Distribution of glycine immunoreactivity in the brain of the Siberian sturgeon (Acipenser baeri): comparison with γ-aminobutyric acid.
ABSTRACT Glycine and γ-aminobutyric acid (GABA) are the main inhibitory neurotransmitters in the central nervous system (CNS) of vertebrates. Studies on the distribution of glycinergic neurons and fibers have been carried out mainly in rodents and lampreys. With the aim of discovering more about the early evolution of this system in vertebrates, we analyzed the distribution of glycine-immunoreactive (Gly-ir) neurons and fibers in the CNS of a basal ray-finned fish, the Siberian sturgeon (Chondrostei, Acipenseriformes), by use of immunohistochemical techniques. We also compared the distribution of glycine and GABA by the use of double-immunofluorescence techniques and confocal microscopy. Our results revealed the presence of Gly-ir cells in different regions of the CNS, such as olfactory bulbs, preoptic area, hypothalamus, thalamus, pretectum, optic tectum, tegmentum and rostral spinal cord, although most of the Gly-ir cells and the most intensely immunoreactive cells were located in the rhombencephalon, mainly in the octavolateral area and reticular formation. In addition, coronet cells of the basal hypothalamus and saccus vasculosus were Gly-ir. Glycinergic fibers coursed along most brain regions and were more abundant in the thalamus, hypothalamus, optic tectum, tegmentum, isthmic region, and basal rhombencephalon. The Mauthner cell perikaryon was richly innervated by Gly-ir boutons, as reported for teleosts. With regard to the colocalization of glycine and GABA, double-immunoreactive cells were located mainly in the rhombencephalon. The results enable us to conclude that the distribution of glycine in the sturgeon brain is more similar to that observed in lampreys than that observed in mammals.
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ABSTRACT: The glycinergic cell populations in the brain of the lesser spotted dogfish were studied by a glycine immunofluorescence method. Numerous glycine-immunoreactive (Gly-ir) neurons were observed in different brain nuclei. In the telencephalon, Gly-ir cells were observed in the olfactory bulb, telencephalic hemispheres and preoptic region. In the hypothalamus, cerebrospinal fluid-contacting Gly-ir neurons were observed in the lateral and posterior recess nuclei. Coronet cells of the saccus vasculosus were Gly-ir. In the diencephalon, Gly-ir neurons were observed in the prethalamus and pretectum. In the midbrain, both the optic tectum and lateral mesencephalic nucleus contained numerous Gly-ir neurons. In the cerebellum, many Golgi cells were Gly-ir. In the rhombencephalon, Gly-ir cells were observed in the medial and ventral octavolateral nuclei, vagal lobe, visceromotor nuclei and reticular formation, including the inferior raphe nucleus. In the spinal cord, some neurons of the marginal nucleus and some cells of the dorsal and ventral horns were Gly-ir. Comparison of dogfish Gly-ir cell populations with those reported in the sea lamprey, Siberian sturgeon and zebrafish revealed some shared features but also notable differences. For example, Gly-ir cells were observed in the dogfish cerebellum unlike in the Siberian sturgeon and zebrafish, whereas the absence of Gly-ir neurons in the isthmus is shared by all these species, except lampreys. Gly-ir populations in the dogfish hypothalamus and telencephalon are notable in comparison with those of the other jawed vertebrates investigated to date. Together, these results reveal a complex and divergent evolution of glycinergic systems in the major groups of fishes. J. Comp. Neurol. , 2013. © 2013 Wiley Periodicals, Inc.The Journal of Comparative Neurology 04/2013; · 3.66 Impact Factor
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ABSTRACT: Glycine is a major inhibitory neurotransmitter in the central nervous system of vertebrates. Here, we report the initial development of glycine-immunoreactive (Gly-ir) neurons and fibers in zebrafish. The earliest Gly-ir cells were found in the hindbrain and rostral spinal cord by 20 hours post-fertilization (hpf). Gly-ir cells in rhombomeres 5 and 6 that also expressed glycine transporter 2 (glyt2) mRNA were highly stereotyped; they were bilaterally located and their axons ran across the midline and gradually turned caudally, joining the medial longitudinal fascicles in the spinal cord by 24 hpf. Gly-ir neurons in rhombomere 5 were uniquely identified, since there was one per hemisegment, whereas the number of Gly-ir neurons in rhombomere 6 were variable from one to three per hemisegment. Labeling of these neurons by single-cell electroporation and tracing them until the larval stage revealed that they became MiD2cm and MiD3cm respectively. The retrograde labeling of reticulo-spinal neurons in Tg(glyt2:gfp) larva, which express GFP in Gly-ir cells, and a genetic mosaic analysis with glyt2:GFP DNA construct also supported this notion. Gly-ir cells were also distributed widely in the anterior brain by 27 hpf, whereas glyt2 was hardly expressed. Double staining with anti-glycine and anti-GABA antibodies demonstrated distinct distributions of Gly-ir and GABA-ir cells, as well as the presence of doubly immunoreactive cells in the brain and placodes. These results provide evidence of identifiable glycinergic (Gly-ir/glyt2-positive) neurons in vertebrate embryos, and they can be used in further studies of the neurons' development and function at the single-cell level. © 2013 Wiley Periodicals, Inc. Develop Neurobiol, 2013.Developmental Neurobiology 12/2013; · 4.42 Impact Factor
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ABSTRACT: Although the neuroanatomical distribution of catecholaminergic (CA) neurons has been well documented across all vertebrate classes, few studies have examined CA connectivity to physiologically and anatomically identified neural circuitry that controls behavior. The goal of this study was to characterize CA distribution in the brain and inner ear of the plainfin midshipman fish (Porichthys notatus) with particular emphasis on their relationship with anatomically labeled circuitry that both produces and encodes social acoustic signals in this species. Neurobiotin labeling of the main auditory endorgan, the saccule, combined with tyrosine hydroxylase immunofluorescence (TH-ir) revealed a strong CA innervation of both the peripheral and central auditory system. Diencephalic TH-ir neurons in the periventricular posterior tuberculum, known to be dopaminergic, send ascending projections to the ventral telencephalon and prominent descending projections to vocal-acoustic integration sites, notably the hindbrain octavolateralis efferent nucleus, as well as onto the base of hair cells in the saccule via nerve VIII. Neurobiotin backfills of the vocal nerve in combination with TH-ir revealed CA terminals on all components of the vocal pattern generator which appears to largely originate from local TH-ir neurons but may include diencephalic projections as well. This study provides strong evidence for catecholamines as important neuromodulators of both auditory and vocal circuitry and acoustic-driven social behavior in midshipman fish. This first demonstration of TH-ir terminals in the main endorgan of hearing in a non-mammalian vertebrate suggests a conserved and important anatomical and functional role for dopamine in normal audition. J. Comp. Neurol., 2014. © 2014 Wiley Periodicals, Inc.The Journal of Comparative Neurology 04/2014; · 3.66 Impact Factor