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Effect of tolbutamide on tetraethylammonium-induced postsynaptic zinc signals at hippocampal mossy fiber-CA3 synapses

Authors: Bastos, Fatima C.; Corceiro, Vanessa N.; Lopes, Sandra A.; de Almeida, Jose G.; Matias, Carlos M.; Dionisio, Jose C.; Mendes, Paulo J.; Sampaio dos Aidos, Fernando D. S.; Quinta-Ferreira, Rosa M.; Emilia Quinta-Ferreira, M.

Ref.: Can. J. Physiol. Pharmacol. 95, 1058-1063 (2017)

Abstract: The application of tetraethylammonium (TEA), a blocker of voltage-dependent potassium channels, can induce long-term potentiation (LTP) in the synaptic systems CA3-CA1 and mossy fiber-CA3 pyramidal cells of the hippocampus. In the mossy fibers, the depolarization evoked by extracellular TEA induces a large amount of glutamate and also of zinc release. It is considered that zinc has a neuromodulatory role at the mossy fiber synapses, which can, at least in part, be due to the activation of presynaptic ATP-dependent potassium (KATP) channels. The aim of this work was to study properties of TEA-induced zinc signals, detected at the mossy fiber region, using the permeant form of the zinc indicator Newport Green. The application of TEA caused a depression of those signals that was partially blocked by the KATP channel inhibitor tolbutamide. After the removal of TEA, the signals usually increased to a level above baseline. These results are in agreement with the idea that intense zinc release during strong synaptic events triggers a negative feedback action. The zinc depression, caused by the LTP-evoking chemical stimulation, turns into potentiation after TEA washout, suggesting the existence of a correspondence between the observed zinc potentiation and TEA-evoked mossy fiber LTP.

DOI: 10.1139/cjpp-2016-0379