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Rostrocaudal distribution of 5‐HT innervation in the lamprey spinal cord and differential effects of 5‐HT on fictive locomotion
Author(s) -
Zhang Weiqi,
Pombal Manuel A.,
El Manira Abdeljabbar,
Grillner Sten
Publication year - 1996
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/(sici)1096-9861(19961014)374:2<278::aid-cne9>3.0.co;2-#
Subject(s) - lamprey , spinal cord , biology , anatomy , neuroscience , cord , central nervous system , medicine , surgery , fishery
5‐hydroxytryptamine (5‐HT) is known to modulate the locomotion generator network in the lamprey spinal cord, but little is known about the pattern of 5‐HT innervation along the spinal cord. The distribution of 5‐HT‐immunoreactive (5‐HT‐ir) cells and fibers, as well as the effects of 5‐HT on the locomotor network in the rostral and caudal parts of the spinal cord were compared in two lamprey species, Lampetra fluviatilis and Petromyzon marinus . Intraspinal 5‐HT cells form a very dense ventromedial plexus in which the dendrites of neurons forming the locomotor network are distributed. The number of 5‐HT cells and varicosities in this plexus decreases in the fin area (segments 70–90), and then increases somewhat in the most caudal segments. The descending 5‐HT fibers from the rhombencephalon are located in the lateral and ventral columns, and their numbers gradually decrease to around 50% in the tail part of the spinal cord. In contrast, the number of 5‐HT‐ir axons in the dorsal column remains the same along the spinal cord. Bath application of both N‐methyl‐D‐aspartic acid (NMDA; 20–250 μM) and D‐glutamate (250–1000 μM) was used to induce fictive locomotion in the isolated spinal cord. Bath application of 5‐HT (1 μM) reduced the burst frequency in the presence of NMDA. The 5‐HT effect was, however, significantly greater in the rostral as compared to the caudal part. With D‐glutamate, the 5‐HT effect was instead more pronounced in the caudal spinal cord. To account for this difference in 5‐HT effects on NMDA‐ and D‐glutamate‐induced fictive locomotion, the cellular effect of D‐glutamate was further investigated. It activates not only NMDA, but also alpha amino‐3‐hydroxy‐5‐methyl‐4‐isoxyl propionate (AMPA)/kainate and metabotropic glutamate receptors. In contrast to NMDA, D‐glutamate did not elicit tetrodotoxin (TTX)‐resistant membrane potential oscillations. This difference in action between NMDA (selective NMDA receptor agonist) and D‐glutamate (mixed agonist) may partially account for the differences in effect of 5‐HT on the locomotor pattern. © Wiley‐Liss, Inc.