TITLE AMPA and NMDA receptor with presynaptic short-term plasticity 


COMMENT
AMPA and NMDA receptor conductance using a dual-exponential profile
presynaptic short-term plasticity based on Fuhrmann et al. 2002
Implemented by Srikanth Ramaswamy, Blue Brain Project, July 2009
Etay: changed weight to be equal for NMDA and AMPA, gmax accessible in Neuron

ENDCOMMENT


NEURON {

        POINT_PROCESS ProbUDFsyn2  
        RANGE tau_r, tau_d
        RANGE Use, u, Dep, Fac, u0
        RANGE i, g, e, gmax
        NONSPECIFIC_CURRENT i
	POINTER rng
}

PARAMETER {

        tau_r = 0.2   (ms)  : dual-exponential conductance profile
        tau_d = 1.7    (ms)  : IMPORTANT: tau_r < tau_d
        Use = 1.0   (1)   : Utilization of synaptic efficacy (just initial values! Use, Dep and Fac are overwritten by BlueBuilder assigned values) 
        Dep = 100   (ms)  : relaxation time constant from depression
        Fac = 10   (ms)  :  relaxation time constant from facilitation
        e = 0     (mV)  : AMPA and NMDA reversal potential
    	gmax = .001 (uS) : weight conversion factor (from nS to uS)
    	u0 = 0 :initial value of u, which is the running value of Use
}

COMMENT
The Verbatim block is needed to generate random nos. from a uniform distribution between 0 and 1 
for comparison with Pr to decide whether to activate the synapse or not
ENDCOMMENT
   
VERBATIM

#include<stdlib.h>
#include<stdio.h>
#include<math.h>

double nrn_random_pick(void* r);
void* nrn_random_arg(int argpos);

ENDVERBATIM
  

ASSIGNED {

        v (mV)
        i (nA)
	g (uS)
        factor
	rng
	weight_NMDA
}

STATE {
        A       : state variable to construct the dual-exponential profile - decays with conductance tau_r_AMPA
        B       : state variable to construct the dual-exponential profile - decays with conductance tau_d_AMPA
}

INITIAL{

  LOCAL tp
        
	A = 0
  B = 0
	
        
	tp = (tau_r*tau_d)/(tau_d-tau_r)*log(tau_d/tau_r) :time to peak of the conductance
	      
	factor = -exp(-tp/tau_r)+exp(-tp/tau_d) : Normalization factor - so that when t = tp, gsyn = gpeak
        factor = 1/factor
 
}

BREAKPOINT {

        SOLVE state METHOD cnexp
        g = gmax*(B-A) :compute time varying conductance as the difference of state variables B and A
        i = g*(v-e) :compute the driving force based on the time varying conductance, membrane potential, and reversal
}

DERIVATIVE state{

        A' = -A/tau_r
        B' = -B/tau_d
}


NET_RECEIVE (weight, Pv, Pv_tmp, Pr, u, tsyn (ms)){
	
        INITIAL{
                Pv=1
                u=u0
                tsyn=t
            }

        : calc u at event-
        if (Fac > 0) {
                u = u*exp(-(t - tsyn)/Fac) :update facilitation variable if Fac>0 Eq. 2 in Fuhrmann et al.
           } else {
                  u = Use  
           } 
           if(Fac > 0){
                  u = u + Use*(1-u) :update facilitation variable if Fac>0 Eq. 2 in Fuhrmann et al.
           }    

        
            Pv_tmp  = 1 - (1-Pv) * exp(-(t-tsyn)/Dep) :Probability Pv for a vesicle to be available for release, analogous to the pool of synaptic
                                                      :resources available for release in the deterministic model. Eq. 3 in Fuhrmann et al.
            Pr  = u * Pv_tmp                          :Pr is calculated as Pv * u (running value of Use)
            Pv_tmp  = Pv_tmp - u * Pv_tmp             :update Pv as per Eq. 3 in Fuhrmann et al.
            :printf("Pv = %g\n", Pv)
            :printf("Pr = %g\n", Pr)
                
		   if (erand() < Pr){
                    tsyn = t
	            Pv = Pv_tmp
                    A = A + weight*factor
                    B = B + weight*factor
                }
}

PROCEDURE setRNG() {
VERBATIM
    {
        /**
         * This function takes a NEURON Random object declared in hoc and makes it usable by this mod file.
         * Note that this method is taken from Brett paper as used by netstim.hoc and netstim.mod
         * which points out that the Random must be in negexp(1) mode
         */
        void** pv = (void**)(&_p_rng);
        if( ifarg(1)) {
            *pv = nrn_random_arg(1);
        } else {
            *pv = (void*)0;
        }
    }
ENDVERBATIM
}

FUNCTION erand() {
VERBATIM
	    //FILE *fi;
        double value;
        if (_p_rng) {
                /*
                :Supports separate independent but reproducible streams for
                : each instance. However, the corresponding hoc Random
                : distribution MUST be set to Random.negexp(1)
                */
                value = nrn_random_pick(_p_rng);
		        //fi = fopen("RandomStreamMCellRan4.txt", "w");
                //fprintf(fi,"random stream for this simulation = %lf\n",value);
                //printf("random stream for this simulation = %lf\n",value);
                return value;
        }else{
ENDVERBATIM
                : the old standby. Cannot use if reproducible parallel sim
                : independent of nhost or which host this instance is on
                : is desired, since each instance on this cpu draws from
                : the same stream
                erand = exprand(1)
VERBATIM
        }
ENDVERBATIM
        :erand = value :This line must have been a mistake in Hay et al.'s code, it would basically set the return value to a non-initialized double value.
                       :The reason it sometimes works could be that the memory allocated for the non-initialized happened to contain the random value
                       :previously generated (or if _p_rng is always a null pointer). However, here we commented this line out.
}