Study of neural networks and control substances for insect photoperiodism

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This study morphologically examined neural networks and control substances involved in photoperiodic mechanisms regulating reproductive diapause in the blow fly Protophormia terraenovae. We obtained following results by focusing on neural connections from small type PDF neurons (circadian clock neurons) to pars lateralis neurons (diapause controlling neurons) and pars intercerebralis neurons important for reproduction.Morphological analysis of neural networks for photoperiodism: PERIOD-immunoreactivity was found in 5 groups of cells in the brain. Among the 5 groups two including small type PDF neurons were double-labeled with anti- PERIOD and anti-PDF (pigment-dispersing factor) antisera. Surgical ablation of the somata region of small type PDF neurons disrupted photoperiodism, suggesting that circadian clock neurons were involved in photoperiodism. Immunocytochemistry and backfills classified two types in the pars lateralis and 6 types of pars lateralis neurons. In the pars intercerebralis neurons, FMRFamide-immunoreacrtivity and in the pars lateralis FMRFamide-, PDF-, cholescystokinin-, corazonin-immunoreacrtivity were found.Control substances in neural networks for photoperiodism: Direct MALDI-TOF MS, and ESI-Q-Tof MS and MS/MS suggested that myosuppressin and SIFamide were present in the pars intercerebralis, corazonin and a corazonin-related peptide in the pars lateralis. Real-time PCR analysis revealed daily fluctuations in the expression of two circadian clock genes period and timeless under photoperiodic conditions, but no differences between long-day and short-day conditions were found. It has to be determined how the circadian clock genes are involved in photoperiodism.