TITLE AMPA synapse for nucleus accumbens model : see comments below NEURON { POINT_PROCESS AMPA RANGE gbar, tau_r, tau_d, scale, spkcnt, countflag, i, t1, ca_ratio, ical, itmp, qfact, g NONSPECIFIC_CURRENT i USEION cal WRITE ical VALENCE 2 } UNITS { (nA) = (nanoamp) (mV) = (millivolt) (umho) = (micromho) } PARAMETER { gbar = 8.5e-4 (umho) : approx 0.5:1 NMDA:AMPA ratio (Myme 2003) : with mg = 0, vh = -70, one pulse, NMDA = 300 pS : here AMPA = 593 pS (NMDA set to Dalby 2003) tau_r = 2.2 (ms) : Gotz 1997, Table 1 - rise tau tau_d = 11.5 (ms) : Gotz 1997, Table 1 - decay tau Erev = 0 (mV) : reversal potential, Jahn 1998 saturate = 1.2 : causes the conductance to saturate - matched to : Destexhe's reduced model in [1] qfact = 2 : convert 22 degC to 35 degC ca_ratio = 0.005 : ratio of calcium current to total current : Burnashev/Sakmann J Phys 1995 485:403-418 : with Carter/Sabatini Neuron 2004 44:483-493 g_factor : factor used to scale the gbar of the AMPA } ASSIGNED { g (umho) v (mV) : postsynaptic voltage itmp (nA) : temp value of current i (nA) : nonspecific current = g*(v - Erev) ical (nA) : calcium current through AMPA synapse (Carter/Sabatini) t1 (ms) y1_add (/ms) : value added to y1 when a presynaptic spike is registered y1_loc (/ms) countflag : start/stop counting spikes delivered spkcnt : counts number of events delivered to synapse scale : scale allows the current to be scaled by weight } : so NetCon(...,2) gives 2*the current as NetCon(...,1) STATE { y1 (/ms) y2 : sum of beta-functions, describing the total conductance } INITIAL { y1_add = 0 scale = 0 spkcnt = 0 countflag = 0 t1 = 0 y1_loc = 0 g_factor = 1 } BREAKPOINT { SOLVE betadyn METHOD cnexp g = gbar * g_factor * y2 itmp = scale * g * (v - Erev) i = (1-ca_ratio) * itmp ical = ca_ratio * itmp } DERIVATIVE betadyn { : dynamics of the beta-function, from [2] y1' = -y1 / (tau_d/qfact) y2' = y1 - y2 / (tau_r/qfact) } NET_RECEIVE( weight, y1_loc (/ms) ) { : updating the local y1 variable y1_loc = y1_loc*exp( -(t - t1) / (tau_d/qfact) ) : y1_add is dependent on the present value of the local : y1 variable, y1_loc y1_add = (1 - y1_loc/saturate) : update the local y1 variable y1_loc = y1_loc + y1_add : presynaptic spike is finaly registered y1 = y1 + y1_add : store the spike time t1 = t spkcnt = spkcnt + 1 scale = weight } COMMENT Author Johan Hake (c) spring 2004 : Summate input from many presynaptic sources and saturate : each one of them during heavy presynaptic firing : [1] Destexhe, A., Z. F. Mainen and T. J. Sejnowski (1998) : Kinetic models of synaptic transmission : In C. Koch and I. Segev (Eds.), Methods in Neuronal Modeling : [2] Rotter, S. and M. Diesmann (1999) Biol. Cybern. 81, 381-402 : Exact digital simulation of time-invariant linear systems with application : to neural modeling Dalby, N. O., and Mody, I. (2003). Activation of NMDA receptors in rat dentate gyrus granule cells by spontaneous and evoked transmitter release. J Neurophysiol 90, 786-797. Gotz, T., Kraushaar, U., Geiger, J., Lubke, J., Berger, T., and Jonas, P. (1997). Functional properties of AMPA and NMDA receptors expressed in identified types of basal ganglia neurons. J Neurosci 17, 204-215. Jahn K, Bufler J, Franke C (1998) Kinetics of AMPA-type glutamate receptor channels in rat caudate-putamen neurones show a wide range of desensitization but distinct recovery characteristics. Eur J Neurosci 10:664-672. Myme, C. I., Sugino, K., Turrigiano, G. G., and Nelson, S. B. (2003). The NMDA-to-AMPA ratio at synapses onto layer 2/3 pyramidal neurons is conserved across prefrontal and visual cortices. J Neurophysiol 90, 771-779. Gutfreund H, Kinetics for the Life Sciences, Cambridge University Press, 1995, pg 234. (suggested by Ted Carnevale) ENDCOMMENT