Glia-related circadian plasticity in the visual system of Diptera

Jolanta Górska-Andrzejak

doi:10.3389/fphys.2013.00036

Abstract

The circadian changes in morphology of the first visual neuropil or lamina of Diptera represent an example of the neuronal plasticity controlled by the circadian clock (circadian plasticity). It is observed in terminals of the compound eye photoreceptor cells, the peripheral oscillators expressing the clock genes. However, it has been found also in their postsynaptic partners, the L1 and L2 monopolar cells, in which the activity of the clock genes have not yet been detected. The circadian input that the L1 and L2 receive seems to originate not only from the retina photoreceptors and from the circadian pacemaker neurons located in the brain, but also from the glial cells that express the clock genes and thus contain circadian oscillators. This paper summarizes the morphological and biochemical rhythms in glia of the optic lobe, shows how they contribute to circadian plasticity, and discusses how glial clocks may modulate circadian rhythms in the lamina.

Highlights

The visual system of Diptera exhibits daily rhythmic changes in morphology and physiology (Pyza and Górska-Andrzejak, 2008; Pyza, 2010)
It has been shown that in the fruit fly the volume of photoreceptor terminals changes in a circadian manner (Barth et al, 2010), whereas in the housefly the endogenous reorganization of organelles within R1–R6 terminals is maintained under circadian modulation (Pyza and Meinertzhagen, 1997)
L2 dendrites that are postsynaptic to photoreceptors are the longest at the beginning of the day (Weber et al, 2009), which coincides with the increase of the number of tetrad synapses in photoreceptor terminals and with the level of BRP in the lamina (Pyza and Meinertzhagen, 1993; Górska-Andrzejak et al, 2013)

Summary

INTRODUCTION

The visual system of Diptera exhibits daily rhythmic changes in morphology and physiology (Pyza and Górska-Andrzejak, 2008; Pyza, 2010). L2 dendrites that are postsynaptic to photoreceptors are the longest at the beginning of the day (Weber et al, 2009), which coincides with the increase of the number of tetrad synapses in photoreceptor terminals (shown in Musca) and with the level of BRP in the lamina (shown in Drosophila) (Pyza and Meinertzhagen, 1993; Górska-Andrzejak et al, 2013). This coincidence strongly suggests the possibility of correlation, which. In Drosophila, the glial cells of the visual system belong to the per expressing glia (Siwicki et al, 1988; Ewer et al, 1992)

GLIA DERIVED CIRCADIAN MODULATION OF THE LAMINA NEURONAL CIRCUITRY

CONCLUSIONS