Peptides controlling behavior in Aplysia

Area of Science:

• Neuroendocrinology
• Comparative Physiology
• Molecular Endocrinology

Background:

• The bag cells and atrial gland in molluscs produce hormonal peptides regulating reproductive behavior.
• These peptides exhibit actions on the central nervous system, analogous to mammalian neurohormones like LHRH and TRH.
• Peripheral targets of these molluscan peptides are also being identified, expanding our understanding of their functions.

Purpose of the Study:

• To elucidate the intricate relationships between bag cells, atrial gland, their peptides, the central nervous system, and reproductive behavior.
• To investigate the potential for multiple receptor binding sites within single peptide molecules.
• To draw parallels between molluscan and mammalian neuropeptidergic systems.

Main Methods:

• Summarizing current understanding of the neuroendocrine system controlling reproductive behavior (as depicted in Figure 11).
• Analyzing the actions of hormonal peptides (e.g., ELH) on both central nervous system and peripheral targets.
• Comparing the organization and principles of molluscan neuropeptidergic systems with those in mammals.

Main Results:

• Identified three key hormonal peptides (ELH and two atrial gland peptides) with specific actions on the central nervous system.
• ELH demonstrates multiple specific peripheral targets, indicating complex signaling pathways.
• The atrial gland serves as a peripheral peptide source with significant nervous system actions, similar to mammalian gut peptides.

Conclusions:

• Large peptides like ELH may possess multiple receptor binding sites or 'messages' within a single molecule, enabling diverse target activation.
• The organizational principles of neuropeptidergic systems in molluscs show striking resemblances to those in mammals.
• These findings underscore the evolutionary conservation of neuropeptidergic signaling, suggesting invertebrate studies offer insights applicable to mammalian systems.