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Bursicon, a hormone which mediates tanning of the cuticle in the adult fly and other insects

1965; Elsevier BV; Volume: 11; Issue: 5 Linguagem: Inglês

10.1016/0022-1910(65)90137-x

1879-1611

G. Fraenkel, Catherine Hsiao,

Insect Utilization and Effects

Bursicon is the term for a hormone which occurs in the blood of newly emerged flies and of insects of other orders at the time of the moult, and which is necessary for the tanning of the adult fly and presumably other insects. The blood of a fly at the instant of emergence is devoid of this hormone. If the head is ligatured at this time the rest of the body never tans. It tans when injected with blood taken from a fly a short time after emergence. Bursicon activity begins to show up in the blood 2–3 min after emergence. It reaches a maximum titre after 30–60 min, when it produces tanning in a ligatured fly in thirty-times dilution. Then the activity decreases and has disappeared about 10 hr later. The blood of all other stages, larvae, pupae, or older adults, is devoid of activity. Bursicon was found in the blood of 3 different fly species, with the effect interchangeable in all combinations. It was also found at the time of the moult in the blood of insects of four other orders: Orthoptera, Hemiptera, Coleoptera, and Lepidoptera, but appears to be confined to stages which tan after the moult. Bursicon is secreted by the neurosecretory cells of the pars intercerebralis of the brain. This region contains the whole activity of the brain, while the brain without this region is devoid of activity. Bursicon activity is also contained in the combined ganglion of the thorax in about six times the concentration in the brain. Secretion from the thoracic ganglion is activated by a nervous stimulus from the brain travelling via the ventral connective. The initiation of tanning is affected by two different mechanisms: (1) Activating stimuli from sensory receptors in the cuticle conducted to the brain via the central nervous system and operating when the fly is no longer confined to the medium in which it emerges. Cutting the connective in the neck prevents these stimuli from reaching the brain. (2) The removal of an inhibition which is in effect while the newly emergedfly is actively digging. Bursicon acts on the cuticle directly, and not via another hormone system. The initiation of pumping air into the intestine and that of tanning seem to be independent processes. All tests so far conducted on the chemical nature of bursicon indicate it to be a protein. It is precipitated by typical protein precipitants, with loss of activity in the case of TCA, alcohol, acetone, but full retention of activity after (NH4)2SO4 precipitation. It is not dialysable. The activity is lost after treatment with trypsin or pronase. Bursicon is not a phenolic substrate necessary in tanning. There is overwhelming direct and indirect evidence that bursicon is neither one of the conventional brain hormones known in insects, nor the juvenile hormone, nor ecdyson, nor a newly discovered hormone, proctodone. In view of these facts, and of its occurrence in many orders of insects at the time of the moult, it was deemed necessary to coin a name for it (from the Greek ßvϱσικóς (bursikos)—pertaining to tanning).