Contribution of NMDA and non-NMDA glutamate receptors to locomotor pattern generation in the neonatal rat spinal cord.
The motor programme executed by the spinal cord to generate locomotion involves glutamate-mediated excitatory synaptic transmission. Using the neonatal rat spinal cord as an in vitro model in which the locomotor pattern was evoked by 5-hydroxytryptamine (5-HT), we investigated the role of N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors in the generation of locomotor patterns recorded electrophysiologically from pairs of ventral roots. In a control solution, 5-HT (2.5-30 microM) elicited persistent alternating activity in left and right lumbar ventral roots. Increasing 5-HT concentration within this range resulted in increased cycle frequency (on average from 8 to 20 cycles min-1). In the presence of NMDA receptor antagonism, persistent alternating activity was still observed as long as 5-HT doses were increased (range 20-40 microM), even if locomotor pattern frequency was lower than in the control solution. In the presence of non-NMDA receptor antagonism, stable locomotor activity (with lower cycle frequency) was also elicited by 5-HT, albeit with doses larger than in the control solution (15-40 microM). When NMDA and non-NMDA receptors were simultaneously blocked, 5-HT (5-120 microM) always failed to elicit locomotor activity. These data show that the operation of one glutamate receptor class was sufficient to express locomotor activity. As locomotor activity developed at a lower frequency than in the control solution after pharmacological block of either NMDA or non-NMDA receptors, it is suggested that both receptor classes were involved in locomotor pattern generation.
Beato
M
M
INFM Unit, International School for Advanced Studies (SISSA), Trieste, Italy.
Bracci
E
E
Nistri
A
A
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D004305:Dose-Response Relationship, Drug; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology*; D010879:Piperazines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017470:Receptors, Glutamate / Q000502:physiology*; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology*; D013126:Spinal Nerve Roots / Q000187:drug effects / Q000502:physiology*
D018691:Excitatory Amino Acid Antagonists; D010879:Piperazines; D017470:Receptors, Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; D012702:Serotonin Antagonists; D012701:Serotonin; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; C015068:1-(3-chlorophenyl)piperazine