Serotonergic systems in the spinal cord of the amphibian urodele Pleurodeles waltl.
The role of the monoamine serotonin (5-HT) in modulating the neural networks underlying axial locomotor movements was studied in an adult amphibian urodele, Pleurodeles waltl. 5-HT was applied to an in vitro brainstem-spinal cord preparation of P. waltl, which displayed fictive axial locomotor patterns following bath application of N-methyl-D-aspartate (5 microM) with D-serine (10 microM). Our results showed that 5-HT (1-25 microM) produces a reversible increase in the cycle duration and the duration of rhythmic bursting activity recorded extracellularly from ventral roots innervating the axial musculature. When applied alone, 5-HT does not trigger axial locomotor activity. The distribution pattern of 5-HT immunoreactive (5-HT-ir) cells along the spinal cord was investigated both in intact and in chronic spinal animals. The number of 5-HT-ir cell bodies is higher at brachial levels and decreases through crural levels. Sparse oval or fusiform 5-HT-ir somata are present within the gray matter, just ventrolateral to the central canal. Longitudinal fibers were detected throughout the entire white matter, except in the medial part of the dorsal funiculi. Two columns of intensely labeled and profusely branching thick and thin fibers associated with numerous varicosities run continuously along the ventrolateral surface of the spinal cord. Three weeks following full spinal cord transection at the level of the second spinal root, all longitudinal processes had disappeared, indicating their supraspinal origin, whereas the ventrolateral plexes remained, suggesting that they originated from intraspinal 5-HT-ir cell bodies. Our data showing that spinal 5-HT is organized according to a rostrocaudal gradient suggest that the 5-HT systems of P. waltl are not related to the presence of limb motor pools but more likely are related to axial central pattern generators (CPGs) networks down the length of the spinal cord. The possible involvement of these two sources (descending vs. intraspinal) of 5-HT innervation in the modulation of the axial CPGs is discussed.
Branchereau
P
P
Laboratoire de Neurobiologie des Réseaux, C.N.R.S. et Université Bordeaux 1, U.M.R. 5816, F-33405 Talence, France. p.branchereau@lnr.u-bordeaux.fr
Rodriguez
J J
JJ
Delvolvé
I
I
Abrous
D N
DN
Le Moal
M
M
Cabelguen
J M
JM
D000818:Animals; D001369:Axons / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure*; D001933:Brain Stem / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D004525:Efferent Pathways / Q000166:cytology* / Q000378:metabolism*; D007150:Immunohistochemistry; D008124:Locomotion / Q000502:physiology; D010999:Pleurodeles / Q000033:anatomy & histology* / Q000378:metabolism*; D012701:Serotonin / Q000032:analysis* / Q000494:pharmacology*; D013116:Spinal Cord / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*
D012701:Serotonin