Weighting of synaptic response - Next Epsiode

[Brad J. Harris]

Joshua,
    Although my understading is limited, and primarily based on
neuro-muscular junctions (thus not quite perfect for what you want to
know) there are a few things I understand that you might find helpful
in your quest for knowledge (my post is largely prompted by an aparent
lack of responce to your first post - or maybe the server I'm using is
just slow - in any case:

rreich at shell01.ozemail.com.au (Rose Reich) wrote:

>As far as i see it, there are 4 possible ways of strengthening a 
>transmission, could anyone out there either confirm or deny any of my 
>guesses.

>1) More neurotransmitter is released by the presynaptic cell.

just one brief comment that may or may not hold much relavance to your
real question:  as you release more transmitter you near (and many
times exceed) the reversal potential of the cell, especially in the
localized region (the reversal potential being the point where opening
further channels results in as many ions leaving the cell as entered
it)

>2) Less enzymes (ie. acetylcholinesterase) present in synapse.

   Use of anti-acetylcholinesterase generally results in a lengthening
of the mean open time of the channels, (i.e. on voltage clamped cells,
the peak current generally does not increase, but the length of time
the current flows into the cell increases)
  I know there are quite a few articles you should be able to easily
find on this, you may  also  look at a  text book called 'From Neuron
to Brain' printed by associated press

>3) More receptors on the postsynaptic neuron.

  The same text book cites research by Doju Yoshikami (and associates)
in around 1976 which showed a complete carpeting of the post synaptic
cleft by ach receptors, although subsequent research has shown these
receptors to become locally saturated, it is my understanding that no
one believes that it would be possible to better the exhisting
efficiency

>4) More ion channels (or less depending on particular ion in question) on
>  post-syn. cell.

  I've not seen any research on this area, I hope you can find
something  

  One point that occured to me, repetative firing of the pre-synaptic
axon would also increase the observed effects on the post-synaptic
neuron (i.e. facilitation etc.) K channel blockers are known to have
this effect.

I hope that I am not just serving to add to the general confusion, and
that my input will be benificial in pointing you toward places to
emphasize your efforts (or at least increase your curiosity) I realize
that comparisons to neuro-muscular junctions are not completely
relevant.  But the simplest system can often lend itself to the
understanding of those that are more compex.

________________________
Brad J. Harris
brad at pegus.com

 Pegus Research
 a pharmacoepidemiological 
 research organization
 &
 The Doju Yoshikami Lab
 University of Utah
 specializing in
 neurophysiology
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