Journal of Neuroscience, Vol 8, 3822-3826, Copyright © 1988 by Society for Neuroscience
Glycine potentiates strychnine-induced convulsions: role of NMDA receptors
AA Larson and AJ Beitz
Department of Veterinary Biology, University of Minnesota, St. Paul 55108.
Strychnine poisoning leads to seizures that have traditionally been
attributed to competitive antagonism of glycine receptors in the spinal
cord. Although glycine is thought to act as an inhibitory neurotransmitter,
a strychnine-insensitive glycine (Gly2) receptor has been recently
described in cultured mouse neurons that is thought to be allosterically
linked to the excitatory amino acid NMDA receptor. The present study
demonstrates that intrathecally administered glycine, in contrast to other
putative inhibitory transmitters, potentiates rather than inhibits
strychnine-induced convulsions in mice. The seizure- potentiating effects
of glycine are blocked by aminophosphonovaleric acid, an NMDA antagonist.
In addition, in animals pretreated with a subconvulsive dose of strychnine
to block strychnine-sensitive glycine receptors (Gly1), glycine enhances,
rather than inhibits, NMDA-induced convulsions. Together, these results
indicate that the seizure- potentiating effects of glycine involve
activation of NMDA receptors. This study provides the first evidence that
glycine is capable of modulating the activity of NMDA receptors in the
spinal cords of adult animals. In light of the elevated concentrations of
glycine found in epileptogenic brain foci, these data also suggest that
glycine may be a positive modulator in the production of epileptic
seizures.