The aims of the planned series of studies are to analyze how spinal interneurons provide the cerebellar neuronal systems with information concerning their actions on motoneurons, thereby ensuring a basis for on-line cerebellar corrections of movements. To date, only scarce data have been available on this subject.
The first aim of the study will therefore be to establish which of the main populations of premotor interneurons interposed in disynaptic reflex pathways between muscle receptors and hind limb motoneurons forward information regarding their actions to the four main populations of lumbar spinocerebellar neurons, including ventral spinocerebellar tract neurons, spinal border cells, Clarke4s column and dorsal horn dorsal spinocerebellar tract neurons. Using intracellular records from individual spinocerebellar neurons we will verify 1) the origin of disynaptically evoked EPSPs and IPSPs (from group Ia, Ib and II afferents) in the same spinocerebellar neurones;2) whether stimuli applied in the major lumbar motor nuclei evoke monosynaptic EPSPs or IPSPs;3) whether interactions between PSPs evoked from motor nuclei and by peripheral afferents indicate that they are mediated by the same interneurones and 4) how these PSPs modulate activation of spinocerebellar neurons.
The second aim will be to investigate how the modulation of responses of spinocerebellar tract neurons is decoded by cerebellar neurons. Using the newly developed techniques of whole cell patch clamp in vivo recordings will be performed in the spinal cord as well in the cerebellum. Simultaneous records will be obtained from cerebellar neurons and single spinocerebellar neurons while their activity is modulated by premotor interneurons. Recordings in the cerebellum will be made within the specific termination regions of different spinocerebellar populations in the posterior lobe of the cerebellum as well as in deep cerebellar nuclei. The results should greatly improve our understanding of how cerebellar neuronal networks encode feed-back information on ongoing actions of spinal interneurons on motoneurons, essential for purposeful cerebellar corrections. As these interneurones may mediate centrally initiated movements (including voluntary and locomotor) as well as spinal reflexes, analysing their actions on cerebellar neurons should provide important insights on the integration between spinal and supraspinal neuronal networks. It should also contribute to a better understanding of deficits in patients with motor disorders and provide a reference for studies at different developmental stages and in genetically modified animals.
The results of the study should improve our understanding of how cerebellar neuronal networks utilize feed-back information concerning spinal interneuronal actions on motoneurons as the basis for on-line cerebellar corrections of movements, thus providing important data on the integration between spinal and supraspinal neuronal networks. They should also link deficits in patients with different motor disorders and in motor behavior of genetically modified strains of animals to interrelations between spinal and supraspinal neuronal networks.
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