Effects of serotonin on fictive locomotion coordinated by a neural network deprived of NMDA receptor-mediated cellular properties.
The neural network coordinating fictive locomotion in the isolated lamprey spinal cord can be activated by either N-methyl-D-aspartate (NMDA) or kainate/AMPA receptors. Serotonin (5-HT) is known to affect the pattern of fictive locomotion induced by NMDA receptor activation by increasing spike rate within a burst, increasing burst duration, and increasing the intersegmental delay. Two cellular mechanisms contribute to these 5-HT induced effects: The after-hyperpolarization following individual action potentials is reduced and the depolarizing plateau induced by NMDA is prolonged. Both of these serve as important burst-terminating factors in the locomotor network. In order to isolate these two mechanisms, the 5-HT effect on plateau potentials was eliminated by applying 5-HT during fictive locomotion induced by activation of kainate/AMPA receptors. In the absence of NMDA-mediated plateau potentials, the 5-HT-induced increase in burst duration and cycle period was greater than that previously reported during NMDA-induced fictive locomotion. In addition, the prolonged burst period of a single side was subdivided into brief multiple bursts with a shorter cycle period than the control reciprocal burst activity. Intracellular recordings of spinal neurons combined with chloride injection to reverse inhibitory post-synaptic potentials revealed that, in a proportion of these cells, the bursting within a single side may be generated solely or predominantly by phasic excitation.
Schotland
J L
JL
Nobel Institute for Neurophysiology, Karolinska Institute, Stockholm, Sweden.
Grillner
S
S
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000818:Animals; D004305:Dose-Response Relationship, Drug; D007608:Kainic Acid / Q000494:pharmacology; D007798:Lampreys; D008124:Locomotion / Q000187:drug effects* / Q000502:physiology; D009415:Nerve Net / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D018091:Receptors, AMPA; D017470:Receptors, Glutamate / Q000187:drug effects; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology*; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D013550:Swimming
D018091:Receptors, AMPA; D017470:Receptors, Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; D012701:Serotonin; D015763:2-Amino-5-phosphonovalerate; D007608:Kainic Acid