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Embryonic development of synapses on spiking local interneurones in locust

Record type: Article

The development of synapses on an identified population of spiking local interneurones in the thoracic ganglia of embryonic locusts was examined by means of intracellular horseradish peroxidase injection and electron microscopy. In adult locusts, spiking local interneurones of the midline group receive direct inputs onto a ventral field of branches from leg mechanosensory afferents and in turn make output synapses, mainly from a dorsal field of branches, directly upon leg motor neurones, nonspiking local interneurones, and intersegmental interneurones. The aim of this study is to examine the development of these connections. These interneurones are born relatively late in embryogenesis and are not identifiable until approximately 55% of development. At this time (55-60%) only simple filopodial contacts or punctate contacts are evident between the stained interneurones and other neurones. By 65-70% embryogenesis, vesicles are found adjacent to regions where apposed membranes are symmetrically thickened with amorphous electron-dense material. These symmetrical contacts lack distinct presynaptic bar-shaped densities and therefore, are not considered to be synapses. At this stage, the interneurones do not produce action potentials upon intracellular injection of depolarising current. Morphologically identifiable synapses, with vesicles, a presynaptic bar, and relatively little postsynaptic density, are first evident at 70-75%, coincident with the time of arrival of the majority of leg mechanosensory afferents into the central nervous system. At this stage, action potentials and synaptic potentials are also recorded for the first time. The midline spiking interneurones thus become electrically excitable when synapses are first recognisable, at approximately 70% embryogenesis. Most of the synapses found on the interneurones are outputs. The ratio of outputs to inputs on ventral branches is 7.5:1 which contrasts markedly to the adult ratio of 1:2. By 85-90%, output synapses still predominate on the ventral branches, but the ratio of outputs to inputs is reduced to almost 2:1. Dorsal branches have predominantly output synapses throughout embryogenesis. The ratio of dorsal outputs to inputs at 85-90% is 8.5:1 which compares with the adult ratio of 6.5:1 At this stage, action potentials and synaptic activity are always recorded.

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Citation

Leitch, Beulah, Laurent, Gilles and Shepherd, David (1992) Embryonic development of synapses on spiking local interneurones in locust Journal of Comparative Neurology, 324, (2), pp. 213-236. (doi:10.1002/cne.903240206).

More information

Published date: 16 October 1992
Keywords: insect, embryo, synaptogenesis, horseradish peroxidase, ultrastructure

Identifiers

Local EPrints ID: 56804
URI: http://eprints.soton.ac.uk/id/eprint/56804
ISSN: 0021-9967
PURE UUID: 0c9deccb-21e5-4dd3-992e-4235156c7f1c
ORCID for David Shepherd: ORCID iD orcid.org/0000-0002-4561-8184

Catalogue record

Date deposited: 22 Aug 2008
Last modified: 17 Jul 2017 14:30

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Contributors

Author: Beulah Leitch
Author: Gilles Laurent
Author: David Shepherd ORCID iD

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