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The Journal of Neuroscience, December 15, 2001, 21(24):9877-9887
Role of Calcium, Glutamate Neurotransmission, and Nitric Oxide in
Spreading Acidification and Depression in the Cerebellar Cortex
Gang
Chen,
Robert L.
Dunbar,
Wangcai
Gao, and
Timothy J.
Ebner
Department of Neuroscience, University of Minnesota, Minneapolis,
Minnesota 55455
This study investigated the mechanisms underlying the recently
reported fast spreading acidification and transient depression in the
cerebellar cortex in vivo. Spreading acidification was evoked by surface stimulation in the rat and mouse cerebellar cortex
stained with the pH-sensitive dye neutral red and monitored using
epifluorescent imaging. The probability of evoking spreading acidification was dependent on stimulation parameters; greater frequency and/or greater amplitude were more effective. Although activation of the parallel fibers defined the geometry of the spread,
their activation alone was not sufficient, because blocking synaptic
transmission with low Ca2+ prevented spreading
acidification. Increased postsynaptic excitability was also a major
factor. Application of either AMPA or metabotropic glutamate receptor
antagonists reduced the likelihood of evoking spreading acidification,
but stronger stimulation intensities were still effective. Conversely,
superfusion with GABA receptor antagonists decreased the threshold for
evoking spreading acidification. Blocking nitric oxide synthase (NOS)
increased the threshold for spreading acidification, and nitric oxide
donors lowered the threshold. However, spreading acidification could be
evoked in neuronal NOS-deficient mice
(B6;129S-Nos1tm1plh). The depression in cortical
excitability that accompanies spreading acidification occurred in the
presence of AMPA and metabotropic glutamate receptor antagonists and
NOS inhibitors. These findings suggest that spreading acidification is
dependent on extracellular Ca2+ and glutamate
neurotransmission with a contribution from both AMPA and metabotropic
glutamate receptors and is modulated by nitric oxide. Therefore,
spreading acidification involves both presynaptic and postsynaptic
mechanisms. We hypothesize that a regenerative process, i.e., a
nonpassive process, is operative that uses the cortical architecture to
account for the high speed of propagation.
Key words:
cerebellum; calcium; glutamate; nitric oxide; optical
imaging; neutral red; rat; transgenic mouse; spreading depression; calcium waves
Copyright © 2001 Society for Neuroscience 0270-6474/01/21249877-11$05.00/0
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