TRACING OF A NEURONAL NETWORK IN THE LOCUST BY PRESSURE INJECTION OF MARKERS INTO A SYNAPTIC NEUROPIL

Central neuronal circuits of vertebrates have often been investigated using injection of markers into synaptic neuropils, whereas similar te chniques have rarely been applied in invertebrates. In this study we t ested several neuroanatomical tracers for their ability to mark centra l neuronal circuits in insects, using the well described auditory netw ork of the locust, Locusta migratoria. After physiological localizatio n of an auditory neuropil various tracers were pressure injected. Hors eradish peroxidase, dextrans (3 and 10 kDa) and especially biocytin an d neurobiotin were effectively incorporated by auditory interneurons, which resulted in their extensive labeling. Postsynaptic regions turne d out to be the major, if not exclusive sites of uptake of injected ma rkers, which is deduced from two lines of evidence: (i) for labeling o f identified auditory neurons it was necessary to apply the tracer to postsynaptic sites of the neuron, (ii) only a few non-auditory neurons were labeled (probably by lesioning axons during electrode impalement ). No evidence could be found for an activity dependent uptake. We con clude that pressure injection of certain tracers into synaptic areas c an be used to identify central nervous circuits in insects. (C) 1998 E lsevier Science B.V. All rights reserved.