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Topic: B.04.a. Sodium channels: Physiology
Support: BMBF
GIF
UConn
Title: Temperature dependence of action potential generation in neurons and models
Authors: E. NIKITIN 1 , A. MALYSHEV 1,2 , P. BALABAN 1 , G. BARANAUSKAS 3 , M.
CHISTIAKOVA 4,2 , *M. A. VOLGUSHEV 4,1 ;
1 Inst. Higher Nervous Activity & Neurophysiology, Russian Acad. of Sci., Moscow, Russian
Federation; 2 Neurophysiol., Ruhr-University Bochum, Bochum, Germany; 3 Robotics, Brain and
Cognitive Sci., Italian Inst. of Technol., Genova, Italy; 4 Dept Psychol, Univ. Connecticut, Storrs,
CT
Abstract: Action potentials (APs) in the soma of neocortical neurons exhibit a sharp, step-like
onset dynamics. The rapid initiation of cortical APs may reflect genuine properties of cortical AP
generation [1], in which case it may facilitate encoding of rapid signals by neuronal populations
[2]. An alternative hypothesis suggests that in neocortical neurons the APs have a smooth onset
at the initiation site in the axon initial segment, while the rapid onset of somatic APs is an
epiphenomenon, caused by invasion of lateral current from the initiation site into the soma [3].
To reproduce in the Hodgkin-Huxley type multicompartment models the onset dynamics of
somatic APs, comparable to that of recorded neurons, a careful selection of parameters, which
represent marginal cases of cell geometry and electrophysiological properties was necessary.
Moreover, these simulations were performed at virtual temperature of 37°C [3]. Since operation
of channels strongly depends on temperature, and high temperature coefficients are implemented
in the models (for sodium channels, Q10=2.3), fastest possible channel kinetics was exploited in
these simulations. Here we studied, how critical is the recording or virtual temperature as a
parameter for the onset dynamics of APs in neurons and in the models. To this end, we have
compared onset dynamics of somatic APs recorded in neocortical neurons to those simulated
with Hodgkin-Huxley type multicompartment models at physiological temperatures, room
temperature and 10-15°C. APs recorded in neocortical neurons exhibited sharp onset dynamics at
physiological as well as at room temperatures. In some neurons, the AP onset remained fast,
step-like even at 15 or 10°C. In contrast to the experimental results, the onset of somatic APs
simulated with the models became invariably smooth when virtual temperature was set to 20°C
or below. This discrepancy between temperature dependence of the AP onset dynamics in the
neurons and the models show that the invasion-based scenario alone cannot reconcile the
smooth, Hodgkin-Huxley type onset of APs at the initiation site with a sharp, step-like onset of
somatic APs.
[1] Naundorf et al., Nature 2006 440:1060
[2] Fourcaud-Trocme et al., J Neurosci 2003 23:11628; Naundorf et al., J Comput Neurosci 2005
18: 297
[3] Yu et al., J Neurosci 2008 28:7260
Supported by the grants from the BMBF, GIF and UConn to MV.