The mesencephalic locomotor region. I. Activation of a medullary projection site

Locomotion produced in mesencephalic cats by injections of putative transmitter substances and antagonists into the medial reticular formation and the pontomedullary locomotor strip

“…The locations of the cell bodies in the lower brain stem that are capable of initiating locomotion correspond to the MLR fiber terminations reported previously (Steeves and Jordan, 1984) and to the site where cooling to block synapse transmission reversibly abolished locomotion produced by electrical stimulation of the classical MLR (Shefchyk et al, 1984). The present study extends the MRF region previously shown to be capable of generating locomotion when electrically stimulated (Mori et al, 1978(Mori et al, , 1980Garcia-Rill and Skinner, 1987) and shows that an area from the midline to L2 can be stimulated electrically to induce locomotion. This confirms the previous finding by Mori et al (1978) that midline stimulation is effective for production of locomotion, but it is in contrast to the report by Garcia-Rill and Skinner (1987) who claim that midline stimulation does not produce locomotion.…”

“…The present study extends the MRF region previously shown to be capable of generating locomotion when electrically stimulated (Mori et al, 1978(Mori et al, , 1980Garcia-Rill and Skinner, 1987) and shows that an area from the midline to L2 can be stimulated electrically to induce locomotion. This confirms the previous finding by Mori et al (1978) that midline stimulation is effective for production of locomotion, but it is in contrast to the report by Garcia-Rill and Skinner (1987) who claim that midline stimulation does not produce locomotion. The fact that the electrical threshold for the initiation of locomotion by stimulation of the MRF is higher than that observed for the MLR (Mori et al, 1980) or PLS (this study) suggests that a larger volume of tissue must be stimulated to produce locomotion, possibly due to a more diffuse distribution of neurons within the reticular formation.…”

“…The excitatorv compounds DL-HCA and GA, were infused on the assumption that they would produce effects similar to those seen with electrical stimulation, since iontophoresis of these compounds is known to excite cells in both the MRF and PLS regions (Tebecis, 1973;Henry et al, 1977;Greene and Carpenter, 1985). SP has been shown to excite cells within the region of the PLS (Henry et al, 1977) and to induce locomotion after injection into either the MRF or MLR (Garcia-Rill and Skinner, 1987). PIC was used because it has been shown to be effective in inducing locomotion after infusion into the MLR (Garcia-Rill et al.…”

“…Garcia-Rill and Skinner (1987) suggest that a cholinergic and/or SP input from the MLR to the reticular formation may act to trigger locomotor events. However, recent studies using both the fictive (Noga et al, 1987) and treadmill locomotor preparations (B. R. Noga, S. J. Shefchyk, D. A. McCrea, and L. M. Jordan, unpublished observations) demonstrate that no significant alteration of the electrical threshold for MLR-evoked locomotion is seen following the intravenous administration of the ACh antagonists mecamylamine and atropine.…”

“…As summarized by Jordan (1986) reticulospinal cells in the MRF then produce locomotion by pathways traveling in the ventral lateral funiculus (VLF) of the spinal cord. Electrical stimulation of the MRF can produce locomotion (Mori et al, 1978(Mori et al, , 1980Garcia-Rill and Skinner, 1987) and cells in this region show increased metabolic activity during MLR-evoked fictive locomotion . The direct evidence implicating the involvement of cells in the MRF in the mediation of locomotion includes the observation that cooling restricted areas in the MRF to block synaptic transmission can reversibly abolish both spontaneous and MLR-evoked locomotion (Shefchyk et al, 1984) and the finding that injections of cholinergic agonists or substance P into the MRF can elicit locomotion (Garcia-Rill and Skinner, 1987).…”