Differences between cerebellar mossy and climbing fibre responses to natural stimulation of forelimb muscle proprioceptors

Abstract

Forelimb muscle proprioceptors were activated by passive stretch in intact, regionally anaesthetized cats. Input from single muscles provided an adequate stimulus to activate both granule cells and mossy fibre responses in Purkinje cells in the anterior lobe of the cerebellar cortex. The zone of cells responsive to mossy fibre inputs was sharply localized within lobule V of the ipsilateral pars intermedia. The responses within the zone were excitatory, and inputs activated from synergistic and antagonistic muscles acting upon the same joints converged upon single granule and Purkinje cells to produce similar excitatory responses. Climbing fibre responses in Purkinje cells were also activated by proprioceptive inputs from single muscles. The threshold for these responses was slightly higher than for responses carried by mossy fibre pathways, and the spatial extent of the cortical climbing fibre response zone coincided with and extended beyond that of the mossy fibre response zone. Relatively few purely inhibitory Purkinje cell responses were found with these single inputs in this preparation, and latency measurements indicated that they were mediated by mossy fibre pathways. The inhibited cells were found in narrow strips on the rostral and caudal sides of the zone of excited Purkinje cells, affording an example of lateral inhibition in the cerebellar cortex in a physiological context. The results are discussed in terms of anatomical and functional distinctions between the two afferent systems.