title: Distribution of synapses on two local auditory interneurones, ON1 and ON2, in the prothoracic ganglion of the cricket: relationships with GABA-immunoreactive neurones.
abstract: In the prothoracic ganglia of the cricket Gryllus bimaculatus two local auditory interneurones, ON1 and ON2, were labelled for electron microscopy by intracellular injection of horseradish peroxidase following physiological characterisation. The neurones branch in the median ventral association centre and the root of nerve 5 on both sides of the ganglion. As they are very similar in shape and position they may share a common embryological origin. Differences are found in the details of the fine branching pattern and in their physiology as ON1 is tuned particularly to low sound frequencies of 4-5 kHz whereas ON2 is more sensitive to frequencies above 8 kHz. Although the ON1 neurones inhibit each other and are involved in the inhibition of other auditory neurones they were not labelled by antibodies against the inhibitory transmitter GABA and their vesicles differ significantly from those in neurones that are. The same is true of the ON2 neurones whose vesicles also differ significantly from those in ON1 supporting light-microscope evidence that they may use different transmitters. The distribution of input and output synapses on the ipsilateral and contralateral branches of ON1 and ON2, and the proportion of the synapses made from and onto neuropilar processes immunoreactive for GABA was determined. In ON1 94% of the input synapses were received on the ipsilateral branches and 62% of the outputs made from the contralateral branches. This confirms previous physiological evidence that input is received ipsilaterally and output made contralaterally but the presence of some contralateral input and a significant ipsilateral output was unsuspected. Thirty percent of the input synapses on the ipsilateral side and 75% on the contralateral side were made from GABA-immunoreactive processes but processes postsynaptic to ON1 were rarely immunoreactive. The distribution of input synapses on ON2 was similar with 90% received on ipsilateral branches but a higher proportion of outputs (83%) was made from the contralateral side than in ON1. Thirty one percent of ipsilateral inputs were GABA-immunoreactive but only 14% on the contralateral side.
authors.affiliation: Anatomy Unit, School of Molecular and Medical Biosciences, University of Wales College of Cardiff, PO Box 911, Cardiff CF1 3US, UK.
authors.forename: A H
authors.initials: AH
authors.lastname: Watson
authors.forename: M
authors.initials: M
authors.lastname: Hardt
mesh_terms: D000818:Animals; D001306:Auditory Pathways / Q000648:ultrastructure*; D001307:Auditory Perception / Q000502:physiology; D001522:Behavior, Animal; D017952:Ganglia, Invertebrate / Q000166:cytology*; D006135:Gryllidae / Q000033:anatomy & histology* / Q000502:physiology; D006735:Horseradish Peroxidase; D007395:Interneurons / Q000502:physiology / Q000648:ultrastructure*; D007546:Isoquinolines; D008854:Microscopy, Electron; D013569:Synapses / Q000648:ultrastructure*; D005680:gamma-Aminobutyric Acid / Q000032:analysis
chemical_list: D007546:Isoquinolines; D005680:gamma-Aminobutyric Acid; C017475:lucifer yellow; D006735:Horseradish Peroxidase