Involvement of glial cells in rhythmic size changes in neurons of the housefly's visual system

Abstract

In the housefly's first optic neuropile, or lamina, the axons of two classes of monopolar cell interneurons, L1 and L2, exhibit a daily rhythm of size changes: swelling during the day, and shrinking by night. At least for the L2 cells this rhythm is circadian. Moreover, epithelial glial cells that enwrap each lamina cartridge, its monopolar cell axons, and their surrounding crown of input photoreceptor terminals also change size, but in the opposite direction to the changes in L1 and L2-swelling by night and shrinking by day. The rhythmic changes in glia indicate the possible involvement of these cells in the lamina's circadian system. To examine their role in regulating the rhythmic changes of L1 and L2's axon sizes we have injected three chemicals into the haemolymph of the fly's head: fluorocitrate (FL) and iodoacetate (IAA), which affect the metabolism of glial cells, and octanol (OC), which closes gap junction channels. All chemicals exerted an effect on L1 and L2, which depended on the time of injection, the drug concentration, and the postinjection times at which we examined the fly's brains. Moreover, day/night changes in the axon sizes of L1 and L2 were increased in FL- and IAA-treated flies, indicating that glial cells may normally inhibit these changes by regulating the sizes of L1 and L2's axons during the day and night. In turn, lack of a day/night rhythm in L1 and L2 after OC injections shows that the rhythm's persistence depends on communication between the lamina cells through gap junction channels.

PDF receptor expression reveals direct interactions between circadian oscillators in drosophila

“…PDFR-MYC expression in or near the sub-retinal region represents a good candidate to mediate such actions and hence PDF modulation of photosensitivity may operate by targeting non-neuronal cells. I In insects, glia of the retina and of the first optic neuropil have been implicated in nutritive regulation of photoreceptors (Coles et al ., 2008), in neurotransmitter metabolism (Borycz et al ., 2002), and in circadian control of neuronal size changes (Pyza and Górska-Andrzejak, 2004). At what level PDF exerts its actions on glia and how this affects circadian photoreception are questions our results have newly-generated.…”

Circadian rhythms in the morphology of neurons in Drosophila

“…Glial cells are good candidates for testing this hypothesis, because they are important for neuronal plasticity in general (Parker and Auld 2006;Stacey et al 2007) and display their own circadian rhythms in Drosophila (Pyza and Górska-Andrzejak 2004;Suh and Jackson 2007;Jackson 2010).…”

Circadian release of pigment‐dispersing factor in the visual system of the housefly, Musca domestica

“…In the retina of vertebrates daily and circadian rhythms have been detected both in physiology and structure (Cahill and Besharse, 1993) and most of these rhythms are generated by an autonomous clock in the retina itself (Tosini and Fukuhara, 2002). In flies circadian rhythms have been found in ERG amplitude (Chen et al, 1999), migration of screening pigment granules and structural changes in eye photoreceptors (Pyza and Meinertzhagen, 1997a), and in size and structure of the first-order interneurons, termed L1 and L2 monopolar cells, as well as in glial cells of the first optic neuropil, the lamina Meinertzhagen, 1995, 1999;Pyza and Górska-Andrzejak, 2004). Circadian rhythms in L1 and L2 sizes seem widespread among dipterans, since they have been detected in the housefly Musca domestica (Pyza and Meinertzhagen, 1995), the blowfly Calliphora vicina (Pyza and Cymborowski, 2001), and the fruit fly Drosophila melanogaster .…”