Journal of Neuroscience, Vol 9, 2792-2800, Copyright © 1989 by Society for Neuroscience
Endogenous activation of glycine and NMDA receptors in lamprey spinal cord during fictive locomotion
S Alford and TL Williams
Physiology Department, St. George's Hospital Medical School, Tooting, London, England.
Strychnine is shown to abolish left-right alternation in fictive locomotion
induced by sensory stimulation. Robust rhythmic activity, characterized by
left-right coactivation at each segmental level, is seen in the presence of
strychnine at all doses used (0.5-20 microM). The proportion of the cycle
occupied by the ventral root bursts and the rostral-caudal coordination is
similar to that seen in the absence of strychnine. Furthermore, the rhythm
is abolished by cis-2,3-piperidine dicarboxylic acid (PDA),
2-amino-5-phosphonovalerate (APV), or the removal of Mg2+ from the
perfusate, as in the absence of strychnine. Voltage clamp was applied to
ventral horn neurons during stimulation in the presence of strychnine, with
holding potentials negative to the plateau potential associated with a
ventral root burst but positive to the potential in the interburst. Inward
current was seen during the ventral root burst, but no outward current was
seen at burst termination or during the interburst. The results indicate
that in fictive locomotion induced by endogenous release of NMDA receptor
agonists, left-right alternation is dependent on glycinergic transmission.
Furthermore, evidence is provided that in the absence of glycinergic
transmission, burst termination may depend on NMDA receptor- linked
voltage-sensitive processes.