Brain Hormone of the Silkworm, Bombyx mori

Abstract

IT is generally accepted that the neurosecretory cells concerning the metamorphosis of insects contain a small amount of a secretory substance at any time of development^1,2, notwithstanding a marked effect which they exert when implanted or transplanted. This means that accumulation of the secretory substance released continuously from the cells in the brain is necessary to become effective. This is the reason why a great many brains were used to extract a sufficient amount of the active principle³. However, we have found that only several devitalized brains of Bombyx mori could cause adult differentiation when inserted into the non-diapausing pupæ of Philosamia cynthia ricini caused to diapause by prompt removal of their brains just after pupation. Devitalization was brought about by various ways such as subjecting brains to freezing in a deep-freezer at −18° C. for 21 days, desiccating them over silica gel for one day, or heating them at 90° C. for 90 min. After being treated, the brains were all proved to be as effective as live ones, so far as they were tested by five for each test pupa. Needless to say that in this case the brain hormone, enough to stimulate adult differentiation of the recipient, had to be present in the five inserted brains. The possibility that the adult differentiation was caused by the prothoracic gland hormone which contaminated the inserted brains can be ruled out, since neither the same amount of fatty tissue nor blood similarly treated exerted any perceptible effect on the dormant pupæ. It seems, however, worthy of mentioning that after treatment brains of Philosamia were inferior to brains of Bombyx in their effectiveness. This presumably indicates that the situation at a given moment is different between the two species, a larger amount of the hormone being contained in the latter.