Figure 4.

Simplified scheme showing the output pathways of the clock neurons in the brain of D. melanogaster. The somata of the clock neurons in the lateral and dorsal brain are depicted in gray with the s-LN_v and DN₁ highlighted. The clock neurons are connected with each other and most of them have neurites in the accessory medulla (aMe), where they receive major light-input, as well as in the dorsal brain where they connect different neuropeptidergic neurons. The prothoracotrophic hormone (PTTH) positive neurons receive rhythmic signals via sNPF from the s-LN_v and control the timing of eclosion by triggering the release of ecdysone from the prothoracotropic glands (shown in the left brain hemisphere). The leukokine (LK) positive neurons receive also rhythmic signals from the s-LNv and perhaps from other lateral neurons and contact via tubercular-bulbar neurons (not shown) the bulb (Bu) where ring neurons of the ellipsoid body (EB) have their dendrites (shown in the right brain hemisphere). The corresponding EB ring neurons contribute to the rhythmic control of activity. In addition, the morning neurons (s-LN_v) and evening neurons (not highlighted) signal via PDF (stippled) and unknown pathways (E?) to dopaminergic neurons (not shown) that arborize in the Bu and the EB and contact putatively the same activity promoting ring neurons in the EB in order to stimulate morning and evening activity. Other ring neurons in the EB receive rhythmic signals from the DN₁ and control sleep, while still others may get rhythmic input from the clock neurons via still unknown pathways and control orientation. Furthermore, activity, feeding and metabolism are controlled by diuretic hormone 44 (DH44), SIFamide (SIFa), and Insulin-like peptide (ILP) expressing neurons in the pars intercerebralis (PI), which receive rhythmic signals from the clock neurons. Finally, the clock neurons control learning and contribute to time memory via still unknown pathways (?) to the mushroom bodies (MB).