COMMENT
Updated Exp2Syn synapse with Mg-blocked nmda channel.
Defaul values of parameters (time constants etc) set to match synaptic channels in
striatal medium spiny neurons (Du et al., 2017; Chapman et al., 2003; Ding et al., 2008).
Robert . Lindroos @ ki . se
original comment:
________________
Two state kinetic scheme synapse described by rise time tau1,
and decay time constant tau2. The normalized peak condunductance is 1.
Decay time MUST be greater than rise time.
The solution of A->G->bath with rate constants 1/tau1 and 1/tau2 is
A = a*exp(-t/tau1) and
G = a*tau2/(tau2-tau1)*(-exp(-t/tau1) + exp(-t/tau2))
where tau1 < tau2
If tau2-tau1 -> 0 then we have a alphasynapse.
and if tau1 -> 0 then we have just single exponential decay.
The factor is evaluated in the
initial block such that an event of weight 1 generates a
peak conductance of 1.
Because the solution is a sum of exponentials, the
coupled equations can be solved as a pair of independent equations
by the more efficient cnexp method.
ENDCOMMENT
NEURON {
POINT_PROCESS adaptive_glutamate_test
RANGE tau1_ampa, tau2_ampa, tau1_nmda, tau2_nmda
RANGE erev_ampa, erev_nmda, g, i
NONSPECIFIC_CURRENT i
RANGE i_ampa, i_nmda, g_ampa, g_nmda, ratio, I, G, mg, q, alpha, eta
RANGE w_ampa_min, w_ampa_0, w_ampa_max, w_nmda_0, w_nmda_plateau
RANGE glu_thresh1, glu_thresh2, thresh_LTP, thresh_LTD, learning_rate
POINTER glu, dopamine
USEION ca_nmda READ ca_nmdai WRITE ica_nmda VALENCE 2
USEION cal READ cali VALENCE 2
}
UNITS {
(nA) = (nanoamp)
(mV) = (millivolt)
(uS) = (microsiemens)
}
PARAMETER {
erev_ampa = 0.0 (mV)
erev_nmda = 15.0 (mV)
tau1_ampa = 1.9 (ms)
tau2_ampa = 4.8 (ms) : tau2 > tau1
tau1_nmda = 5.52 (ms) : old value was 5.63
tau2_nmda = 231 (ms) : tau2 > tau1
ratio = 1 (1) : both types give same maximal amplitude of current
mg = 1 (mM)
alpha = 0.062
q = 2
eta = 18
w_ampa_min = 0.055 (uS)
w_ampa_0 = 0.11e-3 (uS)
w_ampa_max = 0.165e-3 (uS)
w_nmda_0 = 0.08e-3 (uS)
w_nmda_plateau = 0.8e-3 (uS)
glu_thresh1 = 0.05
glu_thresh2 = 0.05
thresh_LTP = 0.025
thresh_LTD = 0.005
learning_rate = 0.01
}
ASSIGNED {
v (mV)
i (nA)
g (uS)
factor_nmda
factor_ampa
i_ampa
i_nmda
g_ampa
g_nmda
block
I
G
glu
dopamine
ica_nmda (nA)
ca_nmdai (mM)
cali (mM)
}
STATE {
A (uS)
B (uS)
C (uS)
D (uS)
w_nmda (uS)
w_ampa (uS)
}
INITIAL {
LOCAL tp
if (tau1_nmda/tau2_nmda > .9999) {
tau1_nmda = .9999*tau2_nmda
}
if (tau1_ampa/tau2_ampa > .9999) {
tau1_ampa = .9999*tau2_ampa
}
: NMDA
A = 0
B = 0
tp = (tau1_nmda*tau2_nmda)/(tau2_nmda - tau1_nmda) * log(tau2_nmda/tau1_nmda)
factor_nmda = -exp(-tp/tau1_nmda) + exp(-tp/tau2_nmda)
factor_nmda = 1/factor_nmda
: AMPA
C = 0
D = 0
tp = (tau1_ampa*tau2_ampa)/(tau2_ampa - tau1_ampa) * log(tau2_ampa/tau1_ampa)
factor_ampa = -exp(-tp/tau1_ampa) + exp(-tp/tau2_ampa)
factor_ampa = 1/factor_ampa
w_nmda = w_nmda_0 +2e-6
w_ampa = w_ampa_0 +2e-6
}
BREAKPOINT {
SOLVE state METHOD cnexp
: NMDA
g_nmda = (B - A)*w_nmda
block = MgBlock()
i_nmda = g_nmda * (v - erev_nmda) * block
ica_nmda = i_nmda
: AMPA
g_ampa = (D - C)*w_ampa
i_ampa = g_ampa * (v - erev_ampa)
: total current
G = g_ampa + g_nmda
I = i_ampa
i = I
}
DERIVATIVE state {
A' = -A/tau1_nmda*q
B' = -B/tau2_nmda*q
C' = -C/tau1_ampa
D' = -D/tau2_ampa
w_nmda' = (gluind1(glu)*(w_nmda_plateau - w_nmda) - gluind2(glu)*(w_nmda - w_nmda_0))
w_ampa' = learning_rate * active_syn(g_nmda)* dopamine * ( pind_LTP(ca_nmdai)*0.5*(dopamine+1)*(w_ampa_max-w_ampa) - pind_LTD(cali)*0.5*(dopamine-1)*(w_ampa - w_ampa_min) )
}
NET_RECEIVE(dummy (uS)) {
A = A + factor_nmda
B = B + factor_nmda
C = C + factor_ampa
D = D + factor_ampa
}
FUNCTION MgBlock() {
MgBlock = 1 / (1 + mg * eta * exp(-alpha * v) )
}
FUNCTION gluind1(glu) {
UNITSOFF
if (glu >= glu_thresh1) {
gluind1 = 1
} else {
gluind1 = 1e-6
}
UNITSON
}
FUNCTION gluind2(glu) {
UNITSOFF
if (glu <= glu_thresh2) {
gluind2 = 1
} else {
gluind2 = 0
}
UNITSON
}
FUNCTION pind_LTP(conc) {
if (conc > thresh_LTP) {
pind_LTP = 1
} else {
pind_LTP = 1e-6
}
}
FUNCTION pind_LTD(conc) {
if (conc > thresh_LTD) {
pind_LTD = 1
} else {
pind_LTD = 1e-6
}
}
FUNCTION trap(g) {
if (g < 1e-6) {
trap = 1e-6
} else {
trap = g
}
}
FUNCTION active_syn(g) {
if (g < 1e-4) {
active_syn = 1e-6
} else {
active_syn = 1
}
}