sanazt at neda.net
Thu Feb 20 10:08:39 EST 1997
I'm a second year medical student and I have a question about
the mechanism of presynaptic inhibtion .I'm wondering if anyone
can help me.
I've read about two different mechanisms and I don't know which
one is correct.Both of them are on GABA .
The first one is that the GABA acts on GABAa receptors to increase
the conductance to cl(-) ,but as the boutons actively accumulate
cl(-) the result is an efflux of cl(-) and depolarization of
the terminal and partial inactivation of the voltage dependent
Na(+) mechanism, so the amplitude of any action potential that
arrives at the axon terminal will reduce.
The second one is that the GABA opens anion channels ,allowing
large numbers of chloride ions to diffuse into the terminal
fibril.The negative charges of these ions cancel much of the
excitatory effect of the positively charged sodium ions that
eneter the terminal fibril when an action potential arrives.
Thanks in advance for your help,
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