Spike initiation in central neurones

Matt Jones jonesmat at ohsu.edu
Mon Dec 14 14:14:16 EST 1998


In article <74pvvj$mc1$1 at pegasus.csx.cam.ac.uk> Koye,
aao20 at hermes.cam.ac.uk writes:
>Hi guys,
>Does anyone have information on current research (i.e 1yr old or less) that
>produced results that have thrown further light on the site of action
>potential initiation in mammalian central neurones? I am doing a critical
>review on a paper that discusses this topic and I need current information.


Here's a repost of an email message from Dan Johnston (who's textbook,
Johnston and Wu, Foundations of Cellular Neurophysiology, is excellent).

Matt Jones


Regarding the site of initiation of an action potential, we found that
the  
density of Na channels in the soma, axon hillock, or initial segment of  
subicular neurons is fairly uniform with no obvious "hot spots" of high  
density (Colbert et al, J. Neurosci., 16:6676-6686, 1996).  Using local  
application of TTX, we also found that the action potential initiates (ie
 
lowest threshold) in the axon about 50um from the soma, probably at the
first  
node of ranvier.  We chose to study subicular neurons, which are right
next to  
the CA1 region, because the axon is easily distinguished from basal
dendrites  
in these cells.  This conclusion of axonal spike initiation may not be
true  
for all neurons, however, but the evidence for other cells is not
available.   
A uniform Na channel density in soma and axon hillock of neocortical
neurons  
has also has been seen by Greg Stuart in Layer V neurons.  It is also
clear  
that action potentials can initiate in dendrites under certain conditions
such  
as in response to large amplitude synaptic input.  In mitral cells this
has  
been demonstrted very nicely by W.R. Chen et al, Science, 278:463-467,
1997  
and recently by Golding and Spruston in CA1 neurons, Neuron 21:1189-1200,
 
1998.  There are lots of reviews on these and other related topics during
the  
past two years.  We have two annual reviews on the topic, Yuste and Tank
have  
a review in Neuron, and Greg Stuart has a TINS article.  Let me know if
you  
would like more info or help with references.

sincerely,
dan
---
Dan Johnston
Division of Neuroscience (S603)
Baylor College of Medicine
1 Baylor Plaza
Houston, TX 77030-3498



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