Item

Abstract

Autoradiographs of the brains of the visual mutantsouter rhabdomeres absent JK84 (ora),small optic lobes KS58 (KS58) andno object fixation E B12 (B12) have been obtained by the deoxyglucose method. The patterns of metabolic activity in the optic lobes of the visually stimulated mutants is compared with that of similarly stimulated wildtype (WT) flies which was described in Part I of this work (Buchner et al. 1984b).

In the mutantKS58 the optomotor following response to movement is nearly normal despite a 40–45% reduction of volume in the visual neuropils, medulla and lobula complex. InB12 flies the volume of these neuropils and the optomotor response are reduced. In autoradiographs of both mutants the pattern of neuronal activity induced by stimulation with moving gratings does not differ substantially from that in the WT. It suggests that only neurons irrelevant to movement detection are affected by the mutation. However, in the lobula plate of someKS58 flies and in the second chiasma of allB12 flies, the pattern of metabolic activity differs from that observed in WT flies. Up to now no causal relation has been found between the modifications described in behaviour or anatomy and those observed in the labelling of these mutants.

In the ommatidia ofora flies the outer rhabdomeres are lacking while the central photoreceptors appear to be normal. Stimulus-specific labelling is absent in the visual neuropil of these mutants stimulated with movement or flicker. This result underlines the importance of the outer rhabdomeres for visual tasks, especially for movement detection.