Main script: thalmodes.g
/************************************************************************ *** All the files in this directory have been converted to GENESIS *** 2.0 using the convert command and some extra edits. Will run under *** Neurokit (thalcell.p) and as thalmodes.g. -lauren jones *** July 9, 1997 ljones@wesleyan.edu ***********************************************************************/
Pratik Mukherjee
[from Methods in Computational Neuroscience Project Report - August 1991]
This is a model of slow oscillatory bursting in thalamic relay cells in GENESIS, based on one by McCormick et. al. (1991). This is a single compartment lumped-soma model which includes four active membrane conductances: a fast Na+ current, a delayed rectifier K+ current, a low-threshold Ca+2 current (T-current), and a hyperpolarization-activated K+ current (H-current). The interaction of these last 3 conductances produces oscillatory bursting at 2-5 Hz when the resting membrane potential of the cell is more negative than -65 mV. The resting membrane potential is regulated by a passive K+ leak conductance. I obtained the kinetics for the T-current from Lytton & Sejnowski (1991) rather than using those of McCormick, because I feel that their inactivation time constant is more accurate. The GENESIS model is called THALMODES and exists in a directory of the same name. It illustrates the two distinct firing modes of thalamocortical relay cells: the single-spike relay mode at depolarized resting potentials, and the oscillatory bursting mode at hyperpolarized potentials. The switching between these two modes is dependent on the magnitude of the K+ leak conductance. This K+ leak conductance is in turn regulated by various neurotransmitters, but for the purposes of this model, the leak conductance is a parameter that can be set by hand.
If the simulation is run at the default values, the cell will remain at the baseline resting membrane potential of -50 mV. But if the resting membrane potential is depolarized by reducing the leak conductance, then repetitive spiking will result. This same effect can be achieved by depolarizing current injections (e.g. 0.5 nA). However, if the resting membrane potential is made more negative by increasing the leak conductance to 31 nS, then the neuron will burst at an oscillatory frequency of about 3 Hz. This frequency can be adjusted by varying the size of the H-current: larger values will give higher frequencies, while smaller values will generate lower frequencies.
References:
Bloomfield SA, JE Hamos, & SM Sherman (1987) "Passive cable properties of neurons in the lateral geniculate nucleus of the cat." J. Physiol. 383: 653-692.
Crunelli V, N Leresche, & JG Parnavelas (1986) "Electrophysiological study of morphologically identified X and Y geniculate cells of the cat in vitro" J. Physiol. 377: 23P.
Kaplan E & RM Shapley (1984) "The origin of the slow (S) potential in cells of the mammalian lateral geniculate nucleus" Exp. Brain Res. 63:??.
Lytton WW & TJ Sejnowski (1991) "Simulations of cortical pyramidal neurons synchronized by inhibitory interneurons" J. Neurophysiol. (in press).
McCormick DA, J Huguenard, & B Strowbridge (1991) "Determination of state dependent processing in thalamus by single neuron properties and neuro- modulators" In: Single Neuron Computation (ed. McKenna et. al.) Academic Press.
McCormick DA & HC Pape (1990), "Properties of a hyperpolarization-activated cation current and its role in rhythmic oscillation in thalamic relay neurons" J. Physiol. 431: 291-318.
*cartesian *relative // Specifying constants *set_global RM 0.55 *set_global RA 1.00 *set_global CM 0.017 *set_global EREST_ACT -0.050
*set_spherical
soma none 55 0 0 55.0 Na_sej_tab 1737 K_lgn_hh 206.9 Ca_sej_tab 52.61
H_lgn_tab 10.55 K_leak 3.0
// (the above is all on one line)