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: Measurements of branchial cavity water pressures and flow patterns, arterial blood PO2 and pH, and oxygen utilization and uptake have been made in undisturbed, free swimming sturgeon, Acipenser transmontanus. Although the jaws are degenerate and the oral apparatus is highly modified for feeding, gill ventilation is nonetheless powered by a buccal force pump and an opercular suction pump common to most bony fishes. The reduced spiracles play little or no role in gill ventilation. In sturgeon in which water intake through the ventrally located mouth was experimentally eliminated, a condition which may often develop when these fish forage in mud and sand on river substrates, effective ventilation of the gills was maintained with water drawn into the branchial cavities in a retrograde fashion solely through permanent openings in the upper regions of the opercular slits. O2 uptake and transport also remained at control levels. It is suggested that this unusual alternative mode of gill ventilation in the sturgeon represents an important respiratory adaptation to bottom dwelling and feeding.Respiration Physiology 09/1978; 34(2):153-70.
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ABSTRACT: 1. Spinal and cerebellar-brainstem areas of fetal mouse were dissociated and grown in tissue culture until large enough to permit stable intracellular recording. 2. The tissue-cultured neurones, growing as a monolayer and accessible under direct vision using phase contrast optics, allowed precise placement of intracellular recording and extracellular ionophoretic pipettes. 3. Ionophoresis of GABA and glutamate revealed a non-uniform distribution of responses over the cell surface, with a lack of spatial coincidence in sensitivity between the two. GABA inhibited and glutamate excited all cells tested. 4. GABA responses evoked at the cell body and on nearby process membrane were almost uniformly hyperpolarizing, while those at some peripheral process membrane were either hyperpolarizing, depolarizing or a combination of both events. All responses were associated with an increase in membrane slope conductance. 5. Membrane polarization showed that all hyperpolarizing events extrapolated to about the same inversion potential, which averaged about 9 mV more negative than resting potential (n = 95 cells). The depolarizing phases of responses evoked at peripheral membranes extrapolated to about 0 mV (n = 5 cells). 6. The hyperpolarization and increase in membrane conductance of GABA responses at the cell body were dependent on Cl- ions and the inversion potential of the response was dependent on the Cl- ion concentration gradient. The inversion potentials of GABA, glycine and beta-alanine responses were identical. 7. When matched in magnitude for evoked conductance increase, glycine responses decayed more rapidly than GABA. Glycine and beta-alanine voltage responses both decayed faster than GABA responses of comparable size. 8. In about half the cells tested sustained or rapidly repeated application of GABA and glycine transformed hyperpolarizing responses into depolarizations which were associated with a maintained conductance increase. Results from conditioning-test experiments with pairs of GABA and glycine responses suggest that the reversal of response polarity is due to a rapid redistribution of Cl- ions. 9. The limiting slope of log-log dose-response curves for GABA-induced conductance averaged about 2, while those for glutamate-induced depolarizations averaged about 1. The results suggest that two molecules of GABA and one molecule of glutamate participate in the respective post-synaptic responses. 10. The observation indicate that mammalian C.N.S. tissue grown in culture is a suitable model to study C.N.S. membrane pharmacology with increasing precision.The Journal of Physiology 08/1978; 280:331-54. · 4.38 Impact Factor
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ABSTRACT: The anterior lateral line nerve (ALLN) in the chondrostean fishes (sturgeon and paddlefishes) consists of both fibers innervating ampullary electroreceptors and fibers innervating the mechanoreceptive neuromasts of the cephalic lateral line system. The fibers of the posterior lateral line nerve (PLLN) innervate only mechanoreceptive neuromasts on the body trunk. The ALLN enters the medulla via dorsal and ventral roots; the dorsal root projects to the dorsal octavolateralis nucleus (DON), whereas the ventral root and the PLLN project principally to the medial octavolateralis nucleus (MON). Previous studies in elasmobranchs have demonstrated that fibers of the dorsal root of the ALLN convey electrosensory information, and fibers of the ventral root are concerned with mechanoreceptive information. Electrophysiological and neuroanatomical methods are employed in this study in order to determine if there exists a similar segregation of electroreceptive and mechanoreceptive lateral line afferents within the chondrostean medulla. In specimens of shovelnose, Scaphirhynchus platorynchus, and Atlantic sturgeon, Acipenser oxyrhynchus, and paddlefish, Polyodon spathula, evoked potentials recorded from the hindbrain and elicited by electric fields reached maximum amplitude within the DON and decreased in amplitude through the cerebellar crest. Evoked potentials elicited by stimulation of the posterior lateral line nerve achieved maximum amplitude within the MON. Single and multiple unit recordings revealed that units within the DON responded only to electric field stimulation, whereas units recorded in the MON responded only to mechanical stimulation. Horseradish peroxidase implanted beneath isolated patches of ampullae in Polyodon revealed fibers innervating electroreceptors projecting to the DON via the dorsal root of the ALLN. These results demonstrate a segregation of electroreceptive and mechanoreceptive lateral line afferent fibers in the chondrostean hindbrain, similar to that seen in elasmobranchs. This supports the contention that the electrosensory systems of elasmobranchs and chondrosteans are homologous, and are derived from the common ancestor of elasmobranch and actinopterygian fishes.Brain Research 07/1985; 336(1):89-98. · 2.88 Impact Factor