Pseudopodia formation by neurosecretory granules

Area of Science:

• Neuroendocrinology
• Cell Biology
• Electron Microscopy

Background:

• The neurohypophysis releases hormones like vasopressin.
• The precise mechanisms of neurosecretory granule (NSG) release are not fully understood.
• Ultrastructural studies are crucial for investigating cellular processes.

Purpose of the Study:

• To investigate the ultrastructure of mouse neurohypophysis under various experimental conditions.
• To identify and quantify specific structures involved in neurosecretory granule release.
• To explore the relationship between granule morphology and hormone secretion.

Main Methods:

• Ultrastructural analysis of mouse neurohypophysis using electron microscopy.
• Quantification of neurosecretory granules (NSG) with pseudopodia-like protrusions.
• In vivo experiments involving injections of horseradish peroxidase (HRP), hypertonic saline, and histamine.
• In vitro incubation of isolated neural lobes with secretagogues (HRP, di-butyryl cyclic AMP, histamine, excess potassium).
• Measurement of vasopressin release using antidiuretic bioassay.

Main Results:

• Neurosecretory granules (NSG) in the mouse neurohypophysis were observed with pseudopodia-like protrusions.
• Pseudopodia formation on NSG increased significantly following in vivo administration of HRP, hypertonic saline, and histamine.
• In vitro, HRP and di-butyryl cyclic AMP induced both pseudopodia formation and elevated vasopressin release.
• Histamine and excess potassium increased hormone secretion but did not induce pseudopodia formation in vitro.
• No pseudopodia were observed in controls or with ineffective secretagogues.

Conclusions:

• The pseudopodia on neurosecretory granules (NSG) may represent active sites on the granule membrane involved in hormone release.
• Multiple modes of hormone release may operate within the neurohypophysis.
• The specific role of horseradish peroxidase (HRP) in pseudopodia formation and vasopressin release requires further investigation.