Chemical neuroanatomy of the fly's movement detection pathway.
ABSTRACT In Diptera, subsets of small retinotopic neurons provide a discrete channel from achromatic photoreceptors to large motion-sensitive neurons in the lobula complex. This pathway is distinguished by specific affinities of its neurons to antisera raised against glutamate, aspartate, gamma-aminobutyric acid (GABA), choline acetyltransferase (ChAT), and a N-methyl-D-aspartate type 1 receptor protein (NMDAR1). Large type 2 monopolar cells (L2) and type 1 amacrine cells, which in the external plexiform layer are postsynaptic to the achromatic photoreceptors R1-R6, express glutamate immunoreactivity as do directionally selective motion-sensitive tangential neurons of the lobula plate. L2 monopolar cells ending in the medulla are accompanied by terminals of a second efferent neuron T1, the dendrites of which match NMDAR1-immunoreactive profiles in the lamina. L2 and T1 endings visit ChAT and GABA-immunoreactive relays (transmedullary neurons) that terminate from the medulla in a special layer of the lobula containing the dendrites of directionally selective retinotopic T5 cells. T5 cells supply directionally selective wide-field neurons in the lobula plate. The present results suggest a circuit in which initial motion detection relies on interactions among amacrines and T1, and the subsequent convergence of T1 and L2 at transmedullary cell dendrites. Convergence of ChAT-immunoreactive and GABA-immunoreactive transmedullary neurons at T5 dendrites in the lobula, and the presence there of local GABA-immunoreactive interneurons, are suggested to provide excitatory and inhibitory elements for the computation of motion direction. A comparable immunocytological organization of aspartate- and glutamate-immunoreactive neurons in honeybees and cockroaches further suggests that neural arrangements providing directional motion vision in flies may have early evolutionary origins.
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ABSTRACT: The NMDA subtype of ionotropic glutamate receptors has been implicated in the activity-dependent modification of synaptic efficacy in the mammalian brain. Here we describe a cDNA isolated from Drosophila melanogaster which encodes a putative invertebrate NMDA receptor protein (DNMDAR-I). The deduced amino acid sequence of DNMDAR-I displays 46% amino acid identity to the rat NMDAR1 polypeptide and shows significant homology (16-23%) to other vertebrate and invertebrate glutamate receptor proteins. The DNMDAR-I gene maps to position 83AB of chromosome 3R and is highly expressed in the head of adult flies. Our data indicate that the NMDA subtype of glutamate receptors evolved early during phylogeny and suggest the existence of activity-dependent synaptic plasticity in the insect brain.FEBS Letters 07/1993; 324(2):171-7. · 3.58 Impact Factor
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ABSTRACT: The first synaptic region of the fly's visual system contains sets of climbing fibres enclosing each optic cartridge in a double basket-like arrangement of processes. The two sets of processes, termed α and β, can be separately identified by their fine structure. αfibres are more electron dense than β; they are postsynaptic to receptor endings from the retina and contain synaptic specializations apposed to epithelial cell membranes, to β fibres and to the distal processes of the L4 monopolar neurone. β is postsynaptic to receptors and to α. It has a lighter cytoplasm and contains peculiar glial invaginations called ‘gnarls’. Degeneration experiments, where the optic chiasma between the 1st and 2nd synaptic regions has been severed, demonstrate that α fibres are intrinsic to the lamina. Golgi impregnation and electron microscopy of Golgi-impregnated cells have demonstrated that β fibres belong to a type of medulla-to-lamina cell, T1, whereas α fibres belong to an intrinsic (amacrine) cell in the lamina. The amacrine cells have wide fields through several cartridges. However, Golgi—EM studies show that each cartridge must be invaded by the processes of at least two cells. The synaptology of these elements is discussed with respect to previous data about the lamina, and certain analogies with the vertebrate plexiform layer are drawn.Brain Research 10/1973; 59:119-36. · 2.88 Impact Factor
Article: The glutamate receptor ion channels.Pharmacological Reviews 04/1999; 51(1):7-61. · 22.35 Impact Factor