An in vitro preparation for studying motor pattern generation in the cerebellorubrospinal circuit of the turtle.

In vivo studies in mammals have suggested that the cerebellorubrospinal circuit functions as a recurrent excitatory loop that generates motor commands and transmits them to the spinal cord via the rubrospinal pathway. Here we describe an in vitro preparation from the turtle exhibiting functional synaptic connections between the cerebellum, brainstem and upper spinal cord that is suitable for detailed analysis of this circuit. Electrical stimulation of the spinal cord was used to activate the cerebellorubrospinal circuit while activity was sampled with extracellular recordings from single cells in the red nucleus. Single units responded to stimulation with short and long latency synaptic responses, in addition to antidromic activation. Some cells showed bursts of activity lasting several hundred milliseconds suggesting the presence of recurrent excitation. Interruption of Purkinje cell inhibitory input impinging on the cerebellorubrospinal loop prolonged bursting and enhanced spontaneous activity. This preparation should facilitate the examination of the role of the cerebellorubrospinal circuit in motor pattern generation.