Interneurons and synaptic symmetry
m.kirkcaldie at removethis.unsw.edu.au
Mon May 3 03:15:11 EST 2004
In article <Xns94DEC4B89C385BilZ0rhotmailcom at 220.127.116.11>,
BilZ0r <BilZ0r at TAKETHISOUThotmail.com> wrote:
> In a review paper I'm reading, there is constant reference to interneurons
> of various sizes (i.e. small, medium and large), and asymmetric synapses.
> I was hoping someone could a) tell me if there is going to a general or
> specific correlation between neurotransmitter type and the size of
In general they all employ GABA, at least if you're speaking about the
cerebral cortex. In other parts of the CNS, glycine is used as well,
and that may bear some relationship to the size of the neurons. But
most, if not all, neurons called "interneurons" are inhibitory via GABA
>, b) what's the story with asymmetric synapses is
Well, at the electrophysiological level a synapse can be identified as
inhibitory or excitatory, and immunohistochemistry can do much the same
by inference. At the electron microscopic level, unless you're using an
EM-detectable immunolabelling technique, the chief distinction between
synaptic types is the appearance of the presynaptic and postsynaptic
membranes. Studies correlating electrophysiology and EM appearance have
established the empirical relationship that a symmetric synapse (one
with darkening of roughly equal thickness on the presynaptic and
postsynaptic sides) is inhibitory (GABAergic in the cortex). If the
postsynaptic membrane has a larger thickness of dark material (the
post-synaptic density) then it's an asymmetric synapse, and likely to be
excitatory (glutamatergic) in nature.
The post-synaptic density is thought to be a complex of membrane
proteins, receptors, scaffold proteins and other complexes which go
about the business of synaptic alteration, and the effects of synaptic
transmission *other* than changes in membrane potential.
> c) if
> there is a good text I can read for further readings/citations.
I seem to remember learning these things from a 1989 book called
"Cortical Circuits" by White. But I'll bet there are newer references.
It's a good book, however.
Hope that helps.
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