Peripheral visual function in the fly
Date
1978
Authors
Hardie, Roger Clayton
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Abstract
Receptors and peripheral neurons of the dipteran visual
system have been studied in the flies, Calliphora stygia
(wild type), Musca domestica (white-eyed mutant) and
Calliphora erythrocephala (chalky mutant), principally by
means of intracellular recording. Recordings were made from:
the large peripheral retinula cells, Rl-6; the small, central,
retinula cells, R7 and R8; and the large monopolar cells
(LMC' s), Ll, L2 and L4. Representatives of each cell type
were identified by intracellular dye injection with Procion
yellow. The angular sensitivity functions of the receptors are shown
to be at, or near the limit set by lens diffraction and
rhabdomere diameter. Receptors R7 and R8, whose rhabdomeres
are narrower than those of Rl-6,also have narrower angular
sensitivity functions. Many of the basic response properties of photoreceptors are
described in detail for the first time. For R7 and R8,
spectral sensitivities, polarisation sensitivities, absolute
sensitivities, and dark and light-adapted intensityjresponse
functions have been determined. In Rl-6 cells, lightadaptation
shifts the peak of spectral sensitivity, and
narrows the angular sensitivity function, but had no effect
upon the polarisation sensitivity. These new results from
identified receptors lead to a reappraisal of receptor
involvement in optomotor behaviour. A new functional class of photoreceptor (Rl-6) is described
in which the spectral and polarisation sensitivity are both
dependent upon the intensity of the test flash-used to
measure them. In addition, the polarisation sensitivity is
strongly dependent upon the stimulus wavelength. The
experimental analysis suggests that these anomalous properties
derive from the events occurring in a single cell, and this
finding may have important implications with respect to the
process of transduction in photoreceptors. A detailed study is made of the processes of light-adaptation
2
in receptors Rl-6 and their postsynaptic elements, the LMC's.
Consecutive stages of light-adaptation are isolated by comparing
the performance of receptors and LMC's when subjected to
identical regimes of dark- and light-adaptation over a 5 log
unit range of intensities, and possible mechanisms of lightadaptation
are considered. A comparison with the performance
of higher order visual interneurons indicates that the majority
of adaptation is completed at the level of the LMC. A
comparison of the results with those of similar studies in
other arthropods and, also the lower vertebrates reveals
striking analogies, which, it is argued, represent an optimal
strategy for light-adaptation. The receptors R7 and R8 are intensively investigated to
elucidate their function in terms of the pigments in their
rhabdome res. There are two spectral classes of R7 which
appear to have completely different pigments in their rhabdomeres. The properties of RB are profoundly influenced
by the absorption of light in the overlying rhabdomere of R7.
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