Red nucleus projections to distinct motor neuron pools in the rat spinal cord

Abstract

Despite being one of the more extensively investigated descending pathways of the rat spinal cord, the termination pattern and postsynaptic targets of the rubrospinal tract (RST) still present some unresolved issues. In addition to locomotor functions, the RST is implicated in the control of limb movements such as reaching and grasping. Although a strong RST projection onto interneurons of intermediate Rexed's laminae V and VI have been described through the entire length of the rat spinal cord, the existence of direct rubro-motoneuronal connections have not been demonstrated. In the present study, anterograde tracing of the rat RST with biotinylated dextran amine (BDA) was combined with injections of cholera toxin beta-subunit (CTbeta) into selected groups of forelimb muscles to analyze in detail the rubral projections to the forelimb areas of the cervical spinal cord. The double-staining procedure suggested a direct projection from the RST to specific populations of motoneurons. Three populations of forelimb muscles were distinguished, i.e., paw, "distal" muscles; forearm, "intermediate" muscles; and upper arm, "proximal" muscles. A somatotopic distribution of the corresponding motor neuron pools was present in the spinal cord segments C4-Th1. Rubrospinal axons were seen in close apposition to the distal and intermediate muscle motoneurons, but were consistently absent in the most ventrally situated motor column projecting to proximal muscles. Microstimulation of the red nucleus resulted in electromyographic responses with shorter latency in the distal forelimb muscles than in proximal muscles. These experiments support a specific, preferential role of the RST in distal forelimb muscle control.

Prion Interference Is Due to a Reduction in Strain-Specific PrP Sc Levels

“…The HY TME agent is transported within the CNS via three descending motor tracts (5). These motor tracts either directly synapse on VMNs or synapse on interneurons that (1,9,23,24). Consistent with this finding, HY TME PrP Sc is first detected in VMNs of the lumbar spinal cord ipsilateral to the site of inoculation.…”

Transneuronal tracing of neural pathways that regulate hindlimb muscle blood flow

“…Vestibular signals participate in regulating hindlimb blood flow (20,22,41), and thus the infected neurons in the lateral vestibular nucleus likely are components of the neural pathway that mediates this response. The red nucleus is not typically considered to participate in autonomic regulation but instead plays a fundamental role in motor control in the rat (13,24). Red nucleus neurons could potentially contribute to altering limb blood flow in parallel with movement and thus may comprise elements in the neural circuit underlying central command (39).…”

Glutamatergic reinnervation through peripheral nerve graft dictates assembly of glutamatergic synapses at rat skeletal muscle

“…In addition, VGluT-1 expression was specifically detected in cells of the gigantocellular reticular nucleus (38). Red nucleus and brainstem neurons extend their axons along the lateral white matter of the spinal cord to form rubrospinal, reticulospinal, and vestibulospinal tracts (18,(39)(40)(41). We found that a number of these neurons were retrogradely labeled by CT␤ application at the muscular synaptic terminals of the grafted nerve, demonstrating they were primarily involved in the new glutamatergic innervation of obliquus muscle.…”

“…The retrograde tracing in the regenerated nerve was performed by injecting the cholera toxin ␤-subunit (CT␤, 1 mg͞ml, List Biological Laboratories, Campbell, CA) into the reinnervated obliquus muscle (18). Six days later, the animals were perfused, and CT␤ was immunodetected in sections from brain and spinal cord by using the anticholeragenoid antibody (1:4,000; List Biological Laboratories).…”