Blue adaptation: an experimental tool for the study of visual receptor mechanisms and behaviour of Drosophila.

Physiological and behavioural studies with Drosophila to elucidate visual mechanisms have exploited the bi-stability of the visual pigment in the peripheral retinula cells R1-6, and the 'off-on switch' action of blue and orange light. Measurements of flicker fusion and response waveform from both receptor and lamina regions prior and subsequent to blue adaptation, which induces a prolonged depolarising afterpotential and loss of visual function in R1-6, show these retinula cells to have a high fusion frequency and R7/8, the central retinula cells, a lower fusion frequency. Such measurements also allow analysis of the extracellular response in terms of contributing cells, and its potential for studying the fly's ability to respond to various potential visual cues such as a rotating plane of polarised light. Blue adapted flies fail to fixate normally a black stripe, confirming a role for R1-6 in orientation behaviour requiring a competent degree of acuity.