Competition for AP initiation sites in a circuit controlling simple learning (Cruz et al. 2007)

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Accession:117459
"The spatial and temporal patterns of action potential initiations were studied in a behaving leech preparation to determine the basis of increased firing that accompanies sensitization, a form of non-associative learning requiring the S-interneurons. ... The S-interneurons, one in each ganglion and linked by electrical synapses with both neighbors to form a chain, are interposed between sensory and motor neurons. ... the single site with the largest initiation rate, the S-cell in the stimulated segment, suppressed initiations in adjacent ganglia. Experiments showed this was both because (1) it received the earliest, greatest input and (2) the delayed synaptic input to the adjacent S-cells coincided with the action potential refractory period. A compartmental model of the S-cell and its inputs showed that a simple, intrinsic mechanism of inexcitability after each action potential may account for suppression of impulse initiations. Thus, a non-synaptic competition between neurons alters synaptic integration in the chain. In one mode, inputs to different sites sum independently, whereas in another, synaptic input to a single site precisely specifies the overall pattern of activity."
Reference:
1 . Cruz GE, Sahley CL, Muller KJ (2007) Neuronal competition for action potential initiation sites in a circuit controlling simple learning. Neuroscience 148:65-81 [PubMed]
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Model Information (Click on a link to find other models with that property)
Model Type: Realistic Network; Neuron or other electrically excitable cell;
Brain Region(s)/Organism: Leech;
Cell Type(s): Leech S cell;
Channel(s): I Na,t; I K,leak;
Gap Junctions:
Receptor(s):
Gene(s):
Transmitter(s): Serotonin;
Simulation Environment: NEURON;
Model Concept(s): Action Potential Initiation; Activity Patterns; Spatio-temporal Activity Patterns;
Implementer(s): Cruz, Ginny [gcruz at monell.org];
Search NeuronDB for information about:  I Na,t; I K,leak; Serotonin; 
COMMENT
-----------------------------------------------------------------------------

  Leak potassium current
  ----------------------

  This mechanism was written to be used as a potassium channel that is
  open or closed by neuromodulators.  

  WARNING: this current is NOT inserted as a standard current, but as a 
  point process (same way as a synapse or current injection).

  Procedure for insertion:

	objectvar kl
	kl = new kleak()

	access <compartment_name>
	kl.loc(0.5)

	kl.gmax = ...



  A. Destexhe , The Salk Institute, Feb 1994.

-----------------------------------------------------------------------------
ENDCOMMENT

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

NEURON {
	POINT_PROCESS kleak
	RANGE gmax
	GLOBAL Erev
	NONSPECIFIC_CURRENT i
}
UNITS {
	(nA) = (nanoamp)
	(mV) = (millivolt)
	(umho) = (micromho)
}

PARAMETER {
	gmax	= 0.004	(umho)		: maximum conductance (microSiemens)
	Erev	= -100	(mV)		: reversal potential (potassium)
}


ASSIGNED {
	v		(mV)		: postsynaptic voltage
	i 		(nA)		: current = g*(v - Erev)
}

INITIAL {
}

BREAKPOINT {
	i = gmax * (v - Erev)
}