Cerebellar units show several types of long-lasting posttetanic responses to telencephalic stimulation in catfish.

Extracellular spikes from Purkinje and eurydendroid cells as well as evoked field potentials were recorded from the cerebellum in a catfish following trains of 50-100 stimuli at 2-10 Hz delivered to the area dorsalis centralis (Dc) of the telencephalon. Forty out of 48 Purkinje cells tested showed some response, either an increase or a decrease in the level of ongoing spike discharge following the 10- to 25-second tetanic pulse trains. The altered level lasted for greater than 3 min. Four out of 16 eurydendroid cells showed an increase in posttrain ongoing discharge; none showed a decrease. In those Purkinje cells responding to single pulse stimulation with early excitation, that response was converted to early inhibition during the later cycles of a tetanic pulse train. When tested with posttrain stimulation, they resumed the pretrain early excitation about 100 s after the train; before that, the recovery stages are complex, neither a simple continuation of, nor a simple rebound from, the later cycles of the stimulus train. Bursting discharge of Purkinje cells is often induced or, if already present, enhanced and regularized, typically at approximately 3/s, by train stimulation of Dc. This pattern begins during the train but continues for tens of seconds after its end. The effects of a stimulus train on the mean frequency and on the pattern of ongoing discharge depend on the train parameters: intensity, duration and stimulus rate within the train; 4-5 Hz is most effective. Higher rates or repeated trains produce a more intense but shorter-lasting effect. Evoked field potentials change during a train, and posttrain test stimuli show a slow recovery, especially after longer pulse trains. The cerebrocerebellar influence in a teleost is nontrivial, widespread, differentiated and shows long-lasting posttetanic plasticity.