Responses ofDrosophilagiant descending neurons to visual and mechanical stimuli

Abstract

In Drosophila, the paired giant descending neurons (GDNs), also known as giant fibers, and the paired giant antennal mechanosensory descending neurons (GAMDNs), are supplied by visual and mechanosensory inputs. Both neurons have the largest cell bodies in the brain and both supply slender axons to the neck connective. The GDN axon thereafter widens to become the largest axon in the thoracic ganglia, supplying information to leg extensor and wing depressor muscles. The GAMDN axon remains slender, interacting with other descending neuron axons medially. GDN and GAMDN dendrites are partitioned to receive inputs from antennal mechanosensory afferents and inputs from the optic lobes. Although GDN anatomy has been well studied in Musca domestica, less is known about the Drosophila homolog, including electrophysiological responses to sensory stimuli. Here we provide detailed anatomical comparisons of the GDN and the GAMDN, characterizing their sensory inputs. The GDN showed responses to light-on and light-off stimuli, expanding stimuli that result in luminance decrease, mechanical stimulation of the antennae, and combined mechanical and visual stimulation. We show that ensembles of lobula columnar neurons (type Col A) and mechanosensory antennal afferents are likely responsible for these responses. The reluctance of the GDN to spike in response to stimulation confirms observations of the Musca GDN. That this reluctance may be a unique property of the GDN is suggested by comparisons with the GAMDN, in which action potentials are readily elicited by mechanical and visual stimuli. The results are discussed in the context of descending pathways involved in multimodal integration and escape responses.

Organization of projection neurons and local neurons of the primary auditory center in the fruit flyDrosophila melanogaster

“…In larger flies Calliphora erythrocephala , the GF will spike only if visual and mechanical stimuli coincide (Milde and Strausfeld, ). Mu et al () recently analyzed the response of the GF in D. melanogaster to such multimodal stimuli. In their experiments, either an air puff to the fruit fly's antennae or a light‐off stimulus elicited an excitatory postsynaptic potential in the GF.…”

“…They further found that intensity of responses to combined stimuli was significantly larger than the response to either the light‐off or air‐puff stimulus alone. The simultaneous paring of these two types of sensory signals seems more likely to induce reliable GF activity than when either stimulus is presented alone (Mu et al, ).…”

The functional organization of descending sensory-motor pathways inDrosophila

“…We did not include ascending neurons and neck 829 motor neurons in this analysis. For the physical definitions and nomenclature of the brain neuropils, we 830 followed the virtual fly brain (http://www.virtualflybrain.org/; Ito et al 2014). Abbreviations used in the 831 document are summarized in Supplementary Table 6.…”

Colour vision in mantis shrimps: understanding one of the most complex visual systems in the world

“…In Drosophila, relays from the glomeruli in the lateral protocerebrum projects to higher centres of processing such as the central complex (Liu et al, 2006, Strausfeld andOkamura, 2007) through the dorsal protocerebral lobes. But they also convey information to the rest of the body through interactions with the giant descending neurons (Mu et al, 2014), which project to the thoracic ganglia. Although we still do not know the function of the glomeruli and why they are gathered in a large glomerular complex in the stomatopod protocerebrum, it is likely that the large variety of shapes and sizes of glomeruli indicate different types of information inputs, possibly from different types of visual modalities.…”