AMPA/NMDA and GABAa/GABAb conductance ratios

Bryan Price jprice1661 at earthlink.net
Fri Sep 13 17:17:26 EST 2002


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 activity
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), "Dendridic
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 the
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 use
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 be
inclusive. However, I suspect that individual synapses (containing both AMPA
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 AMPA
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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