On Thu, 18 Dec 2003 11:21:22 -0500, r norman <rsn_ at _comcast.net>
wrote:
} On Thu, 18 Dec 2003 12:49:39 GMT, "Glen M. Sizemore"
} <gmsizemore2 at yahoo.com> wrote:
}
} >The monoamines have both too, right?
}
} Yes. Even glutamate has both in the retina. I misspoke
} about "all" the known glutamate receptors. Glutamate is
} "ordinarily" excitatory in the CNS.
}
} Your point is absolutely correct, though. Whether a synapse is
} excitatory or inhibitory depends on the postsynptic channel involved,
} not the transmitter.
And when that synapse modulates another, the results become even more
involved.
Keep in mind too, there will be electrophysiological implications of
an autapse. The autapse will serve as a delay line, by feeding the
axon charge back into the dendritic tree over a small time delay. This
would act to prolong the effect of any potential transmitted. If the
cell fired very often, the feedback could be delayed to the point of
being the opposite polarity, diminishing the electrical potential
being fed to the soma by the dendrites.
If the cell fires infrequently, there'll be no such interference.
In between, there'd be a frequency at which firing could be
facilitated by the feedback helping to overcome the refractory period.
My money says the autapses are a tuning mechanism which makes the cell
tend to fire at a certain rate in the absence of other input. Think of
the "resting" oscillations of visual alpha, motor mu, auditory tau,
etc. I think this would probably be most evident in the GABAergic
interneurons that drive the 40 Hz "binding" (used here in the sense of
functional Hebbian assemblies, not that of experiential gestalt).
Something tunes them very tightly, and all the work trying to pin this
on some characteristic inherent in the cell membrane has been
unsatisfying.
