Developmental change of bombyxin content in the brain of the silkmoth Bombyx mori

Abstract

Accumulation of bombyxin in the brain of Bombyx mori was examined throughout post-embryonic development. Immunohistochemically, four pairs of large dorsomedial neurosecretory cells of brain were shown to contain bombyxin throughout the stages from larval hatching to adult eclosion. The bombyxin content in the brain that was estimated by immunohistochemistry, immunoblotting and bioassay remarkably changed during larval-larval and larval-pupal development. The bombyxin level in penultimate-instar larvae was high in the first half while low in the second half of the stage. It became high again at the time of ecdysis to the final instar, but gradually decreased afterward until the larvae began wandering. After wandering the bombyxin content increased gradually until pupation when a level as high as that in the newly ecdysed, final-instar larvae was regained. Immunoblotting of brain extracts demonstrated that bombyxin consisted of many molecular forms, all of which were present through larval-larval development. Based on the developmental changes in the bombyxin content in the brain, the physiological role of this neuropeptide is discussed.