Ascending spinal influences on rubrospinal cells in the cat

Abstract

Somaesthetic input to rubrospinal cells, bypassing the cerebellum and cerebral cortex, has been demonstrated in the cat. The detailed organization of this somatic afferent system was studied using electrophysiological methods on multiple-lesion, chloralose-anaesthetized preparations. Stimulation of the dorsal column (DC) at upper cervical cord segments induced significant responses in magnocellular red nucleus (RNm) cells in cats without a cerebellum and with ablation of the frontal cortex. As classic descriptions state that primary afferent fibres have ascending and descending branches in the DC, with many collaterals arborizing in the grey matter at the segmental level of the cord, this procedure is equivalent to stimulating the somatic fibres coming from a large portion of the body, leading to the simultaneous activation of most ascending spinal pathways. To show that the pathway responsible for the rubral responses ascends in the ventral spinal cord, and that the synaptic relays are located at the segmental level, the stimulation was applied to the DC, caudally to the sectioned dorsal spinal half. Various tests confirmed that the activation was conducted to rubral cells through antidromically activated primary afferents. Their multiple collaterals relay the messages to cells located caudal to the spinal lesion, with fibres ascending in the ventral cord. Any relay of the somatic rubral responses in the DC's nuclei was excluded. When the DC was sectioned and its rostral end was dissected free and lifted onto two hook electrodes for stimulation, no response was obtained in the rubral cells. This dissection indeed sectioned all DC fibre collaterals entering the grey matter, thus excluding the possibility of segmental relay. Single shocks applied to the ventral quadrant of the cord or in the medial lemniscus (LM) in the medulla oblongata induced monosynaptic excitatory post-synaptic potentials (EPSPs) in most rubrospinal cells. The spinal EPSPs could be collided by stimulation in the LM, thus demonstrating the existence of direct connections from the cord to the RNm. This somaesthetic pathway to the RNm could be involved in on-line correction of movements and in learning new motor strategies.

Complete Compensation in Skilled Reaching Success with Associated Impairments in Limb Synergies, after Dorsal Column Lesion in the Rat

“…Additionally, after dorsal column lesions, rats effected fewer manual searches and used a rapid grasp, rather than an arpeggio movement, as do rats with red nucleus lesions. These similarities in dorsal columnlesioned and pyramidal-or rubral-lesioned rats suggest that dorsal column afferent input contributes significantly to cortical and rubral motor control in the rat, as has been proposed in the cat (Rathelot and Padel, 1997) and in primates (Leonard et al, 1992). Thus, a dorsal column lesion would cause partial deafferentation of red nucleus as well as basilar pontine gray (Kosinski et al, 1986) and somatosensory cortex.…”

Theta Oscillations during Active Sleep Synchronize the Developing Rubro-Hippocampal Sensorimotor Network

“…Accordingly, we propose that twitch-reafferent theta constitutes a distinct—type 3—category of theta. Th e pathways conveying twitch-related reafference to the RN likely bypass the cerebellum [12] and involve direct spinorubral projections [61]; on the other hand, the pathway to the hippocampus likely passes first through somatosensory cortex [40]. …”

Mapping of Cbln1‐like immunoreactivity in adult and developing mouse brain and its localization to the endolysosomal compartment of neurons

“…, 2005). In addition, there is a small projection from the dorsal column nuclei to another CLI‐positive structure, the red nucleus (Rathelot & Padel, 1997). Indeed, the strongly CLI‐positive red nucleus has both afferent and efferent connections to many nuclei that express cbln1 , e.g.…”