Immunoreactivity of neurosecretory granules in the brain-retrocerebral complex of Manduca sexta to heterologous antibodies against Bombyx prothoracicotropic hormone and bombyxin

Summary

A monoclonal antibody against a synthetic pentadecapeptide corresponding to the N-terminal end of Bombyx-prothoracicotropic hormone (PTTH: 1–15) and a monoclonal antibody against a synthetic decapeptide corresponding to the N-terminal portion of the A-chain of bombyxin-1, bombyxin (1–10), were used as parallel probes to localize both molecules at the cellular and subcellular levels in the brain-retrocerebral complex of Manduca sexta. Immunohistochemical analysis revealed that molecules immunochemically similar to Bombyx-PTTH were localized in the cytoplasm of two pairs of dorso-lateral neurosecretory cells (L-NSC III) and could be traced along their axons to the corpora cardiaca (CC) and corpora allata (CA), whereas bombyxin-like material was absent from these cells and was detected only in the cytoplasm of four pairs of median neurosecretory cells (M-NSCs). Immunocytochemical labelling at the ultrastructural level using the PTTH antibody showed high specificity with the 5 nm immunogold particles restricted to the neurosecretory granules of the L-NSCs III, their axons and their axon endings in the CC and CA. An entirely different labelling pattern was observed when the bombyxin monoclonal antibody was used with the immunogold paradigm, i.e., the particles seemed to be present in the mitochondria and rough endoplasmic reticulum in addition to the neurosecretory granules of the M-NSCs. The significant of these data is discussed in light of the absence of any known physiological role for Bombyx PTTH in Manduca.

Key words:

• Immunoreactivity
• Manduca sexta
• neurosecretory granules