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AMPA/NMDA and GABAa/GABAb conductance ratios

Bryan Price jprice1661 at earthlink.net
Fri Oct 4 04:15:11 EST 2002

I officially apologize for every time I secretly loathed people in the NG
who snobbishly redirect people to Google...


>From this study, it seems that, interestingly, the AMPA to NMDA conductance
ratio (or maybe the receptor ratio, which may translate to a different
conductance ratio) is on the order of 4 - 5 to 1, and is quite well
moderated by (according to the article) as-yet unknown processes. I'm not
sure of the equivalent ratio of GABAa to GABAb, nor whether any recent
research shows plasticity on these inhibitory conductances and whether such
plasticity also maintains a fixed ratio.

Even lacking such a ratio in the face of plasticity on the inhibitory side,
I should be able to determine the appropriate ratio without plasticity based
on the numbers I cited.


"Bryan Price" <jprice1661 at earthlink.net> wrote in message
news:Wttg9.4994$Os3.351275 at newsread1.prod.itd.earthlink.net...
> I may be asking the wrong group with this - please redirect me if needed.
> I've been looking at some network models that focus on the delayed
> of NMDA currents in addition to the quick AMPA currents in biological
> neurons. The ranges of the conductances I have for these are
> Excitatory
> AMPA: g(peak) ~ 0.1 - 0.3 ns, t(peak) ~ 0.3 - 1 ms
> NMDA: g(peak) ~ 0.05 - 0.5 ns, t(peak) ~ 5 - 50 ms
> Inhibitory
> GABAa: g(peak) ~ 0.4 - 1 ns, t(peak) ~ 0.2 - 1.2 ms
> GABAb: g(peak) ~ 0.1 - 0.3 ns, t(peak) ~ 40 - 150 ms
> [The Handbook of Brain Theory and Neural Networks (Arbib, 1995),
> Processing" (Segev), Table 1]
> 1) Easy question: What is an 'ns'? It's not just 1/giga-ohms, is it?
> 2) Harder question: I'm trying to calculate the range of ratios between
> AMPA and NMDA (and GABAa and GABAb) time-summed currents. I am, of course,
> applying a membrane decay convolution function to the beta functions I'm
> using to approximate the currents, with Tm ~ 7 - 50 ms. Clearly I could
> the maximum AMPA and the minimum NMDA conductances for one limit of the
> ratios, and the opposite conductances for the other limit, as this would
> inclusive. However, I suspect that individual synapses (containing both
> and NMDA receptors) maintain some sort of relationship between the numbers
> of each type of receptor - I don't believe that a synapse would have no
> receptors while also having a plethora of NMDA receptors, or vice-versa.
> Does anyone know of research that might reveal such a relationship?
> Thanks you,
> Bryan Price
> [ Also posted to comp.ai.neural-nets ]

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