Neurosecretory control of ecdysone release during puparium formation of flies

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Larvae of Sarcophaga argyrostoma fail to pupariate while kept wet, but do so upon transfer to dry conditions after about 28 hr. This period is lengthened to 42 hr after injection of tetrodotoxin, and shortened to 12 hr after injection of ecdysone, independently of whether they are kept wet or dry. It is 12 hr in larvae injected with ecydsone plus tetrodotoxin (which inhibits the puparial contraction) or ecdysone plus α-MDH (which inhibits subsequent tanning). It is rather the lack of inhibitory stimulation arising from a wet surrounding which allows the CNS to activate the ring gland (RG), than a positive stimulation caused by dry conditions. Hind parts of larvae, previously kept wet, were implanted with the CNS-RG complex, or CNS or RG alone, taken from wet-treated larvae kept dry for various periods. Implantation with the CNS-RG complex from donors of any age induced a high percentage of pupariation, but it occurred sooner, the older the donors. When implanted with RG alone, the age of the donors was decisive; almost no effect at the time of transfer to the dry, and an increasing effect thereafter. When the donors were prepupae at various periods after puparium formation the effect decreased with increasing age, but was identical when CNS-RG or RG alone were implanted. CNS alone from donors of any age before or after pupariation had no effect. Before pupariation the ring gland becomes increasingly more active while the reverse holds after pupariation. The nervous connection between CNS and RG is important rather as a duct for the neurosecretory material, than for its electrical charge-carrying properties.