Histamine potentiates neuronal excitation by blocking a calcium-dependent potassium conductance
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Histaminergic neurones send their axons to the whole forebrain. The diffuse projection is consistent with a modulatory role of these pathways. In hippocampal slices from rats a mechanism for this modulation is described, on pyramidal neurones of the CA 1 area: Strong excitations induced by intracellular current injection, ionophoretic administration of glutamate or synaptic stimulation normally restrict themselves by the activation of the calcium-dependent potassium current (gK(Ca)). This current causes a long lasting afterhyperpolarization and an accommodation of firing. Their block by histamine and impromidine (reversed by metiamide and cimetidine) leads to a profound potentiation of excitatory signals. It is suggested that HA, through H2 receptors, accelerates the removal of intracellular free Ca++ ions.
KeywordsGlutamate Histamine Cimetidine Pyramidal Neurone Hippocampal Slice
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