NONUNIFORM CONDUCTION TIME IN THE OLIVOCEREBELLAR PATHWAY IN THE ANESTHETIZED CAT

1. It has recently been demonstrated that conduction velocities of cer ebellar climbing fibre afferents in the rat are tuned according to fib re length such that conduction time between their origin in the inferi or olive and their target cortical Purkinje cells is constant. Here we have examined the situation in the cat, where individual climbing fib res are substantially longer. Complex spike responses of Purkinje cell s located at various depths in the vermis (zones a and b) were evoked by electrical stimulation of olivocerebellar fibres dose to their orig in and were recorded either extra- or intracellularly. 2. The onset la tencies of directly evoked complex spikes ranged from 2.6 to 6.9 ms. A consistent trend in each electrode penetration was that the complex s pike latencies were longer for the superficially encountered cells (wh ere olivocerebellar fibre length is greatest) and shorter for deeper c ells (where olivocerebellar fibre length is shorter). 3. Linear regres sion analysis suggests that conduction time in olivocerebellar fibres in the cat is not fixed but varies linearly with conduction distance. Our findings would be consistent with a conduction conduction velocity in olivocerebellar fibres of about 6.6 m s(-1).