Selective effects of serotonin upon excitatory amino acid-induced depolarizations of Purkinje cells in cerebellar slices from young rats.

The effects of serotonin on responses induced in Purkinje cells (PCs) by microiontophoretic administration of excitatory amino acids (EAAs) in their dendritic fields were tested in vitro by extracellular recording and by single electrode voltage clamp methods in cerebellar slices from rats aged 16-22 days. Serotonin diminished excitations produced by glutamate (Glu) and quisqualate (Quis) selectively, those caused by N-methyl-D-aspartate (NMDA) being affected much less. These suppressions of Glu- and Quis-induced responses generally occurred without there being any effect on intrinsic membrane properties of PCs, although on occasion serotonin increased membrane conductance slightly and/or induced an outward current in the recorded cells. All these effects of serotonin were maintained in the presence of tetrodotoxin and reversed upon removal of the amine. On the few occasions when serotonin enhanced Quis-induced responses, the effect was mimicked by ejection from a control solution of saline, made up at the same pH as the drug solution of serotonin.