synapse weight modif. & glia role

[Eugen Leitl]

Hi neuro.netters,

learning seems to be attributed to synapse weight changes,
whatever the cause. At least, that's what all the authorities
say.

What happens in/at the synapse when it gets modified?

Some ad hoc hypotheses/flights of fancy:

1) it might be the postsynaptic membrane
   (not bloody likely, since the protein density 
   (channels/neurotransmitterase) is very high 
   already (low-defect 2d crystal. Not too much
   room for modulation, sorry.)

2) it might be the presynaptic membrane
   (permeability to neurotransmitter packets? might be. but
   what would be the modifications, if any? ideas?)

3) it might be the neurotransmitter vesicle density
   (not likely, since it would be much too flimsy/transient medium
   of information storage. This vesicle balance equilibrium would
   be precarious and easily disturbed. Not a good choice, imo.)

4) it might be the mitochondria density in the vesicle
   (quantization level way too coarse? What would be the
   assumed possible modulation dynamic range, at all?
   I would say not beyond 6 bits (64 levels). True?)

5) it might be synapse-internal proteins 
   (this would be tough. Especially, if one considers 
   immunostaining of large tissue specimens. Can DMSO
   enhance membrane permeability enough to let such
   large beasts (immunoglobulins) pass?)

I think the above list is pretty complete. Or have I overlooked
some other alternatives?

The main question would be: are any of above points true?
is there any evidence? Or is it all totally unknown?
Is there any literature on it? (A simple yes no yes response
on above 5 points would be very valuable, already).

The second big question would be: do the glia cell have any
information-processing task or are they simple auxiliary
infrastructure?

And, since it is big question time: has anyone in this list
experience on abrasive STM/AFM imaging of frozen (immunostained?)
brain tissue at submicrometer resolution?


Thank you very much for any information on these matters,

-- eugene