Development of glycine immunoreactivity in the brain of the sea lamprey: Comparison with γ‐aminobutyric acid immunoreactivity

Abstract

The development of glycine immunoreactivity in the brain of the sea lamprey was studied by use of immunofluorescence techniques at embryonic to larval stages. Glycine distribution was also compared with that of gamma-aminobutyric acid (GABA) by use of double immunofluorescence. The first glycine-immunoreactive (ir) cells appeared in the caudal rhombencephalon of late embryos, diencephalon of early prolarvae, and mesencephalon of late prolarvae, in which glycine-ir cells were observed in several prosencephalic regions (preoptic nucleus, hypothalamus, ventral thalamus, dorsal thalamus, pretectum, and nucleus of the medial longitudinal fascicle), mesencephalon (M5), isthmus, and rhombencephalon. In larvae, glycine-ir populations were observed in the olfactory bulbs, preoptic nucleus and thalamus (prosencephalon), M5 and oculomotor nucleus (mesencephalon), dorsal isthmic gray, isthmic reticular formation, and various alar and basal plate rhombencephalic populations. No glycine-ir cells were observed in the larval optic tectum or torus semicircularis, which contain glycine-ir populations in adults. A wide distribution of glycine-ir fibers was observed, which suggests involvement of glycine in the function of most lamprey brain regions. Colocalization of GABA and glycine in prolarvae was found mainly in cell groups of the diencephalon, in the ventral isthmic group, and in trigeminal populations. In larvae, colocalization of GABA and glycine was principally observed in the M5 nucleus, the reticular formation, and the dorsal column nucleus. The present results reveal for the first time the complex developmental pattern of the glycinergic system in lamprey, including early glycine-ir populations, populations transiently expressing glycine, and late-appearing populations, in relation to maturation changes that occur during metamorphosis.

Distribution of glycine immunoreactivity in the brain of the Siberian sturgeon (Acipenser baeri): Comparison with γ-aminobutyric acid

“…These results contrast with those obtained in the forebrain of the rat with either the Gly transporter GLYT2 (Rampon et al, 1996;Zeilhofer et al, 2005) or Gly immunohistochemistry (Rampon et al, 1996), which showed only a few glycinergic cells in the diencephalon. However, Gly-ir populations have been reported in the olfactory bulbs, preoptic nucleus, and thalamus of the adult sea lamprey (VillarCerviño et al, 2008a), and other regions containing Gly-ir cells in this sturgeon (hypothalamus, posterior tubercle and pretectum, and nucleus of the medial longitudinal fascicle) transiently exhibit Gly-ir cells in the developing sea lamprey (Villar-Cerviño et al, 2009). Together, these data indicate similar expression of Gly in the forebrains of agnathans and chondrosteans, suggesting that shared Gly-ir populations were already present in the common ancestor of all vertebrates.…”

D‐serine is distributed in neurons in the brain of the sea lamprey

“…No staining was observed in these controls. In addition, the antibody was tested by Western blot with lamprey brain protein extracts (Villar-Cerviño et al, 2009). No protein bands were stained in these blots, indicating that the antibody did not react with native proteins.…”

“…For descriptive purposes, the reticular populations were subdivided transversely into medial (magnocellular) and lateral (parvocellular) zones and longitudinally into isthmic, trigeminal, middle, and posterior rhombencephalic reticular regions, following Stefanelli (1934) and Villar-Cerviño et al (2009). This isthmic reticular region includes the isthmus sensu stricto and the anterior rhombencephalon, i.e., rhombomeres 0 -1.…”

“…No immunoreactivity was detected when the primary antibody was omitted from the immunohistochemical procedure. In addition, the antibody was tested by Western blot with lamprey brain protein extracts (Villar-Cerviño et al, 2009). No protein bands were stained in these blots.…”

“…Some of these glycine-immunoreactive neurons showed colocalization with ␥-aminobutyric acid (GABA) immunoreactivity, and a combination of GABA and glycine double immunofluorescence proved useful for identifying brain and spinal cell populations (Villar-Cerviño et al, 2008a, 2008b. Moreover, expression of glycine and GABA immunoreactivity in lamprey brain perikarya is largely maintained from larvae to adulthood (Villar-Cerviño et al, 2009), indicating that lampreys are highly useful for investigating the neuronal distribution of amino acid neurotransmitters in the brain. With regard to the glia, lampreys lack oligodendrocytes, and glial cells of the brain are ependymal tanycytes or small astrocytes (Merrick et al, 1995), which may greatly facilitate the identification of cells containing D-serine.…”