Electrotonic coupling among neuroendocrine cells in Aplysia

Area of Science:

• Neuroscience
• Cellular Electrophysiology
• Marine Biology

Background:

• Neuroendocrine bag cells in Aplysia are crucial for reproductive behaviors.
• Understanding their communication mechanisms is key to deciphering their function.

Purpose of the Study:

• To investigate and characterize direct electrotonic synaptic coupling among Aplysia neuroendocrine bag cells.
• To determine the properties and functional significance of this electrical coupling.

Main Methods:

• In vitro electrophysiological recordings using microelectrodes in Aplysia dactylomela.
• Application of current pulses to measure postsynaptic responses.
• Manipulation of ionic concentrations (low Ca2+/high Mg2+) to differentiate synaptic types.
• Electrolytic lesions to map coupling sites and assess neurite involvement.

Main Results:

• Direct electrotonic coupling was confirmed between bag cells, with a mean postsynaptic/presynaptic amplitude ratio of 0.0075.
• Coupling exhibited weak amplitude, long latency (up to 50 ms), and slow time courses, distinct from chemical synapses.
• Low-Ca2+/high-Mg2+ solutions blocked chemical synapses but not bag cell electrotonic coupling.
• Electrolytic lesions indicated widespread electrical interconnectivity of neurites, with significant coupling at the base of the pleurovisceral connective.

Conclusions:

• Electrotonic coupling among Aplysia bag cells is widespread and occurs primarily via their neurites.
• This electrical coupling mechanism underlies the synchronized firing of the bag cell population.
• The findings reveal a novel mode of communication influencing neuroendocrine function in Aplysia.