Title:
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The role of group I mGluRs and KCNQ/M channels in synaptic and non-synaptic neuronal activity in hippocampal slices
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The overall aim of this work was to establish the role of group I mGluR and KCNQ/M
channels in aspects of the neurophysiology of area CA1 of the rat hippocampus.
Specifically we studied the role of these putative drug targets in a form of epileptiform
activity and in the slow fEPSP recorded using extracellular methods.
First, we have described here the extracellular recording of an excitatory slow fEPSP
which is predominantly mediated by acetylcholine, as evidenced by the increase in
physostigmine and inhibition in the presence of atropine. This type of response is
significantly enhanced by two KCNQ/M channels blockers Iinopiridine and XE-991
highlighting an involvement of M currents. Furthermore, this response has a glutamatergic
component, as application of a glutamate uptake inhibitor (L-trans-PDC) significantly
affected the slow fEPSP. Specifically, the response is 4-CPG sensitive but not MCPG
sensitive suggesting an involvement of group I mGluRs in the modulation of this response.
Another interesting finding was given by KCNQ/M channels which play a role in the
regulation of synchronous population firing activity in the absence of synaptic acivity (low
Ca2+ epileptiform activity). More specifically, application of retigabine, a KCNQ/M channel
modulator, completely abolished the bursts, in an XE-991-sensitive manner. Furthermore,
application of the KCNQ/M channel blockers, linopirdine or XE-991 alone, abolished the
gamma frequency, but not the higher-frequency population spike firing observed during
low Ca2+/high K+ bursts.
Finally, it has been demonstrated that activation of group I mGluRs by application of the
potent agonist DHPG causes a dramatic long lasting alteration in the frequency of low Ca2+ epileptiform activity. This long lasting effect on the burst frequency, is MCPG
sensitive (group 1/11 mGluRs antagonist), showing a strong modulation by mGluRs in this
non-synaptic epileptiform acitvity. Application of two tyrosine phosphatase inhibitors, PAD
and SDV blocked the DHPG effect on the bursting frequency, providing that tyrosine
phosphorylation is involved in DHPG-induced synaptic plasticity.
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