Inking in Aplysia californica. III. Two different synaptic conductance mechanisms for triggering central program for...

Area of Science:

• Neuroscience
• Marine Biology
• Cellular Biology

Background:

• Previous studies identified motor elements and membrane properties of ink-gland motor cells in Aplysia inking behavior.
• The central program for inking involves a specific accelerating burst of action potentials in motor cells.

Purpose of the Study:

• To investigate the mechanisms by which the central program for inking in Aplysia can be triggered.
• To elucidate the role of excitatory postsynaptic potentials (EPSPs) in initiating the inking response.

Main Methods:

• Electrophysiological recordings from Aplysia ink-gland motor cells.
• Stimulation of the animal at single or multiple sites with suprathreshold or subthreshold stimuli.
• Analysis of synaptic currents and membrane properties.

Main Results:

• The inking central program can be initiated by a single suprathreshold stimulus or two temporally close subthreshold stimuli.
• A suprathreshold stimulus primarily triggers the program via an increased-conductance EPSP.
• Subthreshold stimuli trigger the program through a decreased-conductance EPSP that augments subsequent synaptic input.

Conclusions:

• A novel mechanism involving a decreased-conductance EPSP facilitates spatial and temporal summation for initiating the Aplysia inking response.
• This decreased-conductance EPSP enhances synaptic augmentation by increasing motor cell input resistance and electrotonic coupling.
• The findings reveal distinct pathways for triggering a complex motor program based on stimulus characteristics.