Abstract
The neurosecretory cells (NSC) in brains of larvae destined for pupal diapause and diapausing pupae of M. brassicae were compared with those of larvae destined for pupal non-diapause and of non-diapausing pupae, histologically and functionally. In the larval stage, the group I-NSC in the medial part of the brain showed no differences in stainability with paraldehyde-fuchsin (AF) between the larvae destined for diapause and those for non-diapause. These NSC were stained well in early instars or at the end of the last instar but stained only slightly from the 2nd to the 5th day of the last instar. In the pupal stage the stainable neurosecretory material of the type II-NSC in medial part was apparent in the brain of diapausing pupae, but was much reduced in the brain of non-diapausing pupae. When NSC-ablated brains or NSC-clusters were implanted into dauer pupae or neck-ligated larvae to ascertain the role of NSC on adult development or pupation, both the medial NSC (MNC) and the lateral NSC (LNC) showed the activity secreting prothoracotropic hormone (PTTH); but activity of the MNC was higher than that of the LNC. Histological studies and implantation experiments indicated that that the type II-NSC in the MNC of M. brassicae pupal brain may be able to secrete PTTH.

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