Projection patterns of commissural interneurons in the lumbar spinal cord of the neonatal rat

Abstract

We have studied the axonal projection patterns of commissural interneurons (CINs) in the neonatal rat spinal cord. Some CINs are integral components of the neuronal networks in the vertebrate spinal cord that generate locomotor activity. By using differential retrograde labeling protocols with fluorescent dextran amines, we show that CINs with ascending axons (ascending CINs, or aCINs) and CINs with descending axons (descending CINs, or dCINs) constitute largely different populations. We show that aCINs and dCINs occupy partially overlapping domains in the transverse plane. The aCINs are located at the dorsal margin, within the dorsal horn, centrally within the intermediate zone, and in the medial region of the ventral horn, whereas the dCINs are located predominantly among the ventral and central aCINs and in smaller numbers within the dorsal horn. The labeled aCINs and dCINs project for at least one and a half segment rostrally or caudally and are present in roughly equal numbers. We also demonstrate the presence of a third, smaller population of CINs whose axons bifurcate to project for at least one and a half segment both rostrally and caudally (adCINs). The adCINs are located predominantly among the central and ventral groups of aCINs and dCINs. Finally, we demonstrate the presence of CINs with axons projecting for fewer than one and a half segment in either direction. These "short-range CINs" are intermingled with the aCINs, dCINs, and adCINs. Our results provide an anatomical framework for further electrophysiological studies aimed at identifying the CINs that participate in the mammalian locomotor central pattern generator.

Adult human hematopoietic stem cells produce neurons efficiently in the regenerating chicken embryo spinal cord

“…Spinal motoneurons and interneuron populations were labeled retrogradely with 3 kDa of rhodamine dextran amine (Molecular Probes) in an in vitro preparation of the spinal cord, as described (23)(24)(25). The preparations were then fixed in 4% paraformaldehyde and sectioned and analyzed by immunohistochemistry.…”

Differential Projections of Excitatory and Inhibitory Dorsal Horn Interneurons Relaying Information from Group II Muscle Afferents in the Cat Spinal Cord

“…Although these bilaterally projecting cells have some similarities to the inhibitory population labeled in this study, it is likely that they belong to a separate population that originates principally from laminas III-IV. It is more difficult to make satisfactory comparisons between our sample of interneurons and projections of spinal neurons with crossed axonal projections that were labeled by less localized application of tracer substances [e.g., to the whole transverse face of one side of the neonatal spinal cord in vitro (Eide et al, 1999;Stokke et al, 2002) or to the ventral and lateral part of the ventral horn (Birinyi et al, 2003)]. Nevertheless, these studies also revealed the presence of retrogradely labeled commissural neurons in the dorsal horn, which might include the inhibitory dorsal horn interneurons analyzed in this study.…”

Organization of Functional Synaptic Connections between Medullary Reticulospinal Neurons and Lumbar Descending Commissural Interneurons in the Neonatal Mouse

“…In the neonatal rodent, four classes of CINs can be identified on the basis of contralateral axonal trajectory: intrasegmental (short-range CINs), intersegmental ascending, descending (aCINs, dCINs), and bifurcating [ascending, descending (adCINs)] (Eide et al, 1999;Stokke et al, 2002;Nissen et al, 2005). Since dCINs can be labeled retrogradely with calciumsensitive probes without compromising the integrity of reticulospinal projections, we have focused on this population.…”