Postsynaptic calcium contributes to reinforcement in a three-neuron network exhibiting associative plasticity

Area of Science:

• Neuroscience
• Cellular Neuroscience
• Neurobiology

Background:

• Synaptic plasticity underlies learning and memory.
• Modulatory neurotransmitters like serotonin play key roles in neural circuit function.
• Understanding cellular mechanisms of associative learning is fundamental in neuroscience.

Purpose of the Study:

• To investigate the cellular mechanisms by which a single serotonergic cell activation induces long-term associative enhancement of synaptic input.
• To determine the role of intracellular calcium in mediating this synaptic plasticity.
• To elucidate the function of a single modulatory cell in a simple neural network.

Main Methods:

• Utilized a simple three-cell network in the terrestrial snail Helix.
• Employed 1,2-bis (2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA) injection to chelate intracellular calcium.
• Measured intracellular calcium levels and membrane potential changes.
• Applied serotonin and thapsigargin to study their effects on synaptic responses.

Main Results:

• Activation of a single serotonergic cell was sufficient to enhance synaptic input to the withdrawal interneuron.
• BAPTA injection abolished this pairing-specific enhancement.
• Modulatory cell activation and serotonin application increased intracellular calcium in the withdrawal interneuron without altering membrane potential or input resistance.
• Serotonin and thapsigargin increased responses to glutamate, dependent on intracellular calcium and sensitive to heparin.

Conclusions:

• A single modulatory cell's activity can mediate reinforcement through increased postsynaptic intracellular calcium.
• This mechanism operates within a simple neural network with identified neuronal roles.
• The findings provide insights into the cellular basis of associative learning and memory.