TITLE Low threshold calcium current
                             :
                             :   Ca++ current responsible for low threshold spikes (LTS)
                             :   RETICULAR THALAMUS
                             :   Differential equations
                             :
                             :   Model of Huguenard & McCormick, J Neurophysiol 68: 1373-1383, 1992.
                             :   The kinetics is described by standard equations (NOT GHK)
                             :   using a m2h format, according to the voltage-clamp data
                             :   (whole cell patch clamp) of Huguenard & Prince, J Neurosci.
                             :   12: 3804-3817, 1992.  The model was introduced in Destexhe et al.
                             :   J. Neurophysiology 72: 803-818, 1994.
                             :   See http://www.cnl.salk.edu/~alain , http://cns.fmed.ulaval.ca
                             :
                             :    - Kinetics adapted to fit the T-channel of reticular neuron                                            :    - Q10 changed to 5 and 3
                             :    - Time constant tau_h fitted from experimental data
                             :    - shift parameter for screening charge
                             :
                             :   ACTIVATION FUNCTIONS FROM EXPERIMENTS (NO CORRECTION)
                             :
                             :   Reversal potential taken from Nernst Equation
                             :
                             :   Written by Alain Destexhe, Salk Institute, Sept 18, 1992
                             :

                             INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}

                             NEURON {
                                     SUFFIX it2
                                     USEION ca READ cai, cao WRITE ica
                                     RANGE gcabar, m_inf, tau_m, h_inf, tau_h, shift
                             }

                             UNITS {
                                     (molar) = (1/liter)
                                     (mV) =  (millivolt)
                                     (mA) =  (milliamp)
                                     (mM) =  (millimolar)

                                     FARADAY = (faraday) (coulomb)
                                     R = (k-mole) (joule/degC)
                             }

                             PARAMETER {
                                     v               (mV)
                                     celsius = 36    (degC)
                             :       eca     = 120   (mV)
                                     gcabar  = .00175 (mho/cm2)
                                     shift   = 2     (mV)            : screening charge for Ca_o = 2 mM
                                     cai     = 2.4e-4 (mM)           : adjusted for eca=120 mV
                                     cao     = 2     (mM)
                             }

                             STATE {
                                     m h
                             }

                             ASSIGNED {
                                     ica     (mA/cm2)
                                     carev   (mV)
                                     m_inf
                                     tau_m   (ms)
                                     h_inf
                                     tau_h   (ms)
                                     phi_m
                                     phi_h
                             }

                             BREAKPOINT {
                                     SOLVE castate METHOD euler
                                     carev = (1e3) * (R*(celsius+273.15))/(2*FARADAY) * log (cao/cai)
                                     ica = gcabar * m*m*h * (v-carev)
                             }

                             DERIVATIVE castate {
                                     evaluate_fct(v)

                                     m' = (m_inf - m) / tau_m
                                     h' = (h_inf - h) / tau_h
                             }

                             UNITSOFF
                             INITIAL {
                             :
                             :   Activation functions and kinetics were obtained from
                             :   Huguenard & Prince, and were at 23-25 deg.
                             :   Transformation to 36 deg assuming Q10 of 5 and 3 for m and h
                             :   (as in Coulter et al., J Physiol 414: 587, 1989)
                             :
                                     phi_m = 5.0 ^ ((celsius-24)/10)
                                     phi_h = 3.0 ^ ((celsius-24)/10)

                                     evaluate_fct(v)
                                     m = m_inf
                                     h = h_inf
                             }

                             PROCEDURE evaluate_fct(v(mV)) { 
                             :
                             :   Time constants were obtained from J. Huguenard
                             :

                                     m_inf = 1.0 / ( 1 + exp(-(v+shift+50)/7.4) )
                                     h_inf = 1.0 / ( 1 + exp((v+shift+78)/5.0) )

                                     tau_m = ( 3 + 1.0 / ( exp((v+shift+25)/10) + exp(-(v+shift+100)/15) ) ) / phi_m
                                     tau_h = ( 85 + 1.0 / ( exp((v+shift+46)/4) + exp(-(v+shift+405)/50) ) ) / phi_h
                             }
                             UNITSON