title: Retinal amino acid neurochemistry of the southern hemisphere lamprey, Geotria australis.
abstract: Lampreys are one of the two surviving groups of the agnathan (jawless) stages in vertebrate evolution and are thus ideal candidates for elucidating the evolution of visual systems. This study investigated the retinal amino acid neurochemistry of the southern hemisphere lamprey Geotria australis during the downstream migration of the young, recently-metamorphosed juveniles to the sea and during the upstream migration of the fully-grown and sexually-maturing adults to their spawning areas. Glutamate and taurine were distributed throughout the retina, whilst GABA and glycine were confined to neurons of the inner retina matching patterns seen in most other vertebrates. Glutamine and aspartate immunoreactivity was closely matched to Müller cell morphology. Between the migratory phases, few differences were observed in the distribution of major neurotransmitters i.e. glutamate, GABA and glycine, but changes in amino acids associated with retinal metabolism i.e. glutamine and aspartate, were evident. Taurine immunoreactivity was mostly conserved between migrant stages, consistent with its role in primary cell functions such as osmoregulation. Further investigation of glutamate signalling using the probe agmatine (AGB) to map cation channel permeability revealed entry of AGB into photoreceptors and horizontal cells followed by accumulation in inner retinal neurons. Similarities in AGB profiles between upstream and downstream migrant of G. australis confirmed the conservation of glutamate neurotransmission. Finally, calcium binding proteins, calbindin and calretinin were localized to the inner retina whilst recoverin was localized to photoreceptors. Overall, conservation of major amino acid neurotransmitters and calcium-associated proteins in the lamprey retina confirms these elements as essential features of the vertebrate visual system. On the other hand, metabolic elements of the retina such as neurotransmitter precursor amino acids and Müller cells are more sensitive to environmental changes associated with migration.
authors.affiliation: School of Optometry and Vision Science, University of New South Wales, Sydney, New South Wales, Australia.
authors.forename: Lisa
authors.initials: L
authors.lastname: Nivison-Smith
authors.forename: Shaun P
authors.initials: SP
authors.lastname: Collin
authors.forename: Yuan
authors.initials: Y
authors.lastname: Zhu
authors.forename: Sarah
authors.initials: S
authors.lastname: Ready
authors.forename: Monica L
authors.initials: ML
authors.lastname: Acosta
authors.forename: David M
authors.initials: DM
authors.lastname: Hunt
authors.forename: Ian C
authors.initials: IC
authors.lastname: Potter
authors.forename: Michael
authors.initials: M
authors.lastname: Kalloniatis
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism; D007473:Ion Channels / Q000378:metabolism; D007798:Lampreys / Q000378:metabolism*; D010539:Permeability; D012160:Retina / Q000166:cytology / Q000378:metabolism*; D055351:Retinal Neurons / Q000378:metabolism
chemical_list: D000596:Amino Acids; D002135:Calcium-Binding Proteins; D007473:Ion Channels