Maturation of evoked mossy fiber input to rat cerebellar Purkinje cells (II.)

Abstract

The aim of this work was to establish a time sequence for the functional maturation of the mossy fiber afferent system to the cerebellum, in order to place it in the context of overall cerebellar cortical development. Rat pups at various ages were anesthetized with 0.5% halothane, and Purkinje cell activity was monitored extracellularly as limbs were electrically stimulated. The results showed that Purkinje cells can receive input from the periphery via the mossy fiber system at least by the seventh postnatal day, which is relatively early in overall cerebellar development. It is clear that synaptic transmission begins soon after the mossy fiber terminals and granule cell dendrites are in physical proximity. Initially, such input has a long latency (66 msec), is easily fatigued (at 10/sec), and has a prolonged duration of excitatory effect on Purkinje cells (27 msec). These and other functional parameters become mature by the third postnatal week (6–9 msec latency, following frequency above 20/sec), which is well before overall cerebellar cortical cytological development is completed. The maturation of many functional parameters of the cerebellar afferent systems and the acquisition of new motor behaviors are shown to emerge in parallel. Motor function appears to correlate with the establishment of a mature time scale of operation of the cerebellar circuitry.