentials and currents.
- Application of fluorescent dyes (Lucifer yellow) and tracers (Neurobiotin) to study substance diffusion.
Main Results:
- Depolarizing postsynaptic currents in the Mauthner cell can induce backfiring in presynaptic afferent fibers.
- The amplitude of the electrotonic coupling potential is voltage-dependent, increasing with depolarization due to nonlinear membrane properties and junctional membrane characteristics.
- Retrograde diffusion of low molecular weight substances from the M-cell to afferent terminals was observed.
Conclusions:
- Gap junctions at this synapse support not only anterograde transmission but also retrograde intercellular communication.
- Electrical coupling via gap junctions can synchronize active afferent fibers and recruit new fibers through backfiring, thereby modulating the Mauthner cell's input-output relationship.
- This retrograde signaling mechanism offers a novel way to enhance synaptic responses and refine neural processing.