SIGNAL TRANSMISSION IN THE PARALLEL FIBER PURKINJE-CELL SYSTEM VISUALIZED BY HIGH-RESOLUTION IMAGING

We investigated the synaptic transmission in the parallel fiber-Purkin je cell system at high spatio-temporal resolution by using voltage sen sitive dyes and an imaging system. In rat cerebellar slices, cut in th e frontal plane or in a plane of the cerebellar surface, local electri cal stimulation induced volleys of action potentials in the parallel f ibers; subsequent postsynaptic responses from Purkinje cells were obse rved along the volleys' entire trajectories. Furthermore, the formatio n of an ordered spatial gradient in parallel fiber conduction velocity across the depth of the molecular layer during postnatal development was observed. In preparations of adult, but not of immature rats, the conduction velocity of parallel fibers in the deep molecular layer was faster than in its more superficial regions. Our observations demonst rate that parallel fibers can mediate Purkinje cell excitation effecti vely acid over considerable distances in a well-organized spatiotempor al manner, thus supporting the classical view of the physiological rol e assigned to the parallel fibers.