The effects of serotonin on functionally diverse isolated lamprey spinal cord neurons.
The experiments reported here showed that application of serotonin (5-hydroxytryptamine, 5-HT) (100 microM) did not induce any significant current through the membranes of any of the spinal neurons studied (n = 62). At the same time, the membranes of most motoneurons and interneurons (15 of 18) underwent slight depolarization (2-6 mV) in the presence of 5-HT, which was not accompanied by any change in the input resistance of the cells. Depolarization to 10-20 mV occurred in some cells (3 of 18) of these functional groups, this being accompanied by 20-60% decreases in input resistance. The same concentration of 5-HT induced transient low-amplitude depolarization of most sensory spinal neurons (dorsal sensory cells), this changing smoothly to long-term hyperpolarization by 2-7 mV. The input resistance of the cell membranes in these cases showed no significant change (n = 8). Data were obtained which provided a better understanding of the mechanism by which 5-HT modulates the activity of spinal neurons. Thus, 5-HT facilitates chemoreceptive currents induced by application of NMDA to motoneurons and interneurons, while the NMDA responses of dorsal sensory cells were decreased by 5-HT. 5-HT affected the post-spike afterresponses of neurons. 5-HT significantly decreased the amplitude of afterhyperpolarization arising at the end of the descending phase of action potentials in motoneurons and interneurons and increased the amplitude of afterdepolarization in these types of cells. In sensory spinal neurons, 5-HT had no great effect on post-spike afterresponses. The results obtained here support the suggestion that 5-HT significantly modulates the activity of spinal neurons of different functional types. 5-HT facilitates excitation induced by subthreshold depolarization in motoneurons and some interneurons, facilitating the generation of rhythmic discharges by decreasing afterhyperpolarization. In sensory cells, 5-HT enhances inhibition due to hyperpolarization, suppressing NMDA currents. The differences in the effects of 5-HT on functionally diverse neurons are presumed to be associated with the combination of different types of 5-HT receptors on the membranes of these types of spinal neurons.
Batueva
I V
IV
Laboratory for the Evolution of Intercellular Interactions, I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St Petersburg.
Buchanan
J T
JT
Veselkin
N P
NP
Suderevskaya
E I
EI
Tsvetkov
E A
EA
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D002469:Cell Separation; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D007395:Interneurons / Q000502:physiology; D007798:Lampreys / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D009046:Motor Neurons / Q000502:physiology; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D012701:Serotonin / Q000494:pharmacology*; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects*
D018691:Excitatory Amino Acid Antagonists; D001224:Aspartic Acid; D012701:Serotonin; D018698:Glutamic Acid; D016202:N-Methylaspartate