Hypothyroidism induces Fos-like immunoreactivity in ventral medullary neurons that synthesize TRH.

Abstract

Altered thyroid statuses are associated with autonomic disorders. Thyrotropin-releasing hormone (TRH) in medullary nuclei regulates vagal efferent activity. Induction of Fos-like immunoreactivity (IR) in medullary TRH-synthesizing neurons was investigated in 24-h fasted rats with different thyroid statuses. Hypo- and hyperthyroidism were induced by 6-N-propyl-2-thiouracil (PTU) in drinking water and a daily intraperitoneal injection of thyroxine (T(4); 10 microgram. 100 g(-1). day(-1)), respectively, for 1-4 wk. The numbers of Fos-like IR positive neurons in the raphe pallidus, raphe obscurus, and parapyramidal regions, which were low in euthyroid rats (0-2/section), increased remarkably as the hypothyroidism progressed and were negatively correlated with serum T(4) levels. At the 4th wk, Fos-like IR positive neurons were 10- to 70-fold higher compared with euthyroid controls. Simultaneous T(4) replacement (2 microgram. 100 g(-1). day(-1)) prevented the increases of Fos-like IR in PTU-treated rats. Hyperthyroidism did not change the number of Fos-like IR neurons in the raphe nuclei but reduced it in the parapyramidal regions. Double immunostaining revealed that most of the Fos-like IR induced by hypothyroidism was located in the prepro-TRH IR positive neurons. The selective and sustained induction of Fos-like IR in TRH-synthesizing neurons in ventral medullary nuclei by hypothyroidism indicates that these neurons play a role in the autonomic disorders observed in altered thyroid statuses.

• Authors: P Q Yuan, H Yang
• Journal: The American journal of physiology (Am J Physiol) Vol. 277 Issue 5 Pg. E927-36 (11 1999) ISSN: 0002-9513 [Print] United States
• PMID: 10567022 (Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Antibodies
• Antithyroid Agents
• Protein Precursors
• Proto-Oncogene Proteins c-fos
• prepro-thyrotropin-releasing hormone
• Thyrotropin-Releasing Hormone
• Propylthiouracil
• Thyroxine

Topics

• Animals
• Antibodies
• Antithyroid Agents
• Cell Count
• Hypothyroidism (chemically induced, metabolism)
• Male
• Medulla Oblongata (cytology)
• Neurons (chemistry, cytology, metabolism)
• Propylthiouracil
• Protein Precursors (analysis, immunology)
• Proto-Oncogene Proteins c-fos (analysis, biosynthesis, immunology)
• Raphe Nuclei (metabolism)
• Rats
• Rats, Sprague-Dawley
• Thyrotropin-Releasing Hormone (analysis, biosynthesis, immunology)
• Thyroxine (biosynthesis, blood)