Common synaptic drive to segmentally homologous interneurons in the locust.

The aim of the present study was to examine the pattern of synaptic interactions among a set of identified homologous interneurons in the segmental nervous system of the locust. This paper presents two main findings: first, serially homologous interneurons that are the progeny of neuroblast 7-4 in the mesothoracic, metathoracic, and first abdominal neuromeres of the locust central nervous system all receive synaptic drive from one and the same presynaptic interneuron. This interneuron has its entire arborization located in these three neuromeres of the central nervous system. It synapses with cells that are siblings, bilateral homologs, and serial homologs, and is itself connected monosynaptically with auditory afferents. The neuronal network that results comprises postsynaptic cells with the same developmental lineage. The second finding is that there is an additional set of synaptic connections among the homologous neurons themselves. All these connections are excitatory, and the pattern of information flow within the network is highly directional. This may relate to the morphologies of the neurons involved and will influence the contribution of homologs from different segments to behavior.