Abstract
Light-activated large ventral lateral clock neurons (large LNv) modulate behavioral arousal and sleep in Drosophila while their counterparts, the small LNv (s-LNv) are important for circadian behavior. Recently, it has been proposed that the pattern of day-night locomotor behavioral activity is mediated by two anatomically distinct oscillators composed of a morning oscillator in the small LNv and an evening oscillator in the lateral dorsal neurons and an undefined number of dorsal pacemaker neurons. This contrasts with a circuit described by network models which are not as anatomically constrained. By selectively ablating the small LNv while sparing the large LNv, we tested the relative importance of the small and large LNv for regulating morning behavior of animals living in standard light/dark cycles. Behavioral anticipation of the onset of morning and the high amplitude morning startle response which coincides with light onset are preserved in small LNv functionally-ablated animals. However, the amplitude of the morning behavioral peak is severely attenuated in these animals during the transition from regular light/dark cycles to constant darkness, providing further support that small LNv are necessary for circadian behavior. The large LNv, in combination with the network of other circadian neurons, in the absence of functional small LNv are sufficient for the morning anticipation and the high amplitude light-activated morning startle response.
Highlights
Pittendrigh and Daan proposed that circadian clocks simultaneously ‘‘measure’’ daily and seasonal changes in day lengths using mutually coupled binary oscillators: the ’’Morning’’ (‘‘M’’) oscillator that tracks dawn and the ’’Evening’’ (‘‘E’’) oscillator that tracks dusk [1]
To clarify whether the small LNv are required for the morning behavioral anticipation and peak activity, and to distinguish between acute light versus circadian effects on the light-activated high amplitude morning startle response, we examined these questions using a method developed recently in our laboratory which functionally ablates the small LNv while the large LNv and the other circadian neurons remain functionally intact [31]
Spontaneous action potential firing of large LNv Drosophila pacemaker neurons can be measured by whole cell patch in current clamp mode [17,29,30,31,35], a recording method adapted from techniques devised for recording from olfactory neurons in adult Drosophila whole brain [36]
Summary
Pittendrigh and Daan proposed that circadian clocks simultaneously ‘‘measure’’ daily and seasonal changes in day lengths using mutually coupled binary oscillators: the ’’Morning’’ (‘‘M’’) oscillator that tracks dawn and the ’’Evening’’ (‘‘E’’) oscillator that tracks dusk [1]. Several papers indicate that the ‘‘M’’ and ‘‘E’’ oscillators in Drosophila may have distinct anatomical locations as shown by the effects of eliminating different subgroups of clock neurons or by restoring clock gene expression in specific neurons in clock mutants [4,5,6,7]. These studies conclude that the small LNv function as the ‘‘M’’ oscillator in the Drosophila circadian pacemaker circuit, while the LNd and an unspecified number of dorsal neurons function as the ‘‘E’’ oscillator
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