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Local circuit for the computation of object approach by an identified visual neuron in the locust
Author(s) -
Rind F. Claire,
Simmons Peter J.
Publication year - 1998
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/(sici)1096-9861(19980808)395:3<405::aid-cne9>3.0.co;2-6
Subject(s) - locust , neuroscience , biology , excitatory postsynaptic potential , inhibitory postsynaptic potential , cholinergic , neuron , acetylcholine , postsynaptic potential , biochemistry , botany , receptor , endocrinology
The lobula giant movement detector (LGMD) neuron in the locust visual system is part of a motion‐sensitive pathway that detects objects approaching on a collision course. Here we show that the retinotopic units presynaptic to the LGMD make synapses directly with each other and these synapses are immediately adjacent to their outputs onto the LGMD. Synapses occur along the fine dendrites of the LGMD in the distal lobula, often in large numbers and completely covering the LGMD processes. Gamma aminobutyric acid (GABA) was eliminated as a possible neurotransmitter at these synapses when immunogold‐tagged monoclonal GABA antibody did not specifically label the afferent processes. We used a histochemical method to demonstrate that acetylcholine esterase, the enzyme that hydrolyses acetylcholine at cholinergic synapses, was present in the synaptic clefts between the retinotopic units and along the membrane of the LGMD. It is well established that acetylcholine has both excitatory and inhibitory effects and we propose that these retinotopic units excite the LGMD, but inhibit each other; and that the synapses form the substrate for a critical race between excitation caused by edges moving out over successive photoreceptors, and inhibition spreading laterally. This results in the selective response to objects approaching on a collision course. J. Comp. Neurol. 395:405–415, 1998. © 1998 Wiley‐Liss, Inc.