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The aim of this study was to investigate the secretion of brain-derived neurotrophicfactor (BDNF)-like neuropeptide in the silkworm, Bombyx mori, by usingimmunocytochemical techniques on the brain and retrocerebral complex of fifthinstar larvae. In the brain, four pairs of median neurosecretory cell (MNC) bodiesand six pairs of lateral neurosecretory cell (LNC) bodies had distinctimmunoreactivities to this peptide, suggesting that this peptide is produced fromtwo types of brain neuron. These reactivities were much stronger in the MNC thanin the LNC. Labeled MNC projected their axons into the contralateral corporaallata, to which axons of labeled MNC were eventually innervated, throughdecussation in the median region, contralateral nerve corporis cardiaci I and nervecorpora allata I. Labeled LNC extended their axons into the ipsilateral corpora allatato be innervated through the ipsilateral nerve corporis cardiaci II and nerve corporaallata I. These results suggest that BDNF is secreted as a neurohormone from MNCand LNC of the brain into the corpora allata.