DIFFERENTIAL BLOCKING ACTION OF JORO SPIDER TOXIN ANALOG ON PARALLEL FIBER AND CLIMBING FIBER SYNAPSES IN CEREBELLAR PURKINJE-CELLS

Synaptic potentials were recorded intracellularly from Purkinje cells in guinea pig cerebellar slices. EPSPs evoked by stimulation of parallel fibers were effectively blocked by perfusion of a slice with the synthetic analog of Joro spider toxin, 1-naphthylacetyl-spermine (NAS) at 250-mu-M. However, it did not influence those responses evoked by stimulation of climbing fibers. This action of NAS is in contrast to other commonly used glutamate antagonists, CNOX or APV: CNQX (5-mu-M) blocked both parallel fiber- and climbing fiber-induced responses, while APV (up to 1 mM) did not influence either except for a weak reduction observed in climbing fiber responses. NAS thus provides a useful tool for pharmacologically distinguishing parallel fiber and climbing fiber synapses.