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Long term potentiation and long term depression

Nicolas Le Novere lenov at ebi.ac.uk
Thu Mar 23 10:56:56 PST 2006


On Thu, 23 Mar 2006, Doug howe wrote:

> You are correct that LTP (Long Term Potentiation) and LTD (Long Term 
> Depression) both reflect changes in synaptic activity (at the level of 
> individual synapses) over the long term (at least hours...ranging up to weeks 
> or more).  So a GO term like GO:0048172 (regulation of short-term neuronal 
> synaptic plasticity) will not be useful for LTD or LTP.

I think our problems here are coming from the notions of long and
short, that are 1) subjective 2) applied differently according to the
level we consider. Long term potentiation and depression effectively
belong to long term synaptic adaptation but to the short term neuron
adaptation.

So we have (funny characters chosen to avoid semantic relations):

- short-term neuroadaptation
==>short term synaptic plasticity
e.g. receptor desenzitisation or potentiation
==>long term synaptic plasticity
e.g. LTP and LTD
- mid-term neuroadaptation
e.g. synapse creation/suppression
- long-term neroadaptation
e.g. dendritic remodelling
e.g. axonal reorganisation

"long term synaptic plasticity" would actually overlap "mid-term
neuroadaptation"

> Further, LTP and LTD 
> are the results of synaptic plasticity...they are not the plasticity itself, 
> so terms like "positive regulation of synaptic plasticity" will not be useful 
> either I don't think.

If "plasticity" was viewed as a property, I would agree. It would
characterize the possibility to adapt. An increase of plasticity would
render LTP or LTD easier to induce. But this is not the usual sense as
far as I am aware. Extract from one of the latest review of Graham
Collingridge [http://www.nature.com/nrn/journal/v5/n12/abs/nrn1556_fs.html]:

"Long-term potentiation and long-term depression are processes that
have been widely studied to understand the molecular basis of
information storage in the brain. Glutamate receptors are required for
the induction and expression of _these forms of plasticity_"

That's an isA relationship to me.

Or, if you don't like Graham, one from Calabresi [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T0R-4DSR003-1&_coverDate=12%2F01%2F2004&_alid=381436523&_rdoc=1&_fmt=&_orig=search&_qd=1&_cdi=4869&_sort=d&view=c&_acct=C000042238&_version=1&_urlVersion=0&_userid=776054&md5=70eb34480a858e5c5e3c38380367625d]:

"Long- and short-term changes in the efficacy of synaptic transmission
are known as synaptic plasticity. Phenomena such as long-term
depression (LTD) and long-term potentiation (LTP) are two classical
forms of synaptic plasticity"

> It looks to me like new terms would be needed to represent LTP and LTD 
> specifically.
>
> I propose the following...open for discussion...
>
> positive regulation of synaptic transmission (GO:0050806)
> ---[i]long term potentiation (GO:new)
>
> negative regulation of synaptic transmission (GO:0050805)
> ---[i]long term depression (GO:new)

I'm thinking aloud here: I often read that LTP and LTD were regulation
of "synaptic efficacy" or "synaptic strength". Could-we find a subtle difference between
synaptic efficacy and synaptic transmission? Would synaptic efficacy
be a potential while synaptic transmission would be the revelation of
that synaptic efficacy when a signal is received? In that sense, LTP
and LTD would characterise different synaptic transmissions caused by
be modified efficacies. Now a gene that we would annotate would be
involved in the change of efficacy, not transmission.

> erika wrote:

>>  GO:0048169 regulation of long-term neuronal synaptic plasticity: A process 
>> that modulates long-term neuronal synaptic plasticity, the ability of 
>> neuronal synapses to change long-term as circumstances require.

That is OK.

>> Long-term 
>> neuronal synaptic plasticity generally involves increase or decrease in 
>> actual synapse numbers.

That is not. At least not "generally".

>> GO:0048172 regulation of short-term neuronal synaptic plasticity: A process 
>> that modulates short-term neuronal synaptic plasticity, the ability of 
>> neuronal synapses to change in the short-term as circumstances require.

That is OK.

>> Short-term neuronal synaptic plasticity generally involves increasing or 
>> decreasing synaptic sensitivity.

That is not. Cf comment of Doug.

>> Researches in Geneva, Switzerland have demonstrated that formation of LTP 
>> in rat brains coincides with the formation of additional synapses (at least 
>> one more) between the presynaptic axon terminal and the dendrite it 
>> synapses with. (Report by Toni, N., et al, Nature, 25 Nov 99).

This is definitively not the majority of the cases. In addition, Toni
et al deal with additional spines, something even more drastic than
just multiplication of synapses.

-- 
Nicolas LE NOVERE,  Computational Neurobiology, 
EMBL-EBI, Wellcome-Trust Genome Campus, Hinxton, Cambridge, CB10 1SD, UK
Tel: +44(0)1223 494 521,  Fax: +44(0)1223 494 468,  Mob: +33(0)689218676
http://www.ebi.ac.uk/~lenov                   AIM screen name: nlenovere



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