Summary
Neurons within the compound eye of the flyCalliphora erythrocephala, suspected of containing gamma-aminobutyric acid were revealed immunocytochemically, using antibodies directed against gamma-aminobutyric acid (GABA) and glutamic acid decarboxylase (GAD). The GABA content within putative GABAergic neurons was increased by high affinity uptake of GABA and selective blocking of GABA metabolism with Gabaculine. Only neuronal populations which were labelled with the GABA as well as the GAD antibodies were presumed to be GABAergic. The first optic neuropil (lamina) exhibited two distinct GA-BAergic fibre populations amongst a larger population comprised of fourteen cell classes. One fibre population was formed by the axons of the photopic photoreceptors R7 which pass through the lamina and terminate in the second optic neuropil (the medulla). The identity of R7 was established from longitudinal and transverse sections of the retina where R7 can be unequivocally distinguished from the six scotopic photoreceptors R1-6 and the other photopic receptor, R8.
The other fibre population matched the profiles in the lamina of terminals of efferent C2 neurons. These neurons project distally from beneath the medulla out to the lamina ganglionaris where each retinotopic unit (cartridge) contains a characteristic hook-like terminal arbor distally. We propose from these data that the photoreceptors R7 and the efferent C2 neurons use GABA as a neurotransmitter.
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Datum, KH., Weiler, R. & Zettler, F. Immunocytochemical demonstration ofγ-amino butyric acid and glutamic acid decarboxylase in R7 photoreceptors and C2 centrifugal fibres in the blowfly visual system. J. Comp. Physiol. 159, 241–249 (1986). https://doi.org/10.1007/BF00612306
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DOI: https://doi.org/10.1007/BF00612306