The code provided models synaptic transmission processes specific to pyramidal cells within the realm of computational neuroscience. It simulates the activity of two types of glutamatergic synaptic receptors commonly involved in excitatory neurotransmission in the brain: NMDA receptors and AMPA receptors. These receptor types play crucial roles in synaptic plasticity, a cellular mechanism underlying learning and memory.
Role and Importance: NMDA (N-methyl-D-aspartate) receptors are ionotropic glutamate receptors that allow the flow of ions, particularly calcium (Ca²⁺), sodium (Na⁺), and potassium (K⁺), across the cell membrane. They are unique due to their voltage-dependent magnesium (Mg²⁺) block, which requires both ligand binding (glutamate) and postsynaptic depolarization to relieve the block, allowing Ca²⁺ entry. This dual requirement makes them critical for synaptic plasticity processes, such as long-term potentiation (LTP).
Dynamics Modeled: The code models NMDA receptor currents (inmda) by incorporating exponential rise and decay dynamics controlled by time constants taun1 and taun2, respectively. These dynamics reflect the receptor's slow kinetics. The function sfunc models the voltage sensitivity of the receptors likely reflecting the Mg²⁺ block.
Role and Importance: AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors are also ionotropic and primarily mediate fast excitatory synaptic transmission through Na⁺ and K⁺ fluxes. Unlike NMDA receptors, AMPA receptors do not require concurrent depolarization for activation, making them fundamental for rapid synaptic communication.
Dynamics Modeled: The code models AMPA receptor-mediated currents (iampa) using different rise and decay time constants (taua1 and taua2). These reflect the faster kinetics of AMPA receptors compared to NMDA receptors. The receptor's conductance (gampa) adjusts dynamically during synaptic activity to model the synaptic response.
Weight Parameter (wgt): The code includes a parameter for synaptic weight, which modifies the strength of synaptic input. This conceptually represents the amount of neurotransmitter released or the number of receptors available and is adjustable through the NET_RECEIVE block.
Receptor Conductance Limits: Both NMDA and AMPA conductances are limited to a maximum value (gNMDAmax and gAMPAmax), reflecting biological constraints on the maximum current flow through these receptors under physiological conditions.
Voltage and Reversal Potentials: The membrane potential v and equilibrium potentials (enmda and eampa) are included to calculate the driving force on ions through the receptors, a critical aspect of synaptic current calculation.
The code models processes that are fundamental to understanding excitatory synaptic transmission and its modulation in pyramidal neurons. It delineates the temporal characteristics and voltage-dependent properties of NMDA and AMPA receptor-mediated synaptic currents, capturing crucial aspects that influence neuronal activity and plasticity in the mammalian brain. Such models are vital for investigating how these synaptic properties contribute to broader neuronal network dynamics and cognitive functions.