IUBio

Neurotransmitter Release???

Bill Skaggs bill at darwin.bns.pitt.edu
Wed Jan 27 09:54:29 EST 1999


Gerthory Toussaint <toussain at idi.ntnu.no> writes:
>     I would like to ask you a question about the release of
> neurotransmitter. Does it possible for a neuron to release several
> different type a neurotransmitter a the same time ? I read that neurons
> have several transmitter. Can someone tell me if this mechanism is based
> on the frequency of the input signal/the area of the brain which is 
> excited or both ?

A difficult set of questions, and I'm sure the answer isn't known in
full, and I'm sure there are many people who know more about it than I
do, but I'll spell out what I do know:

1. Many neurons release more than one neurotransmitter, most commonly
one of the "classical" transmitters (acetylcholine, GABA, glutamate,
etc) plus one or more peptides.

2. Dale's Principle, which to my knowledge is universal so far, states
that every neuron releases the same neurotransmitter, or set of
neurotransmitters, from all of its synapses.  That is, when there are
multiple transmitters, every synapse releases all of them.  Dale's
principle, though, does not state that they are all released at the
same time.  Also, postsynaptic cells can vary greatly in the types of
receptors they have, so even if the same set of neurotransmitters is
released, their effects at different synapses may be very different.

3. Neurotransmitters are packaged inside vesicles in the presynaptic
terminals, and when multiple transmitters are present, they are
packaged inside different vesicles.  I know this is the usual case,
but I don't know whether it is universal.  So, on the time scale of
individual vesicle release, different neurotransmitters are NOT
released together.

4. As I understand it, many synapses in the brain are thought to
contain only a single release site, meaning that they can only release
at most one vesicle per action potential.  A synapse of this sort
would presumably not be able to release more than one kind of
neurotransmitter during a single action potential.

5. A series of action potentials in quick succession usually changes
the probability of transmitter release (increasing or decreasing it).
The vesicles for different transmitters often differ in size and
appearance, so they may also differ in the way release probability
changes.  It is possible, for example, that a synapse could release
glutamate with almost every action potential but require a burst in
order to release a peptide.  I don't know whether there is evidence
for or against such a mechanism.

I expect that I've gotten at least a couple of things wrong here, and
would be interested in seeing corrections.

> 
> By the way, is it possible for a neuron to distinguish a pain signal?
> (does they release a special neurotransmitter ?)

Many pain-related neurons use Substance P as neurotransmitter, but it
is pretty widely dispersed in the CNS and may be used by
non-pain-related neurons as well.  It has been a difficult
neurotransmitter to study functionally.

	-- Bill




More information about the Neur-sci mailing list

Send comments to us at biosci-help [At] net.bio.net