Serotonergic innervation of the rat pituitary intermediate lobe: decrease after stalk section.

Area of Science:

• Neuroscience
• Endocrinology
• Cell Biology

Background:

• Serotonin (5-HT) is a neurotransmitter with diverse roles in the central nervous system and periphery.
• The presence and origin of serotonergic innervation in the pituitary gland, particularly the intermediate lobe, remain incompletely understood.

Purpose of the Study:

• To investigate the origin of serotonin (5-HT)-containing nerve fibers in the intermediate lobe of the rat pituitary.
• To determine the impact of pituitary stalk transection on serotonin levels in different pituitary lobes.

Main Methods:

• Light and electron microscopic immunocytochemistry were used to visualize 5-HT immunoreactive nerve fibers and terminals.
• High-performance liquid chromatography with electrochemical detection was employed to quantify 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) concentrations.
• Pituitary stalk transection and sympathectomy were performed to assess the origin of 5-HT.

Main Results:

• 5-HT-containing nerve fibers, but not cell bodies, were identified in the rat pituitary intermediate lobe.
• Pituitary stalk transection led to the near-complete disappearance of 5-HT immunoreactive fibers from the intermediate lobe within seven days.
• Intermediate lobe concentrations of 5-HT and its metabolite 5-HIAA decreased significantly post-transection.
• No significant changes in 5-HT levels were observed in the anterior or posterior pituitary lobes, or the median eminence.
• Sympathectomy did not affect 5-HT levels in the intermediate lobe.

Conclusions:

• The results strongly suggest that neuronal 5-HT in the rat pituitary intermediate lobe originates from nerve cells located in the central nervous system.
• The pituitary stalk serves as the crucial pathway for the transport of these serotonergic fibers to the intermediate lobe.