shibirets1, a temperature-sensitive mutation of the Drosophila gene encoding a Dynamin orthologue, blocks vesicle endocytosis and thus synaptic transmission, at elevated, or restrictive temperatures. By targeted Gal4 expression, UAS-shibirets1 has been used to dissect neuronal circuits. We investigated the effects of UAS-shibirets1 overexpression in Drosophila photoreceptors at permissive (19° C) and restrictive (31° C) temperatures. At 19° C, overexpression of UAS-shits1 causes decelerated phototransduction and reduced neurotransmitter release. This phenotype is exacerbated with dark adaptation, age and in white mutants. Photoreceptors overexpressing UAS-shibire ts1 contain terminals with widespread vacuolated mitochondria, reduced numbers of vesicles and bundled microtubules. Immuno-electron microscopy reveals that the latter are dynamin coated. Further, the microtubule phenotype is not restricted to photoreceptors, as UAS-shibirets1 overexpression in lamina cells also bundles microtubules.Weconclude that dynamin has multiple functions that are interrupted by UAS-shibirets1 overexpression in Drosophila photoreceptors, destabilizing their neural communication irreversibly at previously reported permissive temperatures.