Direction-selective adaptation in fly visual motion-sensitive neurons is generated by an intrinsic conductance-based mechanism

Abstract

Motion-sensitive neurons in the blowfly brain present an ideal model system to study the cellular mechanisms and functional significance of adaptation to visual motion. Various adaptation processes have been described, but it is still largely unknown which of these processes are generated in the motion-sensitive neurons themselves and which originate at more peripheral processing stages. By input resistance measurements I demonstrate that direction-selective adaptation is generated by an activity-dependent conductance increase in the motion-sensitive neurons. Based on correlations between dendritic Ca2+ accumulation and slow hyperpolarizing after-potentials following excitatory stimulation, a regulation of direction-selective adaptation by Ca2+ has previously been suggested. In the present study, however, adaptation phenomena are not evoked when the cytosolic Ca2+ concentration is elevated by ultraviolet photolysis of caged Ca2+ in single neurons rather than by motion stimulation. This result renders it unlikely, that adaptation in fly motion-sensitive neurons is regulated by bulk cytosolic Ca2+.