Biological Basis of the Mossy Cell Model

The provided code models the electrophysiological properties of a mossy cell in the dentate gyrus of the hippocampus. These cells are part of a broader neural network within the hippocampal formation, playing crucial roles in the modulation of excitatory pathways and influencing memory and learning processes. Here, we'll explore the biological components reflected in the code.

Mossy Cells in the Dentate Gyrus

Mossy cells are excitatory neurons located in the hilus of the dentate gyrus. They receive input from granule cells and other sources and project to both local and distant targets, such as other granule cells, influencing network excitability and plasticity.

Structural Components

• Compartments: The model divides the mossy cell into compartments:

  • A main soma compartment representing the cell body.
  • Four dendritic branches (mcdend1 to mcdend4), each with sub-compartments (0-3) to represent the proximal to distal segments of the dendrites. This reflects the spatial distribution of synaptic inputs and ionic conductances across the neuron's geometry.

• Integration and Propagation: By dividing the dendrites into proximal and distal compartments, the model captures how signals are integrated and propagated toward the soma.

Ionic Channels and Conductances

The code simulates various ion channels critical for generating action potentials and synaptic integration:

• Calcium Channels:

  • ccanl (Calcium Current Associated with the Long-lasting type [L-type]), modulating intracellular calcium dynamics.
  • nca and lca (neuronal calcium channels), contributing to depolarization and generating synaptic responses.

• Potassium Channels:

  • ka (A-type Potassium Current) and bk (Big Potassium Current), crucial for action potential repolarization and regulating firing patterns.
  • sk (Small conductance Potassium current), involved in calcium-activated afterhyperpolarization.

• Sodium Channels:

  • ichan2, representing fast sodium currents essential for action potential initiation and propagation.

• Ih (Hyperpolarization-activated Cyclic Nucleotide-gated Channels):

  • ih, contributing to the control of membrane potential in dendritic compartments, playing a role in rhythmic oscillations and recovery from hyperpolarization.

Synaptic Inputs

The code defines various synaptic mechanisms, modeled using Exp2Syn to incorporate post-synaptic potentials:

• AMPA-type Synapses:

  • Associated with glutamatergic excitatory input originating from both proximal (e.g., granule cells and mossy cells) and distal (e.g., perforant path) sources. Characterized by specific time constants (tau1, tau2) and reversal potentials (e).

• GABA-type Synapses:

  • BC (Basket Cell) Synapses: Fast inhibitory post-synaptic potentials directly influencing the soma.
  • HIPP (Hilar Interneurons) Synapses: Provide slower inhibitory input to distal dendrites, modulating synaptic integration.

Cellular Properties

• Membrane Resistance and Capacitance: The axial resistivity (Ra) and specific membrane capacitance (cm) are set for different compartments, tailoring the passive electrical properties to resemble a mossy cell's physiology.

• Reversal Potentials: Specific ion equilibrium potentials (ena, ek, etc.) are essential for determining the direction and driving force of ionic currents.

Purpose and Use

Overall, the model captures the complex interactions and dynamics of a mossy cell, integrating various synaptic and intrinsic conductances. This setup allows researchers to study how these cells process synaptic inputs, maintain excitability, and influence neural circuit behavior in the hippocampus.