Journal of Neuroscience, Vol 8, 2074-2086, Copyright © 1988 by Society for Neuroscience
Locomotion produced in mesencephalic cats by injections of putative transmitter substances and antagonists into the medial reticular formation and the pontomedullary locomotor strip
BR Noga, J Kettler and LM Jordan
Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
The purpose of this study was to determine the distribution of cells in the
medial reticular formation (MRF) and the pontomedullary locomotor strip
(PLS), which can induce locomotion when activated. Controlled
microinjections of neuroactive substances (Goodchild et al., 1982) into the
MRF or PLS were made in order to activate cell bodies in those areas. The
ability of trigeminal receptive field stimulation to induce locomotion
before and after drug infusion into the PLS was also assessed since the PLS
and the spinal nucleus of the trigeminal nerve are similar in their
anatomical distribution. Experiments were performed on
precollicular-postmamillary decerebrate cats walking on a treadmill.
Injections of glutamic acid (GA; 500 nmol) into the MRF produced locomotion
that was antagonized by infusion of glutamic acid diethyl ester into the
same spot. Decreases in the current threshold for locomotion produced by
electrical stimulation of the MRF were observed when the MRF was infused
with either GA (40-80 nmol), DL- homocysteic acid (DL-HCA; 200 nmol), or
picrotoxin (PIC; 15 nmol). Injections of GA (100 nmol), DL-HCA (700 nmol),
PIC (10-50 nmol), and substance P (2 nmol) into the PLS also produced
locomotion. Locomotion produced by injections of PIC into the PLS was
blocked by infusion of equal amounts of muscimol or GABA. Effective PLS
injection sites were all confined to the trigeminal spinal nucleus or
immediately ventral and medial to this in the adjacent lateral reticular
formation. Trigeminal nerve peripheral field stimulation evoked locomotion
after microinjection of PIC into the PLS, although this same facial
stimulus was not effective prior to drug injection. We conclude that the
MRF and PLS regions of the cat brain stem contain cells that produce
locomotion when chemically stimulated, and we suggest that the PLS is
closely related to or synonymous with the spinal nucleus of the trigeminal
nerve. Furthermore, we suggest that stimulation of trigeminal afferents is
analogous to stimulation of segmental afferent pathways in the production
of locomotion (Sherrington, 1910; Jankowska et al., 1967; Afelt, 1970;
Budakova, 1972; Grillner and Zangger, 1979).