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Axon collaterals ?

r norman rsn_ at _comcast.net
Thu Jan 1 22:35:15 EST 2004

On Fri, 02 Jan 2004 12:17:46 +1100, Matthew Kirkcaldie
<Matthew.Kirkcaldie at removethis.newcastle.edu.au> wrote:

>In article <erk3uvs9tqjkgkg2fklq2o4fls4u05ne2s at 4ax.com>,
> r norman <rsn_ at _comcast.net> wrote:
>> Yes.  Even glutamate has both in the retina.  I misspoke
>> about "all" the known glutamate receptors.  Glutamate is
>> "ordinarily" excitatory in the CNS.
>What's the inhibitory glutamate receptor in the retina?
>While we're on the subject, it's worth remembering that GABA is 
>excitatory in the immature CNS.

The synapse from receptor to bipolar is supposed to be glutamatergic,
even though "on" and "off" bipolars have opposite responses.  Here is
a reference
  Grant GB, Dowling JE
  A glutamate-activated chloride current in cone-driven ON 
  bipolar cells of the white perch retina.
  J Neurosci. 1995 May;15(5 Pt 2):3852-62

  Grant GB, Dowling JE.
  On bipolar cell responses in the teleost retina are generated by 
  two distinct mechanisms.
  J Neurophysiol. 1996 Dec;76(6):3842-9

I learned of it from indirect souces like a Neuro text (which one I
don't remember) or
  How the Retina Works 
  American Scientist 91:28 (2003)


However, the situation may be complicated -- the glutamate response
may be indirect and actually mediated by GABA -- see
  Hartveit E.
  Membrane currents evoked by ionotropic glutamate receptor 
  agonists in rod bipolar cells in the rat retinal slice preparation.
    J Neurophysiol. 1996 Jul;76(1):401-22.

Invertebrate are more clearcut -- there are distinct  inhibitory
glutamate receptors as described in
  Cleland TA.
  Inhibitory glutamate receptor channels.
  Mol Neurobiol. 1996 Oct;13(2):97-136

  Thomas A. Cleland and Allen I. Selverston 
  Dopaminergic Modulation of Inhibitory Glutamate Receptors in 
  the   Lobster Stomatogastric Ganglion 
  J Neurophysiol 78: 3450-3452, 1997

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