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Glycine‐immunoreactive neurons in the developing spinal cord of the sea lamprey: Comparison with the γ‐aminobutyric acidergic system
Author(s) -
VillarCerviño Verona,
Holstein Gay R.,
Martinelli Giorgio P.,
Anadón Ramón,
Rodicio María Celina
Publication year - 2008
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/cne.21661
Subject(s) - lamprey , glycine receptor , spinal cord , gabaergic , colocalization , glycine , biology , immunocytochemistry , inhibitory postsynaptic potential , central nervous system , neuroscience , microbiology and biotechnology , commissure , anatomy , endocrinology , biochemistry , amino acid , fishery
The development and cellular distribution of the inhibitory neurotransmitter glycine in the spinal cord of the sea lamprey were studied by immunocytochemistry and double immunofluorescence and compared with the distribution of γ‐aminobutyric acid (GABA). Results in lamprey embryos and prolarvae reveal that the appearance of glycine‐immunoreactive (‐ir) spinal neurons precedes that of GABA‐ir neurons. Throughout development, glycine‐ir cells in the lateral and dorsomedial gray matter of the spinal cord are more numerous than the GABA‐ir cells. Only a subset of these neurons shows colocalization of GABA and glycine, suggesting that they are primarily disparate neuronal populations. In contrast, most cerebrospinal fluid (CSF)‐contacting neurons of the central canal walls are strongly GABA‐ir, and only a portion of them are faintly glycine‐ir. Some edge cells (lamprey intraspinal mechanoreceptors) were glycine‐ir in larvae and adults. The glycine‐ir and GABA‐ir neuronal populations observed in the adult spinal cord were similar to those found in larvae. Comparison of glycine‐ir and GABA‐ir fibers coursing longitudinally in the spinal cord of adult lamprey revealed large differences in diameter between these two types of fiber. Commissural glycine‐ir fibers appear in prolarvae and become numerous at larval stages, whereas crossed GABA‐ir are scarce. Taken together, results in this primitive vertebrate indicate that the spinal glycinergic cells do not arise by biochemical shift of preexisting GABAergic cells but instead suggest that glycine is present in the earliest circuitry of the developing lamprey spinal cord, where it might act transiently as an excitatory transmitter. J. Comp. Neurol. 508:112–130, 2008. © 2008 Wiley‐Liss, Inc.