DRt neuron model (Sousa et al., 2014)

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Accession:151949
Despite the importance and significant clinical impact of understanding information processing in the nociceptive system, the functional properties of neurons in many parts of this system are still unknown. In this work we performed whole-cell patch-clamp recording in rat brainstem blocks to characterize the electrophysiological properties of neurons in the dorsal reticular nucleus (DRt), a region known to be involved in pronociceptive modulation. We also compared properties of DRt neurons with those in the adjacent parvicellular reticular nucleus (PCRt) and in neighboring regions outside the reticular formation. We found that neurons in the DRt and PCRt had similar electrophysiological properties and exhibited mostly tonic-like firing patterns, whereas neurons outside the reticular formation showed a larger diversity of firing-patterns. The dominance of tonic neurons in the DRt supports previous conclusions that these neurons encode stimulus intensity through their firing frequency.
Reference:
1 . Sousa M, Szucs P, Lima D, Aguiar P (2014) The pronociceptive dorsal reticular nucleus contains mostly tonic neurons and shows a high prevalence of spontaneous activity in block preparation. J Neurophysiol 111:1507-18 [PubMed]
Model Information (Click on a link to find other models with that property)
Model Type: Neuron or other electrically excitable cell;
Brain Region(s)/Organism:
Cell Type(s): Hodgkin-Huxley neuron;
Channel(s): I Na,t; I K; I K,Ca; I Calcium;
Gap Junctions:
Receptor(s):
Gene(s):
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Activity Patterns;
Implementer(s): Aguiar, Paulo [pauloaguiar at fc.up.pt];
Search NeuronDB for information about:  I Na,t; I K; I K,Ca; I Calcium;
TITLE high threshold calcium current (L-current)

COMMENT
        *********************************************
        reference:      McCormick & Huguenard (1992) 
			J.Neurophysiology 68(4), 1384-1400
        found in:       hippocampal pyramidal cells
        *********************************************
	Assembled for MyFirstNEURON by Arthur Houweling
	
ENDCOMMENT




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


NEURON {
	SUFFIX iCaL
	USEION ca READ cai,cao WRITE ica
        RANGE pcabar, m_inf, tau_m, ica
}

UNITS {
	(mA)	= (milliamp)
	(mV)	= (millivolt)
	(mM)	= (milli/liter)
        FARADAY = 96480 (coul)
        R       = 8.314 (volt-coul/degC)
}

PARAMETER {
	v			(mV)
	celsius			(degC)
        dt              	(ms)
	cai			(mM)
	cao			(mM)
	pcabar= 0.000276	(cm/s)		
}

STATE {
	m
}

ASSIGNED {
	ica		(mA/cm2)
	tau_m		(ms)
	m_inf 
	tadj
}

BREAKPOINT { 
	SOLVE states :METHOD euler
	ica = pcabar * m*m * ghk(v,cai,cao,2)
}

:DERIVATIVE states {
:       rates(v)
:
:       m'= (m_inf-m) / tau_m 
:}
  
PROCEDURE states() {
        rates(v)
	
        m= m + (1-exp(-dt/tau_m))*(m_inf-m)
	:printf("\n iCaL tau_m=%g", tau_m)
}

UNITSOFF

INITIAL {
	tadj = 3.0 ^ ((celsius-23.5)/10)
	rates(v)
	m = m_inf
}

FUNCTION ghk( v(mV), ci(mM), co(mM), z)  (millicoul/cm3) {
        LOCAL e, w
        w = v * (.001) * z*FARADAY / (R*(celsius+273.16))
        
	if (fabs(w)>1e-4) 
          { e = w / (exp(w)-1) }
        else
	: denominator is small -> Taylor series
        { e = 1-w/2 }
	
        ghk = - (.001) * z*FARADAY * (co-ci*exp(w)) * e
}
UNITSOFF

PROCEDURE rates(v(mV)) { LOCAL a,b
	a = 1.6 / (1+ exp(-0.072*(v-5)))
	b = 0.02 * vtrap( -(v-1.31), 5.36)

	tau_m = 1/(a+b) / tadj
	m_inf = 1/(1+exp((v+10)/-10))
}

FUNCTION vtrap(x,c) { 
	: Traps for 0 in denominator of rate equations
        if (fabs(x/c) < 1e-6) {
          vtrap = c + x/2 }
        else {
          vtrap = x / (1-exp(-x/c)) }
}
UNITSON

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