Abstract
Summary The effects of serotonin (5-HT) on extracellular potassium concentration ([K + ] 0 ) were measured with ion-selective microelectrodes in rat hippocampal slices. Electrical stimulation of an excitatory afferent system, the Schaffer collateral commissural pathway, caused a 2–4 mM rise in [K + ] 0 in the stratum pyramidale of area CA1. 5-HT caused a 0.6–1.1 mM rise in [K + ] 0 . This rise was associated with hyperpolarization of neurons and cessation of their spontaneous spike discharge. Methysergide, a 5-HT antagonist, reduced the 5-HT effect. The change in [K + ] 0 was highest in stratum moleculare and lowest in stratum pyramidale, the opposite gradient to that found with excitatory electrical stimulation. The 5-HT-induced [K + ] 0 changes were maximal in CA1 stratum moleculare, intermediate in the dentate stratum granulare and almost non-existent in the CA3 stratum pyramidale. GABA, but not norepinephrine, produced a small (up to 0.5 mM) rise in [K + ] 0 in stratum pyramidale. Extracellular calcium concentration measured with a Ca 2+ -sensitive microelectrode was reduced by electrical stimulation but unchanged by 5-HT or norepinephrine. It is suggested that 5-HT hyperpolarizes hippocampal cells by activation of sodium- and calcium-independent potassium channels, which cause a rise in [K + ] 0 .
Published Version
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