Arrangement of neurons in the medullary reticular formation and raphe nuclei projecting to thoracic, lumbar and sacral segments of the spinal cord in the cat

Abstract

The distribution of neurons in the medullary reticular formation and raphe nuclei projecting to thoracic, lumbar and sacral spinal segments was studied, using the technique of retrograde transport of horseradish peroxidase (HRP), alone or in combination with nuclear yellow (NY). Retrogradely labeled cells were observed in the lateral tegmental field (FTL), paramedian reticular nucleus, magnocellular reticular nucleus (Mc), in the gigantocellular nucleus (Gc), lateral reticular nucleus (LR), lateral paragigantocellular nucleus (PGL), rostral ventrolateral medullary reticular formation (RVR), as well as in the medullary raphe nuclei following the injection of the tracer substance(s) into various levels of the spinal cord. The FTL, the ventral portion of the paramedian reticular nucleus (PRv), Mc, LR, PGL and the raphe nuclei were found to project to thoracic, lumbar and sacral spinal segments. This projection was bilateral; the contralaterally projecting fibers crossed the midline at or near their termination site. The dorsal portion of the paramedian reticular nucleus (PRd), Gc and the RVR projected mainly to thoracic segments. This projection was unilateral. Experiments in which the HRP-injection was combined with lesion of the spinal cord showed that some descending raphe-spinal axons coursed presumably alongside the central canal. Experiments with two tracer substances suggested that some reticulo- and raphe-spinal neurons had axon collaterals terminating both in thoracic and sacral spinal segments.

Descending spinal projections from the rostral gigantocellular reticular nuclei complex

“…Labeling has been consistently reported in these same regions. Taken together with results from previous anterograde studies (Zemlan et al, 1984;Jones and Yang, 1985;Martin et al, 1985b;Holstege and Tan, 1987;Kausz, 1991), the ventral portion of the gigantocellular and the lateral paragigantocellular nuclear complex (Gi-LPGi) appears to be a likely source of supraspinal influence over a variety of spinal reflexes.Extensive review of the inhibitory role of the Gi-LPGi on sexual function is presented elsewhere (McKenna, 2000;Steers, 2000). To briefly summarize, behavioral studies support the hypothesis that this ventral medullary reticular area exerts descending inhibitory control of sexual reflexes (Marson and McKenna, 1990;Yells et al, 1992;Liu and Sachs, 1999).…”

Neuronal Basis of Crossed Actions from the Reticular Formation on Feline Hindlimb Motoneurons

“…Monosynaptic EPSPs could be mediated by ipsilaterally descending reticulospinal neurons, via crossed axon collaterals terminating in the ven-tral horn (Nyberg-Hansen, 1965;Kausz, 1991;Matsuyama et al, 1999), as indicated by connections labeled 1 and 2 in Figure 1 A. Monosynaptic EPSPs could also be evoked by contralaterally descending reticulospinal neurons (Nyberg-Hansen, 1965;Mitani et al, 1988b,c;Matsuyama et al, 1993) and their local axon collaterals ( Fig. 1 A, 3).…”

Neurons in the rat brain and spinal cord labeled after pseudorabies virus injected into the external urethral sphincter

“…Allen and Cechetto (1994) used unilateral dye injections in the rat thoracic IML to label neurons in the gigantocellular and raphe nuclei in the medulla. In the cat, Kausz (1991) injected horseradish peroxidase into the IML on one side of the S2 spinal cord segment (the cat homolog to the corresponding region L6-Sl in the rat) and found labeled neurons bilaterally in the medullary reticulum homologous to those regions in the rat containing PRV-IR neurons, including GiV, GiA, and the raphe pallidus and obscurus. Taken together, these reports clearly support the current results and suggest that there is a direct connection between PRV-IR labeled neurons in the lumbosacral cord and the reticular neurons in the medulla.…”